Matrix optimization for matrix-assisted laser desorption/ionization mass spectrometry of oligosaccharides from human milk

Neutral and acidic oligosaccharides from human milk were analyzed by matrix -assisted laser desorption/ionization mass spectrometry (MALDI/MS). These e xperiments require suitable matrices; their selection and particularly thei r preparation protocols must be optimized. Important criteria are sensitivi ty, reproducibility, tolerance against impurities and resolution over a wid e mass range. For analytical investigations of these oligosaccharides, cont aining labile fucosylated and sialylated components, another property of a matrix becomes a significant factor, namely the influence on ion stability and the extent of (metastable) fragmentation. The experience gained with th e MALDI/MS of neutral and acidic oligosaccharides is summarized taking into account different intentions of measurement and typical problems, such as impurities after enzymatic treatment. For a rapid screening of an oligosacc haride sample, superior results were obtained with a new preparation techni que using 5-chloro-2-mercaptobenzothiazole (CMBT) as the first layer for 2, 5-dihydroxybenzoic acid. For structural analysis by post-source decay, CMBT as the first layer for 3-aminoquinoline is a favoured preparation protocol , because extensive fragmentation is achieved. For acidic oligosaccharides, a special preparation protocol makes it possible to determine the number o f sialic acids by inducing highly effective cationization. matrix-assisted laser desorption/ionization mass spectrometry; matrices; oligosaccharides; post-source decay. Copyright (C) 1999 John Wiley & Sons, Ltd.