Figure 1. Strategies for isolation, identification, and quantitation of N-glycans from biological specimens.

Proteins extracted from biological samples are digested with enzymes for glycan extraction in solution or on resin. Glycans from in-solution digestion require chromatographic cleanup prior to derivatization by reducing end labeling or permethylation; while the immobilized glycoproteins can be derivatized directly on the solid support. Sialic acids can be stabilized before glycans are released for derivatization. Glycans are further quantitatively analyzed through different separation techniques, or in combination with fluorescent/stable isotopic labeling and mass spectrometry.