Abstract: A simple admittance vector presentation, common in telecommunication signal processing, is examined to separate mathematically two overlapping analytical amperometric signals. The method is based on a theoretical derivation of a constant potential amperometric electrochemical system experiencing an ac perturbation. For a given reaction at different concentrations of the electrochemically active species, the current measured during an ac perturbation at a particular frequency on a constant bias potential E-dc, has constant phase angle (phi) of the admittance and only its magnitude (Y) changes with concentration. The complex admittance vector space is spanned by the basis vectors of the individual components of a mixture. The admittance measurement is thus given in terms of the contribution from these components. The concentration calibration may be computed by taking the distance to each admittance point. In the context of the conventional constant potential amperometric methods for detection of H2O2 and ascorbic acid via their oxidation currents, where there is an inherent problem of interference and overlap of each electroactive species, their simultaneous estimation is taken as a model case to illustrate the methodology to extract the basis vectors for each species and obtain the concentration calibration vectors for the mixture. Evaluation of the use of the technique in complex mixtures is introduced. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: Immobilized reagent phase flow injection analysis can be configured as discrete reagent cells upstream of the sensor element or as an integral reagent/transduction system (flow injection analysis-biosensor). The former approach has attracted greater attention because several assays can be assembled with greater versatility in reagent column units employing a single sensor, than can be co-immobilized on the surface of a transducer. A review is presented, with 19 references.

Abstract: Polymer membranes have been explored for the analysis of ions that do not require plasticizers and with photo-curable properties, This work was focused on investigating the viability of the methacrylic-acrylic copolymers as new self-plasticizing membrane matrixes for ion-selective electrodes or other ion-sensor applications, Copolymers with glass transition temperatures ranging from -20 to -44°C could be prepared without added plasticizer and were found to be functional as ion-selective membranes, Both free-radical solution polymerization and photopolymerization could be used, and self-plasticizing behavior of copolymers was observed with a high alkylacrylate (R = C-4) content. This was found to be compatible with most commercially available ionophores, and sensors for potassium, sodium, calcium and pH were fabricated entirely by photocure procedures; single-step procedures for the immobilization of benzo-15-crown-5 ionophore on these self-plasticizing copolymer matrixes were also developed. Even though the ionophore was immobilized, potentiometric studies revealed that the ionophore remained functional, and thus, these copolymers have the advantage of suffering neither leaching of ionophore nor plasticizers. All these sensors exhibited a Nernstian or near Nernstian response with selectivity comparable to plasticized PVG membranes or other plasticized and photocurable polymer membranes. The long-term response of the potassium sensor with immobilized ionophore and the sodium sensor showed little deterioration for as long as one month and three months, respectively, under continuous use.