An automated method has been developed for determining the concentration of inorganic arsenic. The technique uses sequential injection/anodic stripping voltammetry with a long-lasting gold-modified screen-printed carbon electrode. The long-lasting gold electrode was electrochemically deposited onto a screen-printed carbon electrode at a potential of −0.5V vs. Ag/AgCl in a supporting electrolyte solution of 1M hydrochloric acid. Under optimal conditions and the applied potentials, the electrode demonstrated that it can be used for a long time without a renewal process. The linear range for the determination of arsenic(III) was 1–100μgL −1 , and the limit of detection (LOD) in standard solutions was as low as 0.03μgL −1 for a deposition time of 120s and sample volume of 1mL. This method was used to determine the concentration of arsenic(III) in water samples with satisfactory results. The LOD in real samples was found to be 0.5μgL −1 . In addition, speciation between arsenic(III) and arsenic(V) has been achieved with the proposed method using deposition potentials of −0.5V and −1.5V for the determination of the arsenic(III) concentration and the total arsenic concentration, respectively; the results were acceptable. The proposed method is an automated system that offers a less expensive alternative for determining trace amounts of inorganic arsenic.