The transfer of electrogenerated iodine from generator to collector microelectrodes has been studied with an interdigitated array system. The high value of the collection efficiency (ca. 85%) compared with that of rotating ring-disk electrodes, measured as the slope of the collector versus generator current plot, was observed. The plot was linear with a positive intercept on the generator current axis. An oxidation wave associated with surface redox processes of materials used for interdigitated array (IDA) fabrication was found to cause the intercept. An analytical technique was developed based upon the evaluation of the influence of As(III) on the iodine collector Versus generator current plot. Increasing the As(III) concentration leads to a proportional increase of the intercept on the generator current axis. The collector potential is set at the limiting current value of iodine cathodic reduction and serves as its amperometric detector. The collector current will remain zero until the current flowing through the IDA generator produces an iodine flux larger than the flux of incoming As(III). Titration curves (collector versus generator current plots) measured with a slowly scanning generator current show very good reproducibility. Since no chemical reaction takes place in the bulk of the sample (diffusion layer titration), the experiment can be repeated many times in the same solution. The sensitivity of this method is 1920 mu AM(-1) and the determination limit estimate is 7 X 10(-6)M As(III).