5-Methoxysalicylic acid and spermine: a new matrix for the matrix-assisted laser desorption/ionization mass spectrometry analysis of oligonucleotides.

5-Methoxysalicylic acid (MSA) is demonstrated to be a useful matrix for matrix-assisted laser desorption/ionization time-of-flight (TOF) mass spectrometry of oligonucleotides, when desorption/ionization without fragmentation is desired. When MSA is combined with the additive spermine, the need for desalting is reduced. The MSA/spermine matrix yields linear TOF mass spectra with improved resolution, less fragmentation, and less intense alkali ion adduct peaks than those spectra obtained using 3-hydroxypicolinic acid and 6-aza-2-thiothymine with spermine or diammonium hydrogen citrate as additives. Instrumental conditions are discussed to improve the spectral resolution, specifically the use of longer delay times in the delayed-extraction ion source.