Microfabricated ionic liquid column for separations in dry air

Abstract

Micro gas chromatography (µGC) is a technique developed for rapid, in situ analysis of volatile organic compounds (VOCs) for environmental protection, industrial monitoring, and toxicology. While reduced µGC size and power requirements allow for increased portability, the low moisture and oxygen resilience of current microcolumn technology result in increased peak broadening and tailing for humid samples, which necessitates the use of bulky helium or nitrogen carrier gas cartridges. Developing a microcolumn to address these deficiencies is desirable to improve µGC field performance and further reduce µGC system size. This paper reports the development and characterization of a microfabricated phosphonium ionic liquid (µIL) column and demonstrates separation of both polar and nonpolar compounds using this column via analyses of alcohols, chloroalkanes, aromatics, aldehydes, fatty acid methyl esters, and alkanes. The µIL column achieved operation at temperatures up to 345 °C for fatty acid methyl ester and alkane separation. Notably, all separations in this study used dry air as the carrier gas, showing that analysis of a diverse range of compounds was possible in the presence of oxygen. After exposure to dry air for 48 h at temperatures up to 220 °C, the µIL column's peak capacity was only degraded by 8.92%, which validated its long-term robustness against oxygen. The column's separation performance was not degraded by high moisture concentrations or long-term moisture exposure, also manifesting its robustness to moisture. The high temperature, moisture, and oxygen resilience of the µIL column enable more rapid separations in varying field environments without requiring additional µGC accessories (e.g., humidity filters and carrier gas cartridges). The µIL column is therefore expected to be useful for integration into future µGC devices.