Preconcentration and Permselectivity

CA films by using the phase inversion process. These CA films were cast from solvent/nonsolvent solutions to yield size exclusion membranes consisting of a thin permselective outer layer and a more porous sublayer. These membranes permitted the rapid permeation of a 1500-dalton poly (ethylene glycol) ester of ferrocene however the reproducibility of results presents a problem with these CA mem-branes. Christie et demonstrated that thin films of plasticized polyvinylchloride (PVC), normally used for potentiometric ion-selective electrode applications, applied to electrodes over a polycarbonate dialysis membrane offered improved selectivity ratios for the amperometric detection of phenolic compounds and H2O2 in the presence of the common biological interferents, ascorbic acid and uric acid, over those observed at the dialysis membrane alone or at a composite dialysis/membrane. 

FIGURE 10.6. The FIA traces at poly aniline (7-min anodization, top) and polyphenol (0.5-mM phenol concentration, bottom) modified electrodes (B) to determine catechol top) and acetaminophen bottom). Corresponding traces for the unmodified electrodes are shown in (B). Traces in (a) show the response to the injection of 0.1-mM uric acid top) or NADH bottom), with traces (bMd) representing the response on adding 50-//M catechol top) or acetaminophen bottom). (From Ref. 32 with permission from Elsevier) 

The most frequently used anion-exchange material is protonated or quatemized poly(4-vinylpyridine) (QPVP), which has been used for the electrostatic incorporation of anionic metal complexes and for the preconcentration and detection of low levels of these metal complexes in solution. Cassidy and Tokuda reported the use of a QPVP layer to detect reversibly low levels of Cu(II) 

FIGURE 10.7. Array response pattern obtained for flow injection of 2-//M promethazine (cross-hatch), dopamine (open), and catechol (hatch) at electrodes modified with 20-min hydrolyzed CA (1), PVP (2), Nafion (3), and lipid (4) films. The operating potential was set at 0.8 V, and the background electrolyte consisted of a 0.05-M phosphate buffer at pH 5.5. (From Ref. 124 with permission for the American Chemical Society) 

FIGURE 10.8. Postulated oxidation-reduction processes for (I) polypyrrole, (II) polythiophene, and (III) polyaniline. (Adapted from Ref. 156 with permission from the Royal Society of Chemistry) 

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