Mass spectra Sterols

Fig. 5. Examples of GC-MS data for vitamin E in a vegetable oil and cattle feedlot soil (a) vegetable oil, sum of key ions mjz 129 (TMS for sterols), 474, 488 and 502 of tocopherols as TMS), (b) feedlot soil, sum of key ions ra/z 416 and 430 for tocopherols, a-tocopheryl acetate, and the metabolite (as free phenols), and (c) mass spectrum of a-tocopherol hydroquinone (V).

Maquestiau et al. [209] identified fractions in complex mixtures of free marine sterols with MIKE/CAD of molecular ions formed in El. The method was tested on six samples from corals and sponges. For example, the El conventional mass spectrum of the fraction isolated from Emicella stricta is especially complex high-mass peaks are located... 

Although sterols carry a core signature of four fused rings (Figure 1.4a), individual sterol species are different from each other with the additional group(s) or modifications on the core structure. These differences lead to the very different fragmentation patterns after CID. Therefore, there is no common fragmentation pattern(s) available for the sterol species. Individual sterol species has to be characterized and elucidated separately. It is too complicated and beyond the scope of this book to describe each individual product-ion mass spectrum of sterol species. Any advanced readers may... 

GC-MS analysis is used to confirm the identities of ions in the LSI-MS urine spectrum and show that the excretion of abnormal cholanoids is >20 times normal. In the case of 5 ff-reductase deficiency GC-MS analysis should show that S-oxo-A" bile acids account for >70% of the total urinary bile acid excretion. In the case of sterol 27-hydroxylase deficiency (CTX), GC-MS analysis should indicate that the major cholestane pentols in the urine are 3,7,12,22,25 and 3,7,12,23,25-pentols. (One patient has been described who had familial cholestatic liver disease associated with greatly increased urinary excretion of 5jff-cholestane-3a,7a,12a,24 S,25-pentol [see previous table]). Liquid secondary ion-tandem mass spectrometry (LSI-MS/ MS) is an alternative method to GC-MS and can rapidly confirm the identity of a number of diagnostic ions that are found in the LSI-MS spectrum of urine. These include sulphated and taurine-conjugated abnormal metabolites such as those observed in 3 ff-HSDH deficiency (32.1), 5)9-reductase deficiency (32.2), oxysterol 7a-hydroxylase deficiency (32.4) and peroxisomal disorders [13]. 

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