Laser ablation generation of cluster ions from concentrated sulfuric and selenic acids

The generation and identification of novel homo- and hetero-polyacid clusters was achieved using a standard matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer. The formation of several singly charged species was achieved via the interaction of a laser beam with concentrated sulfuric acid, selenic acid or their mixtures, applied on a graphite microcrucible. A higher yield of the species was observed in the negative detection mode, where sulfuric acid adducts HSO(4) (-) . mH(2)SO(4) (m = 0-3) and HSO(4) (-) . mH(2)SO(4) . SO(3) (m = 1, 2), and selenic acid adducts HSeO(4) (-), HSeO(4) (-) . X (X = SeO(3), H(2)SeO(4), 2SeO(3), H(2)SO(4) . SeO(3)) and NaSeO(4) (-). Y (Y = H(2)SeO(4), H(2)SeO(4). SeO(3), 2H(2)SO(4), H(2)SeO(4) . 2SeO(3), 2H(2)SeO(4) . SeO(3), 3H(2)SeO(4)), were identified. In the mass spectra of the mixture of acids, besides the homo-polyacidic adducts, eleven mixed species containing both sulfuric and selenic acid molecules or ions were identified, of which the heaviest was found to correspond to NaSeO(4) (-) . H(2)SeO(4) . 3SO(3). The stoichiometry of the species was confirmed using isotopic pattern modeling.