This review article updates recent developments in chemically modified electrodes (CMEs) towards analytical applications for the year of 2000 ± 2002 with 179 references. The broad topics are subdivided into four main categories: i) physisorption/chemisorption, ii) covalently linked, iii) homogenous (uniform) multilayer and iv) heterogeneous (non-uniform) multilayer CMEs. The criteria for the preparation of CMEs in elecrocatalytic systems are clearly described in Section 1. Some of the encouraging results related to Au-nanoparticles for DNA detection and new ceramic carbon, carbon nanotubes, copper-plated screen-printed and Nafion/lead ruthenate pyrochlore CMEs for catalytic application were especially discussed in this review.

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A silica sol-gel glass-coated ferricyanide-doped Tosflex-modified screen-printed electrode (designated as SG/FeCNTs/SPE) was used for the mediated oxidation of ascorbic acid in neutral pH. The sol-gel overlayer was found to stabilize the Fe(CN) 3À 6 -Tosflex system without any foul-off and deterioration behavior through chemical interaction between the hydrophilic sites of Tosflex and oxy-and/or -hydroxy surface functional groups of silicate. The electrochemical mediation of ascorbic acid was found to follow the Michaelis-Menten kinetic pathway. The SG/FeCNTs/SPE was very stable for repetitive measurements by flow injection analysis at 0.3 V (vs. Ag/AgCl). A linear calibration plot was obtained for ascorbic acid determination up to 300 mM with sensitivity and detection limit (S/N 3) of 2.85 nA/mM and 46 nM, respectively. The system also showed tolerable interference to uric acid, urea and carbohydrates and was used for the determination of ascorbic acid in human urine, clinical tablet and apple juice.