Gas chromatography analysis, there must be no "qi", that is, carrier gas. The carrier gas, as a gas for gas chromatograph , requires good chemical stability and high purity; it is cheap and easy to obtain; it can be used with the detector used, and the commonly used carrier gas is nitrogen, hydrogen, helium, argon, and the like.
First, there are many types of carrier gases, how to choose?
To choose which gas to use as the carrier gas, first consider which detector to use.
When using the thermal conductivity detector, hydrogen or helium is used as the carrier gas to improve the sensitivity. The hydrogen carrier gas can also extend the life of the thermocouple tungsten wire. The hydrogen flame detector should use nitrogen as the carrier gas or hydrogen. The capture detector is generally high in nitrogen purity; the flame photometric detector is commonly used for nitrogen and hydrogen.
The diffusion coefficient is related to the carrier gas property and inversely proportional to the square root of the molar mass of the carrier gas. Therefore, the use of a carrier gas with a large molar mass can reduce the molecular diffusion coefficient and improve the efficiency of the column. However, the carrier gas with a small molar mass is used to increase , the gas phase mass transfer resistance coefficient is reduced, and the column efficiency is improved. Therefore, when using a low line rate carrier gas, the molar mass should be selected. When using a high line speed, the molar amount should be small.
Second, how to ensure the purity of the carrier gas?
Carrier gas purity is critical to extending column lifetime, reducing noise background interference, and maintaining peak integrity. The detector gas is also susceptible to contamination, and the carrier gas is not pure, which can result in increased background signals, increased noise, and reduced sensitivity.
The three main types of gas pollution are oxygen, hydrocarbon magazines and moisture. Oxygen and moisture can diffuse into the carrier gas stream through the pipe joint. The hydrocarbon magazine is produced by grease and lubricant in the pipe, air compressor or plastic tube of the gas generator. Oxygen and moisture consume the stationary phase of the column through oxidative degradation, reducing column life. Hydrocarbon magazines can lead to ghost peaks, increased background noise, and reduced detector sensitivity.
In order to reduce gaseous contaminants, high purity gases are usually used in conjunction with gas purifiers (traps). The trap should be installed as close as possible to the gas chromatograph to reduce contamination between the valve and the instrument.
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