To monitor the oxidation of arsenite to arsenate in oxidizing and bioleaching reactors, speciation analysis of the inorganic arsenic compounds is required. Existing arsenic speciation analysis techniques are based on the use of liquid chromatography columns coupled to detector equipment such as inductively coupled plasma optical emission spectrometry (ICP-OES). These techniques are fairly complex and expensive. Therefore, for analysis of arsenic speciation in our studies on thermophilic iron and arsenic oxidation, we developed a simple (and inexpensive) method based on anionic ion exclusion chromatography using sulfuric acid as mobile phase, followed by UV detection. The detection limit was 0.1¿mg¿L-1 of arsenite (As3+) and 0.1¿mg¿L-1 of arsenate (As5+). The method was validated with samples from an iron-oxidizing bioreactor containing 0.12¿mol¿L-1 H2SO4, 1¿g¿L-1 arsenic, and 3¿g¿L-1 iron. Samples from arsenopyritic gold concentrates by partial bio-oxidation and leaching samples were analyzed, showing the usefulness of the method for arsenic contained in environmental compartments. We also describe the apparent effect of the arsenic valence state on ICP-OES detection for total arsenic.