JP3752850B2 - Headspace sample introduction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a headspace sample introduction device that collects a gas sample volatilized from a liquid sample or a solid sample by a headspace method and introduces the sample into a gas chromatograph device or the like.
[0002]
[Prior art]
The headspace analysis method volatilizes components having a relatively low boiling point by heating a liquid sample or solid sample contained in a container to a certain temperature for a certain period of time, and a certain amount of gas containing these components from the upper space in the container. It is collected and introduced into a gas chromatograph or the like for analysis. Chromatographic analysis using such a method is suitable, for example, for measurement of fragrances in foods, measurement of volatile organic compounds in water, and the like.
[0003]
[Problems to be solved by the invention]
In a conventional head space analysis gas chromatograph apparatus, analysis by so-called batch processing is generally performed in which a predetermined amount of sample liquid is previously stored in a dedicated container, and this is set in the apparatus and analysis is started. However, for example, when monitoring organic compounds contained in wastewater from a factory, it is necessary to collect wastewater every predetermined time (regardless of day or night) and repeat the analysis. Analysis cannot be performed. Therefore, in order to cope with such applications, a sample introduction device that automatically collects a certain amount of sample liquid in a head space container and introduces the gas taken out from the upper space (head space) in the container into the gas chromatograph apparatus. Is desired.
[0004]
In such a sample introduction apparatus, the head space container and the gas sampling tube connected thereto are housed in a thermostatic bath, and volatilization of the sample components from the sample liquid and the period of taking out the gas containing the components from the container at a predetermined temperature ( For example, about 60 ° C.). However, for example, when the user temporarily opens the door of the thermostatic bath in order to see the measurement state, the temperature in the thermostatic bath rapidly drops. If the sample liquid contains water, the container and the gas sampling tube are filled with water vapor, so that condensation occurs due to a temperature drop, and water droplets adhere to the inner wall surface of the gas sampling tube. If such water is introduced into the gas chromatograph apparatus in the subsequent stage together with the gas, the amount of the sample component is relatively reduced, which may hinder accurate analysis.
[0005]
The present invention has been made in view of these points, and an object of the present invention is to provide a headspace sample introduction device that can prevent water from being sent out through a gas sampling tube. is there.
[0006]
[Means for Solving the Problems]
The present invention, which has been made to solve the above problems, collects sample gas from the upper space of the liquid level in the container and analyzes it through a gas sampling tube connected to the upper part of the container in which the liquid sample is stored. In the headspace sample introduction device to be sent to the device,
a) gas holding means for holding the compressed inert gas;
b) a flow path switching means provided on the gas sampling pipe and selectively connecting the gas holding means and the sample gas supply destination to the container;
c) Control means for connecting the container and the gas holding means by the flow path switching means immediately before collecting the sample gas from the container, and for flowing an inert gas from the gas holding means to the container side at a high pressure. When,
It is characterized by having.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the head space sample introduction device according to the present invention, the control means connects the container and the gas holding means by the flow path switching means before sucking the gas from the upper space of the container. Then, an inert gas (for example, nitrogen, helium or other rare gas) flows from the gas holding means through the gas sampling pipe to the container with a high pressure. Due to the pressure of the gas, the water droplets accumulated in the gas sampling pipe from the container to the flow path switching means are pushed back into the container. As a result, the water in the gas sampling pipe is wiped out. If a dry gas with extremely low humidity is used as the inert gas, it is more effective because fine water droplets that cannot be pushed out only by the pressure of this gas can be evaporated and returned to the container.
[0008]
【The invention's effect】
According to the headspace sample introduction device of the present invention, the moisture in the gas sampling tube is wiped out before sampling the sample gas from the headspace container, so that the sample gas supply destination (for example, a gas metering tube or a subsequent analysis device) ) Can be prevented from being sent out. For this reason, it becomes possible to accurately measure the sample gas, and the accuracy and reproducibility of the analysis are improved.
[0009]
【Example】
Hereinafter, an embodiment of a headspace sample introduction apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a main part of the headspace sample introduction device of this embodiment. A gas chromatograph apparatus is connected to the subsequent stage of the head space sample introduction apparatus, and FIG. 1 also shows a column 40 that is a part of the gas chromatograph apparatus.
[0010]
First, the configuration of this apparatus will be described with reference to FIG. A discharge port of the liquid feed pump 3 is connected to the lower opening of a 100 mL head space container (hereinafter simply referred to as “container”) 1 having a narrow opening at the top and bottom via a three-way valve 2. 5 is connected. The suction port of the liquid feed pump 3 is connected to a sample solution supply port 4 to which a sample solution is supplied from the outside. On the other hand, a valve 6 connected to the carrier gas supply port 8 and a gas discharge valve 7 are connected to the upper opening of the container 1. In addition, a gas sampling pipe 9 reaching the port d of the first six-way valve (6-port 2-position valve) 10 is also connected to the upper opening.
[0011]
A port e of the first six-way valve 10 is connected to a port d of a second six-way valve (6-port two-position valve) 11. A gas metering pipe 12 (for example, a predetermined pipe) is connected between the ports e and f of the second six-way valve 11. A loop tube having an internal volume of 2). The port c of the second six-way valve 11 is connected to the vacuum pump 16 through the valve 15 and to the pressure gauge 14. The port b of the second six-way valve 11 serves as a sample gas outlet of the sample introduction device and is connected to the column 40 of the gas chromatograph device.
[0012]
The port b of the first six-way valve 10 is connected to the carrier gas supply port 18 via the valve 17. The port c of the first six-way valve 10 is connected to the port d of the third six-way valve (6-port two-position valve) 19, and a predetermined capacity (for example, between the ports e and f of the third six-way valve 19 is used. 5 mL) of gas holding tube 20 is connected. Further, the port a of the third six-way valve 19 is connected to a high-pressure carrier gas supply port 21 that can supply a carrier gas with a high gas pressure (for example, 600 kPa). The other ports of the first to third six-way valves 10, 11, 19 are all closed with closing plugs.
[0013]
The container 1 and the first to third six-way valves 10, 11, 19 and the like are installed in a thermostatic chamber 22, and can be maintained at an arbitrary constant temperature. On the other hand, the column 40 of the gas chromatograph apparatus is installed in a column oven 41 capable of controlling the temperature independently of the thermostatic chamber 22. The control unit 30 includes a microcomputer and the like, and executes a predetermined program in accordance with various settings and instructions given through the operation unit 31 provided thereto. Controls switching operation and pump operation.
[0014]
Next, a series of operations until the sample liquid is stored in the container 1 in the above configuration, the sample gas volatilized from the sample liquid is collected and sent to the column 40 will be described. If the previously measured sample liquid remains in the container 1, first, the valve 5 is opened and the remaining sample liquid is discharged, then the valve 5 is once closed and the liquid feed pump 3 is driven to turn the sample The liquid is fed into the container 1 through the three-way valve 2. When an appropriate amount of the sample solution is accumulated in the container 1, the three-way valve 2 is switched and the valve 5 is opened to discard the sample solution in the container 1. By repeating such an operation a plurality of times as necessary, the inside of the container 1 is washed with a new sample liquid (that is, a measurement liquid to be measured). Thereafter, the carrier gas is introduced into the container 1 by opening the valve 6 with the valve 7 closed, and the sample liquid droplets remaining in the container 1 are discharged together with the carrier gas through the valve 5. Thereby, the carrier gas is filled in the container 1.
[0015]
Thereafter, the sample solution is weighed as follows. First, the first six-way valve 10 is set to a solid connection state in FIG. 1 and the second six-way valve 11 is set to a dotted line connection state. Accordingly, the container 1 is connected to the pressure gauge 14 via the ports d and e of the first six-way valve 10 and the ports d and c of the second six-way valve 11. While the valves 5, 6, 7, and 15 are closed, the three-way valve 2 is connected to the container 1 side to drive the liquid feeding pump 3, and the sample liquid is fed into the container 1 at a predetermined flow rate. When the sample liquid accumulates in the container 1 and the liquid level rises, the volume of the upper space in the container 1 decreases. As described above, since all the pipes communicating with the upper space are closed by the valves, this space is a sealed space. Accordingly, as the liquid level rises, the gas pressure detected by the pressure gauge 14 increases.
[0016]
Such a correspondence relationship between the liquid level, that is, the amount of the sample solution and the detected gas pressure is measured in advance by experiments, and the correspondence relationship is stored in the memory of the control unit 30. When a sample collection amount is instructed by the user via the operation unit 31, the control unit 30 obtains a gas pressure corresponding to the liquid amount from the above correspondence and sets it as a control target value. Then, when the gas pressure detected by the pressure gauge 14 reaches the control target value, the three-way valve 2 is switched, and the supply of the sample liquid into the container 1 is stopped. Thereafter, the liquid feed pump 3 is stopped. As a result, the sample liquid corresponding to the sample collection amount is stored in the container 1. Usually, a sample solution of about 50 to 60 mL is stored in a 100 mL container.
[0017]
After taking a predetermined amount of the sample solution in the container 1 in this way, the sample gas is taken out from the upper space in the container 1 as follows. First, the thermostat 22 is raised to a predetermined temperature (for example, about 60 ° C.) and kept constant, and the volatilization of the sample components from the sample solution in the container 1 is promoted. Further, the first six-way valve 10 is switched to the dotted line connection state, the second six-way valve 11 is switched to the solid line connection state, and the valve 17 is closed. Then, the valve 15 is opened and the vacuum pump 16 is driven. Then, the inside of the pipe line connected to the vacuum pump 16 from the port e of the first six-way valve 10 through the gas metering pipe 12 is in a vacuum state. On the other hand, the third six-way valve 19 is set to a dotted connection state, and the dried carrier gas is fed from the high-pressure carrier gas supply port 21. Then, the gas holding pipe 20 is filled with a carrier gas with a high gas pressure that is almost close to the gas supply pressure.
[0018]
After the temperature of the thermostatic chamber 22 is maintained at the above-mentioned predetermined temperature for a predetermined time, before the sample gas is sent to the gas metering tube 12, first, the third six-way valve 19 is switched to a solid line connection state. Then, since the gas holding pipe 20 and the gas sampling pipe 9 are connected via the first six-way valve 10 and the third six-way valve 19, the carrier gas stored in the gas holding pipe 20 urges the flow path. It passes well and flows into the container 1.
[0019]
Usually, since the container 1 and the gas sampling tube 9 are maintained at the predetermined temperature by the thermostat 22, the water contained in the sample liquid in the container 1 is vaporized to become water vapor, and the upper space and gas in the container 1 The sampling tube 9 is full. In such a state, for example, when the user opens the door of the thermostatic chamber 22 by mistake or confirming the internal state, the temperature inside the thermostatic chamber 22 rapidly decreases, the water vapor condenses, and the inner wall of the container 1 or gas It adheres to the inner wall of the sampling tube 9 (that is, condensation). When the carrier gas is flown as described above, water droplets adhering to the inner wall of the container 1-first 6-way valve 10 port d-first 6-way valve 10 port c-third 6-way valve 19 port d are caused by the carrier gas. It is pushed back into the container 1. Further, since the carrier gas is dry, very fine water droplets that are difficult to move only by the pressure of the carrier gas are volatilized in the carrier gas and carried away into the container 1.
[0020]
After the purge of water is performed in this way, when the first six-way valve 10 is switched to the solid line connection state, the sample gas in the upper space in the container 1 is sucked into the vacuum line. . Thereby, the sample gas is filled in the gas metering pipe 12. Since water flows into the gas metering tube 12 only as water vapor rather than as a liquid, the sample gas can be accurately metered in the gas metering tube 12. After that, when the second six-way valve 11 is switched to the dotted connection state, the sample gas is pushed out from the gas metering tube 12 by the carrier gas supplied from the carrier gas supply port 13 to the port a of the second six-way valve 11, and the column 40.
[0021]
It should be noted that the above embodiment is merely an example, and it is obvious that changes and modifications can be made as appropriate in accordance with the spirit of the present invention.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a main part of an embodiment of a headspace sample introduction device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Head space container 2 ... Three-way valve 3 ... Liquid feed pump 4 ... Sample liquid supply port 5, 6, 7, 15, 17 ... Valve 9 ... Gas sampling pipe 10, 11, 19 ... Six-way valve 8, 13, 18, 21 ... Carrier gas supply port 12 ... Gas metering pipe 20 ... Gas holding pipe 30 ... Control section

Claims (1)

In a headspace sample introduction device that collects a sample gas from an upper space of a liquid level in the container and sends it to an analyzer through a gas sampling tube connected to an upper portion of a container in which a liquid sample is stored.
a) gas holding means for holding the compressed inert gas;
b) a flow path switching means provided on the gas sampling pipe and selectively connecting the gas holding means and the sample gas supply destination to the container;
c) Control means for connecting the container and the gas holding means by the flow path switching means immediately before collecting the sample gas from the container, and for flowing an inert gas from the gas holding means to the container side at a high pressure. When,
A headspace sample introduction device comprising:

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