Titrations with electrogenerated hypobromite in the diffusion layer of interdigitated microelectrode array Original Research Article

An interdigitated array system composed of generator and collector microelectrodes was used to study the transfer of hypobromite between the two electrodes. Influence of ammonium and iodide on the transfer has been evaluated and applied for their determination. The technique has been named diffusion layer titration. It utilizes a chemical reaction proceeding quantitatively only in a close vicinity of the electrode. One set of segments of an interdigitated microelectrode array serves for galvanostatic anodic generation of hypobromite and the second set immersed in the diffusion layer of the generator, detects its unreacted flux. The detector (collector) is kept by a potentiostat at the potential of the limiting diffusion current of hypobromite reduction. The diffusion layer titration curves (collector current versus generator current plots) measured “point by point” or by slowly scanning the generator current, show very good reproducibility. Since no bulk phase chemical reaction actually proceeds, the experiment can be repeated extensively in the same solution. The sensitivity of this method is 2383 μA M−1 and the detection limit is 2.4×10−6 M for the determination of ammonium. For the determination of iodide the sensitivity was 4810 μA M−1 and detection limit 5×10−7 M. The method was applied to the trace determination of ammonium in river water as well as to the analysis of iodide content in the edible salt.