Comprehensive two-dimensional gas chromatography using a high-temperature phosphonium ionic liquid column

Abstract

A high-temperature ionic liquid, trihexyl(tetradecyl)phosphonium bis(trifluoromethane)sulfonamide, was used as the primary column stationary phase for comprehensive two-dimensional gas chromatography (GC x GC). The ionic liquid (IL) column was coupled to a 5% diphenyl/95% dimethyl polysiloxane (HP-5) secondary column. The retention characteristics of the IL column were compared to polyethylene glycol (DB-Wax) and 50% phenyl/50% methyl polysiloxane (HP-50+). A series of homologous compounds that included hydrocarbons, oxygenated organics, and halogenated alkanes were analyzed with each column combination. This comparison showed that the ionic liquid is less polar than DB-Wax but more polar than HP-50+. The most unique feature of the IL x HP-5 column combination is that alkanes, cyclic alkanes, and alkenes eluted in a narrow band in the GC x GC chromatogram; whereas, these compounds occupied a much larger portion of the DB-Wax x HP-5 and the HP-50+ x HP-5 chromatograms. Each column combination was used to analyze diesel fuel. The IL x HP-5 chromatogram displayed narrow bands for three major compound classes in diesel fuel: saturates, monoaromatics, and diaromatics. The IL column was used at temperatures as high as 290 degrees C for several months without any noticeable changes in column performance.