JPH04301555A - Heat conductivity detector for gas chromatograph - Google Patents

Abstract

PURPOSE:To enable correct measurement of a flow rate to be conducted without requiring a separate flow rate measuring device by providing cells which are subjected to the same carrier gas and at a flow rate of zero in a cell block and providing a hot wire filament here. CONSTITUTION:A reference cell A and a measuring cell B as well as a third cell C are provided in a cell block 1 inside an oven 14, while filaments FA to FC with constant current supplied from a constant current power source 15 are provided in respective cells. Carrier gas flows through the cell A, a sample vaporizing chamber 12, a column 13 and the cell B to a vent by a flow controller 11. Change in electric resistance of the filaments FA, FB according to change in gas concentration records concentration on a gas concentration recorder 18. At the same time difference in electric resistance of the filament FC and the filament FA of the cell C which are connected to a purge flow path 9 wherein it is communicated with the cell A and a valve is closed during operation and whose flow rate is zero when sealed is detected and the flow rate is displayed on a flow rate display 19. Thus a detector which does not require a separate flow meter and which is electric and highly accurate can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a gas chromatograph used for analyzing various substances, and more particularly to a thermal conductivity type detector for detecting separated component gases.

0002

2. Description of the Related Art In conventional gas chromatographs, a carrier gas flow rate detector and a sample gas detector have been provided completely separately. In other words, the flow meter for gas chromatographs is generally equipped with a rotameter or the like on the upstream side of the carrier gas flow path, and heat pulse type and other electronic types have also been proposed, but these all have a rotameter installed at the column outlet. It was installed in the carrier gas supply system completely independently of the sample gas detector provided.

0003

[Problems to be Solved by the Invention] The present invention utilizes a thermal conductivity detector for detecting sample components to accurately measure and detect the flow rate of a carrier gas supply path without installing a separate flow rate detector. It was planned.

0004

[Means and operations for solving the problem] A thermal conductivity detector detects gas concentration by utilizing the change in electrical resistance of a hot wire filament in accordance with changes in gas concentration. The resistance value also changes depending on the gas flow rate.

Utilizing this principle, a chamber (third cell) is provided in the cell block of a conventional thermal conductivity detector, which is exposed to the same carrier gas and whose flow velocity is zero.
A third hot wire filament is arranged here to detect the difference in change in electrical resistance between the carrier gas detection filament and this third filament,
As a result, the thermal conductivity detector itself also functions as a flow rate detector, eliminating the need for a separate flow rate detector.

[0006]

[Embodiment] Fig. 1 is a structural diagram showing an embodiment of the present invention. (a) is a top view of a cross section of a metal cell block 1 constituting a thermal conductivity detector, where A is a reference cell and B is a Measuring cell C is a third cell specifically provided according to the invention. 2 is a heater for heating the cell block, and each cell A. B
．． C is housed in the same block 1 and placed in a constant temperature bath. FA. FB. Each FC is a hot wire filament with the same rating, and a constant current is supplied from a constant current power supply. A carrier gas is introduced into the cell A from a carrier gas source through a flow path 3 via a flow controller, and is discharged from a flow path 4 into the sample vaporization chamber. Column outlet gas is introduced into cell B through channel 5 and is discharged to the vent via channel 6. Cell C communicates with cell A through a narrow resistive passage 7, and is connected to a purge passage through a flow passage 8 and an on-off valve 9. Since this valve 9 is closed during operation, the cell C chamber is in a sealed state and is filled with carrier gas, but there is no flow inside and the flow velocity is zero. The voltage difference across the filaments FA and FB is the difference in resistance between TA and TB at the same temperature, and F
This is caused by the change in resistance of FA due to the amount of heat carried out of the cell by the carrier gas flowing through A. Therefore, by measuring the potential difference between the two, the amount of heat carried away by the carrier gas, that is, the flow rate of the carrier gas can be detected.

FIG. 2 is an explanatory diagram when this thermal conductivity detector is mounted on a gas chromatograph, in which 10 is a carrier gas inlet channel, 11 is a flow controller, 12 is a sample vaporization chamber, 13 is a column, and 14 is a constant temperature It's a tank. As can be seen from the flow path piping indicated by the arrow, the carrier gas from the flow controller 11 enters the reference cell A, then passes through the sample vaporization chamber 12 and is introduced into the column 13 together with the sample.
The sample gas separated by the column passes through measurement cell B and is discharged to the vent.

FIG. 3 is a circuit diagram for measuring the output of each detection cell, and shows the output measurement circuit of each detection cell. FB. This is a circuit that detects resistance changes in FC. 15 is a constant current power supply, 16 is a gate switching circuit for sequentially driving the switching transistor TA TB TC and analog gate GA GB GC, R is a bias resistor, 17 is an output amplifier, RA C
A, RB CB, RC CC are each gate GA
18 is a sample gas concentration recorder, and 19 is a carrier gas flow rate indicator.

In the figure, the filament FA of each cell is shown.
FB. Since FC is connected to the constant current power supply 15, the clock pulse from the gate switching circuit 16 causes the transistors TA. TB. TC, analog gate G
A. GB. When the GCs are driven in this order, the difference between the outputs of the integrating circuits RA CA and RB CB is displayed on the gas concentration recorder 18, and the difference between the outputs of the integrating circuits RA CA and RC CC is displayed on the flow rate display 19, respectively. . That is, one thermal conductivity detector can simultaneously detect the gas component concentration and measure the carrier gas flow rate. When the carrier gas is converted from He to N, for example, the valve 9 of the purge channel may be opened to purge the gas in the third cell C chamber and fill it with new carrier gas.

In the embodiment, the third cell chamber C was connected to the reference cell A through a resistance tube, but it may also be connected to a suitable carrier gas flow path on the output side of the flow controller, in short, the third cell chamber C is connected to the reference cell A through a resistance tube. It is sufficient to fill the fluid so that the flow velocity is zero. It goes without saying that this method can also be applied to double column chromatography.

[0011]

[Effects of the Invention] As described above, the present invention allows the thermal conductivity detector itself to precisely measure the carrier gas flow rate at the same time as detecting the components, so there is no need to separately install a flow meter such as a rotameter, The configuration is simple, and since it is electronic, highly accurate flow rate measurement is possible.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of the thermal conductivity detector block of the present invention (a
) is a top sectional view, and (b) is a developed side sectional view taken along the line XX in FIG.

FIG. 2 is a diagram showing a state in which the thermal conductivity detector of the present invention is mounted on a gas chromatograph.

FIG. 3 is an output measurement circuit diagram of the thermal conductivity detector of the present invention.

[Explanation of symbols]

1...Cell block A...Reference cell B...Measurement cell C...Third cell FA. FB.
FC...Hot wire filament GA. GB. GC...Analog gate
12...Sample vaporization chamber

Claims (1)

[Claims] Claim 1: Three filaments for detecting thermal conductivity having substantially the same rating are housed in separate cell chambers in the same detector block, and the first filament chamber is located upstream of the carrier gas flow path. , the second filament chambers are respectively connected to the column outlet gas passages, and the third filament chamber is filled with a carrier gas such that the flow rate thereof is approximately zero;
A thermal conductivity detector for a gas chromatograph, comprising a circuit for detecting a difference in electrical resistance between a first filament and a third filament.