Unknown isopolyoxovanadate species detected by electrospray mass spectrometry

Electrospray mass spectrometry (ES MS) has been used to identify many previ ously unknown isopolyvanadate anions and cations in aqueous solutions under non-equilibrium conditions. There is direct evidence that the evaporation process in ES MS has resulted in significant chemical effects, thereby gene rating many of these previously undetected species. As a consequence, ES MS offers insight into the polymerisation process. For the ammonium metavanad ate system, negative-ion ES MS yielded two series, namely: [HxVyOz](-) (x = 0 to 1; y = 1 to 10; z = 3 to 26) and [HxVyOz](2-) (x = 0, 1; y = 3 to 17; z = 9 to 44). Also, the [H2VO4](-), [V10O28](6-) and [H5V10O28](-) anions were detected. In the positive-ion mode, three series of polyoxovanadate ca tions were observed, namely: [Hm+1(VO3)(m)](+), [Hm-1VmO3m-1](+) and [Hm-3V mO3m-2](+). For the alkali metal metavanadate systems ions of the form [AV( m)O(3m-2)](-) (m = 2, 4, 6; A = Li+, Na+ and K+) were detected. In the posi tive-ion mode, at least two series Of the form [A(m+1)(VO3)(m)](+) and [A(m +3)V(m)O(3m+1)](+) were observed. In all series, the protonated and unproto nated ions differed by {V2O5} mass units (characterised by ES MS as the for mal building block in these clusters). At high cone-voltages, mixed-valence polyoxovanadate anions were observed for all the systems studied. On the e ther hand, for the positive-ion mode, the only mixed-valence polyoxovandate s cations detected were for the potassium system. (C) 2000 Elsevier Science S.A. All rights reserved.