2,5-DIHYDROXYBENZOIC ACID - A NEW MATRIX FOR LASER DESORPTION IONIZATION MASS-SPECTROMETRY

The performance of 2,5-dihydroxybenzoic acid (DHB) as a matrix for laser desorption-ionization mass spectrometry of proteins is described. Samples from protein/matrix mixtures with mass ratios between 1.5 x 10(-2) and 1 x 10(-4) were prepared by drying solutions onto metal substrates as well as by growing single crystals which contain the proteins at a concentration comparable to that in the solution in an apparently homogeneous distribution. The detection limit is demonstrated with a spectrum of cytochrome c from a 1 fmol preparation. DHB is insensitive to contaminations by inorganic salts, buffers and detergents, even to a 10% sodium dodecylsulfate admixture. Spectra from single crystal preparations taken at threshold irradiance are free of matrix signals in the low mass range. An upper limit of 1-10 amol is determined for the amount of ablated protein per spectrum.