Practical method for the purification of carrier gases for gas chromatography

Abstract

For sensitive analysis of traces of inorganic gases, detectors are employed based on Penning's effect, which requires pure helium or neon as the carrier gas. These gases may be purified by an electric discharge. This method is based on cataphoresis, i.e. the change in composition of a gaseous mixture in an electric field. This change is the result of a flow of contaminant ions and is important when the ionization energy of the contaminant gas is lower than the energy of a metastable level of the carrier gas. The positive ions flow towards the cathode, which is compensated for, in the closed vessel, by a diffusive flow of neutral particles. If the electrodes are hollow and used as gas exit from the chamber, the compensating flow of neutral particles will decrease and the concentration of the contaminant in gas flowing out of the chamber through the cathode will increase. Accordingly, the concentration of the contaminant in gas flowing away through the anode becomes lower than the initial concentration. Construction of the discharge chamber and the value of the electric current depend on the initial concentration of the contaminant and the required level of purity. The experimental results show that the method may be used for the complete purification of helium and neon with low initial concentrations of contaminant. In this case, total ionization and purification can simply be obtained by a corona discharge.