Liquid chromatography (LC) was coupled on-line to Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to perform speciation studies of arsenic. An anion-exchange column in combination with an anion (cation) guard column was used for the separation of six arsenic compounds: arsenite (As(III)), arsenate (As(V)), dimethylarsinate (DMA) or cacodylic acid, monomethylarsonate (MMA). arsenocholine (AsB) and arsenobetaine (AsB) using a phosphate: buffer as eluent (pH approximate to 6). The influence of several parameters such as the composition of the mobile phase and the flow rate, on the separation efficiency were first investigated to determine the best chromatographic conditions. The coupling of LC to ICP-MS gave reproducible results with detection limits in the mu g l(-1) level and a good linearity (r>0.998) over several orders of magnitude. The method was applied to speciate arsenic in mung bean seedlings grown on arsenite/arsenate contaminated substrates. The results of these speciation studies showed that most of the arsenic is accumulated in the roots and that a reduction of As (V) to As (III) occurs in the roots, whereas in the leaves As occurs for a larger part as As (V). (C) 1998 Elsevier Science B.V.