Among the modern ionization techniques for the analysis of biomolecules, electrospray ionization (ESI) has proven the most effective for the mass spectrometry (MS) analysis of sulfated carbohydrates, called glycosaminoglycans (GAGs). GAGs are long linear polysaccharides with numerous sulfate groups. Sulfates are the most acidic functional groups on biomolecules when protonated, which makes GAGs more fragile than peptides or less acidic glycans, and are therefore difficult to analyze by mass spectrometry. However, ESI is more effective for the analysis of GAGs because of its multiple charging characteristics (1). Under negative ESI conditions, sulfated oligosaccharides are likely to ionize with one charge per sulfate group, a condition where those groups are least labile. ESI is also an effective tool for the analysis of sulfated GAGs as it is the softest ionization method available, therefore allowing tandem mass spectra to be acquired through the use of collision induced dissociation (CID). ESI allows direct detection of chromatographic effluents, and is therefore advantageous because it allows for coupling of mass spectrometry with separation methods such as size exclusion chromatography (SEC), normal phase, reversed phase ion pairing or graphitized carbon chromatography. The chromatographic mobile phases must be optimized using only volatile solvent components or they must be operated with an on-line desalting device prior to mass spectrometric detection to avoid a salt contamination of the mass spectrometer.
- Zaia J. (2005) J Biomacromol Mass Spectrom. 1:3–36.