The fabrication and characterization of carbon fibre cone nanometre-sized ultramicroelectrodes (nanoelectrodes, CFCNEs), modified with an over-oxidized polypyrrole (OPPY) film and equipped with an integrated micro Ag/AgCl reference electrode, is reported. The OPPY-modified CFCNEs are suitable for the anodic stripping voltammetric determination of a neurotransmitter, dopamine (DA), in extremely small sample volumes in the presence of ascorbic acid (AA). The observed high selectivity for DA and the ability for its accumulation were found to be a consequence of the exclusion of anionic species by the negative charges in the OPPY film. The OPPY film was prepared via electropolymerization by cycling the potential between -0.2 and 0.7 V versus Ag/AgCl, which also allowed control over its thickness. The permselectivity of the OPPY membrane was thoroughly evaluated. The anodic stripping voltammetric response for DA was found to be dependent on the film thickness, accumulation time and potential and on the pH of the measurement medium. A good linear relationship between the anodic stripping peak current and DA concentration was obtained over the range 2.5 X 10-6-5.0 X 10-4 moll-1, using a CFCNE modified with 15 OPPY coatings and a 2 min preconcentration time. The reproducibility of the measurement cycles (accumulation-detectionregeneration) was satisfactory, with an RSD of 5.6%(n = lo), and the limit of detection achieved with a 2 min preconcentration time was 1.0 x 10-7 mol 1-1 of DA in phosphate buffer solution (pH 7.1). Owing to their ultra small size, and the integrated micro reference electrodes, the proposed OPPY-modified CFCNEs permitted the detection of DA in remarkably small sample volumes (as small as 10 nl), and in the presence of high concentrations of AA.
A commercial indium-tin oxide (ITO) film, deposited on a glass substrate, was investigated for its potential use as a disposable amperometric sensor for hydrogen peroxide determination in aqueous solutions. After a very simple, yet crucial, electrochemical pre-treatment of a fresh IT0 film electrode, a stable and sensitive electrocatalytic response to hydrogen peroxide was exhibited. The electrocatalytic character and factors influencing hydrodynamic amperometric performance of the IT0 film electrode were examined and discussed. Under optimized conditions, the amperometric signal was linearly proportional to the hydrogen peroxide concentration over the range 8.4 X 10-5-2.1 X 10-3 mol 1-1 (2.9-71.4 mg 1-1) with a detection limit of 5.6 X 10-1 mol 1-5 moll-1 (1.9 mg 1-1). The electrode also displayed good reproducibility with an sr value of 1.5% for 20 consecutive chronoamperometric measurements of 2.8 X 10-4 moll-1 hydrogen peroxide.
A sol-gel derived CeO 2 -TiO 2 (CTO) thin film, deposited on a glass substrate with an electrically conductive layer of indium tin oxide (ITO), was investigated with regard to its potential use for amperometric detection in flow injection (FI), using a thin layer cell set-up. Cyclic voltammetry was employed for basic studies on the electrochemical behaviour of the CTO film in aqueous LiOH solutions under batch and continuous flow conditions. The dependence of the amperometric response of the CTO film on experimental parameters under FI conditions, such as flow rate of the carrier, operating potential and injection volume, was investigated with LiOH and LiCl. The amperometric signal was linearly dependent on the Li + concentration over the range 4.0 3 10 24 -4.0 3 10 23 mol l 21 . For a concentration of 10 23 mol l 21 Li + , the RSD of eight consecutive measurements was 5.7% and was comparable to that of conductivity detection (4.7%). Comparison of amperometric with conductometric detection of Li + , Na + , K + , NH 4 + and tetraethylammonium ions, in the presence of different counter ions, indicated that the results of both detection modes correlate well.
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