Advances on the separation of crocetane and phytane using GC–MS and GC×GC–TOFMS

Abstract

The C20 isoprenoid crocetane (2,6,11,15-tetramethylhexadecane) is an environmental diagnostic biomarker that can be used as a proxy for both anaerobic methane oxidation and photic zone euxinia. Crocetane co-elutes with its isomer phytane (2,6,10,14-tetramethylhexadecane) on many gas chromatographic capillary columns, making the detection of crocetane analytically challenging. The separation of crocetane and phytane is reported here using: (i) a one-dimensional gas chromatography (GC) method and (ii) a comprehensive two-dimensional gas chromatography (GC×GC) chiral method. The one-dimensional method employs a (14% cyanopropyl-phenyl)-methylpolysiloxane (DB-1701) capillary GC stationary phase where crocetane and phytane elute isothermally. This resulted in the highest resolution reported to date on a non-chiral column and allows for the analysis of both crocetane and conventional biomarkers in a single injection. The GC×GC chiral method reported here is capable of separating crocetane from phytane in whole oils without any pre-separation work, diminishing any effects and potential losses associated with sample preparation.