A new method allowing the simultaneous determination of arsenic(V), selenium(IV) and selenium(VI) using miniaturised isotachophoresis has been developed. The method uses 0.02 M nitric acid buffered to pH 5.5 with histidine as the leading electrolyte. Using a miniaturised poly(methyl methacrylate) chip device with an integrated conductivity detector, separations of model samples and an industrial process stream sample were achieved. Limits of detection were calculated to be 0.85 mg L−1 for arsenic(V), 0.95 mg L−1 for selenium(IV) and 1.0 mg L−1 for selenium(VI). A method for the analysis of arsenic(III), using a glycolic acid based leading electrolyte to eliminate carbonate interference is also presented.