Comparative voltammetric behavior of indigo carmine at screen-printed carbon electrodes

The redox activity of indigo carmine (IC) at two different commercial screen-printed carbon electrode strips (SPCE) was investigated in this work by different voltammetric techniques. Cyclic voltammograms of this molecule in 0,1 M HClO4, solutions show two well-defined diffusion-controlled signals. one reversible at a formal potential (E-1/2) of -0.57 V vs. Pt pseudoreference electrode (-0.15 V vs. Ag). and a second anodic peak at a potential (E-p.a) of +0.13 V vs. Pt (+ 0.57 V vs. Ag). Both electrodes exhibit good analytical performance towards this analyte. if they were applied in a disposable manner. Their use in consecutive experiments offers substantial differences. since an oxidation wave due to adsorption of indigo carmine superimposed on the anodic peak of the redox pair at one of these SPCEs. In addition, this adsorption component appears to foul the electrode surface. This wave is greatly enhanced if the working electrode is previously activated by applying high positive potentials for a certain period of time. The other SPCE does not exhibit any fouling process. thus allowing the performance of several consecutive experiments with the same strip. With these electrodes. calibration plots were obtained by cyclic, differential pulse. square-wave and alternating current voltammetry. Wide linear ranges of more than two orders of magnitude and limits of the detection down to 10 (7) M were achieved. Relative standard deviations of the peak current in a range of 0.9-7%, recorded in indigo carmine solutions of different concentrations, at one single electrode, give an estimation of the good precision of this data.