Alditols mass spectra

The mass spectrum of alditol acetates are easy to interpret as they fragment at each C—C bond as shown. 

Systematic studies on the mass spectra of alditol acetates have revealed a simple mode of fragmentation for this class of compound. Alditol acetates do not give a molecular ion, but (M — CH3CO0 ) is found in a low abundance. The mass spectra of stereoisomers are almost identical and, therefore, the mass spectrum of D-glucitol hexaacetate (see Fig. 1) is representative of all peracetylated hexitols. 

The component in peak A gave a mass spectrum identical with that of the alditol acetate of a 3,6-dideoxy-2,4-di-0-methyIhexose. As tyvelose is the only 3,6-dideoxy-hexose present, the component of the first peak must be the corresponding alditol acetate, methylated at 0-2 and 0-4. The component in peak B gave a mass spectrum characteristic of a mixture of the alditol acetates from a 6-deoxy-2,3-di-0-methylhexose (27) and a 2,3,4,6-tetra-O-methylhexose (28). 

Figure 3.19 El mass spectra of (a) peracetylated mannitol (mol wt = 434), (b) glycerol-tris-TMS (mol wt = 308), (c) 2-hydroxyethyl glucose-pentakis-TMS (mol wt = 584), and (d) partially methylated alditol acetate of 1,4-linked 2-hydroxyethylated glucose (mol wt = 394). (e) El mass spectrum of partially methylated alditol acetate of l,6-linked glucose (mol wt = 350) derived from dextran.

Amino acid analysis of a strong acid hydrolysate (2 N HCl at 100° C for 3 h) identified only glutamic acid and this was confirmed by gas chromatography-mass spectroscopy (Fig. 4). Mild acid hydrolysis (0.5 N HCl at 80°C for 1 h) followed by direct insertion mass spectroscopy gave a spectrum identical to authentic ribose-5-phosphate (Fig. 5). Borate electrophoresis of the alditol derived from the stored material and of its acid... 

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