Speciation of inorganic arsenic in oxic and in reducing groundwaters using the As(V)-selective ImpAs resin

Knowledge of arsenic inorganic speciation in groundwaters is critical for optimising water treatment approaches. Here, we characterise the on-site analytical performance of the As(V)-selective ImpAs ion-exchange resin to separate As(V) from As(III) in groundwater with contrasting redox conditions. Field speciation results obtained by ImpAs in the oxic, Fe-poor groundwaters of Guanajuato (Mexico) and in the reducing, Fe-rich groundwaters of West Bengal (India) agreed with voltammetry (slope of 0.91 ± 0.03, r = 0.99, p < 0.001, n = 21). Like for arsenic, oxyanions of Mo, V, U and Cr are retained by ImpAs but their reduced hydroxy forms are not. High As(V) extraction by ImpAs (>95%) was obtained in synthetic groundwater for hundreds of samples without any regeneration, highlighting negligible interactions of major anions such as sulfate, a major advantage over common solid phase extraction resins. However, in Fe rich waters, ImpAs reusability is likely constrained by Fe accumulation in the resin and dissolved organic matter. This study demonstrates the successful application of ImpAs resin as a safe and easy to use analytical device for on-site separation of As(V) and As(III) in groundwaters, which opens the potential for including As inorganic speciation analysis into large scale monitoring programs.