Application of direct analysis in real time to a multiphase chemical system : identification of polymeric arsanes generated by reduction of monomethylarsenate with sodium tetrahydroborate

Direct analysis in real time (DART) has been applied in conjunction with high-resolution Orbitrap mass spectrometry to characterize the aqueous reduction of monomethylarsenate by tetrahydroborate (B/As molar ratio ≈ 4 mol/mol). Under these conditions, the reaction gives rise to a complex mixture of arsenic compounds which result in the formation of a reddish precipitate. The use of the DART revealed the presence of a number of polymeric arsanes – up to eight arsenic atoms – associated with the liquid/solid phase of this reaction system. From a reactivity point-of-view, these polymers exhibit an uncommon ionization pathway. In fact, similar to the alkanes, the action of the DART results in the generation of [M − H] + ions. Furthermore, for each oligomer MeHAs–(AsMe) n –AsHMe ( n = 0–8), a series of oxidation products [(M + n O) − H] + were also identified and their formation has been discussed.