Previous investigations on o‐aminophenol (oAP) electropolymerization by cyclic voltammetry (CV), onto platinum, in aqueous solution (phosphate buffer) at neutral pH, have shown the reproducible formation of an insulating film of inherent adherence and thinness, poly(o‐aminophenol) (PoAP). The applicability of this produced film as a permselective membrane for biosensors was demonstrated, as well as the influence of the platinum surface state on its self‐limited growth and morphology. Based on these findings, we have continued our investigation on insulating PoAP by combining compositional (XPS) and electrochemical (CV) analyses. To evaluate the finite film on its compositional homogeneity and stability, we have highlighted, in turn, different analyzed depths by angle‐resolved XPS, repeated experiments and performed stability test in ultra‐high vacuum. This investigation, combined with an accurate curve‐fitting procedure, has allowed the estimation of the PoAP thickness and the assignment of chemical states for determining its polymerization sequence. We show that PoAP thickness is about 7 nm; its repeat formula comprises alternating quinoneimine and oAP units, including approximately one water molecule, and the polymer chains are terminated with carbonyl‐type groups. Copyright © 2014 John Wiley & Sons, Ltd.

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A liquid chromatography (LC) detector based on a fast response and sensitive bienzyme amperometric biosensor for acetylcholine (ACh) and choline (Ch) is described. The detector fabrication consisted of glutaraldehyde co-crosslinking of acetylcholinesterase and choline oxidase with bovine serum albumin on the Pt working electrode of a conventional thin-layer electrochemical flow cell. The influence of some experimental parameters (e.g., enzyme loading, thickness of the bienzyme layer, flow rate) on the detector characteristics has been studied in order to optimize the analyte response while minimizing band-broadening and distortion. A mobile phase consisting of a phosphate buffer (I, 0.1 M; pH, 6.5) containing 5 mM sodium hexane sulfonate and 10 mM tetramethylammonium phosphate was found to give very satisfactory resolution and peak shape in ion-pair, reversed-phase LC. Linear responses were observed over at least four decades and absolute detection limits (at a signal-to-noise ratio of 3) were 12 and 27 fmol injected for Ch and ACh, respectively. After one month of intensive use in the LC system, the detector retained about 70% of its initial sensitivity. The potential of the described approach is demonstrated by the simultaneous determination of Ch and ACh in rat brain tissue homogenates.

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