Static headspace enantioselective comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry...

Static headspace (SHS) sampling, prior to a gas chromatography (GC) separation, is an interesting approach in food analysis inasmuch that the isolated volatile fraction reflects the compounds that reach the human nose. Additionally, the fraction analyzed is free of less volatile compounds and, hence, contamination of the GC system is avoided. Further, such a sample preparation method is environmentally-friendly because organic solvents are not used. The main disadvantage of SHS sampling is a reduced analyte detectability, due to the lack of a pre-concentration step.

The investigation is based on the use of SHS sampling prior to cryogenic modulation enantioselective comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (CM eGC × GC-ToFMS). The samples subjected to analyses were two Citrus essential oils, namely bergamot and sweet orange. A chiral-apolar combination of columns was used, enabling both general analyte profiling and the determination of enantiomer ratios. A direct comparison was made between SHS and the direct injection (DI) of sample solutions. The use of CM counterbalanced, to a certain extent, the SHS reduced analyte detectability. A total of 239 and 84 compounds were tentatively characterized in bergamot essential oil using DI and SHS, respectively, whereas 174 and 58 analytes were tentatively identified in sweet orange essential oil using the same techniques, respectively. The method was further used to investigate the enantiomeric ratios of several chiral components. Both sampling methodologies yielded comparable chiral profiles, although slight variations in enantiomeric distributions were observed.

The use of SHS sampling combined with CM GC × GC has been rarely described. The results obtained through SHS eGC × GC-ToFMS appear to be of interest and, in principle, such an option can be applied to food analysis in general. The untargeted information can be used to confirm authenticity and define geographical origin, along with the determination of products of transformation.