Investigations of 2,5-DHB and succinic acid as matrices for UV and IR MALDI. Part II: Crystallographic and mass spectrometric analysis

Crystallographic, mass spectrometric and spectrophotometric data for the two MALDI-matrices 2,5-dihydroxybenzoic acid (2,5-DHB; UV and IR MALDI) and succinic acid (SA, IR MALDI) are presented. It is shown by absorption spectroscopy that SA single crystals incorporate protein molecules quantitatively up to a molar ratio of protein to matrix of about 2 x 10(-5). This result is comparable with that obtained earlier for 2,5-DHB single crystals. MALDI-MS data obtained from protein-doped single crystals were comparable with standard preparation results (dried droplet method) for both matrices. Threshold fluences as well as quality of spectra are equal for all accessable crystal faces of the 2,5-DHB crystals. Crystallographic data taken from the literature indicate that the crystals of both matrices have no major hydrophobic domains. The observed efficient protein incorporation must, therefore, be based on other than hydrophobic interactions. X-ray crystallography of protein-doped SA single crystals reveals the conserved crystal data of neat SA; results showed that their structure is not altered by the protein incorporation, which is in good agreement with earlier X-ray crystallography results for protein-doped 2,5-DHB single crystals. This contribution is the second in a row published in this issue about systematic investigations using UV (2,5-DHB) and IR (2,5-DHB and SA) matrices. Most of the relevant experimental details are given in Part I, this issue. (C) 1997 Elsevier Science B.V.