A general approach to desalting oligosaccharides released from glycoproteins

Desalting of sugar samples is essential for the success of many techniques of carbohydrate analysis such as mass spectrometry, capillary electrophores is, anion exchange chromatography, enzyme degradation and chemical derivati zation. All desalting methods which are currently used have limitations: fo r example, mixed-bed ion-exchange columns risk the loss of charged sugars, precipitation of salt by a non-aqueous solvent can result in co-precipitati on of oligosaccharides, and gel chromatography uses highly crosslinked pack ings in which separation of small oligosaccharides is difficult to achieve. We demonstrate that graphitized carbon as a solid phase extraction cartrid ge can be used for the purification of oligosaccharides (or their derivativ es) from solutions containing one or more of the following contaminants: sa lts (including salts of hydroxide, acetate, phosphate), monosaccharides, de tergents (sodium dodecyl sulfate and Triton X-100), protein (including enzy mes) and reagents for the release of oligosaccharides from glycoconjugates (such as hydrazine and sodium borohydride). There is complete recovery of t he oligosaccharides from the adsorbent which can also be used to fractionat e acidic and neutral glycans. Specific applications such as clean-up of N-l inked oligosaccharides after removal by PNGase F and hydrazine, desalting o f O-linked glycans after removal by alkali, on-line desalting of HPAEC-sepa rated oligosaccharides and beta-eliminated alditols prior to electrospray m ass spectrometry, and purification of oligosaccharides from urine are descr ibed.