Carrier Gas Type and Purity Selection for Gas Chromatography

As a gas for gas chromatography carrier gas, it is required to have good chemical stability; high purity; cheap and easy to obtain; and can be suitable for the detector used. Commonly used carrier gases are hydrogen, nitrogen, argon, helium, carbon dioxide and the like. Among them, hydrogen and nitrogen are cheap and have good properties, and are good gases used as carrier gases.

(1) Hydrogen: Because it has the characteristics of small molecular weight, large molecular radius, large thermal conductivity, and low viscosity, it is often used as a carrier gas when using TCD. It is mandatory gas in FID. Hydrogen is flammable and explosive, so special attention should be paid to safety when using it.

(2) Nitrogen: due to its small diffusion coefficient and relatively high column efficiency, nitrogen is mostly used as a carrier gas in other forms of detectors except TCD.

(3) Helium: From the perspective of chromatographic carrier gas performance, it is close to hydrogen, and has the excellent characteristics of high safety. But because of the higher price, it is used less.

Selection of Gas Chromatography Carrier Gas Purity

In principle, the choice of gas purity depends primarily on the object of analysis; the packing in the column; the detector. Under the premise of meeting the analysis requirements, the gas with higher purity should be selected as much as possible. This will not only improve the high sensitivity of the instrument, but also prolong the life of the chromatographic column and the entire instrument.

Practice has proved that, as a mid-to-high-end instrument, it is sometimes very difficult to restore the high sensitivity of the instrument when a low-purity gas source is used for a long time. For low-end instruments, high-purity gas is used for constant or semi-trace analysis, which not only increases the operating cost, but also needs to add a purifier in order to purify the gas, which increases the complexity of the gas path and is more prone to air leakage or other problems. affect the normal operation of the instrument.