Separation of Permanent Gases by Surface-Bubble-Modulated Liquid Chromatography with Direct Injection of Gas Samples

Surface-bubble-modulated liquid chromatography (SBMLC) is an aqueous liquid chromatography that has a hybrid stationary phase consisting of gas phase fixed in the pores of a hydrophobic packing material, in addition to the hydrophobic moiety of the material and aqueous mobile phase liquid/hydrophobe interface. Despite the proposition that the fixed gas phase may be utilized as a viable stationary phase for the separation of nonpolar gaseous compounds, such as permanent gases, it remains impractical to attain a satisfactory level of resolution due to the conspicuously low column separation efficiency. In this study, we have explored that the efficiency of an SBMLC column is diminished by high diffusivity of gaseous analytes in the stationary gas phase. However, it was found that the efficiency was remarkably enhanced by preventing contact between the gas phases in the porous particles through mix-packing the column with particles containing fixed gas phase together with those without gas phase. The findings demonstrate that nonporous octadecyl-bonded silica (ODS), pure silica, and large-pore ODS can be utilized as a mix-packing material in conjunction with porous ODS particles for the SBMLC separation of permanent gases. In this method, component gases can be separated by means of direct injection of a gas sample into the SBMLC column. Finally, the efficacy of this advanced SBMLC method is demonstrated by its ability to achieve an efficient separation of argon and oxygen, which is difficult to achieve by the conventional gas chromatographic method. SBMLC can offer unique selectivity for the separation of nonpolar gases without interference from coexisting gaseous components such as water and carbon dioxide.