L‐Valine assisted distinction between the stereo‐isomers of D‐hexoses by positive ion ESI tandem mass spectrometry

Abstract

The binary mixtures of 7 hexoses and 20 amino acids were investigated by electrospray ionization ion trap mass spectrometry (ESI-ITMS). The adduct ions of the amino acid and the hexose were detected for 12 amino acids but not for the other 8 amino acids which are basic acidic amino acids and amides. The ions of amino acid-hexose complexes were further investigated by tandem mass spectrometry (MS/MS), and some of them just split easily into two parts whereas the others gave rich fragmentation, such as the complex ions of isoleucine, phenylalanine, tyrosine, and valine. We found that hexoses could be complexed by two molecules of valine but only by one molecule of the other amino acids. Among seven kinds of valine-hexose complexes coordinated by potassium ion, the MS(2) spectra of the ion at m/z 453 yielded unambiguous differentiation. And the fragmentation ions are sensitive to the stereochemical differences at the carbon-4 of hexoses in the complexes, as proved by the MS(2).