MATRIX-ASSISTED LASER DESORPTION IONIZATION MASS-SPECTROMETRY WITH 2-(4-HYDROXYPHENYLAZO)BENZOIC ACID MATRIX

A novel matrix substance, 2-(4-hydroxyphenylazo)benzoic acid, or HABA, has been found to be very advantageous for matrix-assisted ultraviole t laser desorption ionization mass spectrometry. This compound has bee n successfully used for the desorption of peptides, proteins, and glyc oproteins up to approximately 250 kDa. For these materials, the most a bundant analyte-related peaks correspond to [M + H]+ ions and multiply protonated molecules. Comparisons with sinapic acid, 2,5-dihydroxyben zoic acid, and alpha-cyano-4-hydroxycinnamic acid indicate that the ne w matrix provides comparable sensitivity for peptides and smaller prot eins but results in better sensitivity for larger proteins and glycopr oteins in protein mixtures. Other matrices discriminate against the hi gher mass components in these cases. Somewhat reduced mass resolution has been found for smaller proteins, but for larger proteins and glyco proteins the best mass resolution can often be obtained with the new m atrix. For other classes of compounds that form ions predominantly via cation attachment, at least as good sensitivity and even better resol ution have been obtained. Derivatized glycolipids and synthetic polyme rs have been studied in detail. For the analysis of many synthetic pol ymers, the best performance in terms of sensitivity and mass resolutio n has been observed with HABA matrix. Mass resolution was higher for c ation adducts than for the protonated peptide molecules in the same ma ss range. The new matrix exhibits greatly extended (in time) analyte i on production and reproducibility. Owing to the uniform sample surface with this matrix, barely any spatial variation of.the ion signal coul d be observed. In addition, many hundreds of single-shot mass spectra could be accumulated from the same spot, even for larger proteins.