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Abstract.A method for trace analysis incorporating solid phase extraction (extraction and clean-up) with supercritical fluid chromatography (SFC) for analytes in fats and oils has been developed. Direct coupling (on-line) of supercritical fluid solid phase extraction with supercritical fluid chromatography (SFSPEISFC) allows analysis of solutes in fats and oils for which on-line SFElSFC is unsuitable. The main feature of SFSPEISFC is that extraction and clean-up are accomplished in one step using unmodified supercritical carbon dioxide. Extraction/clean-up is monitored by a photodiode array detector which allows fractionation. The operational set-up and potential usefulness of the SFSPE/SFC system and applications for pesticide analysis of lipid sample matrices are described.

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Methionyl-leucine, leucyl-methionine, phenylalanyl-leucine, and leucyl-phenylalanine have been analyzed to determine dipeptide fragmentation mechanisms in Curie-point pyrolysis tandem mass spectrometry. Results show that fragmentations of dipeptides follow two general pathways, one involving direct cleavage of the dipeptide and the other involving cyclization of the dipeptide. Unique products and strong changes in relative mass spectral peak intensities arise, depending on constituent amino acid residues and their sequence. Also, the length and nature of the side groups strongly direct fragmentation. From these results, the major peaks in the spectra of eight other dipeptides could be readily explained; this suggests that a significant number of dipeptides follow the same general fragmentation mechanisms.