ANALYSIS OF GLYCOALKALOIDS FROM POTATO SHOOTS AND TOMATOES BY 4-SECTOR TANDEM MASS-SPECTROMETRY WITH SCANNING-ARRAY DETECTION - COMPARISON OF POSITIVE-ION AND NEGATIVE-ION METHODS

A wide range of glycoalkaloids from potato shoots and tomatoes, includ ing trisaccharide-containing glycoalkaloids (alpha-chaconine, alpha-so lanine, and alpha-solasonine), tetrasaccharide-containing glycoalkaloi ds (alpha-tomatine and demissine), and disaccharide-containing glycoal kaloids (beta1-chaconine, beta2-chaconine, and beta-solamargine), have been studied by both positive and negative ion liquid secondary ion a nd four-sector tandem mass spectrometry with scanning-array detection. In positive ion mode, collisionally induced dissociation tandem mass spectra of the [M + H]+ ions induce three major fragmentation processe s, Z cleavage, Y cleavage, and 1,5X cleavage, which are structurally i nformative. Signals resulting from Z0, Y0, and 1,5X0 cleavages provide information on the nature of various aglycone moieties in all glycoal kaloids. Linkages and positions of the sugars in trisaccharide- and te trasaccharide-containing glycoalkaloids are indicated by the presence or absence of the ions corresponding to Z(alpha/beta) and Y(alpha/beta ) cleavages and intensity differences of the peaks due to 1,5X(alpha) and 1,5X(beta) cleavages, respectively. In negative ion mode, collisio nally induced dissociation tandem mass spectra of the [M - H]- ions in duce Y cleavage as the major fragmentation process. The location of th e terminal sugars in branched trisaccharide and tetrasaccharide glycoa lkaloids is indicated by the difference in intensity of the ions due t o Y(alpha) cleavage and Y(beta) cleavage. Isomeric structures cannot, however, be differentiated unambiguously; complete structural assignme nt is only possible by NMR of purified components. Both positive and n egative ion tandem mass spectrometry are considered to be suitable for the characterisation of glycoalkaloids in mixtures. The positive ion method has the advantage of (i) a lower detection limit than in conven tional mass spectrometry; (ii) numerous and intense fragment ions whic h are structurally informative; and (iii) the capability of analyzing minor components in crude extracts. Comparable analysis by other analy tical means would not have provided the amount of structural informati on on the components in the glycoalkaloid mixtures. (C) 1994 Academic Press, Inc.