Methylation analysis is particularly useful when no suitable enzymes are available for 'dissection' of wall polysaccharides, or when detailed structural information is required about novel polysaccharides. Details are outside the scope of the present chapter (Waeghe et al. 1983; Harris et al. 1984; Carpita & Shea 1989). GC of sugars (or partially methylated sugars) requires them to be converted to volatile derivatives. Usually this involves reduction of the monosaccharide to an alditol with NaBH4 (or NaB2 H4 so that the original reducing end can be followed during MS) followed by acetylation with acetic anhydride. Resolution of partially methylated alditol acetates by GC is excellent, as is quantification; GC is, however, rarely attempted with radiolabelled samples because of the difficulties involved in measuring and disposing of radiolabelled volatiles.
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