Operationgas chromatographHow to choose gas sources with different gas purity as carrier gas and auxiliary gas, we suggest to choose gas with higher purity as much as possible on the premise of meeting the analysis requirements, which will not only improve (maintain) the high sensitivity of the gas chromatograph, but also prolong the life of the chromatographic column and the whole gas chromatograph (gas path control components and gas filter). However, when the carrier gas purity is found to be insufficient, it will be replaced with gas with higher purity, it can also be solved from the following aspects:

① Analysis object: try to avoid using gas chromatograph to analyze the composition of compounds that are prone to oxidation, reduction and hydrolysis at high temperature, and avoid the distortion or even disappearance of sample components that affect the result analysis;

② Instrument system: Before the gas chromatograph is installed, the carrier gas and auxiliary gas lines should be cleaned, and the gas must be installed with a filter and purification device. Absorb the residual interference components in the gas, at the same time pay attention to whether the filter purification device is invalid, and avoid the gas path control valve is polluted and the adjustment accuracy is reduced, the gas path pollution affects the sensitivity of the gas chromatograph, damages the instrument, etc;

③ Chromatographic column: In order to avoid the influence of impurities in the carrier gas, a section of the same type chromatographic column of about 1m can be connected before the analytical column as a protective column. After a period of time, the front-end protection column can be replaced to avoid shortening the service life of the gas chromatograph analysis column, or after a period of operation, the analysis column is cut off by about 1m to remove part of the chromatographic column with reduced performance.

In actual operation, the purity of the gas should be judged according to the noise level of the gas chromatograph detector. For example, for ECD, impure carrier gas and many impurities such as high oxygen content will lead to obvious noise, reduced sensitivity, narrower linear range, even significant baseline drift, inverted peak, etc.