N- and O-Glycan Release

The derivahzation of oligosaccharides, whether by permethylation or through the formation of a stable Schiff base, improves the ionization efficiency of the carbohydrates. One advantage of labehng the reducing end of oligosaccharides released for MS is that, when fragmentation occurs, it is possible to determine which end 

As early as the mid-1980s, the permethylation of oligosaccharides was applied to for their analysis when employing secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB). Indeed, with the advent of ESI and MALDI a few years later, this method of sample modification was foimd to be perfectly suitable for these techniques, given the enhancement in ionization efficiency that resulted from permethylation of the sample [63]. 

In a recent international, multilaboratory investigation to compare several sample preparation methods for the characterization of glycans [64], permethylation with methyl iodide [65] was identified as the method of choice in terms of adaptability to both ESI-MS and MALDI-MS, and to the sensitivity observed. Notably, permethylation can also be used for positive mode ionization with signal 

2- aminobenzoic add [79], 3-acetamido-6-airiino acridine [80], and anthraniUc acid [81, 82], The use of different labels was compared in a mulhlaboratory study of IgG glycans [64], Additional labels used specifically for MALDl-TOF-MS of glycan samples have been discussed in an extensive review by Harvey [43], Recent examples of redudng end labels have included pyrenebutyric acid hydrazide [83a] and 

Derivatization by permethylation has been shown beneficial for the desorption efficiency and stability of the sialic acid(s) attached [84] however, the permethylation reaction requires strong alkali conditions, which may destroy the alkaline-labile substituents (such as 0-acetyl groups) that may be present as substituents. In order for the selective methylation of sialic acid carboxyl group to achieve a better stability, the same parameters are valid as were presented for glycans (see Section 6.2.5). The coupling of nano-HPLC with MALDI-MS requires a fraction collection step, in order to deposit the separated components arising from the 

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