JP2011257246A - Gas chromatograph and method for using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas chromatograph in which deterioration of detection sensitivity of a semiconductor gas sensor, i.e., a detector, with time is suppressed.SOLUTION: A gas chromatograph 1 includes: a separation column 2; a semiconductor gas sensor 3; a first flow path 4 connecting the separation column 2 and the semiconductor gas sensor 3; and a first valve 5 for opening/closing the flow of gas between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4.

Description

  The present invention relates to a gas chromatograph including a semiconductor gas sensor as a detector and a method of using the gas chromatograph.

  Gas chromatography is widely used for qualitative and quantitative analysis of components in gas. In gas chromatography, the sample gas to be measured is introduced into the separation column together with the carrier gas, and the components contained in the sample gas are separated by the difference in retention time (retention time) due to interaction with the packing material in the separation column. This separated component is derived from the separation column. The components thus separated are sequentially detected by a detector such as a thermal conductivity detector (TCD) or a flame ionization detector (FID), whereby a chromatogram is obtained.

  In recent years, more sensitive semiconductor gas sensors have been used instead of TCD and FID as detectors in gas chromatographs (see Patent Document 1). A gas chromatograph equipped with a semiconductor gas sensor as a detector is expected to be used for analysis of components in exhaled breath in the medical field and analysis of components in buildings and air in the environmental field.

JP-A-6-213780

  However, if a gas chromatograph equipped with a semiconductor gas sensor as such a detector remains unused for a certain period of time, the detection sensitivity of the semiconductor gas sensor may be reduced when the gas is subsequently measured by the gas chromatograph. is there. In such a case, accurate analysis cannot be performed.

  This invention is made | formed in view of this reason, and it aims at providing the usage method of this gas chromatograph and the gas chromatograph by which the time-dependent fall of the detection sensitivity of the semiconductor gas sensor which is a detector is suppressed.

  A gas chromatograph according to a first invention includes a separation column, a semiconductor gas sensor, a first flow path connecting the separation column and the semiconductor gas sensor, the separation column and the semiconductor in the first flow path. A first valve that opens and closes the flow of gas to and from the gas sensor.

  The gas chromatograph according to the first invention further includes a second flow path that branches from the first flow path and communicates with the outside air, and the first valve includes the separation column in the first flow path and the first flow path. The gas flow between the semiconductor gas sensor is open and the gas flow between the separation column and the semiconductor gas sensor and the second flow path is closed; Three-way switching between a state in which gas flow between the separation column and the second flow path is open and a flow of gas between the separation column and the second flow path and the semiconductor gas sensor is closed It may be a valve.

  The gas chromatograph according to the first invention further opens and closes a third flow path connected between the semiconductor gas sensor and the outside air, and a gas flow between the semiconductor gas sensor and the outside air in the third flow path. A second valve may be provided.

  The gas chromatograph according to the first invention further opens a gas flow between the separation column and the semiconductor gas sensor in the first flow path by the first valve at the time of gas measurement, and a carrier gas and A sample gas is sequentially passed through the separation column, the first flow path, and the semiconductor gas sensor, and after the gas measurement is completed, between the separation column and the semiconductor gas sensor in the first flow path by the first valve. A control device that operates the first valve to close the gas flow may be provided.

  In the gas chromatograph according to the first invention, during gas measurement, the first valve opens a gas flow between the separation column and the semiconductor gas sensor in the first flow path, and the second valve Opens the gas flow between the semiconductor gas sensor and the outside air in the third flow path, and after the gas measurement is finished, the first valve is used to connect the separation column and the semiconductor gas sensor in the first flow path. The first valve and the second valve are operated so as to close the gas flow between the semiconductor gas sensor and the outside air in the third flow path by the second valve. A control device may be provided.

  A method of using the gas chromatograph according to the second invention is a method of using the gas chromatograph, and when measuring the gas to be measured, the separation valve in the first flow path and the The gas flow between the semiconductor gas sensor is opened, the carrier gas and the sample gas are sequentially passed through the separation column, the first flow path, and the semiconductor gas sensor. This closes the gas flow between the separation column and the semiconductor gas sensor in the first flow path.

  A method of using a gas chromatograph according to a third aspect of the invention is a method of using the gas chromatograph, wherein at the time of gas measurement, the first valve is used to connect the separation column and the semiconductor gas sensor in the first flow path. The gas flow between the carrier gas and the sample gas is sequentially passed through the separation column, the first flow path, and the semiconductor gas sensor, and the second valve allows the gas flow in the third flow path. Open the gas flow between the semiconductor gas sensor and the outside air, and close the gas flow between the separation column and the semiconductor gas sensor in the first flow path by the first valve after gas measurement is completed, The second valve closes the gas flow between the semiconductor gas sensor and the outside air in the third flow path.

  The present invention reduces the chance that a gas sensitive body of a semiconductor gas sensor, which is a detector in a gas chromatograph, is exposed to a component that degrades the performance of the semiconductor gas sensor, thereby suppressing a decrease in detection sensitivity of the semiconductor gas sensor over time. be able to.

It is the schematic which shows 1st embodiment of this invention. It is a perspective view which shows the separation column in 1st embodiment. It is the perspective view which fractured | ruptured partially which shows the semiconductor gas sensor in 1st embodiment. It is a circuit block diagram in 1st embodiment. It is the schematic which shows 2nd embodiment of this invention. 10 is a graph showing test results of Example 3. 10 is a graph showing test results of Example 4. 10 is a graph showing test results of Comparative Example 3.

  FIG. 1 shows a flow path configuration of a gas chromatograph 1 according to the present embodiment. In this embodiment, the semiconductor gas sensor 3 is used as a detector.

  The present inventors have found that if the gas sensitive body 31 of the semiconductor gas sensor 3 is exposed to the carrier gas while the gas is not measured by the gas chromatograph 1, the detection sensitivity of the semiconductor gas sensor 3 is lowered. It was. This is because the carrier gas contains a component that degrades the performance of the semiconductor gas sensor 3, and this component is mainly generated from the separation column 2. Such a component adheres to or accumulates on the gas sensitive body 31 of the semiconductor gas sensor 3, thereby reducing the detection sensitivity of the semiconductor gas sensor 3.

  Examples of components that volatilize from the separation column 2 and deteriorate the performance of the semiconductor gas sensor 3 include silicon compounds such as siloxane, organosilicon compounds, and silicon resins, triglycerides, and other various high-boiling compounds. The silicon compound poisons the gas sensitive body 31 to reduce the detection sensitivity of the semiconductor gas sensor 3. Triglycerides, various high-boiling compounds, and the like are deposited on the gas sensitive body 31 to cause clogging of the porous gas sensitive body 31, thereby reducing the detection sensitivity of the semiconductor gas sensor 3.

  While the gas is being measured by the gas chromatograph 1, the gas sensitive body 31 of the semiconductor gas sensor 3 is heated. For this reason, components that degrade the performance of the semiconductor gas sensor 3 adhere to the gas sensitive body 31. It is difficult to deposit. On the other hand, the gas sensing element 31 is not heated while the gas is not measured by the gas chromatograph 1, so that components that degrade the performance of the semiconductor gas sensor 3 adhere to the gas sensing element 31. It becomes easy to deposit.

  Therefore, in the gas chromatograph 1 according to the present embodiment, the gas sensitive body 31 and the separation column 2 are shut off while the gas is not measured by the gas chromatograph 1, so that the gas sensitive body of the semiconductor gas sensor 3 is cut off. It is comprised so that 31 may not be exposed to the component which degrades the performance of the semiconductor gas sensor 3. FIG.

  Moreover, the component which degrades the performance of the semiconductor gas sensor 3 may exist in external air. For example, when the gas sensitive body 31 is not heated, VOC (volatile organic compound) in the outside air may poison the gas sensitive body 31. Therefore, in the present embodiment, the gas sensitive body 31 and the outside air are shut off while the gas is not measured by the gas chromatograph 1, so that the gas sensitive body 31 of the semiconductor gas sensor 3 becomes a semiconductor gas sensor in the outside air. 3 is configured so as not to be exposed to a component that deteriorates the performance of No. 3.

  Hereinafter, the configuration of the present embodiment will be described in detail.

  The buffer tank 10 is a hollow container that stores gas. The buffer tank 10 is formed with an intake port 11, an exhaust port 12, and a return port 13. The inside of the buffer tank 10 communicates with the outside air through the intake port 11.

  The air pump 14 is connected to the exhaust port 12 of the buffer tank 10 through the gas flow path 15, and is connected to the return port 13 of the buffer tank 10 through the return gas flow path 16. The air pump 14 operates to take in air from the gas flow path 15 and exhaust it to the return gas flow path 16.

  A gas flow path 17 branches from the return gas flow path 16. The return gas flow path 16 is provided with a flow rate adjusting valve 18 on the buffer tank 10 side of the branch position 19 with the gas flow path 17.

  In the gas flow path 17, a gas purification device 20, a flow rate adjustment valve 21, and a flow rate sensor 22 are provided in order from the branch position 19 side. The gas purification device 20 includes, for example, a gas adsorbent such as activated carbon or silica gel, a gas decomposition catalyst such as an oxidation catalyst, and the carrier gas passing through the gas flow path 17 is purified by the gas purification device 20. The flow sensor 22 detects the gas flow rate in the gas flow path 17.

  The end of the gas flow path 17 (the end opposite to the branch position 19) is connected to the start end of the separation column 2. A gas injection channel 23 is also connected to the starting end of the separation column 2. The sample gas to be measured is supplied to the separation column 2 through the gas injection channel 23.

The buffer tank 10 preferably has a sufficiently large capacity compared to the flow rate of the carrier gas supplied to the separation column 2 by the air pump 14. For example, when the flow rate of the carrier gas is about 10 cm ³ / min, The capacity of the tank 10 is preferably about 1000 cc. In this case, the air taken in from the atmosphere is diluted with the air in the buffer tank 10 and then supplied to the separation column 2 as a carrier gas, thereby suppressing the fluctuation in the baseline of the detection output of the semiconductor gas sensor 3. The

  As shown in FIG. 2, the separation column 2 is composed of an outer cylinder 24 formed of a metal having high thermal conductivity such as stainless steel and copper, and, for example, Teflon (registered trademark) inserted in the outer cylinder 24. It has a double cylinder structure with the inner cylinder 25. The inner cylinder 25 is filled with a filler serving as a stationary phase. The filler may be any appropriate material according to the detection target component in the sample gas, the type of carrier gas, and the like. For example, as a filler used for detecting volatile organic compounds, Shimadzu Corporation Part No. B-19 is listed, and as a filler used for detection of trihalomethane, Part No. S-201 manufactured by Shimadzu GL is listed, and as a filler used for detection of formaldehyde, part number manufactured by GL Sciences Inc. APS-201 is exemplified.

  The heater 26 is a flexible heater including a resistor 27 and an insulating rubber such as a silicone rubber sheet that insulates the resistor 27 from the outside. The resistor 27 is spirally wound on the outer peripheral surface of the separation column 2 so as to be in close contact with the outer surface of the separation column 2. The separation column 2 is provided with a temperature sensor 28 composed of a thermistor (thermocouple). The temperature sensor 28 is covered with an insulating material such as a polyfluorinated ethylene resin (Teflon (registered trademark)) or glass wool. The temperature sensor 28 is disposed on the outer surface of the separation column 2, and the temperature sensor 28 detects the temperature of the separation column 2.

  A semiconductor gas sensor 3 is connected to the end of the separation column 2. The end of the separation column 2 and the semiconductor gas sensor 3 are connected through a first flow path 4. A second flow path 6 is branched from the first flow path 4. The second flow path 6 communicates with the outside air. A third flow path 7 is also connected to the semiconductor gas sensor 3. This third flow path 7 also communicates with the outside air.

  As shown in FIG. 3, the semiconductor gas sensor 3 is attached to a hollow sensor chamber 29. The sensor chamber 29 is formed in a tubular shape, for example. The inside of the sensor chamber 29 communicates with the first flow path 4 and the third flow path 7.

  A metal oxide semiconductor type sensor element 30 is disposed in the sensor chamber 29. The sensor element 30 has a function of converting the concentration of the detection target component in the gas into an electric signal when exposed to the gas. The sensor element 30 includes a gas sensitive body 31 containing a metal oxide semiconductor such as tin oxide, and a detection electrode embedded in the gas sensitive body 31. The gas sensitive body 31 is formed by molding and firing a material containing a metal oxide semiconductor powder. The gas sensitive body 31 is formed in a spherical shape, an ellipsoidal shape, or the like, for example. A coiled heater combined electrode 32 and a core wire electrode 33 are embedded in the gas sensitive body 31 as detection electrodes. The core wire electrode 33 is provided so as to penetrate the inside of the coiled heater combined electrode 32. This detection electrode is made of, for example, platinum or a platinum alloy.

  The gas sensitive body 31 includes an appropriate metal oxide semiconductor according to the type of the detection target component in the sample gas. For example, indium oxide is used as a metal oxide semiconductor used for detection of volatile organic compounds, tungsten oxide is used as a metal oxide semiconductor used for detection of trihalomethane, and metal oxide used for detection of formaldehyde An example of the semiconductor is tin oxide.

  The lead wires 34, 35, 36 support the sensor element 30, and the lead wires 34, 35, 36 are electrically connected to the sensor element 30. The lead wires 34, 35, 36 are made of, for example, platinum or a platinum alloy. The two lead wires 34 and 35 protrude outward from the gas sensitive body 31 from both ends of the heater electrode 32. That is, the lead wires 34 and 35 and the heater combined electrode 32 are formed by molding a single wire, and the heater combined electrode 32 is formed between the lead wires 34 and 35. The remaining lead wire 36 protrudes from the end of the core wire electrode 33 to the outside of the gas sensitive body 31. That is, the lead wire 36 and the core wire electrode 33 are composed of a single wire, and one end portion of the wire rod is a core wire electrode 33, and a portion other than the core wire electrode 33 is a lead wire 36.

  The ends of the lead wires 34, 35, 36 are fixed to the three terminals 37, 38, 39, respectively, and are electrically connected to the terminals 37, 38, 39. The terminals 37, 38, 39 penetrate the base 40, whereby the terminals 37, 38, 39 are supported by the base 40.

  The base 40 is part of the outer wall of the sensor chamber 29 by being fitted into a fitting recess 41 formed on the outer wall of the sensor chamber 29. The three terminals 37, 38, 39 penetrate the outer wall of the sensor chamber 29, and the sensor element 30 is disposed in the sensor chamber 29.

  A first valve 5 is provided in the first flow path 4 at a branch position with respect to the second flow path 6. The first valve 5 is a three-way valve. The first valve 5 is configured such that the gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4 is open, and the separation column 2 and the semiconductor gas sensor 3 and the second flow path 6 are connected to each other. The gas flow between the separation column 2 and the second flow channel 6 in the first flow path 4 is open and the separation column 2 and the second flow are closed. Is switched to a state in which the gas flow between the flow path 6 and the semiconductor gas sensor 3 is closed (see arrow B).

  Further, the third flow path 7 is provided with a second valve 8 for opening and closing the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7.

  Furthermore, the gas chromatograph 1 includes a control device 9 that controls the air pump 14, the first valve 5, the second valve 8, the semiconductor gas sensor 3, the flow sensor, and the like.

  The configuration of the control device 9 is shown in FIG. The control device 9 includes a power supply circuit 42, a column heater control unit 43, an arithmetic processing unit 44 including a microcomputer, a display unit 45, a flow rate measurement unit 46, a measurement unit 47, a valve drive unit 48, a memory 49.

  The power supply circuit 42 generates a power supply voltage + V for operating the air pump 14 and each of the units 42 to 49.

  The column heater control unit 43 controls the energization power to the heater 26 by the PID control by the PID control unit and the phase control by the phase control unit based on the detection result of the temperature of the heater 26 of the separation column 2 by the temperature sensor 28 made of the thermistor. Thus, the temperature of the separation column 2 is kept at a predetermined temperature set in advance.

  The flow rate measurement unit 46 is a circuit that performs A / D conversion on a signal output from the flow rate sensor and then sends the signal to the arithmetic processing unit 44.

  The measurement unit 47 is a circuit that applies a voltage to the heater combined electrode 32 of the sensor element 30 via the terminals 37 and 38 and the lead wires 34 and 35 to electrically heat the heater combined electrode 32. Further, the measurement unit 47 is also a circuit that outputs a concentration signal of the detection target component based on a change in the electric resistance value generated in the gas sensitive body 31 and sends it to the arithmetic processing unit 44. That is, for example, the measurement unit 47 intermittently stops the application of voltage to the heater combined electrode 32, and a constant voltage is applied to a circuit in which the heater combined electrode 32, the core wire electrode 33, and an appropriate resistor are connected in series. The voltage drop generated between the heater combined electrode 32 and the core wire electrode 33 at this time is measured, and the measured value is A / D converted and sent to the arithmetic processing unit 44. Since this voltage drop fluctuates according to a change in the electric resistance value of the gas sensitive body 31, it correlates with the concentration of the detection target component.

  The valve drive unit 48 connects the first valve 5 to the separation column 2 in the first flow path 4 and the second based on a control signal sent from the arithmetic processing unit 44 in a state where power is supplied. From the state in which the gas flow between the first flow path 6 and the separation column 2 and the second flow path 6 and the semiconductor gas sensor 3 is closed, the separation in the first flow path 4 is performed. The gas flow between the column 2 and the semiconductor gas sensor 3 is opened, and the gas flow between the separation column 2 and the semiconductor gas sensor 3 and the second flow path 6 is closed. At the same time, the valve drive unit 48 changes the second valve 8 from a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed to a state in which the gas flow is opened. It is a device to switch. Further, when the supply of electric power is stopped, the valve drive unit 48 operates to return the first valve 5 and the second valve 8 to their original states.

  Examples of the display unit 45 include various display devices such as a liquid crystal display device.

  The memory 49 is composed of a RAM or an appropriate storage medium.

  The operation of the gas chromatograph 1 will be described.

  When the gas chromatograph 1 is stopped, the air pump 14 is stopped and no voltage is applied to the heater electrode 32 of the semiconductor gas sensor 3. The first valve 5 has an open gas flow between the separation column 2 and the second flow path 6 in the first flow path 4, and the separation column 2 and the second flow path 6 and the semiconductor gas sensor 3. The gas flow between is closed. The second valve 8 is in a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed.

  Thus, since the first valve 5 closes the gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4, the semiconductor gas sensor 3 from the separation column 2 to the semiconductor gas sensor 3 is closed. Movement of components that degrade performance is prevented. In addition, since the second valve 8 closes the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7, the performance of the semiconductor gas sensor 3 from the outside air to the semiconductor gas sensor 3 is deteriorated. Component movement is also prevented.

  In this state, when the power switch SW is turned on and the power supply circuit 42 is activated, first, the air pump 14, the measurement unit 47, and the column heater control unit 43 are activated.

  The air pump 14 sucks air from the atmosphere through the buffer tank 10 and pumps the air to the return gas flow path 16. A part of this air is supplied as a carrier gas from the branch position 19 to the gas flow path 17, and surplus air is returned to the buffer tank 10 through the return gas flow path 16. The amount of carrier gas supplied to the gas flow path 17 is adjusted by the two flow rate adjusting valves 21 and 18. The carrier gas supplied to the gas flow path 17 passes through the gas purification device 20 to remove miscellaneous gas components from the carrier gas, and then is sent to the separation column 2, and further to the first flow path 4 and the second flow path. It is sent to outside air through the flow path 6. For this reason, for example, even if a component that deteriorates the performance of the semiconductor gas sensor 3 stays in the separation column 2, such a component is not sent to the semiconductor gas sensor 3 but is released from the second flow path 6 to the outside air. .

  Further, the column heater control unit 43 is operated to heat the separation column 2 to a predetermined temperature.

  Further, when the measuring unit 47 is activated, a voltage is applied to the heater serving electrode 32 of the semiconductor gas sensor 3 via the terminals 37 and 38 and the lead wires 34 and 35. Thereby, the heater combined electrode 32 is energized and heated, and the temperature of the gas sensitive body 31 is heated to a temperature suitable for detection of the detection target component.

  When a certain period of time has elapsed after the air pump 14 has started operating, the arithmetic processing unit 44 generates a control signal and sends it to the valve drive unit 48, and the valve drive unit 48 moves the first valve 5 and the second valve 8. Operate. As a result, the first valve 5 opens the gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4, and the separation column 2, the semiconductor gas sensor 3, and the second flow path 6. The gas flow between is closed. The second valve 8 is in a state where the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is opened. As a result, the carrier gas is sent from the separation column 2 to the semiconductor gas sensor 3 through the first flow path 4, and further released to the outside air through the third flow path 7.

  The arithmetic processing unit 44 displays the flow rate of the carrier gas on the display unit 45 based on the signal taken from the flow rate measurement unit 46, and monitors fluctuations in the flow rate of the carrier gas based on this signal.

  In such a state, the sample gas is supplied to the separation column 2 through the gas injection channel 23. When the sample gas is injected, the flow rate of the carrier gas in the gas channel 17 is temporarily reduced. When the arithmetic processing unit 44 that monitors the change in the flow rate of the carrier gas detects a decrease in the flow rate of the carrier gas, it determines that the sample gas has been injected at the detected timing, and based on this timing, the semiconductor gas sensor The retention time of the gas component detected at 3 is measured. Thereby, the injection of the sample gas is automatically detected and the measurement of the gas is disclosed.

  The sample gas is sent to the separation column 2 together with the carrier gas, the components contained in the sample gas are separated by the interaction with the packing material in the separation column 2, and the separated components are separated from the separation column 2 by the first column. It is sent to the semiconductor gas sensor 3 through the flow path 4. Thus, when gas is supplied to the semiconductor gas sensor 3, the electric resistance value of the gas sensitive body 31 varies according to the concentration of the detection target component of the semiconductor gas sensor 3, and the detection according to the electric resistance value of the gas sensitive body 31 is detected. A concentration signal of the target component is sent from the measurement unit 47 to the arithmetic processing unit 44.

  The arithmetic processing unit 44 creates a chromatogram based on the concentration signal of the detection target component received from the measurement unit 47 and the measurement result of the retention time. The control device 9 may further display the chromatogram on a display device such as a liquid crystal display device or store it in the memory 49. The arithmetic processing unit 44 may output the concentration signal of the detection target component and the measurement result of the retention time to an external device.

  When the switch is turned off after the measurement is completed, the supply of power to the air pump 14, the measurement unit 47, the column heater control unit 43, the valve drive unit 48, etc. is stopped, and these operations are stopped.

  As a result, the first valve 5 allows the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 to be open, and the separation column 2 and the second flow path 6 and the semiconductor gas sensor. The second valve 8 returns to a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed. Further, the application of the voltage to the heater serving electrode 32 of the semiconductor gas sensor 3 is stopped.

  Thus, since the first valve 5 again closes the gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4, the semiconductor gas sensor 3 is separated from the separation column 2 to the semiconductor gas sensor 3. Movement of components that degrade performance is prevented. In addition, since the second valve 8 closes the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7, a component that deteriorates the performance of the semiconductor gas sensor 3 from the outside air to the semiconductor gas sensor 3. Movement is also prevented.

  Even if the operation of the air pump 14 is stopped, the flow of the carrier gas does not stop instantaneously. However, since this carrier gas is discharged to the outside air through the second flow path 6, the internal pressure of the gas flow path or the separation column 2 is reduced. Is not excessively increased, and the occurrence of breakage or the like due to the increase in internal pressure is suppressed.

  When the measurement of the sample gas is repeated a plurality of times with the power switch SW turned on, if the period between the end of the measurement and the start of the next measurement becomes long, The gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 is opened and the gas between the separation column 2 and the second flow path 6 and the semiconductor gas sensor 3 is opened. The second valve 8 may be switched to a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed. In this way, the chance that the gas sensitive body 31 is exposed to a component that degrades the performance of the semiconductor gas sensor 3 is further reduced. In this case, it is preferable to switch the first valve 5 and the second valve 8 again so that the carrier gas is supplied to the semiconductor gas sensor 3 20 to 30 minutes before the start of the next measurement. This is to stabilize the output of the semiconductor gas sensor 3 before starting the next measurement.

  In this embodiment, the second flow path 6 is provided and the first valve 5 is a three-way valve. However, the second flow path 6 is not provided, and the first valve 5 is the second flow path. 6 may be a two-way valve in which the function of opening and closing the gas flow to 6 is omitted.

(Second embodiment)
In the second embodiment shown in FIG. 5, the carrier gas is not supplied from outside air, and the gas chromatograph 1 includes a gas cylinder 50 for storing the carrier gas.

  The gas chromatograph 1 is not provided with the air pump 14, the buffer tank 10, the gas flow path 15, and the return gas flow path 16 in the first embodiment. Instead, a gas cylinder 50 is connected to the start end of the gas flow path 17.

  In the gas flow path 17, a check valve 51, a constant pressure valve 52, a flow rate adjustment valve 21, and a flow rate sensor 22 are provided in order from the gas cylinder 50 side.

  Other configurations are the same as those of the first embodiment.

  The gas chromatograph 1 includes a control device 9 similar to that of the first embodiment. However, since the air pump 14 does not exist, power supply to the air pump 14 is not performed.

  The operation of the gas chromatograph 1 will be described.

  When the gas chromatograph 1 is stopped, the constant pressure valve 52 is closed and no voltage is applied to the heater electrode 32 of the semiconductor gas sensor 3. The first valve 5 has an open gas flow between the separation column 2 and the second flow path 6 in the first flow path 4, and the separation column 2 and the second flow path 6 and the semiconductor gas sensor 3. The gas flow between is closed. The second valve 8 is in a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed.

  Thus, since the first valve 5 closes the gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4, the semiconductor gas sensor 3 from the separation column 2 to the semiconductor gas sensor 3 is closed. Movement of components that degrade performance is prevented. In addition, since the second valve 8 closes the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7, the performance of the semiconductor gas sensor 3 from the outside air to the semiconductor gas sensor 3 is deteriorated. Component movement is also prevented.

  In this state, when gas is supplied from the gas cylinder 50, the constant pressure valve 52 is opened, and a certain amount of carrier gas is supplied to the gas flow path 17. The supply amount of the carrier gas is adjusted by the flow rate adjustment valve 21. The carrier gas supplied to the gas channel 17 is sent to the separation column 2 and further sent to the outside air through the second channel 6. For this reason, for example, even if a component that deteriorates the performance of the semiconductor gas sensor 3 stays in the separation column 2, such a component is not sent to the semiconductor gas sensor 3 but is released from the second flow path 6 to the outside air. .

  Subsequently, when the power switch SW is turned on and the power supply circuit 42 is activated, the measurement unit 47 and the column heater control unit 43 are activated. Thereafter, the sample gas is measured in the same manner as in the first embodiment.

  When the power switch SW is turned off after the measurement is completed, the supply of power to the measurement unit 47, the column heater control unit 43, the valve drive unit 48, etc. is stopped, and these operations are stopped.

  As a result, the first valve 5 allows the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 to be open, and the separation column 2 and the second flow path 6 and the semiconductor gas sensor. The second valve 8 returns to a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed. Further, the application of the voltage to the heater serving electrode 32 of the semiconductor gas sensor 3 is stopped.

  Thus, since the first valve 5 again closes the gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4, the semiconductor gas sensor 3 is separated from the separation column 2 to the semiconductor gas sensor 3. Movement of components that degrade performance is prevented. In addition, since the second valve 8 closes the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7, a component that deteriorates the performance of the semiconductor gas sensor 3 from the outside air to the semiconductor gas sensor 3. Movement is also prevented.

  Thus, even when the first valve 5 and the second valve 8 are switched, the carrier gas is supplied from the gas cylinder 50 to the separation column 2. However, since the carrier gas is discharged to the outside air through the second flow path 6, the internal pressure of the gas flow path and the separation column 2 does not increase excessively, and such damage due to the increase of the internal pressure occurs. Is suppressed. Even if the supply of the carrier gas is continued for a long time after the measurement is completed, the occurrence of the above-described damage or the like is suppressed.

  When the measurement of the sample gas is repeated a plurality of times with the power switch SW turned on, if the period between the end of the measurement and the start of the next measurement becomes long, The valve 5 opens the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 and gas between the separation column 2 and the second flow path 6 and the semiconductor gas sensor 3. The second valve 8 may be switched to a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed. In this way, the chance that the gas sensitive body 31 is exposed to a component that degrades the performance of the semiconductor gas sensor 3 is further reduced. In this case, it is preferable to switch the first valve 5 and the second valve 8 again so that the carrier gas is supplied to the semiconductor gas sensor 3 20 to 30 minutes before the start of the next measurement. This is to stabilize the output of the semiconductor gas sensor 3 before starting the next measurement.

  In this embodiment, the second flow path 6 is provided and the first valve 5 is a three-way valve. However, the second flow path 6 is not provided, and the first valve 5 is the second flow path. 6 may be a two-way valve in which the function of opening and closing the gas flow to 6 is omitted. However, in the present embodiment, the carrier gas is supplied from the gas cylinder 50 to the separation column 2 even when the semiconductor gas sensor 3 is not heated, and the carrier gas from the gas cylinder 50 to the separation column 2 is long even after the measurement is completed. It is particularly preferable that the first valve 5 is a three-way valve because it may be supplied for a time.

[Example 1]
The gas was measured using the gas chromatograph 1 having the same configuration as in the second embodiment except that the second valve 8 was not provided. An air gas cylinder was used as the gas cylinder 50. As the separation column 2, a Teflon (registered trademark) tube having an inner diameter of 5 mm and a length of 30 cm is used, and this is filled with a product number B-19 manufactured by Shimadzu GL Co., Ltd. Covered.

The sensor element 30 of the semiconductor gas sensor 3 was produced as follows. First, indium hydroxide obtained by adding ammonia to an indium chloride aqueous solution was baked at 500 ° C. for 1 hour and then pulverized to obtain an indium oxide powder. Water was added to the indium oxide powder to form a paste, which was applied to the detection electrode, and then fired in air at 700 ° C. for 10 minutes to form a sintered body. By applying 0.05 μl of a chloroauric acid aqueous solution (gold content 3 mg / cm ³ ) to this sintered body and further firing at 700 ° C. for 10 minutes, the gold content with respect to indium oxide is 0.5 wt%. A gas sensitive body 31 was formed.

  The operating conditions of the gas chromatograph 1 were a carrier gas flow rate of 30 cc / min, a sample gas injection amount of 5 cc, a heating temperature of the gas sensitive body 31 of 400 ° C., and a heating temperature of the separation column 2 of 70 ° C.

  Under this condition, the output from the semiconductor gas sensor 3 when the carrier gas flows before the sample gas injection is 2.13 V, and the detected value of toluene derived from the change in output caused by the sample gas injection is 1.1 ppm. Met.

  Subsequently, the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 is opened, and the separation column 2 and the second flow path 6 and the semiconductor gas sensor are connected to the first valve 5. The flow of gas to 3 was switched to a closed state. The heating of the gas sensitive body 31 and the heating of the separation column 2 were stopped. The carrier gas was continuously supplied from the gas cylinder 50 to the separation column 2. After maintaining this state for 70 hours, when the sample gas was measured again, the output from the semiconductor gas sensor 3 during the carrier gas flow before the sample gas injection was 2.10 V, and the output generated by the sample gas injection. The detected value of toluene derived from this change was 1.01 ppm.

  Thus, there was almost no change between the first output and the second output.

[Example 2]
Using the gas chromatograph 1 having the same configuration as that of the second embodiment, first, the first measurement was performed under the same conditions as in the case of Example 1. As a result, a semiconductor gas sensor during carrier gas circulation before sample gas injection was obtained. The output from 3 was 2.18 V, and the detected value of toluene derived from the change in output caused by the injection of the sample gas was 1.15 ppm.

  Subsequently, the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 is opened, and the separation column 2 and the second flow path 6 and the semiconductor gas sensor are connected to the first valve 5. The flow of gas to 3 was switched to a closed state. Furthermore, the second valve 8 was switched to a state in which the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 was closed. The heating of the gas sensitive body 31 and the heating of the separation column 2 were stopped. The carrier gas was continuously supplied from the gas cylinder 50 to the separation column 2. When this state was maintained for 70 hours and measurement was performed again, the output from the semiconductor gas sensor 3 during the carrier gas flow before the injection of the sample gas was 2.17 V. From the change in the output caused by the injection of the sample gas The detected value of derived toluene was 1.12 ppm.

  Thus, the change between the first output and the second output was smaller than that in the first embodiment.

[Comparative Example 1]
A gas chromatograph 1 having the same configuration as that of the second embodiment except that the first valve 5, the second valve 8 and the second flow path 6 are not provided is used under the same conditions as in the case of Example 1. A second measurement was taken. As a result, the output from the semiconductor gas sensor 3 when the carrier gas flows before the sample gas is injected is 2.2 V, and the detected value of toluene derived from the change in output caused by the sample gas injection is 1.12 ppm. It was.

  Subsequently, the carrier gas was continuously supplied from the gas cylinder 50 to the separation column 2. The heating of the gas sensitive body 31 was stopped. When this state was maintained for 52 hours and the second measurement was performed, the output from the semiconductor gas sensor 3 during the carrier gas flow was 1.25 V, and toluene derived from the change in output caused by the injection of the sample gas. The detected value was 0.58 ppm.

  Thus, the output changed greatly between the first time and the second time.

[Comparative Example 2]
A gas chromatograph 1 having the same configuration as that of the second embodiment was used except that the first valve 5, the second valve 8, and the second flow path 6 were not provided. Between the first measurement and the second measurement, the supply of the carrier gas to the separation column 2 was stopped, and the measurement was performed in the same manner as in Comparative Example 1 except that.

  As a result, in the first measurement, the output from the semiconductor gas sensor 3 during the carrier gas flow before the sample gas injection is 2.15 V, and the detected value of toluene derived from the change in output caused by the sample gas injection is It was 1.05 ppm. In the second measurement, the output from the semiconductor gas sensor 3 when the carrier gas flows before the sample gas injection is 1.59 V, and the detected value of toluene derived from the change in output caused by the sample gas injection is 0.83 ppm. Met. Thus, in Comparative Example 2, although not as much as Comparative Example 1, the output changed greatly between the first time and the second time.

[Example 3]
The gas was measured using the gas chromatograph 1 having the same configuration as in the second embodiment except that the second valve 8 was not provided. An air gas cylinder was used as the gas cylinder 50. As the separation column 2, a Teflon (registered trademark) tube having an inner diameter of 5 mm and a length of 30 cm is used, and a product number APS-201 manufactured by GL Sciences Inc. is filled therein, and the outer surface thereof is covered with a rubber heater. It was.

The sensor element 30 of the semiconductor gas sensor 3 was produced as follows. First, an aqueous solution of SnCl ₂ was hydrolyzed with NH ₃ to obtain a stannic acid sol. This stannic acid sol was air-dried and further calcined in air at 500 ° C. for 1 hour to obtain SnO ₂ . This SnO ₂ was impregnated with a hydrochloric acid solution of palladium chloride and heated in air at 500 ° C. for 1 hour to carry Pd on SnO ₂ . SnO ₂ carrying Pd and 1000 mesh alumina as an aggregate are mixed at a mass ratio of 1: 1, and further a solvent is added to form a paste, which is applied to a detection electrode, and then 700 ° C. The gas sensitive body 31 having a Pd content of 0.3% by weight with respect to SnO ₂ was formed by firing for 2 hours.

  The gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4 is opened through the first valve 5 of the gas chromatograph 1 and the separation column 2 and the semiconductor gas sensor 3 are connected to the second flow path. The gas flow to and from 6 was closed. Furthermore, the flow rate of the carrier gas was 14 cc / min, the heating temperature of the gas sensitive body 31 was 400 ° C., and the heating temperature of the separation column 2 was 75 ° C. This state was maintained from 8 am to 6 pm.

  Subsequently, the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 is opened through the first valve 5 of the gas chromatograph 1 and the separation column 2 and the second flow path are opened. The gas flow between 6 and the semiconductor gas sensor 3 was switched to a closed state. The carrier gas was continuously supplied from the gas cylinder 50 to the separation column 2. The heating of the gas sensitive body 31 and the heating of the separation column 2 were stopped. This state was maintained from 6 pm to 8 am the next day.

  While repeating the above operation, the sample gas was measured using the gas chromatograph 1 every few days. As the sample gas, a gas containing formaldehyde at a ratio of 0.1 ppm was used.

  The graph of FIG. 6 shows the change over time in the amount of change between the output from the semiconductor gas sensor 3 when the carrier gas flows before the sample gas is injected and the output from the semiconductor gas sensor 3 when the sample gas is measured. In addition, the numerical value of the vertical axis | shaft of the graph shown in FIG. 6 is the value normalized by setting the output change amount at the time of the first sample gas measurement to 1.

  As shown in FIG. 6, in Example 3, the change with time in the output change amount was gradual.

[Example 4]
The gas was measured using the gas chromatograph 1 having the same configuration as that of the second embodiment. An air gas cylinder was used as the gas cylinder 50. The configurations of the separation column 2 and the sensor element 30 were the same as those in Example 3.

  The gas flow between the separation column 2 and the semiconductor gas sensor 3 in the first flow path 4 is opened through the first valve 5 of the gas chromatograph 1 and the separation column 2 and the semiconductor gas sensor 3 are connected to the second flow path. The gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is opened. Furthermore, the flow rate of the carrier gas was 14 cc / min, the heating temperature of the gas sensitive body 31 was 400 ° C., and the heating temperature of the separation column 2 was 75 ° C. This state was maintained from 8 am to 6 pm.

  Subsequently, the gas flow between the separation column 2 and the second flow path 6 in the first flow path 4 is opened through the first valve 5 of the gas chromatograph 1 and the separation column 2 and the second flow path are opened. 6 is switched to a state in which the gas flow between the semiconductor gas sensor 3 and the semiconductor gas sensor 3 is closed, and the gas flow between the semiconductor gas sensor 3 and the outside air in the third flow path 7 is closed in the second valve 8. Switched to. The carrier gas was continuously supplied from the gas cylinder 50 to the separation column 2. The heating of the gas sensitive body 31 and the heating of the separation column 2 were stopped. This state was maintained from 6 pm to 8 am the next day.

  While repeating the above operation, the sample gas was measured in the same manner as in Example 3.

  The graph of FIG. 7 shows the change over time in the amount of change between the output from the semiconductor gas sensor 3 when the carrier gas flows before the sample gas injection and the output from the semiconductor gas sensor 3 when the sample gas is measured. In addition, the numerical value of the vertical axis | shaft of the graph shown in FIG.

  As shown in FIG. 7, in Example 4, the change with time in the output change amount was gradual.

[Comparative Example 3]
Gas was measured using the gas chromatograph 1 having the same configuration as that of the second embodiment except that the first valve 5, the second valve 8, and the second flow path 6 were not provided. As the gas cylinder 50, an air gas cylinder 50 was used. The configurations of the separation column 2 and the sensor element 30 were the same as those in Example 3.

  In this gas chromatograph 1, the flow rate of the carrier gas was 14 cc / min, the heating temperature of the gas sensitive body 31 was 400 ° C., and the heating temperature of the separation column 2 was 75 ° C. This state was maintained from 8 am to 6 pm.

  Subsequently, in the gas chromatograph 1, the carrier gas was continuously supplied from the gas cylinder 50 to the separation column 2, and the heating of the gas sensitive body 31 and the heating of the separation column 2 were stopped. This state was maintained from 6 pm to 8 am the next day.

  While repeating the above operation, the sample gas was measured in the same manner as in Example 3.

  The graph of FIG. 8 shows the change over time in the amount of change between the output from the semiconductor gas sensor 3 when the carrier gas flows before the sample gas is injected and the output from the semiconductor gas sensor 3 when the sample gas is measured. In addition, the numerical value of the vertical axis | shaft of the graph shown in FIG.

  As shown in FIG. 8, the amount of change in output greatly changed over time in Comparative Example 3 compared to Examples 3 and 4.

DESCRIPTION OF SYMBOLS 1 Gas chromatograph 2 Separation column 3 Semiconductor gas sensor 4 1st flow path 5 1st valve 6 2nd flow path 7 3rd flow path 8 2nd valve 9 Control apparatus

Claims (7)

  A separation column, a semiconductor gas sensor, a first flow path connecting the separation column and the semiconductor gas sensor, and opening and closing a gas flow between the separation column and the semiconductor gas sensor in the first flow path; And a first gas chromatograph.   A second flow path that branches from the first flow path and communicates with the outside air, wherein the first valve is configured to allow gas flow between the separation column and the semiconductor gas sensor in the first flow path; A state in which the gas flow between the separation column and the semiconductor gas sensor and the second flow path is closed, and the separation column and the second flow path in the first flow path, The gas chromatograph according to claim 1, wherein the gas chromatograph is a three-way valve that switches between a state in which a gas flow between the separation column and the second flow path and the semiconductor gas sensor is closed. .   A third flow path connecting between the semiconductor gas sensor and the outside air, and a second valve for opening and closing a gas flow between the semiconductor gas sensor and the outside air in the third flow path. Or the gas chromatograph of 2.   At the time of gas measurement, the gas flow between the separation column and the semiconductor gas sensor in the first flow path by the first valve is opened, and the carrier gas and the sample gas are separated from the separation column, the first gas The first gas passage is sequentially passed through the semiconductor gas sensor, and the gas flow between the separation column and the semiconductor gas sensor in the first flow channel by the first valve is closed after the gas measurement is completed. The gas chromatograph as described in any one of Claims 1 thru | or 3 provided with the control apparatus which operates a valve.   At the time of gas measurement, the first valve opens the gas flow between the separation column and the semiconductor gas sensor in the first flow path, and the semiconductor in the third flow path by the second valve. Open the gas flow between the gas sensor and the outside air, and after the gas measurement is completed, close the gas flow between the separation column and the semiconductor gas sensor in the first flow path by the first valve. 4. The control device according to claim 3, further comprising a control device that operates the first valve and the second valve so as to close the flow of gas between the semiconductor gas sensor and the outside air in the third flow path by the second valve. Gas chromatograph.   A method using the gas chromatograph according to any one of claims 1 to 3, wherein the separation valve and the semiconductor in the first flow path are measured by the first valve when measuring the gas to be measured. The gas flow between the gas sensor is opened, the carrier gas and the sample gas are sequentially passed through the separation column, the first flow path, and the semiconductor gas sensor, and the first gas is measured after the measurement of the measurement target gas is completed. A method for using a gas chromatograph, wherein a valve closes a gas flow between the separation column and the semiconductor gas sensor in the first flow path.   4. A method using the gas chromatograph according to claim 3, wherein during gas measurement, the first valve opens a gas flow between the separation column and the semiconductor gas sensor in the first flow path. The carrier gas and the sample gas are sequentially passed through the separation column, the first flow path, and the semiconductor gas sensor, and between the semiconductor gas sensor and the outside air in the third flow path by the second valve. Open the gas flow, and after the gas measurement is completed, close the gas flow between the separation column and the semiconductor gas sensor in the first flow path by the first valve, and the third valve by the second valve. Of using a gas chromatograph for closing the gas flow between the semiconductor gas sensor and the outside air in the flow path.

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