Improving the resolution of permanent gas analytes using solvent gas in gas chromatography

Gas chromatography (GC) using porous layer open tubular (PLOT) columns provides an accessible approach for the analysis of permanent gases in environmental samples and gaseous processes. However, unlike that in GC of volatile liquids, solvent effects cannot be readily exploited for permanent gas samples. This limitation arises from the low boiling points of permanent gases and the incompatibility of PLOT columns with conventional high-boiling-point solvents. Here, we report an unexpected solvent-like effect of a non-reactive permanent gas (as "solvent") on the separation of permanent gas analytes. When argon-typically inferior to costly helium or less-safe hydrogen in separation efficiency-is used as the carrier gas, the co-injection of "solvent" permanent gases enhances the chromatographic resolution of analytes. Specifically, the addition of helium, hydrogen, carbon dioxide, carbon monoxide, or methane to oxygen-nitrogen mixtures significantly improves the resolution of oxygen and nitrogen in ambient air samples. Column modification experiments with carbon dioxide, together with in-column "band-passing" of helium over oxygen and nitrogen, indicate that the enhanced separation efficiency arises from the co-injection of the analyte and "solvent" gases. This behavior is attributed to two possible contributing mechanisms: (i) a transient pressure drop associated with strongly adsorbing solvent gases (carbon dioxide, methane, and carbon monoxide) and (ii) the temporary role of helium and hydrogen as auxiliary carrier gases, which increase column efficiency while consuming minimal quantities of these gases.