Preparation of zwitterionic cysteine-modified silica microsphere capillary packed columns for the on-column enrichment and analysis of glycopeptides in human saliva

In this work, for the first time, L -cysteine ( L -Cys), a zwitterionic hydrophilic compound containing abundant amino and carboxyl was modified on silica microspheres for the fabrication of SiO 2 @ L -Cys capillary packed column. Since the SiO 2 @ L -Cys capillary packed column possessed great hydrophilicity brought by L -cysteine, they could be utilized to enrich glycopeptides with a low detection limit of 5 fmol μL −1 HRP digests as well as a good selectivity of the mixture of HRP and BSA digests up to a molar ratio of 1:50. The capillary packed column were further applied into the glycosylation analysis of human saliva and 69 glycopeptides were identified from 2 μL human saliva digests.