Production and Fragmentation of Negative Ions from Neutral N-Linked Glycans Ionized by MALDI Mass Spectrometry for Rapid Structural Identification

摘要

Fragmentation spectra of negative ions from neutral carbohydrates, as seen by CID following electrospray ionization, contain much more structural information than corresponding spectra of positive ions. However, neutral carbohydrates are reluctant to form negative ions by MALDI except from specific matrices such as nor-harmane ([M-H]~(-) ions) or by forming adducts with chloride or sulfate; none of these ions yield ideal MS or MS/MS spectra. We now report an improved method for producing negative ions by doping common matrices with anions such as nitrate and phosphate. Subsequent fragmentation yields similar diagnostic spectra to those obtained by ESI/CID allowing rapid glycan identification from mixtures, not possible before by MALDI. MS~(n) spectra allowed several fragmentation pathways yielding diagnostic ions to be deduced.