Novel method for characterization of aqueous vanadium species: A perspective for the transition metal chemical speciation studies

Identification the polymerization nature of vanadium bearing solution is difficult, yet it is of great environmental concern due to the possible carcinogenic effects as well as high-value sustainable necessities. Thus, seeking for simple and efficient characterization methods of tracking vanadium species is in urgent demand. In this work, high-resolution electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) coupled with thermo-dynamic calculations was employed to measure vanadium-containing samples. Evolutions of four characteristic vanadium species, H2VO4- (0-1%), V-2 species (0-1%), V-4 species (1-20%), and V-10 species (60-95%), were comprehensively studied from acidic to neutral conditions, based on which thermodynamic model and vanadium phase diagram were established to visualize transformation pathways. More than 30 types of aqueous vanadium species could be semi-quantitatively detected by employing this method with less than 5% relative error, and the corresponding existing forms and concentration of these vanadium species could be well predicted. The vanadium species identified in MS results were confirmed by NMR. This method can be widely used for the understanding of vanadium speciation in practical examples, especially involving V(V), Cr(VI) ions or organic complexes.