ABSTRACT
Bradford W. Gibson, Jeffrey J. Engstrom, and Constance M. John University o f California-San Francisco, San Francisco, California
Arnold M. Falick PerSeptive Biosystems, Inc., South San Francisco, California
Wade M. Hines and Stephen A. Martin PerSeptive Biosystems, Inc., Framingham, Massachusetts
I. INTRODUCTION
The characterization and analysis of glycoconjugates by mass spectrometry has undergone a number of improvements in the last 10 years, especially with the development of methods capable of ionizing and analyzing these compounds in their native states [1]. Although a number of protocols have been developed for preparing derivatives of oligosaccharides deemed more suitable for mass spectrometric analysis, such as permethylation and acetylation [2], there has always been a need for methods that could analyze these types of compounds directly. Despite some success, underivatized glycoconjugates and oligosaccharides tend to ionize not as well as their derivatized analogs or other classes of biopolymers of similar mass. This is due, in part, to the high polarity of oligosaccharides, which tends to make them less amenable to mass spectrometric analysis than compounds with significant hydrophobic character. Moreover, chromatographic methods for isolating carbohydrates and glycoconjugates often require buffers con taining relatively high levels of salts or other nonvolatile components that tend to interfere with mass spectrometry. Even more troublesome are an ionic oligosaccharides and glycoconjugates, the tendency of which to bind cations can greatly increase the difficulties in their final analysis. Even when rigorous desalting is attempted, salt adducts of highly anionic carbohy drates and glycoconjugates remain a serious problem, and even more so as
one attempts to isolate and/or purify them at subnanomole levels. In addi tion, anionic glycoconjugates can contain acidic sugars, such as sialic acid (or Af-acetylneuraminic acid, NeuAc) or 2-keto-3-deoxyoctulosonic acid (Kdo), the anionic character of which makes their glycosidic bonds espe cially labile.
