Solvent‐derived metal oxides in electrospray mass spectrometry of metal salt solutions

The electrospray mass spectra of MX 2 and MX 3 salts (where X is typically halide or nitrate) in protic and aprotic solvents, and solvent mixtures were examined. Comparisons of species responses with equilibrium aqueous solution concentrations were made. For MX 2 salts, a good correlation between MOH + response and MOH + solution concentration was observed under conditions where the collision energy was nominally zero. Cu(II) is easily reduced in acetonitrile to Cu(I); Cu(I) was the principal species observed in the electrospray mass spectrum of Cu(II) in acetonitrile whereas Cu(II) was the principal species observed in that of Cu(II) in dimethyl sulphoxide. Gas‐phase reactions between solvated clusters produced by electrospray and a second solvent vapour were examined. M 3+ clusters were the principal ions observed when an aqueous solution of MX 3 was sprayed in the presence of aprotic solvent vapours.