A technique is described for the simultaneous determination of a wide range of angiotoxic sterols in foods produced by the oxidation of cholesterol. Gas chromatography using on-column injection onto a bonded phase fused silica capillary column gave excellent separation of the oxides examined. Combined gas chromatographymass spectrometry was used to confirm the identities of the trimethylsilyl ether derivatives of the various sterols and 6-ketocholestanol was found to be an acceptable internal standard for determination. Analysis of powdered scrambled egg mix showed the presence of several cholesterol oxides, with cholesterol&,6a-epoxide, cholesterol-5p,6/3-epoxide and 7-ketocholesterol predominating. Other atherogenic sterols identified included 25-hydroxycholesterol, 7a-hydroxycholesterol, 7P-hydroxycholesterol and Sa-cholestane-30,s ,6p-triol.
Combined use of chemical degradation, derivatization, and tandem mass spectrometry for rapid structural characterization of toxic cyclic peptides from blue-green algae at the nanomole level is described. Previously, all blue-green algal toxins were thought to belong to a family of seven-residue cyclic peptides, having the general structure cyclo-D-Ala-L-Xaa-erythro-,B-methyl-D-isoaspartic acid-L-YaaAdda-D-isoglutamic acid-N-methyldehydroalanine, where Xaa and Yaa represent variable amino acids of the L configuration and Adda is 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid. Structural characterization of two additional toxins indicates that further variability can exist within this family of naturally occurring toxic cyclic peptides. Isoaspartic acid and dehydroalanine can substitute for (3-methylisoaspartic acid and N-methyldehydroalanine, respectively.
A new instrumental method for the characterization of the analyte 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) by selected reaction monitoring (SRM) analysis is investigated. The method uses high-resolution gas chromatography coupled to a hybrid tandem mass spectrometer. The technique was evaluated with regard to four performance parameters: sensitivity, linearity, repeatability and selectivity. The method compares favorably with the traditional selected ion monitoring HRGC/HRMS technique, and the selectivity of the new method is shown to surpass the established HRGC/HRMS method. This new method could allow the characterization of samples that have undergone less rigorous cleanup than is now possible by the traditional mass spectrometric methods. The presence of TCDDs in a real sample was confirmed by using the new HRGC/(hybrid)MS/MS SRM method, which was not possible by using HRGC/HRMS analysis.
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