Utilization of hydralazine as a reactive matrix for enhanced detection and on-MALDI-target derivatization of saccharides

Saccharides are a sort of ubiquitous and vital molecules within the whole life. However, the application of saccharides analysis with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is restricted by their low ionization efficiency and the instability of the sialic acid fraction. Derivatization strategy based on nonreductive amination provides a good solution, however, this is often time consuming and may result in sample loss due to removal of excessive derivatization reagents. Herein, hydralazine (HZN) was utilized as a reactive matrix for labeling reducing saccharides directly on MALDI target which eliminated tedious sample preparation and avoided sample loss. After optimization, effective and reproducible on-MALDI-target derivatization of neutral and acidic saccharides was achieved in both positive and negative modes. Compared with 2,5-dihydroxybenzoic acid (DHB) and 9-aminoacridine (9-AA), HZN improved the detection sensitivity of reducing saccharides and provided more abundant fragment ions in MS/MS analysis. Moreover, 26 kinds of neutral glycans and 5 kinds of sialic glycans were identified from ovalbumin (OVA) and bovine fetuin, respectively. Combined with the statistical models, this strategy could be used to distinguish and predict samples of 6 brands of beer, and discriminate 2 kinds of beer fermentation modes. In addition, HZN was applied for quantitative analysis of glucose in urine samples, and the obtained urine glucose concentrations of diabetic patients were consistent with the clinical test results, showing the potential of qualitative and quantitative analysis of reducing saccharides in complex samples.