Immobilization of N-methyl-D-glucamine (NMDG) on poly(vinylbenzyl chloride) beads yields an effective and highly selective sorbent for arsenate ions. Three important parameters in the resin's high As(V) affinity and selectivity are the structure of the ligand, its ionic form, and the crosslink density of the polymer. The NMDG resin crosslinked with 2 wt % divinylbenzene is far more selective than commercially available analogues, especially when sulfate and chloride ions are present in solution at high concentrations. Selectivity studies at neutral pH indicate that the protonated tertiary amine moiety is an important component of the complexation mechanism. The NMDG resin also has a high affinity for the un-ionized As(V) species at pH 1.