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 + nO) - H]+ were also identified and their formation has been discussed. © 2014 Published by Elsevier B.V. All rights reserved. ; peer reviewed: yes ; system details: This record was machine loaded using metadata from Scopus ; NRC Pub: yes