JP6607090B2 - Thermal conductivity detector - Google Patents

Description

  The present invention relates to a thermal conductivity detector (TCD).

  For example, a thermal conductivity detector is known as a detector used in gas chromatography. The thermal conductivity detector uses heat transfer between a heating element (filament) and a fluid (gas) flowing around the heating element. After the gas is introduced into the space in which the filament is accommodated, the gas is discharged from the space.

  The thermal conductivity detector has a configuration in which a measurement filament is provided on one side of the Wheatstone bridge. In this system, since the output signal is easily affected by the temperature of the cell block, the output signal is likely to drift.

In order to suppress the influence of the temperature of the cell block and the influence of the gas pressure fluctuation, a structure in which a measuring filament R ₃ and a reference filament R ₄ are provided on the side of the Wheatstone bridge as shown in FIG. 6 has been proposed. (See Non-Patent Document 1.) Moreover, as shown in FIG. 7, a structure in which all sides of the Wheatstone bridge are filaments R _{1 to} R ₄ has been proposed (see Non-Patent Document 1).

However, since it is difficult to make the characteristics of the measurement filament and the reference filament uniform, the influence of pressure fluctuations and the influence of the temperature of the cell block cannot be completely eliminated.
Therefore, a gas switching type thermal conductivity detector has been proposed (see, for example, Patent Documents 1 and 2). This thermal conductivity detector controls whether the measurement gas is introduced into the measurement filament or only the carrier gas is introduced into the measurement filament by the pressure difference caused by changing the inflow location of the carrier gas. get

FIG. 8 is a configuration diagram of the entire gas chromatograph including a gas switching type thermal conductivity detector.
Carrier gas is stored in the storage tank 102. The flow controller 104 is connected between the column 106 and the storage tank 102. A sample introduction unit 108 is connected to one end of the column 106. The column 106 has a function of separating each component of the sample over time.

  The gas sent out from the column 106 is sent to one of the pipes 112 and 114 via the connecting portion 110. That is, the gas that has flowed into the pipe 112 is sent to the exhaust port 118 via the coiled pipe 116 and is discarded there.

  On the other hand, the gas flowing into the pipe 114 is sent to the detector 122 via the coiled pipe 120. Which pipe (112 or 114) the gas exhausted from the column 106 is switched to flow into is determined by the method described below.

  The carrier gas stored in the storage tank 102 is sent to the pressure regulators 126 and 128 via the pipe 124. The gas sent out from the pressure regulator 126 is sent to the pipe 112 through the valve 130. Here, the connecting portion 132 between the valve 130 and the pipe 112 is positioned between the coiled pipe 116 and the connecting portion 110.

  In addition, the gas sent out from the pressure regulator 128 is sent to the pipe 114 through the valve 134. Here, the connecting portion 136 between the valve 134 and the pipe 114 is positioned between the coiled pipe 120 and the connecting portion 110.

  As shown in FIG. 8, when the valve 130 is open and the valve 134 is closed, the pressure of the carrier gas at the connecting portion 132 is set to a predetermined pressure value by the pressure regulator 126. Here, the predetermined pressure value means a pressure sufficient to send the gas discharged from the column 106 (a mixed gas of the carrier gas and the gas to be measured) to the detector 122 through the coiled pipe 120.

  On the other hand, when the valve 130 is closed and the valve 134 is open, the pressure of the carrier gas at the connecting portion 136 is set to a predetermined value by the pressure regulator 128. Here, the predetermined pressure means a pressure sufficient to send the gas discharged from the column 106 to the exhaust port 26 via the coiled pipe 116. Therefore, in this case (valve 130: closed, valve 134: open), only the carrier gas is introduced into the detector 122.

  With the switching means described above, it is possible to select whether to introduce only the carrier gas into the detector 122 or introduce the gas to be measured from the column 106. Note that the valve drive circuit 138 controls the opening and closing of the valves 130 and 134.

  The exhaust gas from the column 106 and the carrier gas alone are alternately introduced into the detector 122. Therefore, the bridge output signal 140 of the detector 122 appears as an AC signal. That is, the level difference between the bridge output signal 140 due to the gas discharged from the column 106 and the bridge output signal 140 due to the carrier gas alone is caused by each component of the sample. Therefore, when the gas to be measured is not included, these two output signal levels are equal.

  Note that although the output voltage of the bridge output signal 140 gradually changes in level, this affects both the two signals described above. Therefore, the drift over time of the detector 122 can be eliminated by subtracting the bridge output signal level due to the carrier gas alone.

  In this system, it is not necessary to match the characteristics of the filament, which is a problem of the structure using the measurement filament and the reference filament, and disturbances such as the influence of the temperature of the cell block can be removed.

JP 53-46091 A JP-A-55-50150

・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Robert L. Grob and Eugene F. Barry, 4th Edition, John Wiley & Sons, 2004/08/04, p.277-298

  Thus, with respect to the thermal conductivity detector, attempts have been made to reduce the minimum detection amount and expand the dynamic range. However, in chromatography, analysis conditions vary depending on the analysis target. Therefore, the gas flow condition to be measured is also used under various conditions.

  For example, in a structure optimized so that the performance can be exhibited when the flow rate of the gas to be measured is small, the volume of the flow path in which the filament is arranged is small, and when the flow rate of the gas to be measured is large, the flow velocity increases around the filament. Therefore, there is a problem that the influence of flow rate fluctuation is likely to be affected as signal noise, and the sensitivity and dynamic range are lowered due to the influence of forced convection.

  On the other hand, the structure optimized so that performance can be exhibited when the flow rate of the gas to be measured is high, the volume of the flow path is large, the peak tails when the sample flow rate is low, the response is slow, and it is diluted with switching gas Therefore, there is a problem that sensitivity and dynamic range are lowered.

  An object of the present invention is to provide a thermal conductivity detector that can provide high sensitivity and a wide dynamic range regardless of whether the flow rate of the gas to be measured is relatively small or large.

  The thermal conductivity detector according to the embodiment of the present invention includes a state in which a gas to be measured is introduced into the first channel and a reference gas is introduced into the second channel, and the reference gas is introduced into the first channel and the first A gas flow switching mechanism that switches between a state in which the gas to be measured is introduced into the two flow paths, a first filament section that is connected to the first flow path and includes the first filament, and is connected to the second flow path; A second filament unit including a second filament; and a detection circuit unit configured to detect an electrical signal corresponding to a change in voltage or current of the first filament and the second filament. The second filament part has different detection characteristics of the thermal conductivity of the gas.

  Since the thermal conductivity detector according to the embodiment of the present invention includes two filament parts having different detection characteristics of gas thermal conductivity, high sensitivity can be obtained regardless of whether the gas flow rate to be measured is relatively small or large. Can be obtained, and a wide dynamic range can be obtained.

It is a schematic block diagram for demonstrating an example of the gas chromatograph provided with one Embodiment of the thermal conductivity detector. It is sectional drawing of the typical planar view for demonstrating one structural example of a 1st filament part, and sectional drawing of a side view. It is sectional drawing of the typical planar view for demonstrating one structural example of a 2nd filament part, and sectional drawing of a side view. It is sectional drawing of the typical planar view for demonstrating the other structural example of a 2nd filament part, and sectional drawing of a side view. It is a schematic block diagram for demonstrating an example of the gas chromatograph provided with other embodiment of the thermal conductivity detector. It is a conceptual diagram for demonstrating the conventional thermal conductivity detector. It is a conceptual diagram for demonstrating the conventional thermal conductivity detector. It is a block diagram of the whole gas chromatograph including the conventional thermal conductivity detector of a gas switching system.

  In the thermal conductivity detector according to the embodiment of the present invention, for example, the first filament portion has a performance (the S / N ratio (signal-to-noise ratio) increases) when the gas flow to be measured is relatively small. The second filament portion can be optimized so that performance is obtained when the flow rate of the gas to be measured is relatively large (the S / N ratio increases).

  When measurement is performed under an analysis condition in which the gas flow rate to be measured is relatively small, a signal detected by the first filament of the first filament portion is used. When measurement is performed under an analysis condition in which the gas flow to be measured is relatively large, a signal detected by the second filament of the second filament portion is used. Thereby, the thermal conductivity detector according to the embodiment of the present invention can provide high sensitivity (high S / N ratio) and wide dynamic range regardless of whether the gas flow to be measured is relatively small or large.

  Moreover, the thermal conductivity detector of the embodiment of the present invention improves the minimum detection amount as a thermal conductivity detector by adding only one filament without largely changing the structure of the thermal conductivity detector. At the same time, the dynamic range can be expanded and the flow range where performance can be demonstrated can be expanded.

  In the thermal conductivity detector according to the embodiment of the present invention, for example, the first filament and the second filament may be at least one of length, thickness, shape, material, arrangement, and surrounding space dimensions. Examples where are different from each other. Thereby, the detection characteristics of the thermal conductivity of the gas can be made different between the first filament part and the second filament part. In addition, arrangement | positioning of a 1st filament means arrangement | positioning of the 1st filament in a 1st filament part. The arrangement of the second filament means the arrangement of the second filament in the second filament portion.

  In the thermal conductivity detector of the embodiment of the present invention, for example, the shape of the first filament part and the shape of the second filament part are any of a direct type, a semi-diffusion type, and a diffusion type, and The first filament and the second filament may have different surrounding space dimensions. Thereby, the detection characteristics of the thermal conductivity of the gas can be made different between the first filament part and the second filament part.

  The direct-type filament part means that the cross-sectional area of the filament part is substantially the same as the cross-sectional area of the flow path connected to the filament part. Moreover, the semi-diffusion-type filament part means that the cross-sectional area of the filament part is larger than the cross-sectional area of the flow path connected to the filament part. In addition, the diffusion type filament part is a columnar or protruding structure for diffusing fluid to the inlet of the filament part, in which the sectional area of the filament part is larger than the sectional area of the flow path connected to the filament part. Means that the body is placed.

  Further, the detection circuit section includes, for example, a first detection circuit that detects the electrical signal of the first filament and a second detection circuit that detects the electrical signal of the second filament. Also good. Thereby, the change of the thermal conductivity in the 1st filament part and the change of the thermal conductivity in the 2nd filament part can be detected and outputted simultaneously.

  In addition, the detection circuit unit includes, for example, a detection circuit that detects the electrical signal, and a changeover switch circuit that switches the detection circuit to the first filament and the second filament and electrically connects them. It may be. Thereby, compared with the case where a detection circuit is provided for each of the first and second filaments, the circuit configuration of the detection circuit unit is simplified, and the manufacturing cost can be reduced.

  In addition, the gas flow switching mechanism includes, for example, a measured gas flow path in which the first flow path is connected to one end, the second flow path is connected to the other end, and a measured gas is introduced into an intermediate portion. A branch flow path connected to the first flow path, the first reference gas flow path connected to the one end of the branch flow path, the second reference gas flow path connected to the other end of the branch flow path, You may make it provide the switching valve which switches and connects the reference gas flow path for introducing reference gas to the said 1st reference gas flow path and the said 2nd reference gas flow path. Thus, the reference gas inflow location is switched by switching the switching valve, and the gas to be measured and the reference gas are alternately introduced into the first flow path, and at the same time, the second flow path is opposite to the first flow path. The reference gas and the gas to be measured can be introduced alternately.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram for explaining an example of a gas chromatograph provided with an embodiment of a thermal conductivity detector.

  The gas chromatograph includes a thermal conductivity detector 1 as a detector. The thermal conductivity detector 1 includes a gas flow switching mechanism 3, a first filament unit 5, a second filament unit 7, and a detection circuit unit 9.

  The gas flow switching mechanism 3 switches the reference gas inflow portion to introduce the measurement gas into the first flow path 11 and introduce only the reference gas into the second flow path 13. The state in which only the reference gas is introduced and the gas to be measured is introduced into the second flow path 13 is switched. For example, the gas flow switching mechanism 3 includes a branch channel 15, a first reference gas channel 17, a second reference gas channel 19, and a switching valve 21.

  The branch flow path 15 has a first flow path 11 connected to one end 15a, a second flow path 13 connected to the other end 15b, and a measured gas flow path 23 for introducing a measured gas into the intermediate portion 15c. Has a connected configuration.

  The first reference gas channel 17 is connected to one end 15 a of the branch channel 15. The second reference gas channel 19 is connected to the other end 15 b of the branch channel 15. The switching valve 21 is composed of, for example, a three-way valve, and switches the reference gas flow path 29 for introducing the reference gas to the first reference gas flow path 17 and the second reference gas flow path 19 for connection.

  In the thermal conductivity detector 1, the first filament portion 5 is connected to the first flow path 11. The first filament part 5 includes a first filament 25. The second filament part 7 is connected to the second flow path 13. The second filament part 7 includes a second filament 27. The first filament part 5 and the second filament part 7 are accommodated in the cell block 31. The cell block 31 is kept at a constant temperature by a heater 33.

  The detection circuit unit 9 detects an electrical signal corresponding to a change in voltage or current of the first filament 25 and the second filament 27. The detection circuit unit 9 includes a first detection circuit 35 that detects an electrical signal of the first filament 25 and a second detection circuit 37 that detects an electrical signal of the second filament 27.

  In the thermal conductivity detector 1, the switching valve 21 is switched by control by the valve drive circuit 39. The valve drive circuit 39 switches the switching valve 21 in response to a signal having a constant period from the frequency signal source 41.

  A voltage is applied to the first filament 25 by the first filament driving circuit 45. A voltage is applied to the second filament 27 by the second filament drive circuit 47. The filament drive circuits 45 and 47 control the voltage applied to the filaments 25 and 27 so that the current flowing through the filaments 25 and 27 is constant or the resistance values of the filaments 25 and 27 are constant.

  The voltage applied to the first filament 25 is measured by the first detection circuit 35. The voltage applied to the second filament 27 is measured by the second detection circuit 37. These detection circuits 35 and 37 receive the signal of the frequency signal source 41 and synchronize the measurement timing. Thereby, the voltages of the filaments 25 and 27 are detected in synchronization with the switching timing of the switching valve 21.

  In the gas chromatograph shown in FIG. 1, a measurement sample is introduced into a sample introduction unit 51 and heated, and mixed with a carrier gas supplied from a gas tank 53 and adjusted in flow rate by a flow rate regulator 55 to become a measurement gas. Through the separation column 57. The gas to be measured is separated by the separation column 57 and then sent to the gas flow path 23 to be measured.

  Further, the carrier gas from the gas tank 53 becomes the reference gas via the pressure regulator 59 and is sent to the reference gas flow path 29. The reference gas is adjusted to a constant pressure by the pressure regulator 59 and sent to the switching valve 21 via the reference gas flow path 29.

  The measured gas that has reached the intermediate portion 15c of the branch flow channel 15 through the measured gas flow channel 23 is pushed away by the reference gas when the switching valve 21 is in conduction with the first reference gas flow channel 17. It is introduced into the second filament part 7 through the second flow path 13. At this time, only the reference gas is introduced from the first reference gas channel 17 into the first channel 11 and the first filament unit 5.

  Further, when the switching valve 21 is in conduction with the second reference gas channel 19, the gas to be measured that has reached the intermediate portion 15 c of the branch channel 15 is pushed away by the reference gas and passes through the first channel 11. Are introduced into the first filament portion 5. At this time, only the reference gas is introduced from the second reference gas channel 19 into the second channel 13 and the second filament portion 7.

  The gas that has passed through the first filament portion 5 is exhausted from the exhaust port 61, and the gas that has passed through the second filament portion 7 is exhausted from the exhaust port 63 to the outside of the cell block 31.

  By the gas flow switching mechanism 3 utilizing the pressure difference described above, the state in which the reference gas is introduced into the second filament part 7 at the same time as the measurement gas is introduced into the first filament part 5, and the second filament part The state in which the reference gas is introduced into the first filament portion 5 can be switched simultaneously with the introduction of the gas to be measured into the first filament portion 5.

  For example, by operating the switching valve 21 at a constant period of about 100 milliseconds, the first filament unit 5 and the second filament unit 7 can acquire signals of the gas to be measured and the reference gas, respectively. And the chromatogram of measured gas can be obtained by taking the difference of each signal. The detection signals of the detection circuits 35 and 37 are output to, for example, a workstation outside the gas chromatograph or a personal computer.

  In the thermal conductivity detector 1, the first filament part 5 and the second filament part 7 have different detection characteristics of the thermal conductivity of the gas. For example, the first filament 25 and the second filament 27 are different from each other in at least one of length, thickness, shape, material, arrangement, and dimensions of the surrounding space.

  For example, the 1st filament part 5 is provided with the 1st filament 25 of the direct shape and the linear shape as shown in FIG. Moreover, the 2nd filament part 7 is provided with the semi-diffusion type shape and the 2nd filament 27 of a zigzag folding shape, as shown in FIG.

  As a result, the first filament 25 and the second filament 27 have different dimensions and filament lengths in the surrounding space. The first filament 25 and the second filament 27 are made of, for example, tungsten and have the same thickness. However, the first filament 25 and the second filament 27 may be different in material and thickness.

  Compared with the second filament part 7, the first filament part 5 has a small space size around the filament and the length of the filament is short, so that the sensitivity is high when the gas flow to be measured is relatively small. (S / N ratio is large) and a wide dynamic range can be obtained. On the contrary, the second filament portion 7 can obtain high sensitivity (high S / N ratio) and a wide dynamic range when the gas flow to be measured is relatively large compared to the first filament portion 5. .

  When the measurement is performed under an analysis condition with a relatively large gas flow rate to be measured, the first filament portion 5 is more susceptible to pressure disturbance, so noise increases, the S / N ratio deteriorates, and the minimum detection amount decreases. Also, the linearity is deteriorated and the dynamic range is lowered. Therefore, by using the second filament part 7 optimized for the condition where the gas flow to be measured is high, the influence of pressure disturbance is suppressed, the minimum detection amount is improved, the linearity is ensured, and the dynamic range is improved. Can do.

  In addition, when measuring under analysis conditions with a low flow rate of gas to be measured, the second filament portion 7 optimized for conditions with a high flow rate has a slow cell response due to a large cell volume, and the peak of the chromatogram is tailing. I get out. Therefore, by using the first filament part 5 optimized for the condition with a small flow rate, the sensitivity can be increased, the minimum detection amount can be improved, the linearity can be ensured, and the dynamic range can be improved.

  As described above, the thermal conductivity detector 1 selects the detection signal of the first detection circuit 35 and the detection signal of the second detection circuit 37 in accordance with the measurement gas flow rate, so that the measurement gas flow rate is relatively small. In both cases and cases, high sensitivity can be obtained and a wide dynamic range can be obtained. Note that which one of the detection signals of the first detection circuit 35 and the second detection circuit 37 is selected may be performed by an operator, or may be automatically performed by software in accordance with the measured gas flow rate.

  In addition, since only the measurement gas and the reference gas are alternately introduced into the first filament part 5, only the reference gas and the measurement gas are alternately introduced into the second filament part 7, so that the same measurement gas is used. The detection signal of the first detection circuit 35 and the detection signal of the second detection circuit 37 can also be output.

  With reference to FIGS. 2 and 3, the specific configuration example for making the thermal conductivity detection characteristics of the first filament portion 5 and the second filament portion 7 different from each other has been described. The structure of 5 and the 2nd filament part 7 is not limited to these.

  For example, as shown in FIG. 4, the second filament portion 7 may include a diffusion-type shape and a coil-shaped second filament 27. Compared with the configuration shown in FIG. 3, this configuration of the second filament portion 7 can provide high sensitivity and a wide dynamic range even when the gas flow to be measured is larger.

  If the first filament 25 and the second filament 27 are different from each other in at least one of length, thickness, shape, material, arrangement, and dimensions of the surrounding space, the first filament portion 5 and The detection characteristics of the thermal conductivity of the gas can be made different from each other in the second filament portion 7.

  Contrary to the embodiment described above, the first filament portion 5 is optimized for a relatively large measured gas flow rate, and the second filament portion 7 is optimized for a relatively small measured gas flow rate. It goes without saying that the configuration may be realized.

  Next, an example of a gas chromatograph provided with another embodiment of the thermal conductivity detector will be described with reference to FIG. In FIG. 5, parts having the same functions as those in FIG.

  In the gas chromatograph shown in FIG. 5, the detection circuit unit 65 of the thermal conductivity detector 71 is electrically connected by switching one detection circuit 67 and the detection circuit 67 to the first filament 25 and the second filament 27. The changeover switch circuit 69 is provided. The changeover switch circuit 69 connects the detection circuit 67 to one of the first filament 25 and the second filament 27, for example, based on an external signal or automatically according to the gas flow rate to be measured. Thereby, it is possible to select an appropriate detection condition according to the flow rate of the gas to be measured, and high sensitivity can be obtained and a wide dynamic range can be obtained regardless of whether the flow rate of the gas to be measured is relatively small or large.

  Compared with the thermal conductivity detector 71 shown in FIG. 1, the thermal conductivity detector 1 of this embodiment has a simple circuit configuration of the detection circuit unit. Thereby, the cost reduction of a thermal conductivity detector can be aimed at.

  As mentioned above, although embodiment of this invention was described, the structure, arrangement | positioning, a numerical value, material, etc. in embodiment are examples, This invention is not limited to this, This invention described in the claim Various changes can be made within the range.

DESCRIPTION OF SYMBOLS 1,71 Thermal conductivity detector 3 Gas flow switching mechanism 5 1st filament part 7 2nd filament part 9, 65 Detection circuit part 11 1st flow path 13 2nd flow path 15 Branch flow path 15a One end 15b of a branch flow path The other end 15c of the branch flow path Intermediate portion 17 of the branch flow path 17 First reference gas flow path 19 Second reference gas flow path 21 Switching valve 25 First filament 27 Second filament 29 Reference gas flow path 35 First detection circuit 37 First 2 detection circuit 67 detection circuit 69 changeover switch circuit

Claims (5)

A state in which a gas to be measured is introduced into the first flow path and a reference gas is introduced into the second flow path, and a state in which the reference gas is introduced into the first flow path and the gas to be measured is introduced into the second flow path. a gas flow switching mechanism to switch alternately,
A first filament portion connected to the first flow path and having a first filament;
A second filament part connected to the second flow path and comprising a second filament;
A first detection circuit that detects an electrical signal according to a change in voltage or current of the first filament , and a second detection circuit that detects an electrical signal according to a change in voltage or current of the second filament,
The first filament part and the second filament part are thermal conductivity detectors having different gas thermal conductivity detection characteristics.   2. The thermal conductivity detection according to claim 1, wherein the first filament and the second filament are different from each other in at least one of length, thickness, shape, material, arrangement, and size of surrounding space. vessel.   The shape of the first filament part and the shape of the second filament part are any of a direct type, a semi-diffusion type, and a diffusion type, and the size of the surrounding space between the first filament and the second filament is The thermal conductivity detector according to claim 2, which is different from each other. 2. The S / N ratio of the first filament portion is increased when the measured gas flow rate is relatively low, and the S / N ratio of the second filament portion is increased when the measured gas flow rate is relatively high. To 4. The thermal conductivity detector according to any one of claims 1 to 3 . The gas flow switching mechanism is
A branch flow path in which the first flow path is connected to one end, the second flow path is connected to the other end, and a gas flow path to be measured for introducing the gas to be measured is connected to an intermediate portion;
The first reference gas channel connected to the one end of the branch channel;
The second reference gas channel connected to the other end of the branch channel;
And a switching valve for connecting by switching the reference gas passage for introducing a reference gas into said second reference gas flow path and the first reference gas channel, from claim 1, further comprising a any one of the 4 The thermal conductivity detector described in 1.

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