Positive-ion mode-tandem mass spectrometry has become a frequently used tool for the structural analysis of neutral saccharides. However, their behavior in the positive-ion mode is not always adequate for oligosaccharides structure identification. Thus, fragmentation of [M−H] − or anion adducts produced in the negative-ion mode MS, offers an alternative as their fragmentation patterns provide more structure-related information. The main drawback of the negative-ion mode MS of neutral saccharides is the low sensitivity. In this study, we tested several salts as additives of saccharide samples for sensitivity improvement in the negative-ion mode. The addition of NH 4 H 2 PO 4 forming [M+H 2 PO 4 ] − seemed to be the best choice due to a relatively high sensitivity increase in both MS and MS n spectra. Moreover, the salt content could be monitored by the presence of phosphate clusters at high salt-saccharide ratios and salting effects could thereby be avoided. Compared to other tested salts, fragmentation spectra of phosphate adducts also contained additional fragments which improved both the certainty and accuracy of the structural identification. The NH 4 H 2 PO 4 addition was applied to collected fractions from brewing samples separation where oligosaccharides derived from starch, fructans and oligosaccharides of the raffinose family were detected and identified. Our suggested approach is a promising alternative to a more common mass spectrometric analysis of neutral oligosaccharides in the positive-ion mode or chloride or nitrate additions in the negative-ion mode.