SU151101A1 - Gas chromatograph for the analysis of liquid products - Google Patents

Description

A gas chromatograph for analyzing liquid products is known, consisting of series-connected: sensor, separation column and thermal conductivity detector. The proposed chromatograph differs from the known one in that its sensor is equipped with a metering device, which is a metering plate moved by a pneumatic membrane drive. In addition, the sensor is equipped with a check valve. These differences make it possible to increase the accuracy of the analysis by introducing into the column the analyzed mixture in the liquid phase and to reduce the analysis time for the key component.

The proposed chromatograph is explosion-proof (see drawing). It consists of a detector unit /, separation column 2, a liquid sample inlet unit 5, a reverse purge unit 4, a thermostat unit 5, and mounting parts.

The detector assembly consists of a housing and fittings with sensitive elements. One cell of the detector is of diffusion type, in it there is a choke. The second cell is of semi-flow type. The liquid sample injection unit consists of a pneumatically driven plate with a metering volume of 6. The plate is located between two fixed supports. In the lower support there is a capillary p 7, in which the liquid sample from the dosing volume is pushed out by the carrier gas to the sorbent located in the separation column. The sample volume can be selected from 0.2 to 0.02 cm. Dosing accuracy is ± 1%.

The reverse purge unit is designed to direct the carrier gas flow (either to the head of the column or to the end) and is a pneumatic diaphragm valve controlled from a command device.

No. 151101-2 The thermostatic unit is a metal-enclosed cylinder on which a heating winding 8 is applied. The cylinder with the winding is placed in a heat-insulating chamber, which, in turn, is located in the sensor housing. The thermostat is designed to operate in the temperature range 5 ° above the ambient temperature (up to + 150 ° C) and maintains the set temperature with an accuracy of 0.03 °.

The chromatograph works as follows.

Thermostat 5 is introduced at a predetermined temperature. The flow of carrier gas, heated to the temperature of the thermostat, passes through the diffusion cell (comparative) of the thermal conductivity detector 1 and, having passed through the fluid injection unit 3, enters the separation column 2, and then into the semi-flowing (measuring) cell of the detector and is discharged into the discharge line. Sensing elements of the detector are the active arms of the measuring bridge. The remaining two arms of the bridge can be used from the control unit of the serial chromatograph.

When a carrier gas flows through both cells of the detector, the measuring bridge is balanced. The liquid to be analyzed continuously flows through the valve and is discharged to the flowline.

During sampling, the plate moves and the dosing volume 6 flows into the flow of the analyzed fluid. The dosing volume is located above the capillary 7. The flow of carrier gas pushes the liquid dosed sample onto the sorbent into the column where the sample evaporates instantaneously.

The flow of carrier gas moves the sample through the layer of sorbent in the column, where it is divided into components and in the form of a binary mixture enters the measuring cell of the detector. As a result of thermal disturbance in the detector, an electric voltage is generated in the measuring diagonal of the bridge, which is proportional to the percentage content of the component in the sample. The results obtained can be recorded on a potentiometer of the type EPP-17M1.

The sensor operation can be controlled both from the standard HPA-2 chromatograph control unit and with a specially designed unit.

In the event that it is not necessary to obtain a complete chromatogram, the instrument, using the back flush assembly, allows the remaining components to be blown out (in the opposite direction) from the key component output. The use of reverse blowdown, if the key component goes out and the time is less than 0.5 cycle, leads to a reduction in the entire analysis cycle.

Subject invention

Claims (2)

1. Gas chromatograph for analyzing liquid products consisting of series-connected; sensor, separator column and thermal conductivity detector, characterized in that, in order to increase the analysis accuracy by introducing into the column the analyzed mixture in the liquid phase, the sensor is equipped with a metering device, which is a metering plate moved by a pneumatic diaphragm actuator. 2. Chromatograph according to claim I, characterized in that, in order to reduce the analysis time for the key component, its sensor is equipped with a back flush valve.