Noble, Diatomic and Aliphatic Hydrocarbon Gas Analyses by Aqueous HPLC

Dissolved non-polar gases (five noble, three diatomic, and four unbranched aliphatic hydrocarbon gases) were resolved by aqueous high-performance liquid chromatography using an ion-moderated partition chromatography column (Bio-Rad HPX-87P) originally designed for monosaccharide analysis. The dissolved-gas peaks, which were detected and quantitated by high-sensitivity refractive-index detection, are eluted at 25°C in the order Ne, He, N₂, H₂, O₂, Ar, CH₄, Kr, Xe, C₂H₆, C₃H₈, n-C₄H₁₀. Based on the general elution order, and on the temperature dependences (4-72°C) of elution times for the individual gases, a mixed chromatographic mechanism is proposed, in which separation of the gases results from a mixture of size-exclusion, ion-ion-induced dipole, and classical hydrophobic effects, plus a second type of "hydrophobic" effect involving binding of the clathrate hydrate cages surrounding non-polar solutes to similar cages formed around hydrocarbon portions of the column packing material.