TITRATIONS WITH ELECTROGENERATED HYPOBROMITE IN THE DIFFUSION LAYER OF INTERDIGITATED MICROELECTRODE ARRAY

An interdigitated array system composed of generator and collector mic roelectrodes 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 b een named diffusion layer titration. It utilizes a chemical reaction p roceeding quantitatively only in a close vicinity of the electrode, On e set of segments of an interdigitated microelectrode array serves for galvanostatic anodic generation of hypobromite and the second set imm ersed in the diffusion layer of the generator, detects its unreacted f lux. The detector (collector) is kept by a potentiostat at the potenti al of the limiting diffusion current of hypobromite reduction. The dif fusion layer titration curves (collector current versus generator curr ent plots) measured ''point by point'' or by slowly scanning the gener ator current, show very good reproducibility. Since no bulk phase chem ical reaction actually proceeds, the experiment can be repeated extens ively in the same solution. The sensitivity of this method is 2383 mu A M-1 and the detection limit is 2.4 x 10(-6) M for the determination of ammonium. For the determination of iodide the sensitivity was 4810 mu A M-1 and detection limit 5 x 10(-7) M, The method was applied to t he trace determination of ammonium in river water as well as to the an alysis of iodide content in the edible salt. (C) 1998 Elsevier Science B,V. All rights reserved.