Figure 4.

Comparison of the sensitivities of MALDI-MS analysis of derivatized and underivatized A2F. (A) MALDI mass spectra of underivatized A2F. The MALDI matrix solution consist of 0.2 M DHB/0.06 M HIC [1:1, vol/vol in CH₃CN/water (1:2, vol/vol)] with 10 mM NaCl (to increase the ionization yield). The matrix sample mixture was dried under vacuum on the sample probe. In addition to the (M+H)⁺ ions (peak 2), an (M+Na)⁺ ion (peak 3) and an (M+2Na-H)⁺ (peak 4) were observed (B) Derivatized A2F. The glycopeptide was mixed with matrix solution [4-HCCA in CH₃CN/0.1% TFA in water (1:2, vol/vol)], loaded on the probe, and dried at room temperature in air. The protonated glycopeptide ion (M+H)⁺ is labeled “2.” In A and B, peak 1 corresponds to, respectively, the sodium cationized and protonated molecule with the loss of one sialic acid.