ABSTRACT
In general, free ∆5-sterols produce intensive M+ that may be base peaks. Molecular ions of TMS and acetate derivatives are most commonly desilylated or deacetylated (ROH) and show a strong [M+-ROH] ion (114). In mass spectra of phytosteryl TMS, the [M+] exist, whereas they are absent in those of acetates (113). There are some characteristic ions that can be used to differentiate ∆5-sterols, ∆7-sterols, and stanols from each other. ∆5-Sterols produce typical ions at [M+-129], when a part of the A ring is lost; ∆7-sterols always have an intensive peak at m/z 255 that is a fragment of the four-ring structure; and stanols have a base peak at m/z 215 that is formed after removal of the side chain and part of the D ring. The structure of side chains can be concluded from ions when the whole side chain (SC) or the SC and the ROH are cleaved from M+. ∆5-Sterols lose water more easily than methyl groups, whereas loss of water seldom occurs with ∆7-sterols (72). Acetate derivatives are suitable to detect unsaturation in the SC because fragmentation occurs more often in the SC if it contained an unsaturation, whereas the ring structure was disrupted with a saturated SC (91).
