Processing gas chromatography thermal conductivity can not be zeroed

What is the problem with the thermal conductivity of the gas chromatograph? The thermal conductivity of the gas chromatograph cannot be zeroed. Adjust the following steps:

(1) Attenuation block test: When it is found that there is an offset between the baseline and the zero point, the attenuation block is adjusted from small to maximum, and it is observed whether the baseline deviation gradually decreases.

(2) Check the zero adjustment knob: Rotate the coarse, medium, and fine adjustment knobs respectively to observe whether the baseline response.

(3) Dual flow inspection: Based on the test leak of the air circuit, use the soap film flowmeter to test the flow values ​​of the two airways separately to see if the difference is too large.

(4) Hot wire asymmetry or wire mis-alignment: This usually occurs after the repair of the thermal conductivity cell circuit. In this case, the connection between the hot wire lead wires must be carefully checked. The correct connection is that the four hot wires form a bridge, and the heat of the two pairs of arms in the bridge is exactly in the same air path.

(5) Hot-wire impingement or contamination: The hot-wire impingement can be verified by measuring the insulation resistance between the hot-wire and the cell body. Severe fouling of the hot wire can be eliminated or partially eliminated by cleaning the cell pool, as detailed in the section Cleaning the detector.

(6) Checking the error between the resistance values ​​of the hot-wires: Measure the resistance of the hot-wire lead-out sockets of the thermal conductivity tank. In general, the difference between the resistance values ​​of each group of hot filaments should not exceed 0.2~0.5Ω. If it exceeds this value, it should be treated as (4).

(7) Disposal of too large two-way flow or air leakage: The difference between the two flow rates can be solved by adjusting the air control valve, but there should be no leakage in the two air circuits.

(8) The zero adjustment circuit has an open circuit.

(9) The recorder is open or no response.

3, baseline noise and drift caused by thermal conductivity detector baseline instability for many reasons, there are about dozens of species, common are:

(1) The power supply voltage is too low or fluctuates too much, and the power load on the same phase changes too much;

(2) Condensate or foreign matter in the air outlet pipe;

(3) bad instrument grounding;

(4) Unstable column temperature at room temperature, fluctuations or drift in the room temperature control;

(5) The carrier gas is not clean, the gas path is contaminated, the gas in the carrier gas path leaks, the carrier gas pressure is too low or is used up quickly;

(6) Stable valve and steady flow valve control accuracy is poor;

(7) There is a large difference in gas flow between the two columns and the compensation is poor;

(8) There is wind in the carrier gas outlet or soap liquid in the outlet soap film flowmeter;

(9) Loose column packing;

(10) The mechanical vibration is too large;

(11) The bridge DC stabilized power supply is unstable;

(12) Loss of stationary phase in the column;

When the chromatogram baseline is unstable, first check the chromatographic gas path for contamination. In the case of unclean air lines, many factors that have little effect on baseline stability when the gas path is clean (such as changes in airflow, Temperature fluctuations, etc., affect the stability of the baseline suddenly.