ISSN:
0030-493X
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In the field desorption mass spectrometry of oligosaccharides, traces of contaminating salts in polar solvents decrease the detection sensitivity, and in some cases no ion could be detected in the molecular range. The present work shows that the addition of alkaline salts (NaI or KI) greatly increases the sensitivity, and cationized molecular ions are obtained. The influence of the molar ratio sugar/salt on the nature and relative intensity of the desorbed species has been studied on mixtures of α-D-trehalose and NaI. At the low salt ratio (100:1), high molecular weight clusters [XM + Na]+ are preferentially formed. At the high salt ratio (1:10), mixed clusters [M + NaI + Na]+, doubly charged ions [M + 2Na]2+ and monomeric cationized ions [M + Na]+ are observed along with salt clusters [NaI + Na]+ and [2NaI + Na]+. In the range of molar ratios sugar/salt of 10:1 to 1:1, the field desorption mass spectra exhibit a cationized ion [M + Na]+, which contributes more than 80% of Σ100. This cationization technique has been applied to the field desorption mass spectrometry of several oligosaccharides. In all cases, the salt effect causes the replacement of the [M + H]+ ion by a [M + C]+ ion. (Note: the term [M + C]+ and similar ones mean an association between the whole molecule studied (M) and an alkaline cation [C]+ ([K)]+, [Na]+, [Li]+).) Thus, di, tri- and tetrasaccharides exhibit intense [M + Na]+ ions in the presence of NaI and only a few fragment peaks are observed in their field desorption mass spectra. This technique has been applied successfully to the detection of the hexasaccharide ajugose in a natural sample of pentasaccharide, and has also allowed the unambiguous determination of the composition of a mixture of partially methylated trehaloses. The salt effects are dicussed in terms of selective adsorption on the emitter, pre-existing soluble complexes sugar-salt, interactions between these species in the electric field and dissociative desorption of ionic complexes.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/oms.1210120109
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