Unprecedented separation of long chain alkenones from gas chromatography with a poly(trifluoropropylmethylsiloxane) stationary phase

Abstract

Long chain alkenones (LCAs) have played a central role in reconstructing paleo-sea surface temperature throughout much of the world oceans. The standard method for LCA separation and quantification utilizes gas chromatography (GC) with a non-polar column and flame ionization detection (FID). The method has remained nearly unchanged since the debut of alkenone paleothermometry over three decades ago. The conventional stationary phase used [poly(dimethylsiloxane)] is adequate for calculation of the U37K′ index for most marine samples, but performs poorly in the separation of methyl and ethyl C38 LCAs and fails to separate certain lacustrine LCAs, including structural isomers featuring differing double bond and carbonyl positions. Here, we demonstrate major improvements in the selectivity and resolution of numerous LCAs using a mid-polarity, dipole selective poly(trifluoropropylmethylsiloxane) GC stationary phase with FID. Various columns featuring this phase achieved baseline resolution of all C38 LCAs in a marine sediment and Emiliania huxleyi culture samples, improving peak resolution of C38 LCAs by>350%. Such dipole selective stationary phases also reveal novel tri-unsaturated isomeric LCAs in lacustrine samples, for which we provide the first report and preliminary characterization. We conduct a thorough evaluation of LCA retention behavior on poly(trifluoropropylmethylsiloxane) and poly(dimethylsiloxane) columns and report an optimal range of operating conditions for both phases.