CN110646549A

CN110646549A - Thermal desorption instrument and analysis system for volatile organic compound detection and working method thereof

Info

Publication number: CN110646549A
Application number: CN201911077829.0A
Authority: CN
Inventors: 江超; 何松翰; 张功勇; 卞钧洋; 赵治龙; 陈勇; 杨陈; 孙永利; 尹辉
Original assignee: Sichuan Shengshi Technology Co Ltd
Current assignee: Sichuan Shengshi Technology Co Ltd
Priority date: 2019-11-06
Filing date: 2019-11-06
Publication date: 2020-01-03
Anticipated expiration: 2039-11-06
Also published as: CN110646549B

Abstract

The invention relates to the technical field of volatile organic compound detection, and discloses a thermal desorption instrument, an analysis system and a working method thereof for volatile organic compound detection, which can firstly open two mass flow controllers and a proportional valve in a desorption link, set the flow rates of the two mass flow controllers according to a target flow dividing ratio, and control the flow rate of the proportional valve and the flow rate of an emptying mass flow controller to meet the target flow dividing ratio, so that volatile organic compounds can be quantitatively adsorbed in a temperature control focusing pipe and a sample recovery pipe according to the target flow dividing ratio, then carry out a purging link and a sample injection analysis link, thereby not only realizing accurate flow dividing control, but also being beneficial to carrying out mutual conversion on analysis results under the condition of different flow dividing ratios, leading the analysis results of the sample recovery pipe to be qualitatively and quantitatively analyzed and greatly increasing the fault-tolerant rate of the thermal desorption instrument, therefore, repeated sampling can be avoided, the detection of the volatile organic compounds is convenient, and the practical application and popularization are facilitated.

Description

Thermal desorption instrument and analysis system for volatile organic compound detection and working method thereof

Technical Field

The invention belongs to the technical field of volatile organic compound detection, relates to industries including environmental monitoring, occupational health and the like, and particularly relates to a thermal desorption instrument, an analysis system and a working method thereof for volatile organic compound detection.

Background

The thermal desorption method is mainly used for analyzing VOCs (Volatile Organic Compounds, which refer to Organic Compounds with saturated vapor pressure of more than 133.32Pa at normal temperature, boiling point of 50-260 ℃ below under the standard atmospheric pressure of 101.3kPa and initial boiling point equal to 250 ℃, or any Volatile Organic solid or liquid at normal temperature and normal pressure), the technology has few defects, so that the method is also the most mainstream Volatile Organic compound detection method at present, and the defects mainly refer to the design of each product model.

There are also many thermal desorption devices on the market today, but the most competitive products in terms of performance are two: PERKINELMER company (hereinafter referred to as PE company) in the United states and MARKES company in the United kingdom.

The thermal desorption products of PE company mainly suffer from the following disadvantages:

(11) the method is characterized in that the method can only analyze VOCs in adsorption tubes (stainless steel tubes or quartz tubes of about 6mm multiplied by 9cm, solid adsorbents are filled in the adsorption tubes, the adsorbents can efficiently adsorb VOCs in gas, after collection is completed, the adsorption tubes are returned to a laboratory and placed in a thermal desorption instrument to analyze the VOCs in the adsorption tubes), but cannot analyze VOCs in a sampling tank in a cross-boundary way (the tank is vacuumized before sampling, a gas sample is pumped and sealed during sampling, and the gas sample is returned to the laboratory to detect the content of the VOCs in the gas in an online way;

(12) the device is not provided with a built-in dehydration module, and when the moisture content in the collected sample is high, effective dehydration cannot be realized, so that the accuracy of a measurement result is easily influenced, and even an instrument is damaged;

(13) the inertization degree of the system is not high, and volatile organic compounds (such as methyl mercaptan) with higher activity cannot be analyzed;

(14) the flow control of the split flow is inaccurate, and the content of VOCs in the adsorption tube sample can not be accurately calculated or inversely calculated through the difference of the split flow ratio;

(15) the added internal standard filling module adopts a quantitative ring (1mL) for sample injection, needs high-concentration internal standard gas due to small volume, and in the process of filling the quantitative ring, redundant internal standard gas can be emptied to cause pollution, the flow rate of the internal standard gas is uncontrollable, the consumption is large, and the waste is obvious.

The thermal desorption products from the company marker have mainly the following disadvantages:

(21) although the sample in the sampling tank can be collected across the boundary, and the dehydration capacity can be matched, the sampling tank and the dehydration capacity are independent matching instruments (independent equipment, not modules or elements inside the instrument), the space is not occupied, the integrity of the instrument is reduced, and the defect of high cost is caused;

(22) the heating component of the adsorption tube has poor actual heat insulation effect, the upper limit temperature is generally 300 ℃ out of the head and is far lower than the alleged 450 ℃; between the samples before and after analysis, the heating area is naturally cooled, and the temperature is raised before the next sample is analyzed, if the set temperature is 300 ℃ or above, the temperature rise time is about 10min, and the analysis efficiency is influenced; when the current sample is analyzed, the next sample (adsorption tube) also waits near the heating area, the temperature of the adsorption tube which is easy to wait is increased (generally, the temperature can be increased by 5-15 ℃), if VOCs enriched in the adsorption tube have substances which are difficult to trap and easy to diffuse, the substances can be only barely adsorbed and fixed on a solid adsorbent at normal temperature, and after the temperature of the adsorption tube is increased, the substances are easy to desorb and lose;

(23) the adsorption tube is arranged on the automatic sample injector, the DiffLok sealing caps of MARKES patents are required to be arranged at two ends of the adsorption tube, the sealing caps adopt a one-way ventilation design, but the sealing effect is poor in practice, and after the adsorption tube is arranged on the DiffLok sealing caps and before analysis, the adsorbed VOCs are easy to lose (for the reasons mentioned above) and pollution is easy to introduce;

(24) similar to the products of PE company, the flow distribution control is inaccurate, and even the flow distribution is manually adjusted in standard matching, so that the switching between high and low concentration curves is difficult.

Besides the two foreign manufacturers, a plurality of thermal desorption instrument manufacturers exist in China, most of the thermal desorption instrument manufacturers imitate PE to different degrees, although some manufacturers do some improvement on the basis of the PE, the imitation design causes the defects of the PE, the thermal desorption instrument manufacturers exist to different degrees, the working degree and the PE equipment are obviously different, and the element stability is not good. Therefore, their properties, stability, etc. are difficult to exceed those of PE.

Disclosure of Invention

The invention aims to solve the problems that the existing thermal desorption instrument is inaccurate in flow distribution control and can only qualitatively and not quantitatively analyze the analysis result of a sample recovery tube, and provides a novel thermal desorption instrument, an analysis system and a working method thereof for volatile organic compound detection.

The technical scheme adopted by the invention is as follows:

a thermal desorption instrument for detecting volatile organic compounds comprises a nitrogen connector, a first mass flow controller, a second mass flow controller, a multi-way switching valve, a first electromagnetic switching valve, a second electromagnetic switching valve, a first emptying connector, a second emptying connector, a third emptying connector, an adsorption tube, a sample recovery tube, an eight-way switching valve, a temperature control dehydration tube, a temperature control focusing tube, a carrier gas inlet and outlet pipeline, a proportional valve and a gas pressure sensor, wherein an adsorption tube temperature control unit is arranged around the adsorption tube;

the nitrogen connector is communicated with an input port of the first mass flow controller, an output port of the first mass flow controller is respectively communicated with a second interface of the multi-way switching valve, a normally closed port of the first electromagnetic switching valve and a normally open port of the second electromagnetic switching valve, the normally open port of the first electromagnetic switching valve is communicated with the first emptying connector, a common port of the first electromagnetic switching valve is communicated with a first port of the adsorption pipe, a second port of the adsorption pipe is communicated with a first interface of the multi-way switching valve, and a third interface of the multi-way switching valve is respectively communicated with a first port of the sample recovery pipe and a first interface of the eight-way switching valve;

the second port of the sample recovery pipe is communicated with the input port of the proportional valve, the air pressure sensor is arranged in an air path between the second port of the sample recovery pipe and the input port of the proportional valve, and the output port of the proportional valve is communicated with the second emptying joint;

the second interface of the eight-way switching valve is communicated with the first port of the temperature control dehydration pipe, the second port of the temperature control dehydration pipe is communicated with the eighth interface of the eight-way switching valve, the seventh interface of the eight-way switching valve is communicated with the first port of the temperature control focusing pipe, the second port of the temperature control focusing pipe is communicated with the fourth interface of the eight-way switching valve, the fifth interface of the eight-way switching valve is communicated with an air inlet pipeline in the carrier gas inlet and outlet pipeline, the sixth interface of the eight-way switching valve is communicated with an air outlet pipeline in the carrier gas inlet and outlet pipeline, and the third interface of the eight-way switching valve is communicated with the common port of the second electromagnetic switching valve;

and the normally closed port of the second electromagnetic switching valve is communicated with the input port of the second mass flow controller, and the output port of the second mass flow controller is communicated with the third emptying joint.

The device is optimized to further comprise an air inlet joint and an air pump, wherein the air inlet joint is used for being communicated with a common outlet of the automatic sampler of the sampling tank;

the air inlet joint is communicated with a first interface of the eight-way switching valve, an input port of the air pump is communicated with an output port of the second mass flow controller, and an output port of the air pump is communicated with the third emptying joint.

The optimized eight-way switching valve further comprises an internal standard gas inlet joint and an electromagnetic valve, wherein the internal standard gas inlet joint is communicated with an input port of the electromagnetic valve, and an output port of the electromagnetic valve is communicated with a first interface of the eight-way switching valve.

The other technical scheme adopted by the invention is as follows:

an analysis system for detecting volatile organic compounds comprises the thermal desorption instrument for detecting volatile organic compounds, a nitrogen cylinder and a gas chromatograph;

the nitrogen cylinder is communicated with the nitrogen connector of the thermal desorption instrument, the carrier gas output pipe of the gas chromatograph is communicated with the gas inlet pipeline in the carrier gas inlet and outlet pipeline, and the carrier gas return pipe of the gas chromatograph is communicated with the gas outlet pipeline in the carrier gas inlet and outlet pipeline.

Preferably, when the thermal desorption instrument comprises an air inlet joint and an air pump, the thermal desorption instrument further comprises a sampling tank automatic sampler, wherein the sampling tank automatic sampler at least comprises a nitrogen position and a blocking position;

and a common outlet of the automatic sampler of the sampling tank is communicated with the air inlet joint.

The other technical scheme adopted by the invention is as follows:

a method of operating an analytical system for volatile organic detection as described above, comprising the steps of:

s11, temperature control: respectively starting the temperature control dehydration pipe and the temperature control focusing pipe to enter a refrigeration mode, then maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe is reduced to a dehydration working temperature value, and maintaining the temperature of the focusing pipe when the temperature of the focusing pipe is reduced to a focusing working temperature value;

s12, desorption: firstly, enabling a multi-way switching valve to be in an A position state, enabling a first electromagnetic switching valve and a second electromagnetic switching valve to be respectively powered off, enabling an eight-way switching valve to be in a B position state, then opening a first mass flow controller, a second mass flow controller and a proportional valve, setting the flow of the first mass flow controller and the flow of the second mass flow controller according to a target flow split ratio, controlling the flow ratio of the proportional valve to the flow of the second mass flow controller to meet the target flow split ratio, then starting a desorption pipe temperature control unit to heat and desorb an adsorption pipe when the flow is in a stable state, starting a desorption pipe temperature control unit to refrigerate and cool the adsorption pipe after first time, and finally respectively closing the first mass flow controller, the second mass flow controller and the proportional valve after second time;

s13, purging: firstly, the multi-way switching valve is in an A-position state, the first electromagnetic switching valve and the second electromagnetic switching valve are respectively powered off, the eight-way switching valve is in a B-position state, the proportional valve is closed, then the temperature control dehydration pipe is started to enter a heating mode, so that the temperature of the dehydration pipe is slowly increased, the temperature of the focusing pipe is continuously maintained, simultaneously starting a first mass flow controller and a second mass flow controller, setting the flow of the first mass flow controller as a first blowing working flow value and slightly smaller than that of the second mass flow controller, then when the temperature of the dehydration pipe is raised to a blowing working temperature value, setting the flow of the first mass flow controller as a second purging working flow value and slightly smaller than the flow of the second mass flow controller, and finally closing the first mass flow controller and the second mass flow controller respectively after a third time;

s14, sample injection: the method comprises the steps of firstly starting a temperature control focusing tube to enter a heating mode, enabling the temperature of the focusing tube to be rapidly raised to a desorption working temperature value of the focusing tube, then enabling an eight-way switching valve to be in an A-position state, enabling carrier gas of a gas chromatograph to flow back after passing through the temperature control focusing tube, simultaneously starting the gas chromatograph to perform separation analysis, and finally switching the eight-way switching valve to be in a B-position state after fourth time.

The optimized cleaning method also comprises a cleaning link in any one of the following modes:

(SA1) carrying out adsorption tube heat washing when the sample is fed and the eight-way switching valve is in the A position state: firstly, enabling a multi-way switching valve to be in an A-position state, enabling a first electromagnetic switching valve and a second electromagnetic switching valve to be powered off respectively, enabling a second mass flow controller to be closed, then opening a first mass flow controller and a proportional valve, setting the flow of the first mass flow controller as an adsorption pipe cleaning working flow value, then starting an adsorption pipe temperature control unit to heat an adsorption pipe when the flow is in a stable state, and maintaining the temperature of the adsorption pipe when the temperature reaches a thermal cleaning working temperature value;

(SA2) dehydration tube washing and focusing tube washing after sample injection: the method comprises the steps of firstly enabling a multi-way switching valve to be in a B position state, enabling a first electromagnetic switching valve to be powered off, enabling a second electromagnetic switching valve to be powered on, enabling an eight-way switching valve to be in the B position state, then opening a first mass flow controller and a proportional valve, setting the flow of the first mass flow controller as a thermal cleaning working flow value, then respectively starting a temperature control dehydration pipe and a temperature control focusing pipe to enter a heating mode, maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe reaches the thermal cleaning working temperature value of the dehydration pipe, maintaining the temperature of the focusing pipe when the temperature of the focusing pipe reaches the thermal cleaning working temperature value of the focusing pipe, finally respectively starting the temperature control dehydration pipe and the temperature control focusing pipe to enter a cooling mode after fifth time, and closing the first mass flow controller and the proportional valve when the temperature of the dehydration pipe and the temperature of the focusing pipe reach normal temperature or set.

Preferably, an internal standard gas collection link in any one of the following manners is further included before or after the step S12:

(SB1) when the thermal desorption appearance includes the air inlet and the analytic system still includes the sample jar auto-sampler of public export intercommunication this air inlet: firstly, enabling a multi-way switching valve to be in a B-position state, powering off a second electromagnetic switching valve, enabling an eight-way switching valve to be in the B-position state, closing a proportional valve, maintaining the temperature of a dehydration tube and the temperature of a focusing tube, then starting a second mass flow controller, setting the flow as an internal standard gas acquisition working flow value, switching a sampling tank automatic sampler to the internal standard position state, finally switching the sampling tank automatic sampler to a blocking position state after acquiring the set internal standard gas product, and closing the second mass flow controller;

(SB2) when the thermal desorption instrument comprises an internal standard gas inlet joint and an electromagnetic valve and the analysis system further comprises an internal standard gas cylinder communicated with the internal standard gas inlet joint: the multi-way switching valve is in a B-position state, the second electromagnetic switching valve is powered off, the eight-way switching valve is in the B-position state, the proportional valve is closed, the temperature of the dehydration tube and the temperature of the focusing tube are maintained, then the second mass flow controller is opened, the flow is set to be an internal standard gas collection working flow value, the electromagnetic valve is conducted, and finally the second mass flow controller and the electromagnetic valve are closed after the set internal standard gas product is collected.

Preferably, the method further includes the following steps S101 to S104 before the step S12:

s101, loading: loading the adsorption tube on the installation position;

s102, leak detection: firstly, closing a second mass flow controller, enabling a multi-way switching valve to be in an A-position state, respectively powering off a first electromagnetic switching valve and a second electromagnetic switching valve, enabling an eight-way switching valve to be in a B-position state, closing a proportional valve, then opening a first mass flow controller and setting a leakage detection working flow value of an adsorption tube, if a monitoring result of a pressure sensor shows that the internal pressure does not rise within a first leakage detection time, judging that the adsorption tube is completely leaked or the adsorption tube is not normally loaded, then executing step S104, otherwise, closing the first mass flow controller, if the monitoring result of the pressure sensor shows that the internal pressure drops to atmospheric pressure or a set value within a second leakage detection time, judging that the air tightness of the adsorption tube is poor, then executing step S104, otherwise, judging that the air tightness of the adsorption tube is good, and then executing step S103;

s103, pressure relief: firstly, respectively closing a first mass flow controller and a second mass flow controller, enabling a multi-way switching valve to be in an A-position state, respectively powering off a first electromagnetic switching valve and a second electromagnetic switching valve, enabling an eight-way switching valve to be in a B-position state, and then opening a proportional valve;

and S104, sending a loading error prompt message, and unloading and returning the adsorption tube.

The other technical scheme adopted by the invention is as follows:

s21, respectively starting a temperature control dehydration pipe and a temperature control focusing pipe to enter a refrigeration mode, and then maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe is reduced to a dehydration working temperature value and maintaining the temperature of the focusing pipe when the temperature of the focusing pipe is reduced to a focusing working temperature value;

s22, collecting: firstly, enabling a multi-way switching valve to be in a B-position state, powering off a second electromagnetic switching valve, enabling an eight-way switching valve to be in the B-position state, closing a proportional valve, then switching a sampling tank automatic sampler to a sample position, starting a second mass flow controller and an air pump, setting the flow of the second mass flow controller as a collection working flow value, and finally switching the sampling tank automatic sampler to a plugging position and closing the second mass flow controller and the air pump after a set volume of sample gas is extracted;

s23, purging: firstly, enabling a multi-way switching valve to be in a B-position state, powering off a second electromagnetic switching valve, enabling an eight-way switching valve to be in the B-position state, closing a proportional valve, starting a temperature-controlled dehydration pipe to enter a heating mode, slowly raising the temperature of the dehydration pipe, continuously maintaining the temperature of a focusing pipe, simultaneously switching a sampling tank automatic sample injector to a nitrogen position, starting a second mass flow controller and an air pump, setting the flow of the second mass flow controller to be a third purging working flow value, setting the flow of the second mass flow controller to be a fourth purging working flow value when the temperature of the dehydration pipe is raised to a purging working temperature value, and finally switching the sampling tank automatic sample injector to a plugging position and closing the second mass flow controller and the air pump after a sixth time;

s24, sample injection: the method comprises the steps of firstly starting a temperature control focusing tube to enter a heating mode, enabling the temperature of the focusing tube to be rapidly raised to a desorption working temperature value of the focusing tube, then enabling an eight-way switching valve to be in an A-position state, enabling carrier gas of a gas chromatograph to flow back after passing through the temperature control focusing tube, simultaneously starting the gas chromatograph to perform separation analysis, and finally switching the eight-way switching valve to be in a B-position state after fourth time.

The invention has the beneficial effects that:

(1) the invention provides a novel thermal desorption instrument, an analysis system and a working method thereof, which can complete the analysis and detection of volatile organic compounds by matching with a gas chromatograph, and can firstly open two mass flow controllers and a proportional valve in a desorption link, set the flow rates of the two mass flow controllers according to a target flow dividing ratio, and control the flow rate of the proportional valve and the flow rate of an emptying mass flow controller to meet the target flow dividing ratio, so that VOCs can be quantitatively absorbed in a focusing pipe and a sample recovery pipe according to the target flow dividing ratio, then a purging link and a sample injection analysis link are carried out, thereby not only realizing accurate flow dividing control, but also being beneficial to carrying out conversion on analysis results under the condition of different flow dividing ratios, leading the analysis results of the sample recovery pipe to be qualitatively and quantitatively analyzed and greatly increasing the fault-tolerant rate of the thermal desorption instrument, therefore, repeated sampling can be avoided, detection of volatile organic compounds is facilitated, and practical application and popularization are facilitated;

(2) the thermal desorption instrument can analyze the adsorption tube, and can also analyze a sampling tank (namely a suma tank) or an air bag, so that the purpose of one device with multiple purposes is realized, VOCs (including organic sulfur and n-hexadecane) listed in all standards of a thermal desorption method can be responded and analyzed, and all VOCs in a volatile organic compound monitoring scheme in key areas issued by the country can be analyzed, namely the former is the application of the adsorption tube, the latter is the application of the sampling tank, the two basically contain all VOCs at home and abroad, the thermal desorption instrument is designed by an integrated person, and the application range of the thermal desorption instrument is greatly expanded;

(3) the temperature control dehydration pipe is arranged in the dehydration device, so that the influence of moisture can be effectively eliminated, and the dehydration device is simpler and more convenient to use compared with an independent dehydration device scheme adopted by MARKES company in England;

(4) because the temperature control dehydration pipe and the temperature control focusing pipe both adopt an electronic refrigeration technology, liquid nitrogen and other refrigerants are not needed, and the device is economical and practical, namely if a VOCs preconcentrator (analysis sampling tank) refrigerated by liquid nitrogen is used, the problem of high use cost obviously exists, 1200-element liquid nitrogen can only analyze about 50 samples, and the liquid nitrogen tank also needs thousands to ten thousand of prices, compared with the prior art, the device only consumes electricity and has low power; in addition, liquid nitrogen is more troublesome to supply and replace, the situation of untimely replacement is easy to occur, the delay of sample analysis time is caused, and some three-four-line cities even have no liquid nitrogen manufacturers;

(5) due to the fact that the VOCs flow path is fully inert and fully temperature-controlled, the minimum residual VOCs can be guaranteed;

(6) the internal standard gas collection device can be matched with a sampling tank automatic sampler with an internal standard gas level or an internal standard gas tank to realize internal standard gas collection, so that the purpose of detection and analysis by using an internal standard method or an external standard method is realized, and the application range is further expanded.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a thermal desorption apparatus and an analysis system provided by the present invention.

Fig. 2 is a schematic view of the gas flow of the sorbent tube-based analysis system of the present invention during leak detection of the loop by the sorbent tube.

Fig. 3 is a schematic diagram of the gas flow of the analysis system based on the adsorption tube in the pressure relief link after the leakage detection of the adsorption tube.

FIG. 4 is a schematic view of the gas flow of the sorbent tube-based analytical system of the present invention in a dry-blown loop.

FIG. 5 is a schematic gas flow diagram of a sorbent tube-based analytical system according to the present invention in a split flow desorption loop.

FIG. 6 is a schematic view of the gas flow of a sorbent tube-based analytical system provided by the present invention without diverting the desorption loop.

FIG. 7 is a schematic gas flow diagram of a sorbent tube-based analysis system in a first internal standard collection loop provided by the present invention.

FIG. 8 is a schematic gas flow diagram of a sorbent tube-based analysis system in a second internal standard collection loop configuration provided by the present invention.

FIG. 9 is a schematic of the gas flow at the purge link for a sorbent tube-based analytical system provided by the present invention.

FIG. 10 is a schematic view of the gas flow of the sorbent tube-based analytical system provided by the present invention at the sample introduction loop.

FIG. 11 is a schematic view of the gas flow of a sorbent tube-based analytical system provided in accordance with the present invention during thermal cleaning of the annulus.

Fig. 12 is a schematic of the gas flow during the flushing, desorption and purge cycle for a sample tank based analysis system provided by the present invention.

In the above drawings, 1-nitrogen joint; 201-a first mass flow controller; 202-a second mass flow controller; 3-a multi-way switching valve; 402-a first electromagnetic switching valve; 402-a second electromagnetic switching valve; 403-a third electromagnetic switching valve; 501-a first emptying joint; 502-second drain connection; 503-a third evacuation connection; 6-an adsorption tube; 7-sample recovery tube; 8-eight-way switching valve; 9-temperature control dehydration pipe; 10-temperature control focusing tube; 11-carrier gas inlet and outlet pipeline; 12-a proportional valve; 13-a barometric pressure sensor; 141-a sorbent tube temperature control unit; 142-a dehydration tube port temperature control unit; 143-focus tube port temperature control unit; 144-a central temperature control unit; 145-carrier gas temperature control unit; 146-an intake air temperature control unit; 15-an air inlet joint; 16-an air pump; 17-internal standard gas inlet joint; 18-a solenoid valve; 19-a first containment box; 20-a second containment box; 21-a first speed valve; 22-a second speed valve; 23-a trap; 24-a three-way connector; 30-a pneumatic assembly; 31-compressed air connection; 50-a connector; 100-a housing; 200-nitrogen gas cylinder; 300-gas chromatography; 400-sample tank autosampler; 500-compressed air bottle.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. Specific structural and functional details disclosed herein are merely illustrative of example embodiments of the invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention.

It should be understood that, for the term "and/or" as may appear herein, it is merely an associative relationship that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, B exists alone, and A and B exist at the same time; for the term "/and" as may appear herein, which describes another associative object relationship, it means that two relationships may exist, e.g., a/and B, may mean: a exists independently, and A and B exist independently; in addition, for the character "/" that may appear herein, it generally means that the former and latter associated objects are in an "or" relationship.

It will be understood that when an element is referred to herein as being "connected," "connected," or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Conversely, if a unit is referred to herein as being "directly connected" or "directly coupled" to another unit, it is intended that no intervening units are present. In addition, other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between … …" versus "directly between … …", "adjacent" versus "directly adjacent", etc.).

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.

It should also be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed substantially concurrently, or the figures may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

It should be understood that specific details are provided in the following description to facilitate a thorough understanding of example embodiments. However, it will be understood by those of ordinary skill in the art that the example embodiments may be practiced without these specific details. For example, systems may be shown in block diagrams in order not to obscure the examples in unnecessary detail. In other instances, well-known processes, structures and techniques may be shown without unnecessary detail in order to avoid obscuring example embodiments.

Example one

As shown in fig. 1, the thermal desorption apparatus for detecting volatile organic compounds provided in this embodiment includes a nitrogen connector 1, a first mass flow controller 201, a second mass flow controller 202, a multi-way switching valve 3, a first electromagnetic switching valve 401, a second electromagnetic switching valve 402, a first evacuation connector 501, a second evacuation connector 502, a third evacuation connector 503, an adsorption tube 6, a sample recovery tube 7, an eight-way switching valve 8, a temperature-controlled dehydration tube 9, a temperature-controlled focusing tube 10, a carrier gas inlet/outlet pipeline 11, a proportional valve 12, and a gas pressure sensor 13, wherein an adsorption tube temperature control unit 141 is disposed around the adsorption tube 6; the nitrogen connector 1 is communicated with an input port of the first mass flow controller 201, an output port of the first mass flow controller 201 is respectively communicated with a second port P32 of the multi-way switching valve 3, a normally closed port of the first electromagnetic switching valve 401 and a normally open port of the second electromagnetic switching valve 402, the normally open port of the first electromagnetic switching valve 401 is communicated with the first emptying connector 501, a common port of the first electromagnetic switching valve 401 is communicated with a first port of the adsorption pipe 6, a second port of the adsorption pipe 6 is communicated with a first port P31 of the multi-way switching valve 3, and a third port P33 of the multi-way switching valve 3 is respectively communicated with a first port of the sample recovery pipe 7 and a first port P81 of the eight-way switching valve 8; the second port of the sample recovery pipe 7 is communicated with the input port of the proportional valve 12, the air pressure sensor 13 is arranged in an air path between the second port of the sample recovery pipe 7 and the input port of the proportional valve 12, and the output port of the proportional valve 12 is communicated with the second emptying joint 502; the second port P82 of the eight-way switching valve 8 is communicated with the first port of the temperature-controlled dehydration pipe 9, the second port of the temperature-controlled dehydration pipe 9 is communicated with the eighth port P88 of the eight-way switching valve 8, the seventh port P87 of the eight-way switching valve 8 is communicated with the first port of the temperature-controlled focusing pipe 10, the second port of the temperature-controlled focusing pipe 10 is communicated with the fourth port P84 of the eight-way switching valve 8, the fifth port P85 of the eight-way switching valve 8 is communicated with the air inlet pipeline in the carrier gas inlet and outlet pipeline 11, the sixth port P86 of the eight-way switching valve 8 is communicated with the air outlet pipeline in the carrier gas inlet and outlet pipeline 11, and the third port P83 of the eight-way switching valve 8 is communicated with the common port of the second electromagnetic switching valve 402; the normally closed port of the second electromagnetic switching valve 402 is communicated with the input port of the second mass flow controller 202, and the output port of the second mass flow controller 202 is communicated with the third emptying joint 503.

As shown in fig. 1, in the specific structure of the thermal desorption apparatus, the nitrogen connector 1 is used for communicating with an external nitrogen cylinder 200 so as to introduce dry nitrogen gas required for cleaning, desorption, purging and the like operations into relevant pipelines inside the apparatus. The first mass flow controller 201 is used for accurately controlling the flow of the introduced nitrogen; the second mass flow controller 202 is used for accurately controlling the flow of the derived gas, and both the first mass flow controller 201 and the second mass flow controller 202 can be implemented by using an existing electronic mass flow controller. The multi-way switching valve 3 is used for realizing the following two states of air path switching: in the A-bit state, the first port P31 is communicated with the third port P33, and the second port P32 is cut off; when the B position is in the state, the first interface is communicated with the second interface P32, and the third interface P33 is cut off; the multi-way switching valve 3 may be embodied as a three-way or higher switching valve. The first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are respectively used for realizing the following two states of air passage switching by an electromagnetic control mode: when the power is off, the common port is communicated with the normally closed port, and the normally open port is closed; in the energized state, the common port is connected with a normally open port, and the normally closed port is closed (in this specification, "normally closed" and "normally open" are used, meaning similar to "normally open contact" and "normally closed contact" in a circuit, that is, "open" means "open/close" means "close/open" of a path, and according to this meaning, other names can be named). The first evacuation connector 501, the second evacuation connector 502 and the third evacuation connector 503 are respectively used for exhausting gas in an internal pipeline of the instrument.

The adsorption tube 6 is used as a sample collecting piece for adsorbing and storing VOCs to be detected, generally can be a stainless steel tube or a quartz tube with the thickness of about 6mm multiplied by 9cm, and is internally filled with a solid adsorbent for adsorbing the VOCs; in order to conveniently detect different samples in batches, the adsorption tube 6 is preferably detachably arranged on the installation position, and an existing tube automatic sampler needs to be arranged outside the instrument to automatically load and unload the adsorption tube 6 so as to realize the purpose of changing the samples. Since the temperature of the adsorption tube plays a critical role in the adsorption and desorption processes of VOCs, the adsorption tube temperature control unit 141 must be disposed around the adsorption tube 6 in order to raise, lower and maintain the temperature of the adsorption tube. Specifically, the adsorption tube temperature control unit 141 may include an adsorption tube heating part and an adsorption tube air cooling part, wherein the adsorption tube heating part may be mechanically moved by a motor control, and heated by contacting the adsorption tube and stopped heating by being away from the adsorption tube. In detail, the heating component of the adsorption tube may further be a temperature-controllable existing metal component, such as a heating block and an electric heating wire; the adsorption pipe air cooling component can be a cooling fan; the adsorption tube heating part generally does not stop heating and control the temperature after the start-up, so the adsorption tube air cooling part can be opened simultaneously to make the adsorption tube temperature maintain at the normal temperature state, for example, the normal temperature state needs to be maintained before the desorption link, so as to ensure that the VOCs in the tube are not desorbed.

The sample recovery pipe 7 is used for recovering VOCs passing through during shunting, and VOCs passing through during hot cleaning and possibly remaining on the temperature control dehydration pipe 9 and the temperature control focusing pipe 10 in a very small amount, so that when the detection of the adsorption pipe 6 fails, the sample recovery pipe 7 can be used as an adsorption pipe (the sample recovery pipe 7 needs to adopt the same pipe body structure as the adsorption pipe 6) for reanalysis; in addition, when the split detection is not performed (for example, in the case where the content of VOCs in the adsorption tube 6 is small), the sample recovery tube 7 may be replaced with an empty tube having no recovery adsorption function to keep the tubes in communication. The eight-way switching valve 8 is used for realizing the following two-state air path switching: in the A position state, the first port P81 is communicated with the eighth port P88, the second port P82 is communicated with the third port P83, the fourth port P84 is communicated with the fifth port P85, and the sixth port P86 is communicated with the seventh port P87; in the B-position state, the first port P81 communicates with the second port P82, the third port P83 communicates with the fourth port P84, the fifth port P85 communicates with the sixth port P86, and the seventh port P87 communicates with the eighth port P88. In addition, in order to prevent the gas from remaining condensed due to a low temperature when flowing through the pipelines between the adsorption pipe 6 and the eight-way switching valve 8 and between the multi-way switching valve 3 and the eight-way switching valve 8, a central temperature control unit 144 for common heating may be disposed in a pipeline region between the adsorption pipe 6 and the eight-way switching valve 8, a mounting position of the multi-way switching valve 3, and a mounting position of the eight-way switching valve 8, as shown in fig. 1, and the central temperature control unit 144 may be specifically an aluminum hot plate, for example.

The temperature control dehydration tube 9 is used for freezing the moisture in the gas flowing through the temperature control dehydration tube in a low temperature mode (generally, the temperature is below zero degrees centigrade) during desorption to remove the moisture, so that most of VOCs enter the temperature control focusing tube 10. Because the temperature of the dehydration tube needs low temperature during desorption and high temperature during purging and hot cleaning, a temperature control unit is necessarily arranged around the dehydration tube body so as to conveniently carry out temperature rise, temperature reduction and maintenance control on the temperature of the dehydration tube; as shown in fig. 1, dehydration pipe port temperature control units 142 are respectively arranged at both side ports of the temperature-controlled dehydration pipe 9; in order to facilitate temperature control and reduce temperature control cost, the low-temperature or normal-temperature control mode of the temperature control dehydration pipe 9 can preferentially adopt the existing electronic refrigeration technology, so that liquid nitrogen refrigeration is not needed, the refrigeration cost is greatly reduced, and the temperature control dehydration pipe is convenient and practical; and heating to high temperature, and winding and heating by using a conventional heating wire.

The temperature-controlled focusing pipe 10 is used for focusing and adsorbing the VOCs in the gas flowing through by using an internal solid adsorbent through a lower temperature mode (generally, the temperature is below-20 ℃) during desorption and purging, so that the aim of serving as a temporary VOCs transfer station is fulfilled. Because the temperature of the focusing tube needs low temperature during desorption and purging and high temperature during sample introduction and hot cleaning, a temperature control unit is also needed to be arranged around the focusing tube body so as to conveniently carry out temperature rise, temperature reduction and maintenance control on the temperature of the focusing tube; as shown in fig. 1, a focusing tube port temperature control unit 143 is arranged at a port of the temperature controlled focusing tube 10; in order to facilitate temperature control and reduce the temperature control cost, the low-temperature or normal-temperature control mode of the temperature control focusing tube 10 can also preferentially adopt the existing electronic refrigeration technology; and heating to high temperature, and winding and heating by using a conventional heating wire. In addition, the intraductal volume of control by temperature change focusing pipe 10 can be showing and be less than adsorption tube 6 to when low temperature environment, make VOCs's diffusion zone littleer, and then effectively focus VOCs, obtain the chromatogram of peak shape quality when doing benefit to follow-up separation and analysis, ensure quantitative analysis's effect.

The carrier gas inlet and outlet pipeline 11 is used for butting a carrier gas output pipe and a carrier gas return pipe of the gas chromatograph 300 so as to lead the volatile organic compounds in the temperature-controlled focusing pipe 10 into the gas chromatograph 300 along with the carrier gas, thereby realizing the purposes of sample introduction and separation analysis; in order to avoid the phenomenon of residual VOCs in the flow-through pipeline due to too low temperature of the carrier gas, as shown in fig. 1, a carrier gas temperature control unit 145 may also be disposed on the carrier gas inlet/outlet pipeline 11 so as to appropriately heat the gas flowing through the carrier gas inlet/outlet pipeline 11, for example, the carrier gas temperature control unit 145 may be a heating pipeline.

The proportional valve 12 is also used for accurately controlling the flow rate, the effect is similar to that of two mass flow controllers, and further, in a manner that the ratio of the flow of the proportional valve 12 to the flow of the second mass flow controller 202 is controlled to meet a target split ratio, the VOCs can be respectively and quantitatively adsorbed in the temperature-controlled focusing tube 10 and the sample recovery tube 7 according to the target split ratio. The air pressure sensor 13 is used for acquiring the air pressure data in the pipe between the second port of the sample recovery pipe 7 and the input port of the proportional valve 12 so as to monitor the internal air pressure of the pipe; in particular, it can be realized by an existing pressure sensor or an air pressure sensor. As shown in fig. 1, preferably, the proportional valve 12, the air pressure sensor 13 and the three-way connector 24 together constitute an integrated component structure, wherein a first port of the three-way connector 24 is communicated with a second port of the sample recovery tube 7, a second port of the three-way connector 24 is communicated with an input port of the proportional valve 12, and a third port of the three-way connector 24 is communicated with an air inlet port of the air pressure sensor 13, so that not only the foregoing objects can be achieved, but also multiple components can be integrated for convenient matching.

In addition, the thermal desorption apparatus may further include a housing 100 for enclosing and protecting the internal fittings, a pneumatic assembly 30 for driving the internal fittings to perform mechanical movement (for example, driving the multi-way switching valve 3 and the eight-way switching valve 8 to perform switching), a compressed air connector 31 having two ends respectively communicated with the pneumatic assembly 30 and the external compressed air bottle 500, and a connector 50 (for example, a three-way connector, a four-way connector, etc.) for connecting the multiple components. In addition, in the internal pipelines of the thermal desorption instrument, the pipelines through which the VOCs flow are made of an inerting material (generally, inerting stainless steel, such as silanized stainless steel, which is one type of inerting stainless steel), and the cold spots or cold areas in the pipelines are reduced as much as possible so as to avoid the adsorption loss of the VOCs, while the other pipelines can be made of stainless steel pipes; the nitrogen connector 1, the first evacuation connector 501, the second evacuation connector 502, the third evacuation connector 503, and the compressed air connector 31 may be specifically through-plate connectors penetrating through the casing 100.

The working principle of the thermal desorption instrument is as follows: in the desorption step, the first mass flow controller 201, the second mass flow controller 202 and the proportional valve 12 are opened, the flow of the first mass flow controller 201 and the flow of the second mass flow controller 202 are set according to the target split ratio, and the ratio of the flow of the proportional valve 12 to the flow of the second mass flow controller 202 is controlled to meet the target split ratio, so that the VOCs can be quantitatively adsorbed in the temperature-controlled focusing tube 10 and the sample recovery tube 7 according to the target split ratio, and then the purging step and the sample injection analysis step are performed, so that the purpose of completing analysis and detection of the VOCs by matching the gas chromatograph 300 is achieved. From this through the detailed description of aforementioned concrete structure and theory of operation, a can arrange gas chromatograph and accomplish the novel thermal desorption appearance of volatile organic compounds analysis and detection, it not only can realize accurate reposition of redundant personnel control, can also be under the different split ratio circumstances, do benefit to converting each other to the analysis result, the analysis result that makes sample recovery pipe can carry out qualitative and quantitative analysis, increase substantially the fault-tolerant rate of thermal desorption appearance, thereby can avoid repeated sampling, conveniently carry out the detection of volatile organic compounds, do benefit to practical application and popularization.

Optimally, the device also comprises an air inlet connector 15 and an air pump 16, wherein the air inlet connector 15 is used for being communicated with a common outlet of the sampling tank automatic sampler 400; the air inlet joint 15 is communicated with the first port P81 of the eight-way switching valve 8, the input port of the air pump 16 is communicated with the output port of the second mass flow controller 202, and the output port of the air pump 16 is communicated with the third emptying joint 503. As shown in FIG. 1, the air inlet connector 15 is used for introducing sample gas, nitrogen gas or internal standard gas from a sampling tank autosampler 400 (an existing sampling tank autosampler device, the basic structure is that a plurality of selector valves are communicated with different sampling tanks, when the sampling tank autosampler is switched to a certain sampling position, a common outlet of the plurality of selector valves is communicated with the corresponding sampling tank, besides, one path of the plurality of selector valves needs to be communicated with a nitrogen gas bottle, and the other path needs to be plugged), so as to realize the purpose of 'cross-boundary' collocation analysis of the sampling tanks; in addition, when the thermal desorption instrument has a housing 100, the air inlet joint 15 may also be a plate penetrating joint penetrating through the housing 100; in addition, as shown in fig. 1, in order to avoid the intake air temperature from being too low, an intake air temperature control unit 146 may be disposed at the installation position of the intake air connector 15 so as to appropriately heat the gas flowing through the intake air connector 15, for example, the carrier gas temperature control unit 146 may also be specifically a heating pipeline. The air pump 16 is used to provide pumping power for the gas flow in the internal piping of the instrument at start-up so that the sample gas, nitrogen gas, internal standard gas, or the like from the sample tank autosampler 400 can be introduced normally. Therefore, through the configuration of the elements, a sampling tank (namely a suma tank) or an air bag can be analyzed, the purpose of one device with multiple purposes is achieved, VOCs (including organic sulfur and n-hexadecane) listed in all standards of a thermal desorption method can be responded and analyzed, and all VOCs in volatile organic compound monitoring schemes in key areas issued by the country can be analyzed, namely the VOCs are applied to an adsorption tube and the VOCs are applied to a sampling tank, the VOCs basically cover all VOCs at home and abroad, the device is designed by an integrated person, and the application range of the thermal desorption instrument is greatly expanded. In addition, internal standard gas can be introduced into an internal pipeline of the instrument through a sampling tank automatic sampler provided with an internal standard gas level (namely, one path of the multi-path selection valve is communicated with an internal standard gas tank), so that the purpose of measurement and analysis by an internal standard method is realized, and the application range is further expanded.

Preferably, the eight-way switching valve further comprises an internal standard gas inlet joint 17 and a solenoid valve 18, wherein the internal standard gas inlet joint 17 is communicated with an input port of the solenoid valve 18, and an output port of the solenoid valve 18 is communicated with a first port P81 of the eight-way switching valve 8. As shown in fig. 1, the internal standard gas inlet joint 17 is used for communicating an internal standard gas tank (not shown in the figure), so that an internal standard gas can be introduced into an internal pipeline of the instrument when the electromagnetic valve 18 is controlled to be switched on, the purpose of measurement and analysis by an internal standard method is achieved, and the application range is further expanded. In addition, as shown in fig. 1, when the air inlet joint 15, the internal standard air inlet joint 17 and the electromagnetic valve 18 are included at the same time, the third port P33 of the multi-way switching valve 3, the first port of the sample collection pipe 7, the first port P81 of the eight-way switching valve 8, the air inlet joint 15 and the electromagnetic valve 18 can be communicated with each other by a combination structure of an inerting tee and an inerting four-way.

Preferably, the system also comprises a first containing box 19 for containing the temperature-controlled dehydration pipe 9, a second containing box 20 for containing the temperature-controlled focusing pipe 10, an on-off valve 403, a first speed regulating valve 21 and a second speed regulating valve 22; the first port of the on-off valve 403 is communicated with the nitrogen connector 1, the second port of the on-off valve 403 is respectively communicated with the input port of the first speed regulating valve 21 and the input port of the second speed regulating valve 22, the output port of the first speed regulating valve 21 is communicated with the inner cavity of the first accommodating box 19, and the output port of the second speed regulating valve 22 is communicated with the inner cavity of the second accommodating box 20. As shown in FIG. 1, the first and

second containers

19 and 20 are approximately sealed boxes, which may be made of, but not limited to, a nitrogen-oxygen glass fiber material. The on-off valve 403 may be, but not limited to, an electromagnetic switching valve (which is used for implementing gas circuit switching in an electromagnetic control manner between a normally closed port and a normally open port in a power-off state, and a normally open port and a normally closed port in a power-on state, or an electromagnetic switch valve); as shown in fig. 1, when the on-off valve 403 is an electromagnetic switching valve, a normally closed port of the electromagnetic switching valve is blocked, a normally open port serves as a first port to communicate with the nitrogen gas connector 1, and a common port serves as a second port to communicate with the input port of the first speed regulating valve 21 and the input port of the second speed regulating valve 22, respectively. The first speed regulating valve 21 and the second speed regulating valve 22 are used for regulating the air flow speed respectively, so that nitrogen can be blown into the corresponding accommodating boxes at uniform speed. Therefore, through the structural design, the purpose of blowing nitrogen into the first accommodating box 19 and the second accommodating box 20 at uniform speed can be achieved by electrifying the on-off valve 403 and opening the first speed regulating valve 21 and the second speed regulating valve 22, dry nitrogen is fully filled around the temperature control dehydration pipe 9 and the temperature control focusing pipe 10, the phenomenon that accessories such as heating wires (the service life of the heating wires is easily reduced due to oxygen) or electronic refrigeration elements (water can freeze on the electronic refrigeration elements and damage hardware seriously) are influenced due to the existence of oxygen and moisture is avoided, the service life of a temperature control unit and the like is prolonged, and the temperature control dehydration pipe is particularly suitable for nitrogen blowing protection when the temperature control dehydration pipe 9 and the temperature control focusing pipe 10 are cleaned thermally.

Preferably, the sample recovery device further comprises a trap 23, wherein an input port of the trap 23 is communicated with the second port of the sample recovery pipe 7, and an output port of the trap 23 is communicated with an input port of the proportional valve 12. As shown in fig. 1, the trap 23 is used for adsorbing volatile organic compounds in the exhaust gas to protect the environment, and may be embodied as a quartz tube or a stainless steel tube filled with activated carbon.

To sum up, the thermal desorption instrument for detecting volatile organic compounds provided by the embodiment has the following technical effects:

(1) the embodiment provides a novel thermal desorption instrument capable of completing analysis and detection of volatile organic compounds by matching with a gas chromatograph, which can firstly open two mass flow controllers and a proportional valve in a desorption link, set the flow of the two mass flow controllers according to a target split ratio, and control the ratio of the flow of the proportional valve to the flow of the emptying mass flow controller to meet the target split ratio, so that VOCs can be quantitatively adsorbed in a focusing tube and a sample recovery tube according to the target split ratio, and then perform a purging link and a sample injection analysis link, thereby not only realizing accurate split control, but also being beneficial to converting analysis results mutually under the condition of different split ratios, enabling the analysis results of the sample recovery tube to be qualitatively and quantitatively analyzed, greatly increasing the fault-tolerant rate of the thermal desorption instrument, and avoiding repeated sampling, the detection of the volatile organic compounds is convenient, and the practical application and popularization are facilitated.

Example two

As shown in fig. 1 to 11, the present embodiment, as an analysis system for detecting volatile organic compounds based on the thermal desorption apparatus of the first embodiment, includes a nitrogen gas cylinder 200 and a gas chromatograph 300 in addition to the thermal desorption apparatus for detecting volatile organic compounds of the first embodiment; the nitrogen gas cylinder 200 is communicated with the nitrogen gas joint 1 of the thermal desorption instrument, the carrier gas output pipe of the gas chromatograph 300 is communicated with the gas inlet pipeline in the carrier gas inlet and outlet pipeline 11, and the carrier gas return pipe of the gas chromatograph 300 is communicated with the gas outlet pipeline in the carrier gas inlet and outlet pipeline 11.

As shown in fig. 1, the nitrogen gas cylinder 200 is used to supply dry nitrogen gas required for cleaning, desorption, purging, and the like to the internal piping of the apparatus. The gas chromatograph 300 is configured to guide the VOCs temporarily adsorbed in the temperature-controlled focusing tube 11 from the carrier gas reflux pipe in the sample introduction step in cooperation with the thermal desorption apparatus, and then perform component separation through the internal chromatographic column, and then perform quantitative analysis through the internal detector. Specifically, the detector in the gas chromatograph 300 may be, but is not limited to, any one of a mass spectrometer detector, a hydrogen flame ionization detector, an electron capture detector, a photoionization detector, a flame photometric detector, and the like. In particular, when the gas chromatograph 17 employs a mass spectrometer, the components of the VOCs can still be identified by the characteristic ion fragments in the case of incomplete chromatographic separation, thereby reducing interference of the gas in the constant volume and the difficulty of separation. When specific organic substances are targeted, quantitative analysis may also be performed using a detector such as any one of a hydrogen flame ionization detector, an electron capture detector, a photoionization detector, and a flame photometric detector. Through the structural design of the analysis system, the technical effects described in the first embodiment can be further achieved, which is not described herein again.

The optimized operation method of the analysis system for detecting volatile organic compounds may include, but is not limited to, the following steps S11 to S14.

S11, temperature control: respectively starting the temperature control dehydration pipe 9 and the temperature control focusing pipe 10 to enter a refrigeration mode, then maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe is reduced to a dehydration working temperature value, and maintaining the temperature of the focusing pipe when the temperature of the focusing pipe is reduced to a focusing working temperature value.

In the step S11, the dehydration operating temperature value may specifically be a preset temperature value below zero degrees centigrade, and the focusing operating temperature value may specifically be a preset temperature value below-20 degrees centigrade.

S12, desorption: first, the multi-way switching valve 3 is set to the a-position state, the first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are respectively turned off, the eight-way switching valve 8 is set to the B-position state, the first mass flow controller 201, the second mass flow controller 202 and the proportional valve 12 are then opened, and sets the flow rate of the first mass flow controller 201 and the flow rate of the second mass flow controller 202 according to the target split ratio, and controlling the ratio of the flow rate of the proportional valve 12 to the flow rate of the second mass flow controller 202 to satisfy the target flow division ratio, then starting the desorption tube temperature control unit 141 to perform heating desorption on the adsorption tube 6 when the flow rate is in a stable state, after the first time, the desorption tube temperature control unit 141 is started again to cool the adsorption tube 6, and finally, after the second time, the first mass flow controller 201, the second mass flow controller 202 and the proportional valve 12 are closed respectively.

Before the step S12, if the adsorption tube 6 is detachably installed in the installation position, it is necessary to check the airtightness of the loaded pipeline before the desorption step, and the following steps S101 to S104 may be further included.

S101, loading: the adsorption tube 6 is loaded on the installation site. If the loading is the first loading after the power-on, the loading is performed after the temperature control units are started and reach the corresponding expected temperature, specifically, but not limited to, the loading may include: starting the adsorption temperature control unit 141 to make the temperature of the adsorption tube installation site in a normal temperature state; starting the central temperature control unit 144 to make the corresponding circulation pipeline in a suitable high temperature state; the carrier gas temperature control unit 145 is started to make the corresponding flow pipeline in a proper high temperature state; and so on.

S102, leak detection: first, the second mass flow controller 202 is closed, the multi-way switching valve 3 is set to the a-position state, the first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are deenergized, the eight-way switching valve 8 is set to the B-position state, the proportional valve 12 is closed, first mass flow controller 201 is then turned on and set to the sorbent tube leak detection operating flow value, if the monitoring result of the gas pressure sensor 13 indicates that the internal gas pressure does not rise within the first leak detection time, it is determined that the adsorption tube 6 is completely gas-leaked or the adsorption tube 6 is not normally loaded, then step S104 is executed, otherwise, the first mass flow controller 201 is turned off, if the monitoring result of the gas pressure sensor 13 indicates that the internal gas pressure falls to the atmospheric normal pressure or a set value within the second leak detection time, it is determined that the gas tightness of the adsorption tube 6 is poor, then step S104 is executed, otherwise, it is determined that the air-tightness of the adsorption tube 6 is good, and then step S103 is executed. As shown in fig. 2, after the suction pipe 6 is loaded, it can be determined whether the suction pipe is loaded normally by this step S102. In addition, the value of the flow rate of the adsorption tube leak detection operation is a preset value, and the first leak detection time and the second leak detection time are also preset times, and step S11 can be executed at this time, so as to save the cooling time, and when step S104 is executed, the refrigeration operations of the temperature-controlled dehydration tube 9 and the temperature-controlled focusing tube 10 are suspended at the same time.

S103, pressure relief: first, the first mass flow controller 201 and the second mass flow controller 202 are closed, the multi-way switching valve 3 is set to the a-position state, the first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are deenergized, the eight-way switching valve 8 is set to the B-position state, and then the proportional valve 12 is opened. As shown in fig. 3, the high pressure nitrogen in the pipeline can be discharged by the formed short gas flow. In addition, because the proportional valve 12 can accurately control the flow, the air flow inside the pipeline is not too fast, and the impact air flow generated by flushing the tube fillers in the adsorption tube 6 and the temperature-controlled focusing tube 10 can be avoided.

And S104, sending a loading error prompt message, and unloading and returning the adsorption pipe 6. After unloading and returning the adsorption tube 6, if the next adsorption tube is loaded again, the step S102 needs to be returned again to perform the leak detection operation.

In addition, after the sorbent tube leak detection is passed (i.e., after step S103 is performed), in order to further remove possible impurities and moisture in the sorbent tube 6, the following dry-blowing sorbent tube procedure may be performed: the multi-way switching valve 3 is set to the B-position state, the first electromagnetic switching valve 401 is energized, the second electromagnetic switching valve 402 is de-energized, the first mass flow controller 201 is then opened, the flow rate of the first mass flow controller 201 is set to the dry blow operating flow rate value, and finally, after the seventh time has elapsed, the first mass flow controller 201 is closed. As shown in fig. 4, it is possible to remove possible impurities and moisture in the adsorption tube 6 to some extent and replace the gas in the adsorption tube with nitrogen gas so that no oxygen will cause oxidative damage to the adsorbent when heated. In addition, the dry blowing working flow value is a preset value, and the seventh time is also preset time.

In the step S12, a split-flow manner is adopted for desorption (this manner is suitable for the case where the content of the adsorbed VOCs in the adsorption tube 6 is high), as shown in fig. 5, the purpose is to heat and desorb the VOCs and other substances in the adsorption tube 6, and flow away with the nitrogen, and then condense and dehydrate the VOCs at the temperature-controlled dehydration tube 9 by using a lower dehydration tube temperature, and perform focused adsorption of the VOCs at the temperature-controlled focusing tube 10 by using a lower focusing tube temperature, so as to achieve the purpose of transferring the VOCs to the temperature-controlled focusing tube 10. Because the flow of the first mass flow controller 201 and the flow of the second mass flow controller 202 are set according to the target split ratio, and the ratio of the flow of the control proportional valve 12 to the flow of the second mass flow controller 202 meets the target split ratio, the VOCs can be quantitatively adsorbed in the temperature-controlled focusing tube 10 and the sample recovery tube 7 according to the target split ratio, so that not only can the accurate split control be realized, but also the conversion of analysis results can be facilitated under the condition of different split ratios, the analysis results of the sample recovery tube can be qualitatively and quantitatively analyzed, and the fault tolerance of the thermal desorption instrument can be greatly increased. In addition, the target shunt ratio is a preset ratio, and the first time and the second time are also preset times.

In addition, in the case of low content of volatile organic compounds adsorbed in the adsorption tube 6, since the amount of VOCs entering the gas chromatograph is further reduced by the split flow, as shown in fig. 6, the following non-split flow desorption process may be performed: firstly, the multi-way switching valve 3 is in an A position state, the first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are respectively powered off, the eight-way switching valve 8 is in a B position state, the proportional valve 12 is closed, then the first mass flow controller 201 and the second mass flow controller 202 are opened, the flow rate of the second mass flow controller 202 is set to be larger than that of the first mass flow controller 201, then when the flow rate is in a stable state, the desorption pipe temperature control unit 141 is started to perform heating desorption on the adsorption pipe 6, after the eighth time, the desorption pipe temperature control unit 141 is started to perform cooling on the adsorption pipe 6, and finally, after the ninth time, the first mass flow controller 201 and the second mass flow controller 202 are respectively closed. In addition, the eighth time and the ninth time are respectively preset times.

In addition, if the volatile organic compound is analyzed and detected by using the internal standard method, before or after the step S12 (i.e., the internal standard may be added first and then the desorption focusing is performed, or the desorption focusing may be performed first and then the internal standard is added), an internal standard gas collection procedure may be performed in any one of the following manners:

(SB1) when the thermal desorption apparatus includes the air inlet connector 15 and the analysis system further includes the sample tank autosampler 400 having a common outlet communicating with the air inlet connector 15: firstly, the multi-way switching valve 3 is in a B-position state, the second electromagnetic switching valve 402 is powered off, the eight-way switching valve 8 is in the B-position state, the proportional valve 12 is closed, the temperature of the dehydration tube and the temperature of the focusing tube are maintained, then the second mass flow controller 202 is opened, the flow is set to be an internal standard gas collection working flow value, the sampling tank automatic sampler 400 is switched to the internal standard position state, and finally, after the set internal standard gas product is collected, the sampling tank automatic sampler 400 is switched to a blocking position state, and the second mass flow controller 202 is closed. As shown in fig. 7, internal standard gas collection may be accomplished by sample tank autosampler 400. In addition, the internal standard gas collection working flow value is a preset value.

(SB2) when the thermal desorption apparatus includes the internal standard gas inlet connector 17 and the electromagnetic valve 18 and the analysis system further includes the internal standard gas cylinder communicated with the internal standard gas inlet connector 17: firstly, the multi-way switching valve 3 is in a B-position state, the second electromagnetic switching valve 402 is powered off, the eight-way switching valve 8 is in a B-position state, the proportional valve 12 is closed, the temperature of the dehydration tube and the temperature of the focusing tube are maintained, then the second mass flow controller 202 is opened, the flow is set to be an internal standard gas collection working flow value, the electromagnetic valve 18 is conducted, and finally the second mass flow controller 202 and the electromagnetic valve 18 are closed after the set internal standard gas product is collected. As shown in fig. 8, the internal standard gas collection can be realized by the electromagnetic valve 18 and an external internal standard gas tank.

S13, purging: first, the multi-way switching valve 3 is set to the a-position state, the first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are turned off, the eight-way switching valve 8 is set to the B-position state, the proportional valve 12 is closed, then the temperature control dehydration tube 9 is started to enter a heating mode, so that the temperature of the dehydration tube is slowly increased, the temperature of the focusing tube is continuously maintained, simultaneously starting the first mass flow controller 201 and the second mass flow controller 202, setting the flow of the first mass flow controller 201 as a first purging working flow value and slightly smaller than the flow of the second mass flow controller 202, then when the temperature of the dehydration pipe is raised to a purging working temperature value, the flow rate of the first mass flow controller 201 is set to the second purge operation flow rate value and slightly less than the flow rate of the second mass flow controller 202, and finally after the third time has elapsed, the first mass flow controller 201 and the second mass flow controller 202 are closed, respectively.

In step S13, since the temperature-controlled dehydration pipe 9 is below zero degrees centigrade, in addition to freezing water, condensation of high-boiling-point VOCs and dissolution loss of VOCs with good water solubility may be caused, and few VOCs remain in the pipeline, as shown in fig. 9, the residual VOCs in the temperature-controlled dehydration pipe 9 and other pipelines may be introduced into the temperature-controlled focusing pipe 10 for adsorption through the aforementioned step S13. In addition, the purging operation temperature value is generally a preset temperature above zero, the first purging operation flow value and the second purging operation flow value are preset values respectively, and the third time is also preset time.

S14, sample injection: firstly, starting the temperature control focusing tube 10 to enter a heating mode, rapidly raising the temperature of the focusing tube to a desorption working temperature value of the focusing tube, then enabling the eight-way switching valve 8 to be in an A-position state, enabling carrier gas of the gas chromatograph 300 to flow back after passing through the temperature control focusing tube 10, simultaneously starting the gas chromatograph 300 for separation analysis, and finally switching the eight-way switching valve 8 to be in a B-position state after fourth time.

In the step S14, the desorption operating temperature value of the focusing tube is a preset value, and the fourth time is also a preset time, wherein the fast temperature rise time is generally between 0 and 20 seconds, and is a relative concept with the "slow temperature rise" in the step S13. As shown in fig. 10, when it is determined that the gas chromatograph 300 is in the ready state, step S14 may be executed to heat and desorb the VOCs in the temperature-controlled focusing tube 10 and bring them into the gas chromatograph by the carrier gas of the gas chromatograph 300 for separation and analysis (specifically, including component separation by an internal chromatographic column and then quantitative analysis by an internal detector). In addition, the solid phase adsorbent in the thermal desorption method generally achieves the adsorption of various VOCs in a combined mode, so that the opposite directions of the airflow during the adsorption and desorption have very important significance, and the opposite directions of the airflow during the sample injection for desorbing the VOCs and the direction for adsorbing the VOCs just ensure the point.

Preferably, the thermal cleaning process can be carried out in any one of the following manners:

(SA1) adsorption tube heat washing was performed while the sample was being fed and the eight-way switching valve 8 was in the a-position state: firstly, the multi-way switching valve 3 is in an A position state, the first electromagnetic switching valve 401 and the second electromagnetic switching valve 402 are respectively powered off, the second mass flow controller 202 is closed, then the first mass flow controller 201 and the proportional valve 12 are opened, the flow rate of the first mass flow controller 201 is set as an adsorption pipe cleaning working flow rate value, then when the flow rate is in a stable state, the adsorption pipe temperature control unit 141 is started to heat the adsorption pipe 6, and when the temperature reaches a hot cleaning working temperature value, the temperature of the adsorption pipe is maintained. As shown in FIG. 10, the thermal cleaning of the adsorption tube 6 can be completed at the same time of sample injection, thereby shortening the time for completing the whole detection process. In addition, the adsorption tube cleaning working flow value is a preset value, and the hot cleaning working temperature value is slightly higher than the adsorption tube temperature during desorption.

(SA2) dehydration tube washing and focusing tube washing after sample injection: first, the multi-way switching valve 3 is set to the B-position state, the first electromagnetic switching valve 401 is de-energized, the second electromagnetic switching valve 402 is energized, the eight-way switching valve 8 is set to the B-position state, then the first mass flow controller 201 and the proportional valve 12 are opened, the flow of the first mass flow controller 201 is set as the thermal cleaning working flow value, then the temperature control dehydration pipe 9 and the temperature control focusing pipe 10 are respectively started to enter a heating mode, and when the temperature of the dehydration tube reaches the thermal cleaning working temperature value of the dehydration tube, the temperature of the dehydration tube is maintained, and when the temperature of the focusing tube reaches the temperature value of the thermal cleaning working temperature of the focusing tube, maintaining the temperature of the focusing tube, finally respectively starting the temperature control dehydration tube 9 and the temperature control focusing tube 10 to enter a refrigeration mode after the fifth time, and when the temperature of the dehydration tube and the temperature of the focusing tube reach the normal temperature or the set value, respectively, the first mass flow controller 201 and the proportional valve 12 are closed. As shown in fig. 11, since the hot cleaning operation temperature value of the dehydration tube is a preset temperature value significantly higher than 100 ℃, and the hot cleaning operation temperature value of the focusing tube is a temperature value slightly higher than the desorption temperature of the temperature control focusing tube 10, VOCs possibly remaining in the temperature control focusing tube 10 can be heated and desorbed and are carried away by nitrogen gas and flow through the temperature control dehydration tube 9, water in the temperature control dehydration tube 9 is carried away by other impurities, and finally, the water is purified by the trap and then is evacuated. In addition, the fifth time is a preset time. As shown in fig. 11, the purpose of blowing nitrogen gas into the first container box 19 and the second container box 20 at the same speed can be achieved by energizing the on/off valve 403 and opening the first speed control valve 21 and the second speed control valve 22, and the service life of the temperature control unit and the like can be prolonged; and after the heat cleaning is completed, the cooling fan of the adsorption tube temperature control unit 141 can be turned off, and the adsorption tube 6 is unloaded and returned to the original position so as to load the next adsorption tube for the next detection.

EXAMPLE III

As shown in fig. 1 and 12, in this embodiment, on the basis of the second embodiment, another analysis system for detecting volatile organic compounds is further provided, that is, when the thermal desorption apparatus includes the air inlet connector 15 and the air pump 16, the analysis system further includes a sample tank autosampler 400, where the sample tank autosampler 400 has at least one nitrogen gas level and one blocking level; the common outlet of the sample tank autosampler 400 communicates with the air inlet connector 15.

As shown in fig. 1, the sampling tank autosampler 400 is used for providing a plurality of sample levels to be detected (i.e. the internal multi-way selector valve is communicated with a plurality of sampling tanks) besides providing a nitrogen level and a plugging level, so that when the sampling tank autosampler is switched to a certain sampling level, the public outlet of the multi-way selector valve is communicated with the corresponding sampling tank, so that the sampling gas in the sampling tank enters the thermal desorption apparatus, and volatile organic compound analysis and detection are performed on the sampling gas at a single time through desorption, purging and sample injection links, and the highly automatic characteristics of the sampling tank autosampler 400 can be utilized, thereby realizing serialized batch analysis and detection and greatly improving the working efficiency of the analysis system. Therefore, the technical effects described in the first embodiment can be further achieved through the structural design of the analysis system, which is not described herein again.

The optimized operation method of the analysis system for detecting volatile organic compounds may include, but is not limited to, the following steps S21 to S24.

S21, respectively starting the temperature control dehydration pipe 9 and the temperature control focusing pipe 10 to enter a refrigeration mode, and then maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe is reduced to a dehydration working temperature value, and maintaining the temperature of the focusing pipe when the temperature of the focusing pipe is reduced to a focusing working temperature value.

The details of the step S21 can specifically refer to the step S11 in the second embodiment, which are not described herein again.

S22, collecting: firstly, the multi-way switching valve 3 is in a B position state, the second electromagnetic switching valve 402 is powered off, the eight-way switching valve 8 is in a B position state, the proportional valve 12 is closed, then the sampling tank automatic sampler 400 is switched to a sample position, the second mass flow controller 202 and the air pump 16 are started, the flow of the second mass flow controller 202 is set as a collection working flow value, and finally, after the set volume of sample gas is extracted, the sampling tank automatic sampler 400 is switched to a blocking position, and the second mass flow controller 202 and the air pump 16 are closed.

Before the step S22, an empty tube (in this case, a functional tube) may be loaded at the installation site of the adsorption tube 6 so as to function as a communication line, and the adsorption tube temperature control unit 141 may not be activated. Meanwhile, after loading the empty tube, the steps of detecting the leak of the adsorption tube as steps S102 to S104 also need to be performed, which is not described herein again. In addition, during the sequence in which the sample tank autosampler 400 is used for batch detection analysis, the empty pipe is not unloaded, and loading is started only at the beginning of the sequence in succession.

Before step S22, in order to flush the flow path, a flush segment may be inserted before any one of the analysis sequences or the first sequence, where the following flush segment is performed: firstly, the multi-way switching valve 3 is in a B position state, the second electromagnetic switching valve 402 is powered off, the eight-way switching valve 8 is in an A position state, the proportional valve 12 is closed, then the second mass flow controller 202 is opened, the flow of the second mass flow controller 202 is set as a flushing working flow value, the sampling tank automatic sample injector 400 is switched to a nitrogen position, simultaneously the temperature control dehydration pipe 9 and the temperature control focusing pipe 10 are respectively started to enter a heating mode, the temperature of the dehydration pipe is rapidly increased to a dehydration pipe flushing working temperature value (specifically a preset temperature value which is obviously higher than 100 ℃), the temperature of the focusing pipe is rapidly increased to a focusing pipe flushing working temperature value (specifically a temperature value which is slightly higher than the desorption temperature of the temperature control focusing pipe 10), then after nitrogen with a preset volume is introduced, the sampling tank automatic sample injector 400 is switched to a blocking position, and finally when the flow is reduced to zero, the second mass flow controller 202 is closed and step S21 is performed.

In step S22, the sample collection method used can only be a non-split desorption method, as shown in fig. 12. Similarly, if the volatile organic compound is detected by the internal standard method, the internal standard gas may be collected by the method in example two (SB1) or the method in example two (SB2) before or after the step S22, which is not described herein again. In addition, the acquired working flow value is a preset value, and a schematic gas flow diagram of a flushing, purging and mode (SB1) can also be referred to fig. 12.

S23, purging: firstly, the multi-way switching valve 3 is in a B position state, the second electromagnetic switching valve 402 is powered off, the eight-way switching valve 8 is in a B position state, the proportional valve 12 is closed, then the temperature control dehydration pipe 9 is started to enter a heating mode, the temperature of the dehydration pipe is slowly increased, the temperature of the focusing pipe is continuously maintained, meanwhile, the sampling tank automatic sample injector 400 is switched to a nitrogen position, the second mass flow controller 202 and the air pump 16 are started, the flow of the second mass flow controller 202 is set to be a third purging working flow value, then when the temperature of the dehydration pipe is increased to a purging working temperature value, the flow of the second mass flow controller 202 is set to be a fourth purging working flow value, finally, after the sixth time, the sampling tank automatic sample injector 400 is switched to a blocking position, and the second mass flow controller 202 and the air pump 16 are closed.

The effect and purpose of step S23 are similar to step S13 of example two, except that the nitrogen comes from the nitrogen level of sample tank auto-sampler 400, and will not be described again.

S24, sample injection: firstly, starting the temperature control focusing tube 10 to enter a heating mode, rapidly raising the temperature of the focusing tube to a desorption working temperature value of the focusing tube, then enabling the eight-way switching valve 8 to be in an A-position state, enabling carrier gas of the gas chromatograph 300 to flow back after passing through the temperature control focusing tube 10, simultaneously starting the gas chromatograph 300 for separation analysis, and finally switching the eight-way switching valve 8 to be in a B-position state after fourth time.

The effect and purpose of step S24 and the subsequent thermal cleaning steps are similar to those of step S14 in the second embodiment, and are not repeated here.

Further, if the next sample of the analysis sequence is no longer the sample in the sample tank autosampler 400, the empty tube may be unloaded and returned, whereas if the sample is still in the sample tank autosampler 400, unloading may be skipped and the process returns to steps S22-S24 for performing the detection analysis of the next sample.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: modifications of the technical solutions described in the embodiments or equivalent replacements of some technical features may still be made. And such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Finally, it should be noted that the present invention is not limited to the above alternative embodiments, and that various other forms of products can be obtained by anyone in light of the present invention. The above detailed description should not be taken as limiting the scope of the invention, which is defined in the claims, and which the description is intended to be interpreted accordingly.

Claims

1. The thermal desorption instrument for detecting the volatile organic compounds is characterized by comprising a nitrogen connector (1), a first mass flow controller (201), a second mass flow controller (202), a multi-way switching valve (3), a first electromagnetic switching valve (401), a second electromagnetic switching valve (402), a first emptying connector (501), a second emptying connector (502), a third emptying connector (503), an adsorption tube (6), a sample recovery tube (7), an eight-way switching valve (8), a temperature control dehydration tube (9), a temperature control focusing tube (10), a carrier gas inlet and outlet pipeline (11), a proportional valve (12) and a gas pressure sensor (13), wherein an adsorption tube temperature control unit (141) is arranged around the adsorption tube (6);

the nitrogen connector (1) is communicated with an input port of the first mass flow controller (201), the output port of the first mass flow controller (201) is respectively communicated with a second interface (P32) of the multi-way switching valve (3), the normally closed port of the first electromagnetic switching valve (401) and the normally open port of the second electromagnetic switching valve (402), the normally open port of the first electromagnetic switching valve (401) is communicated with the first emptying joint (501), the common port of the first electromagnetic switching valve (401) is communicated with the first port of the adsorption pipe (6), the second port of the adsorption pipe (6) is communicated with the first port (P31) of the multi-way switching valve (3), the third interface (P33) of the multi-way switching valve (3) is respectively communicated with the first port of the sample recovery tube (7) and the first interface (P81) of the eight-way switching valve (8);

the second port of the sample recovery pipe (7) is communicated with the input port of the proportional valve (12), the air pressure sensor (13) is arranged in an air path between the second port of the sample recovery pipe (7) and the input port of the proportional valve (12), and the output port of the proportional valve (12) is communicated with the second emptying joint (502);

the second port (P82) of the eight-way switching valve (8) is communicated with the first port of the temperature control dehydration pipe (9), the second port of the temperature control dehydration pipe (9) is communicated with an eighth port (P88) of the eight-way switching valve (8), a seventh interface (P87) of the eight-way switching valve (8) is communicated with the first port of the temperature control focusing pipe (10), the second port of the temperature control focusing pipe (10) is communicated with a fourth port (P84) of the eight-way switching valve (8), a fifth interface (P85) of the eight-way switching valve (8) is communicated with an air inlet pipeline in the carrier gas inlet and outlet pipeline (11), a sixth port (P86) of the eight-way switching valve (8) is communicated with an air outlet pipeline in the carrier gas inlet and outlet pipeline (11), a third port (P83) of the eight-way switching valve (8) is communicated with a common port of the second electromagnetic switching valve (402);

the normally closed port of the second electromagnetic switching valve (402) is communicated with the input port of the second mass flow controller (202), and the output port of the second mass flow controller (202) is communicated with the third emptying joint (503).

2. The thermal desorption instrument for detecting the volatile organic compounds according to claim 1, further comprising an air inlet connector (15) and an air pump (16), wherein the air inlet connector (15) is used for being communicated with a common outlet of the sample tank autosampler (400);

the air inlet joint (15) is communicated with a first interface (P81) of the eight-way switching valve (8), the input port of the air pump (16) is communicated with the output port of the second mass flow controller (202), and the output port of the air pump (16) is communicated with the third emptying joint (503).

3. The thermal desorption instrument for detecting the volatile organic compound according to claim 1, further comprising an internal standard gas inlet joint (17) and a solenoid valve (18), wherein the internal standard gas inlet joint (17) is communicated with an input port of the solenoid valve (18), and an output port of the solenoid valve (18) is communicated with the first port (P81) of the eight-way switching valve (8).

4. An analysis system for detecting volatile organic compounds, comprising the thermal desorption apparatus for detecting volatile organic compounds according to any one of claims 1 to 8, further comprising a nitrogen gas cylinder (200) and a gas chromatograph (300);

nitrogen cylinder (200) intercommunication nitrogen gas joint (1) of thermal desorption appearance, the inlet line in gas chromatograph (300) carrier gas output tube intercommunication carrier gas business turn over pipeline (11), the outlet line in gas chromatograph's (300) carrier gas back flow intercommunication carrier gas business turn over pipeline (11).

5. The analytical system for detection of volatile organic compounds according to claim 4, further comprising a sample tank autosampler (400) when the thermal desorption apparatus comprises an air inlet connector (15) and an air pump (16), wherein the sample tank autosampler (400) has at least a nitrogen level and a blocking level;

and the common outlet of the sampling tank autosampler (400) is communicated with the air inlet joint (15).

6. A method of operating an analytical system for volatile organic detection as in claim 4, comprising the steps of:

s11, temperature control: respectively starting a temperature control dehydration pipe (9) and a temperature control focusing pipe (10) to enter a refrigeration mode, then maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe is reduced to a dehydration working temperature value, and maintaining the temperature of the focusing pipe when the temperature of the focusing pipe is reduced to a focusing working temperature value;

s12, desorption: firstly, a multi-way switching valve (3) is in an A position state, a first electromagnetic switching valve (401) and a second electromagnetic switching valve (402) are respectively powered off, an eight-way switching valve (8) is in a B position state, then a first mass flow controller (201), a second mass flow controller (202) and a proportional valve (12) are opened, the flow of the first mass flow controller (201) and the flow of the second mass flow controller (202) are set according to a target flow dividing ratio, the ratio of the flow of the proportional valve (12) to the flow of the second mass flow controller (202) is controlled to meet the target flow dividing ratio, then when the flow is in a stable state, an desorption pipe temperature control unit (141) is started to heat and desorb an adsorption pipe (6), after first time, the desorption pipe temperature control unit (141) is started to refrigerate and cool the adsorption pipe (6), and finally after second time, closing the first mass flow controller (201), the second mass flow controller (202) and the proportional valve (12) respectively;

s13, purging: firstly, a multi-way switching valve (3) is in an A position state, a first electromagnetic switching valve (401) and a second electromagnetic switching valve (402) are respectively powered off, an eight-way switching valve (8) is in a B position state, a proportional valve (12) is closed, then a temperature control dehydration pipe (9) is started to enter a heating mode, the temperature of the dehydration pipe is slowly increased, the temperature of the dehydration pipe is continuously maintained, a first mass flow controller (201) and a second mass flow controller (202) are simultaneously opened, the flow of the first mass flow controller (201) is set to be a first purging working flow value and is slightly smaller than that of the second mass flow controller (202), and then when the temperature of the dehydration pipe is increased to a purging working temperature value, the flow of the first mass flow controller (201) is set to be a second purging working flow value and is slightly smaller than that of the second mass flow controller (202), finally, after a third time, closing the first mass flow controller (201) and the second mass flow controller (202) respectively;

s14, sample injection: the method comprises the steps of firstly starting a temperature-controlled focusing tube (10) to enter a heating mode, enabling the temperature of the focusing tube to be rapidly raised to a desorption working temperature value of the focusing tube, then enabling an eight-way switching valve (8) to be in an A-position state, enabling carrier gas of a gas chromatograph (300) to flow back after passing through the temperature-controlled focusing tube (10), simultaneously starting the gas chromatograph (300) to perform separation analysis, and finally switching the eight-way switching valve (8) to be in a B-position state after fourth time.

7. The method of claim 6, further comprising a cleaning step in any one of the following manners:

(SA1) performing adsorption tube heat washing when the sample is fed and the eight-way switching valve (8) is in the A position state: firstly, enabling a multi-way switching valve (3) to be in an A-position state, enabling a first electromagnetic switching valve (401) and a second electromagnetic switching valve (402) to be respectively powered off, enabling a second mass flow controller (202) to be closed, then opening a first mass flow controller (201) and a proportional valve (12), setting the flow of the first mass flow controller (201) as an adsorption pipe cleaning working flow value, then starting an adsorption pipe temperature control unit (141) to heat an adsorption pipe (6) when the flow is in a stable state, and maintaining the temperature of the adsorption pipe when a thermal cleaning working temperature value is reached;

(SA2) dehydration tube washing and focusing tube washing after sample injection: firstly, a multi-way switching valve (3) is in a B position state, a first electromagnetic switching valve (401) is powered off, a second electromagnetic switching valve (402) is powered on, an eight-way switching valve (8) is in a B position state, then a first mass flow controller (201) and a proportional valve (12) are opened, the flow of the first mass flow controller (201) is set as a hot cleaning working flow value, then a temperature control dehydration pipe (9) and a temperature control focusing pipe (10) are respectively started to enter a heating mode, the temperature of the dehydration pipe is maintained when the temperature of the dehydration pipe reaches the hot cleaning working temperature value of the dehydration pipe, the temperature of the focusing pipe is maintained when the temperature of the focusing pipe reaches the hot cleaning working temperature value of the focusing pipe, finally, the temperature control dehydration pipe (9) and the temperature control focusing pipe (10) are respectively started to enter a refrigeration mode after fifth time, and when the temperature of the dehydration pipe and the temperature of the focusing pipe respectively reach a normal temperature or a set value, the first mass flow controller (201) and the proportional valve (12) are closed.

8. The method of claim 6, further comprising an internal standard gas collection step before or after step S12, wherein the internal standard gas collection step includes any one of the following steps:

(SB1) when the thermal desorption apparatus comprises the air inlet connector (15) and the analysis system further comprises the sample tank autosampler (400) with the common outlet connected with the air inlet connector (15): firstly, enabling a multi-way switching valve (3) to be in a B-position state, powering off a second electromagnetic switching valve (402), enabling an eight-way switching valve (8) to be in the B-position state, closing a proportional valve (12), maintaining the temperature of a dehydration pipe and the temperature of a focusing pipe, then opening a second mass flow controller (202), setting the flow as an internal standard gas acquisition working flow value, switching a sampling tank automatic sampler (400) to the internal standard position state, finally switching the sampling tank automatic sampler (400) to a blocking position state after the set internal standard gas product is acquired, and closing the second mass flow controller (202);

(SB2) when the thermal desorption apparatus comprises the internal standard gas inlet joint (17) and the electromagnetic valve (18) and the analysis system further comprises the internal standard gas cylinder communicated with the internal standard gas inlet joint (17): the multi-way switching valve (3) is in a B position state, the second electromagnetic switching valve (402) is powered off, the eight-way switching valve (8) is in the B position state, the proportional valve (12) is closed, the temperature of a dehydration pipe and the temperature of a focusing pipe are maintained, then the second mass flow controller (202) is opened, the flow is set to be an internal standard gas collection working flow value, the electromagnetic valve (18) is conducted, and finally the second mass flow controller (202) and the electromagnetic valve (18) are closed after the set internal standard gas product is collected.

9. The method of claim 6, further comprising the following steps S101-S104 before the step S12:

s101, loading: loading the adsorption tube (6) on the installation position;

s102, leak detection: firstly, closing a second mass flow controller (202), enabling a multi-way switching valve (3) to be in an A-position state, respectively powering off a first electromagnetic switching valve (401) and a second electromagnetic switching valve (402), enabling an eight-way switching valve (8) to be in a B-position state, closing a proportional valve (12), then opening a first mass flow controller (201) and setting the value as a leakage detection working flow value of an adsorption pipe, if a monitoring result of a pressure sensor (13) shows that the internal pressure does not rise within a first leakage detection time, judging that the adsorption pipe (6) is completely leaked or the adsorption pipe (6) is not normally loaded, then executing a step S104, otherwise, closing the first mass flow controller (201), and if the monitoring result of the pressure sensor (13) shows that the internal pressure falls to the atmospheric normal pressure or the set value within a second leakage detection time, judging that the air tightness of the adsorption pipe (6) is poor, then step S104 is executed, otherwise, the air tightness of the adsorption tube (6) is judged to be good, and then step S103 is executed;

s103, pressure relief: firstly, respectively closing a first mass flow controller (201) and a second mass flow controller (202), enabling a multi-way switching valve (3) to be in an A-position state, respectively powering off a first electromagnetic switching valve (401) and a second electromagnetic switching valve (402), enabling an eight-way switching valve (8) to be in a B-position state, and then opening a proportional valve (12);

s104, sending a loading error prompt message, and unloading and returning the adsorption tube (6).

10. A method of operating an analytical system for volatile organic detection as in claim 5, comprising the steps of:

s21, respectively starting the temperature control dehydration pipe (9) and the temperature control focusing pipe (10) to enter a refrigeration mode, and then maintaining the temperature of the dehydration pipe when the temperature of the dehydration pipe is reduced to a dehydration working temperature value and maintaining the temperature of the focusing pipe when the temperature of the focusing pipe is reduced to a focusing working temperature value;

s22, collecting: firstly, enabling a multi-way switching valve (3) to be in a B-position state, powering off a second electromagnetic switching valve (402), enabling an eight-way switching valve (8) to be in the B-position state, closing a proportional valve (12), then switching a sampling tank automatic sampler (400) to a sample position, opening a second mass flow controller (202) and an air pump (16), setting the flow of the second mass flow controller (202) as a collection working flow value, and finally switching the sampling tank automatic sampler (400) to a plugging position and closing the second mass flow controller (202) and the air pump (16) after a set volume of sample gas is extracted;

s23, purging: firstly, the multi-way switching valve (3) is in a B position state, the second electromagnetic switching valve (402) is powered off, the eight-way switching valve (8) is in a B position state, the proportional valve (12) is closed, then the temperature control dehydration tube (9) is started to enter a heating mode, so that the temperature of the dehydration tube is slowly increased, the temperature of the focusing tube is continuously maintained, simultaneously switching the sample tank autosampler (400) to the nitrogen level, and turning on the second mass flow controller (202) and the air pump (16), setting the flow of the second mass flow controller (202) as a third purging working flow value, and then when the temperature of the dehydration pipe is raised to a purging working temperature value, setting the flow of the second mass flow controller (202) to a fourth purge operating flow value, and finally after a sixth time, switching the sample tank autosampler (400) to the blocking position and closing the second mass flow controller (202) and the air pump (16);

s24, sample injection: the method comprises the steps of firstly starting a temperature-controlled focusing tube (10) to enter a heating mode, enabling the temperature of the focusing tube to be rapidly raised to a desorption working temperature value of the focusing tube, then enabling an eight-way switching valve (8) to be in an A-position state, enabling carrier gas of a gas chromatograph (300) to flow back after passing through the temperature-controlled focusing tube (10), simultaneously starting the gas chromatograph (300) to perform separation analysis, and finally switching the eight-way switching valve (8) to be in a B-position state after fourth time.