Using Laser Desorption/Ionization to Study Heteropoly Acids

The fragmentation of phosphomolybdic acid (PMA) is studied via laser desorption and ionization. It is found that during laser desorption and ionization, acid crystals tend to form cluster-type species of (MoO₃)_n and HPO₃⋅(MoO₃)_n. Species with the general formula HPO₂⋅(MoO₃)_n and containing Mo⁵⁺ and Mo⁶⁺ are identified in the mode of positive ion detection. Hydrated H₃PMo₁₂O₄₀⋅MoO₃⋅4H₂O molecular ions are detected in mass spectrometric studies of PMA solutions with a 2,5-dihydroxybenzoic acid matrix. Studying the effect parameters of laser desorption and ionization have on the information content of mass spectra show that peak intensity, laser power, and number of shots are generally in a symbate relationship. The peak intensity depends on the laser power more than on the number of shots.