CN111579315A - VOCs and IVOCs simultaneous on-line collecting and detecting method - Google Patents

Abstract

The invention belongs to the technical field of environmental monitoring, and in particular relates to a simultaneous online collection and detection method of volatile organic compounds and medium volatile organic compounds. The method for simultaneous online collection and detection of VOCs and IVOCs includes using an online collection and detection device to carry out the following steps: standard samples or ambient air enter the TD system through a temperature-controlled sampling channel, and a set of sampling tube groups in the TD system simultaneously conduct the target substances. Adsorption sampling; at the same time, another group of sampling tubes uses inert gas to desorb the target substance, and the desorbed target substance is loaded into the GC/MS analysis system by high-purity helium gas through the sample transmission line; The Dean-Switch switching system performs secondary separation of the target VOCs separated first, and the secondary separated target VOCs and target IVOCs are simultaneously detected and analyzed by the mass spectrometer. The simultaneous online collection and detection method of VOCs and IVOCs of the present invention realizes the purpose of collecting and analyzing VOCs and IVOCs online at one time sampling.

Description

Simultaneous online collection and detection of VOCs and IVOCs

technical field

The invention belongs to the technical field of environmental monitoring, and in particular relates to a simultaneous online collection and detection method of volatile organic compounds and medium volatile organic compounds.

Background technique

The organic compounds in the atmosphere can be divided into medium volatile organic compounds (IVOCs, the saturation concentration range is 10 ³ μg/m ³ <C*<10 ⁶ μg/m ³ ) and volatile organic compounds ( VOCs, the saturation concentration range is C*>10 ⁶ μg/m ³ ). Since VOCs are considered to be important precursors _of O and secondary organic aerosols (SOA), they have always been the focus of research by researchers and related management departments. Recent studies have shown that IVOCs are also important precursors _of O and SOA in the atmosphere, and have aroused widespread interest among researchers. In addition, VOCs and IVOCs also have important hazards to human health.

The saturated concentration range of VOCs corresponds to that between C ₃ -C ₁₂ n-alkanes, and the range of IVOCs saturation concentration corresponds to that between C ₁₂ -C ₂₂ n-alkanes. At present, the detection technology of VOCs organic matter components and concentration levels is relatively mature, and monitoring technical guidelines or standards have been formulated, such as US EPA 5030C; the European Environmental Protection Agency's monitoring technical guidelines Technical Guidance Note (TGN) M8 and M16; and the Determination of Volatile Organic Compounds in Ambient Air (HJ 759-2015) promulgated by my country, which specifies the monitoring technology for offline collection and analysis of VOCs based on gas chromatography/mass spectrometry (GC/MS) standards. In addition, because of the low boiling point of VOCs, generally between 50 °C and 250 °C, and easy volatilization, online collection and analysis of VOCs based on thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) has been realized. However, compared with VOCs, the concentration level of IVOCs in the environment is relatively low, the viscosity is relatively large, and it is easy to remain in the system. Therefore, the analysis of IVOCs is mainly based on offline collection and analysis by TD-GC/MS with low temporal resolution. At present, there is no effective means to continuously track and observe the pollution level of IVOCs, so it is impossible to accurately obtain the exact response relationship between different IVOCs monomers and SOA, and it is difficult to scientifically evaluate the contribution of IVOCs to SOA generation.

Chinese patent CN201910212822.9 discloses a near-line detection device for medium volatile organic compounds. The original TD-GC/MS system for online collection and analysis of VOCs is modified. On the basis of the original device, online collection is added. and the ability to analyze IVOCs. In addition to the difference in saturated vapor pressure and viscosity, the concentrations of VOCs and IVOCs in the ambient atmosphere are orders of magnitude different, so it is difficult to simultaneously collect online and analyze in real time on one sampling tube. Therefore, the improved device can only collect and analyze one target VOCs or IVOCs online alone. However, both VOCs or IVOCs are considered to have important contributions to the generation of _O3 and SOA. Therefore, if the ability of the original device to analyze organic matter can be expanded, and the simultaneous online collection and analysis of VOCs and IVOCs can be realized, it will provide very valuable data for the analysis and detection in the field of organic matter, and provide data support for environmental pollution and human health risk exposure assessment. .

SUMMARY OF THE INVENTION

Aiming at the technical problem that the existing online detection device is difficult to collect and analyze VOCs and IVOCs at the same time, the present invention aims to provide a simultaneous online collection and detection method of VOCs and IVOCs.

The simultaneous online collection and detection method of VOCs and IVOCs includes the following steps using an online collection and detection device:

The standard sample or ambient air enters the TD (thermal desorption) system through the temperature-controlled sampling channel. A set of sampling tube groups in the TD system simultaneously performs adsorption sampling for the target substance. Sampling tubes for VOCs adsorbents and sampling tubes for IVOCs adsorbents.

The sampling tube group after adsorption and sampling of the target substance is used to desorb the target substance by inert gas, and the desorbed target substance is analyzed by inert gas through a sample connected to a GC/MS (gas chromatography/mass spectrometry) system The transfer line was loaded into the GC/MS analysis system.

In the GC/MS analysis system, the Dean-Switch switching system is used to firstly switch the VOCs target substance separated by the IVOCs gas chromatography column to the VOCs gas chromatography column for secondary separation to obtain the target substance VOCs. After a certain period of time , and then switch the IVOCs target substance separated from the IVOCs gas chromatographic column to the deactivated quartz capillary column to obtain the target substance IVOCs, and the VOCs target substance and the IVOCs target substance after secondary separation are passed through the three-way valve. After confluence, detection and analysis are performed simultaneously by mass spectrometer.

When the sampling tube group performs adsorption sampling on the target substance, the sampling duration is set between 0 and 999 minutes, and the sampling tube controls the temperature of the sampling tube when the standard sample or ambient air is adsorbed and sampled. Between -40°C and 20°C, the temperature of the temperature-controlled sampling channel is set between 220°C and 350°C.

The inert gas desorbs the target substance at 150-350°C;

The inert gas is 99.999% high-purity helium. When desorbing the target substance, the temperature is raised to 300°C at a rate of 1-40°C/s under high-purity helium flow for 5 minutes, and then raised to 350°C at a rate of 1-40°C/s and held for 5-15min for desorption. The target substance is attached.

The TD system includes two sets of the sampling tube groups. One set of the sampling tube sets simultaneously performs adsorption sampling on the target substance, and the other set of the sampling tube set uses an inert gas to desorb the target substance. The sampling tube groups alternately perform sampling and desorption steps.

Two of the sampling tubes in each set of the sampling tubes are connected through a tee, and the ambient air or standard sample is separated by the tee to achieve simultaneous collection of VOCs and IVOCs.

The temperature-controlled sampling channel, the two sets of three-way and the sample transmission pipeline connected to the GC/MS analysis system are connected by a four-way valve, and the two sets of sampling tube groups are alternately realized by switching the four-way valve. Perform sampling, desorption, and analytical detection steps.

When the two sampling tubes in the same group are sampling and adsorbing the target substance, the same mass flowmeter is used to respectively control the two sampling tubes to simultaneously sample at different sampling flow rates.

When the mass flowmeter is used to control the two sampling tubes at the same time and sampling at different sampling flow rates through a flow rate control valve, the sampling tube containing the VOCs adsorbent is controlled at a low sampling flow rate of 0-100ml/min. Sampling tubes with IVOCs sorbent were simultaneously sampled at high sampling flow rates of 100-500 ml/min.

The online collection and detection device includes a temperature-controlled sampling channel, a TD system connected to the temperature-controlled sampling channel, and a GC/MS analysis system connected to the TD system, where the TD system includes at least one sampling tube group Each of the sampling tube groups includes a sampling tube equipped with a VOCs adsorbent and a sampling tube equipped with an IVOCs adsorbent, and the temperature-controlled sampling channel is connected to the two sampling tubes through a three-way valve after passing through a four-way valve.

The GC/MS analysis system includes a sample transmission line connected to the TD system, an injection port, and an IVOCs gas chromatography column connected with the injection port, and the outlet end of the IVOCs gas chromatography column is switched by a Dean-Switch The system is respectively connected to the inlet end of the VOCs chromatographic column and the inlet end of the deactivated quartz capillary column, and the outlet end of the VOCs chromatographic column and the outlet end of the deactivated quartz capillary column are connected to the mass spectrometer detector through a three-way valve.

The TD system includes two sets of the sampling tube groups, and the temperature control sampling channel and the two sets of the sampling tube groups are respectively connected with the two inlet ends of the four-way valve through the interface I end of the three-way valve. The outlet end of the valve is connected to the injection port of the GC/MS analysis system through the sample transfer line.

The three-way and the four-way valve are temperature-controllable solenoid valves, and the temperature-controllable ranges of the three-way and the four-way valve are both room temperature to 350°C.

The sample transmission line adopts a temperature-controllable transmission line, and the temperature controllable range of the transmission line is from room temperature to 300°C.

A shunt pipeline is also provided downstream of the outlet end of the four-way valve.

The inlet end of each sampling tube is connected to the interface II of the tee, and the outlet end of each sampling tube is connected to the mass flow meter through a flow rate control valve, and then communicated with the outside world or an inert gas pipeline.

Both of the flow rate control valves in the same group are connected to the same mass flow meter.

The positive improvement effect of the present invention is that: the simultaneous online collection and detection method of VOCs and IVOCs of the present invention realizes the purpose of one-time sampling and online collection and analysis of VOCs and IVOCs at the same time.

Description of drawings

Fig. 1 is a kind of overall structure schematic diagram of the device of the present invention;

Fig. 2 is a kind of schematic flow chart of the present invention;

3 is a schematic diagram of a gas circuit for alternately sampling and desorbing two groups of sampling tube groups according to the present invention;

4 is a schematic diagram of another gas path for alternately sampling and desorbing two sets of sampling tube groups according to the present invention;

Fig. 5 is a kind of working schematic diagram of the Dean-Switch switching system of the present invention;

FIG. 6 is another working schematic diagram of the Dean-Switch switching system of the present invention.

Detailed ways

In order to make it easy to understand the technical means, creation features, achieved goals and effects of the present invention, the present invention will be further described below with reference to specific drawings.

1, the online collection and detection device includes a temperature-controlled sampling channel 1, a TD (thermal desorption) system 2, and a GC/MS (gas chromatography/mass spectrometry) analysis system 3, and the TD system 2 includes at least one sampling tube group, Each of the sampling tube groups includes a sampling tube 21 containing a VOCs adsorbent and a sampling tube 22 containing an IVOCs adsorbent, and the two sampling tubes are respectively connected to two parallel ports (II ends) of the tee 23 . Preferably, the TD system 2 includes two sets of sampling tube groups, which are the sampling tube group A and the sampling tube group B, respectively. The interface (I end) of the three-way 23 and the temperature-control sampling channel 1 in each sampling tube group are respectively connected to the two inlet ends of the four-way valve 24 . The three-way 23 and the four-way valve 24 adopt temperature-controllable solenoid valves, and the temperature-controllable ranges of the three-way 23 and the four-way valve 24 are both from room temperature to 350°C.

The sampling inlet end of each sampling tube is connected to the II end of the tee 23 , and the sampling outlet end of each sampling tube is communicated with the outside world or the inert gas pipeline through the flow rate control valve 25 . Preferably, a gas flow switching valve may be provided between the flow rate control valve 25 and the outside world or the inert gas pipeline, and the sampling pipe is communicated with the outside world or the inert gas pipeline by switching the gas flow switching valve. Both flow rate control valves in the same group are connected to the same mass flow meter 26 . As shown in FIG. 1 , there are two mass flow meters 26 , mass flow meter 1 and mass flow meter 2 . The two mass flow meters 26 independently control a set of sampling tube groups.

The outlet end of the four-way valve 24 is connected to the injection port 31 of the GC/MS analysis system 3 through the sample transmission line 4. The sample transmission line 4 adopts a temperature-controllable transmission line, and the temperature controllable range of the transmission line 4 is from room temperature to 300° C. . A branch line 5 is also provided downstream of the outlet end of the four-way valve 24 .

The GC/MS analysis system 3 includes a sample transmission line 4 connected to the TD system 2, an injection port 31, an IVOCs gas chromatography column 32 (DB-5MS chromatography column) communicated with the injection port 31, and an outlet of the IVOCs gas chromatography column 32 The ends are respectively connected to the inlet end of the VOCs chromatographic column 34 (DB624 chromatographic column) and the inlet end of the deactivated quartz capillary column 35 through the Dean-Switch switching system 33, the outlet end of the VOCs chromatographic column 34 and the outlet end of the deactivated quartz capillary column 35 The mass spectrometer detector 37 is connected through the three-way valve 36 .

Referring to Figure 2, the simultaneous online collection and detection method of VOCs and IVOCs includes the following steps using an online collection and detection device:

Step S1, sampling: the standard sample or ambient air enters the TD system through the temperature-controlled sampling channel, and a group of sampling tube groups in the TD system simultaneously conduct adsorption sampling for the target substance, and the same group of sampling tube groups contains VOCs adsorbents. Sampling tubes and sampling tubes filled with IVOCs sorbents.

When sampling, the TD system is used, and the TD online sampling and sampling are completed by the temperature-controlled sampling channel and sampling tube group. When the sampling tube is adsorbing the sampling target substance, the sampling duration is set between 0 and 999 min, and the temperature of the sampling tube is controlled between -40 and 20 °C.

The sampling tube group in the TD system consists of VOCs and IVOCs sampling tubes, that is, two sampling tubes filled with VOCs and IVOCs adsorbents. The two sampling tubes in each sampling tube group are connected by a tee, and the simultaneous collection of VOCs and IVOCs is achieved through the shunt of the tee.

When the two sampling tubes in the same group are adsorbing the target substance, the same mass flow meter is used to control the two sampling tubes simultaneously and sample at different sampling flow rates. Specifically, a flow rate control valve can be installed at the end of each sampling tube, and a mass flow meter is used to control the two sampling tubes at the same time and sampling at different sampling flow rates, and control the sampling tube with VOCs adsorbent at 0-100ml/min. Under the low sampling flow rate, the sampling tube with IVOCs adsorbent is simultaneously sampled at the high sampling flow rate of 100-500ml/min, so as to achieve the goal of collecting VOCs and IVOCs that meet the detection requirements of the analysis system within the same sampling time. the total amount of matter.

Step S2, desorption: the sampling tube group after adsorption and sampling of the target substance, uses an inert gas to desorb the target substance, and the desorbed target substance is loaded into the GC/MS analysis by the inert gas through the sample transmission line connected to the GC/MS analysis system in the system.

The inert gas desorbs the target substance at 150-350°C, and the inert gas adopts 99.999% high-purity helium. When desorbing the target substance in this step, it is preferable to raise the temperature to 300°C at a rate of 1-40°C/s under high-purity helium flow for 5 minutes, then raise the temperature to 350°C at a rate of 1-40°C/s and hold for 5-15 minutes. Desorb the target substance.

The TD system includes two sets of sampling tube groups, namely sampling tube set A and sampling tube set B. When one set of sampling tube sets performs adsorption sampling on the target substance at the same time, the following step S2 is performed on the other set of sampling tube sets, using the following steps: The target substance is desorbed by the inert gas, and the sampling and desorption steps are alternately performed by two sampling tube groups. That is: sampling tube group A and sampling tube group B alternately perform sampling and thermal desorption work. When sampling tube group B completes the sampling, sampling tube group A collects VOCs and IVOCs in ambient air under the set sampling conditions, and at the same time Sampling tube group B starts to heat and desorb the target substance under the set thermal desorption conditions.

The temperature-controlled sampling channel, the two sets of three-way and the sample transmission pipeline connected to the GC/MS analysis system are connected by a four-way valve, and the two sets of sampling tube sets can be alternately sampled and desorbed by switching the four-way valve.

Referring to Figure 3, after the ambient air passes through the temperature control sampling channel, after passing through the four-way valve and the three-way, it enters the two sampling tubes of the sampling tube group A for adsorption sampling, and the target substance is enriched in the two sampling tubes of the sampling tube group A respectively. Inside the tube (during sampling, set the temperature of the sampling tube between -40 and 20 °C); at the same time, the sampling tube group B is thermally desorbed, and the desorbed target substance is transported by the carrier gas (helium, 99.999%), followed by After passing through the three-way and four-way valves, under the set split conditions, a part of the target substance is sent to the GC/MS analysis system through the sample transfer line, and the other part of the target substance is discharged into the ambient air through the split line.

Referring to Figure 4, after the sampling tube group A completes the adsorption sampling, and the sampling tube group B completes the thermal desorption, the sampling tube group A performs thermal desorption, and the sampling tube group B performs adsorption sampling, so as to realize the alternate sampling and thermal desorption of the two sampling tube groups. Desorption work.

Step S3, separation and detection: in the GC/MS analysis system, the Dean-Switch switching system is used to switch the VOCs target substance first separated by the IVOCs gas chromatographic column into the VOCs gas chromatographic column for secondary separation to obtain the target VOCs; After the separation of the VOCs target substances is completed within a certain time, the Dean-Switch switching system is used to switch the subsequently separated IVOCs target substances to the deactivated quartz capillary column to obtain the target IVOCs. The target IVOCs of the capillary column are combined by the three-way valve and then enter the mass spectrometer for detection and analysis at the same time.

This step adopts the precise control of the Dean-Switch switching system (commercial system), and the VOCs target substance enters the DB624 chromatographic column for secondary separation, and the IVOCs target substance enters the deactivated quartz capillary column. Finally, the end of the DB624 chromatographic column and the deactivated quartz capillary column are connected by a three-way valve and enter the mass spectrometer detector, so that the mass spectrometer detector can detect VOCs and IVOCs at the same time, and according to the peak time (i.e., the residence time) of the target substance and the ion fragmentation Identify and quantify organic matter based on differences in characteristics.

Referring to Figure 5, the target substance in the TD system is sent to the GC injection port by high-purity helium gas through the sample transmission line, first enters the DB-5MS gas chromatography column, and the VOCs target substance separated first by the DB-5MS gas chromatography column, After the Dean-Switch switching system, switch to the DB624 chromatographic column for secondary separation. At this time, the solenoid valve in the Dean-Switch switching system is in the "ON" state, and the VOCs that have been split through the DB624 chromatographic column enter through the three-way valve. Mass spectrometry detection;

Referring to Figure 6, after a certain set time, the IVOCs target substances separated by the DB-5MS gas chromatographic column are switched from the Dean-Switch switching system to the deactivated quartz capillary column. At this time, the solenoid valve in the Dean-Switch switching system is switched. In the "OFF" closed state, it is transported by high-purity helium gas through the deactivated quartz capillary column and the three-way valve, and then enters the mass spectrometry detection.

The method of the invention continuously takes turns sampling and thermal desorption through two sets of sampling tube groups A and B of the TD system, and the thermally desorbed target substance is sent to the GC/MS system for analysis, so as to realize the online simultaneous collection and analysis of VOCs and IVOCs. Analysis function.

The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments, and the descriptions in the above-mentioned embodiments and the description are only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have Various changes and modifications fall within the scope of the claimed invention. The claimed scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. VOCs and IVOCs online collection and detection method simultaneously, it is characterized in that, comprise adopting online collection and detection device to carry out the following steps: The standard sample or ambient air enters the TD system through the temperature-controlled sampling channel; A group of sampling pipe groups in the TD system simultaneously performs adsorption sampling on the target substance, and the same group of the sampling pipe groups includes a sampling pipe equipped with a VOCs adsorbent and a sampling pipe equipped with an IVOCs adsorbent; The sampling tube group after adsorption and sampling of the target substance uses an inert gas to desorb the target substance, and the desorbed target substance is loaded into the target substance by an inert gas through a sample transfer line connected to the GC/MS analysis system GC/MS analysis system; In the GC/MS analysis system, the Dean-Switch switching system is used to switch the VOCs target substances separated by the IVOCs gas chromatographic column to the VOCs chromatographic column for secondary separation to obtain the target VOCs, and after a certain period of time, the IVOCs The IVOCs target substance separated by the gas chromatography column is switched into the deactivated quartz capillary column to obtain the target substance IVOCs, and the target substance VOCs and the target substance IVOCs after secondary separation are detected and analyzed by a mass spectrometer detector. 2. The method for simultaneous online collection and detection of VOCs and IVOCs as claimed in claim 1, wherein the TD system comprises two groups of the sampling tube groups, and one group of the sampling pipe groups simultaneously adsorbs the target substance During sampling, the target substance is desorbed with an inert gas on another group of the sampling tube groups, and the steps of sampling and desorption are performed alternately in the two groups of the sampling tube groups. 3. The method for simultaneous online collection and detection of VOCs and IVOCs as claimed in claim 2, wherein the temperature of the temperature-controlled sampling channel is set between 220 and 350°C; The sampling duration when the sampling tube group performs adsorption sampling on the target substance is set between 0 and 999 min, and the temperature of the sampling tube during adsorption of the target substance is set between -40 and 20°C; The inert gas desorbs the target substance at 150-350°C; Preferably, high-purity helium gas is used as the inert gas. When desorbing the target substance, it is raised to 300°C at a rate of 1-40°C/s under high-purity helium flow for 5 minutes, and then at a rate of 1-40°C/s. After rising to 350°C and holding for 5-15min, the target substance was desorbed. 4. the simultaneous online collection and detection method of VOCs and IVOCs as claimed in claim 2, it is characterized in that, two described sampling tubes in each described sampling tube group are connected by tee, by the shunt of described tee Realize simultaneous collection of VOCs and IVOCs; The temperature-controlled sampling channel, the two sets of three-way and the sample transmission pipeline connected to the GC/MS analysis system are connected by a four-way valve, and the two sets of sampling tube groups are alternately realized by switching the four-way valve. Perform sampling and desorption steps. 5. the simultaneous online collection and detection method of VOCs and IVOCs as claimed in claim 1, is characterized in that, when two described sampling tubes in the same group are carried out sampling adsorption to described target substance, adopt same mass flowmeter respectively controlling two of the sampling tubes to sample at the same time and at different sampling flow rates; Preferably, when the mass flowmeter is used to control the two sampling tubes simultaneously and sampling at different sampling flow rates, the sampling tube containing the VOCs adsorbent is controlled to be loaded with the IVOCs adsorbent at a low sampling flow rate of 0-100ml/min. The sampling tubes were simultaneously sampled at a high sampling flow rate of 100-500 ml/min. 6. The simultaneous online collection and detection method of VOCs and IVOCs according to any one of claims 1 to 5, wherein the online collection and detection device comprises a temperature control sampling channel, a temperature control sampling channel, and a temperature control sampling channel. A connected TD system, and a GC/MS analysis system connected to the TD system, the TD system includes at least one set of sampling pipe groups, and the sampling pipe groups each include a sampling pipe filled with VOCs adsorbent and a sampling pipe filled with IVOCs adsorbent The sampling tube, the temperature control sampling channel is connected to two sampling tubes respectively through a tee; The GC/MS analysis system includes a sample transmission line connected to the TD system, an injection port, and an IVOCs gas chromatography column connected with the injection port, and the outlet end of the IVOCs gas chromatography column is switched by a Dean-Switch The system is respectively connected to the inlet end of the VOCs chromatographic column and the inlet end of the deactivated quartz capillary column, and the outlet end of the VOCs chromatographic column and the outlet end of the deactivated quartz capillary column are connected to the mass spectrometer detector through a three-way valve. 7. The method for simultaneous online collection and detection of VOCs and IVOCs as claimed in claim 6, wherein the TD system comprises two groups of the sampling tube groups, the temperature-controlled sampling channel, two groups of the sampling pipe groups The I end of the three-way interface is respectively connected to the two inlet ends of the four-way valve, and the outlet end of the four-way valve is connected to the injection port of the GC/MS analysis system through the sample transmission line. 8. The method for simultaneous online collection and detection of VOCs and IVOCs as claimed in claim 7, wherein the three-way and the four-way valve are temperature-controlled solenoid valves, and the three-way and the four-way valve are temperature-controlled solenoid valves. The temperature controllable range of the valve is room temperature to 350°C; the sample transmission line adopts a temperature-controllable transmission line, and the temperature controllable range of the transmission line is room temperature to 300°C. 9. The method for simultaneous online collection and detection of VOCs and IVOCs as claimed in claim 6, characterized in that a shunt pipeline is also provided at the downstream of the outlet end of the four-way valve. 10. The simultaneous online collection and detection method of VOCs and IVOCs as claimed in claim 6, wherein the sampling inlet end of each of the sampling pipes is connected with the interface II end of the three-way, and each of the sampling pipes The sampling outlet end of the sampler is communicated with the outside world or the inert gas pipeline through the flow rate control valve; Both of the flow rate control valves in the same group are connected to the same mass flow meter.

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