Monosaccharides, acetals chromatography

The acetates of monosaccharides are sufficiently volatile that they may be used for gas-liquid chromatography, but they are less readily formed than the trimethylsilyl derivatives, and still present the problem of anomeric derivatives (see Section IV, p. 38). They are, therefore, rarely used, but the method is discussed in Section V.2 (see p. 49), and the known cases are presented in Table II (see p. 111). 

Marsden78 did not attempt to separate mixtures of monosaccharides by gel chromatography the small differences in Ka among the different sugars indicate that separation could be achieved only on very large columns by use of the eluants used by this author, namely, deionized water and buffers of ionic strength 0.05 (pH 7-8) composed of 2-amino-2-(hydroxymethyl)-l,3-propanediol (Tris) and hydrochloric or acetic acid. 

Determination of the monosaccharide composition by gas chromatography of alditol acetates is commonly used for cell wall analyses because the procedure gives a single peak for each sugar. An alternative is to prepare trimethylsilyl (TMS) derivatives. However, these are easily hydrolyzed by moisture in the atmosphere and therefore should be analyzed in the gas chromatograph immediately, whereas alditol acetates are relatively more stable and could be rerun on the gas chromatograph the following day if required. 

Preliminary examinations of dextran structures were conducted by optical rotation, infrared spectroscopy and periodate-oxidation reactions. More detailed results can be achieved by methylation analysis [19]. The hydroxyl groups are methylated with methyl iodide after activation with sodium methylsulfinyl carbanion (Fig. 2). The methyl dextran is hydrolysed to the corresponding different methylated monosaccharides, which are furthermore reduced and peracetylated. The resulting alditol acetates of methylated sugars are separated by gas chromatography and identified by their retention times. In particular, a combined capillary gas-liquid chromatography/mass... 

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