Isotopically-labeled glycans

A method for determining the relative amount of a glycan species in at least two different glycan preparations, comprising steps of:

• (i) reacting a first glycan preparation with a first amine and a first reducing agent, one of which is isotopically-labeled, to provide a first aminated, isotopically-labeled glycan preparation;
• (ii) reacting a second glycan preparation with a second amine and a second reducing agent to provide a second aminated glycan preparation;
• (iii) combining an amount of the first aminated, isotopically-labeled glycan preparation with an amount of the second aminated glycan preparation to provide a glycan mixture;
• (iv) analyzing the glycan mixture by mass spectrometry to provide a mass spectrum which includes at least one pair of peaks that corresponds to aminated versions of a glycan species from the first and second aminated glycan preparations;
• (v) determining the relative intensities of the peaks in the at least one pair of peaks;
• and
• (vi) quantifying the relative amounts of the glycan species provided in the first and second glycan preparations in light of the relative intensities of the peaks.