SU1582121A1 - Method of detecting inorganic gases in gas chromatography - Google Patents

Abstract

This invention relates to gas chromatography. The aim of the invention is to increase the sensitivity and noise immunity. In the method of detecting inorganic substances in gas chromatography, the change in the electrical signal that occurs on a pyroelectric when exposed to a non-uniform thermal field generated by the analyte in a carrier gas stream is measured. The thermal field is periodically changed, the gradient of which is oriented perpendicular to the direction of movement of the carrier gas. 1 il.

Description

This invention relates to gas chromatography.

The aim of the invention is to increase the sensitivity and noise immunity of detection.

The drawing shows a device for implementing the proposed detection method.

The device contains a pyroelectric detector consisting of measuring and comparative pyroelectric sensitive elements (PCE) 1, a pulsed heater 2 with a heat sink 3 and a heat insulator 4 separated from the PCHE by a gas gap 5, a differential amplifier 6, which receives signals from the measuring electrodes PCE 7 source 8 pitch

tani heater and generator 9, which sets the frequency.

The pulse heater 2 is located on a massive heat sink 3 and has good thermal contact with it to achieve the required modulation depth and eliminate temperature drift.

Pyroelectric sensing elements 1 (PCHE) are isolated from the external environment and heater 2 by heat insulator 4 to reduce thermal losses of signals and eliminate the influence of external conditions. The carrier gas passes through the gaps 5 between the PSE J and on. heater 2. Differential electrical, the signal is removed from the measuring electrodes 7 pyroelectric

U1

uh uh

Yu

sensitive elements 1 and is fed to the input of a differential force, a lithium 6 and further to the synchronous detector 10.e

The device works as follows.

In the steady-state mode, streams of pure carrier gas flow through the measuring and comparative channels of the pyroelectric detector. The heater is supplied with the supply voltage from the source 8, changing with the frequency defined by the generator 9. The signals of the pyroelectric sensitive elements 1 with a frequency of 2f (since the heater 2 doubles the frequency of the supply voltage) amplitude. The signal at the output of the differential amplifier 20 6 and the synchronous detector 10 is zero,

When passing through the measuring chamber together with the carrier gas of any component separated by a mixture of 25 having a thermal conductivity different from that of the carrier gas, the temperature of the measuring pyroelectric sensing element 1 will change, which 30 will cause the change in the electrical signal at the output of the synchronous detector to be proportional to the amount of the analyte.

For testing - the proposed method, a detection device was created using the pyroceramics samples as the PCHE.

Example, PCHE Thickness 100 microns, thin-film heater made of nickel with a resistance of 100 Ohms. The modulation of the heat flux was carried out at a frequency of 5 Hz. An operational amplifier was used as a synchronous detector. The modulation depth of the heat flux, perpendicular to the ICE, was at the level of 10%. The use of the device as a detector in a chromatograph made it possible to obtain a detection limit for oxygen at a level of 2-10% with a noticeable (5 times) decrease in the requirements for the stability of gas flows. Helium was used as a carrier gas.

Claims (1)

Invention Formula The method of detecting inorganic gases in gas chromatography by measuring an electrical signal arising on a pyroelectric when exposed to a non-uniform thermal field generated by the analyte in a carrier gas stream, characterized in that, in order to increase the sensitivity and noise immunity, the signal is periodically changed during signal measurement There is a thermal field whose gradient is oriented perpendicular to the direction of movement of the carrier gas.