Gas chromatography

Gas chromatography is a easy, fast, efficient, sensitive, modern separation analysis technology which is widely used in environment, medicine, chemical industrial department, and it’s also an indispensable way to test Pesticide Residues. Gas chromatography has fast analysis, high efficient separation, high sensitivity, high selectivity and other advantages. While during the analysis, Gas chromatograph may face various failures because of complex sample matrix, operator failures, device failures and etc. Therefore, it’s very important to know solving general failures in gas chromatograph. And let’s see below:

Gas Chromatography basic composition

It’s quite important for analysts to know well about the separation analysis principle and each parts functions. There are 7 parts in gas chromatograph: Gas supply system, Feeding system, Separation system, Test system, Temp. control system, signal amplifier, and Record and data processing system.

Common problems and solutions

  1. Incomplete separation

    Chromatograph peaks overlap and they can’t be separated: we can reduce the feeding volume and the column temp. raising speed. The component which was can be separated has bad separation after a while, it might be caused by column effective reducing, we can aging the column and remove the hard volatilizing impurity and half volatilizing impurity, and it also might be seriously losing fixative and end life of the column, so we need to change it.

    Long separation time causes late distilled seal: raising chromatograph column can solve this problem.

    No peaks for the sample, can’t test the low volume component: it might be caused by incorrect column locating, we need locate it again and test the device system. If feeding blocks, low temp. for the column and feeding, it might be low sensitivity of the detector, we can increase feeding and detector sensitivity.
  2. Irregular peak shape

    Trailing peak: if feeding inlet and column is polluted, we need clean the outlet and maintain it, like changing or cleaning the liner, aging the column to decontaminate, or cutting 1~2 rings from column feeding inlet, then re-locate it.

    Front peak: high feeding makes column overload, we need reduce feeding. If the sample components condensate, we need raise the column and inlet temp.

    Flat top peak: we can decrease feeding, increase load gas flow speed and the column temperature.
  3. Detector influence on analysis results

    Taking the thermal conductivity detector as an example, its principle is using load gas and detected component gas’s different thermal conductivity, and detecting the unbalance voltage proportional to the test group density. To analyze the sample component.

    Baseline drifts (or step baseline), high noise: the detector is polluted, need to clean and maintain it.

    Baseline reduces to 0: TCD thermal resistance wire fractures.

    Pulse interference peak: it might be TCD power voltage is unstable, need to check the power.
  4. Carrier gas

    Which is different with the liquid chromatography, the gas is the flowing phase in gas chromatography, the carrier gas crosses stationary phase with sample component, it reaches to the detector after adsorption and desorption and out from column. So the gas speed, gas pipeline tightness and carrier gas pressure are also influencing the separation efficiency.

    Low carrier gas speed: it causes reserve time extending, sensitivity lowing, trailing peak and round top peak.

    High carrier gas flow rate: it makes baseline drifts and high noise.

    We need check if pressure reducing valve is out of using range, need to change it if necessary, and check the air tightness at the same time.
  5. Circuit problem

    If the baseline becomes sine wave, it’s most probably caused by amplifying circuit failture.

    If the power fails to start normally and the column temp. box and feeding inlet can’t be heated, it might be caused by the circuit problem.

    According to these situation, we can change damaged electronic compoments.
  6. FID detector ignition failure

    First, we need to check if the hydrogen and air are open, ignition coil is good. Besides, need to check if the column and detector leak.
  7. Inverted peak

    Inverted peak appears, need to check if the detector or processer is connecting reversely.

If you have any problem or require further information, please contact info@welchmat

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