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The Chromazurol s has been electropolymerized on the glassy carbon electrode and the Poly- Chromazurol s modified glassy carbon electrode (PCSMGCE) has shown excellent electrocatalytic activity toward the oxidation of ascorbic acid in phosphate buffer solution (pH=3). It was used for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Analytical parameters were optimized and electrochemical behavior of modified electrode was studied. The calibration curves were obtained over the range of 3.0-2200.0 µmol Lâ1 AA, 0.09-980.0 µmol Lâ1 DA, and 0.05-900.0 µmol Lâ1 UA. Detection limits of 1.7 µmol Lâ1 AA, 0.05 µmol Lâ1 DA, and 0.03 µmol Lâ1 UA were obtained at pH 3.0. Prepared modified electrode had satisfactory results for determination of DA, AA and UA in dopamine injection solution, vitamin C tablets and human urine samples.

A sensitive and selective procedure is presented for voltammetric determination of cobalt. The procedure involves an adsorptive accumulation of cobalt pyrogallol red (PGR) complex on stationary mercury drop electrode, followed by cathodic stripping voltammetry measurement of reduction current of adsorbed complex at -1.17 V (vs. Ag/AgCl). The optimum conditions for determination of cobalt include pH 11.0, 35 μM pyrogallol red, an accumulation potential of -0.9 V (vs. Ag/AgCl) and scan rate 80 mVs-1. The peak current is proportional to the concentration of cobalt over the concentration range of 5.0 to 280 ng mL-1 with a detection limit of 1 ng mL-1 with an accumulation time of 140 s. The method was applied for the determination of cobalt in analytical grade NaCl and water samples.

A carbon paste electrode modified with multiwall carbon nanotubes (MWCNTPE) was prepared to study the electrocatalytic activity of dopamine (DP) in the presence of homocysteine (HCy) and it was used for determination of HCy. The diffusion coefficient of HCy (D = 6.79×10−6 cm2 s−1), and the kinetic parameters of its oxidation such as electron transfer coefficient (α = 0.46), and rate constant (kh = 7.44×102 dm3 mol-1 s-1) were also determined using electrochemical approaches. Under the optimum pH of 5.0, the peak current of oxidation of HCy at MWCNTPE in the presence of DP occurs at a potential about 530 mV and the results showed that the oxidation peak current of HCy at the modified carbon nanotubes electrode was higher than on unmodified electrode. The peak current of differential pulse voltammograms of HCy solutions increased linearly in the range of 3.0-600.0 μM HCy with the detection limit of 2.08 μM HCy. This method was also examined for determination of HCy in physiological serum and urine samples.

A color changeable optode for thallium(III) ions in aqueous solutions was prepared by physical inclusion of 4-(2-pyridylazo)-resorcinol into a plasticized PVC film. The increase in the absorbance of the optode at 524 nm is proportional to thallium(III) concentration. Different parameters effecting the sensitivity such as sample parameters and composition of the membrane were optimized. The response times of the prepared test-system are found to be 230, 210, and 180 s for 4.8 x [10.sup.-6], 4.8 x [10.sup.-5], and 4.8 x [10.sup.- 4] M Tl(III), respectively. The analytical performance of the optode was evaluated, obtaining a linear concentration range of two decades of concentration, 3.1 x [10.sup.-6] - 4.7 x [10.sup.-4] M Tl(III), with a limit of detection of 1.8 x [10.sup.-6] M Tl(III). Selectivity of the optode is also studied. Application of the optode to the determination of Tl(III) in some aqueous samples yields good results. Keywords: optical test-system, thallium determination, resorcinol derivative, spectrphotometry DOI: 10.1134/S1061934814020026, Recent decades have shown an increase in the development of optical chemical sensors as viable alternatives to other types of sensors. Such optical chemical sensors being termed 'optodes' or 'optrodes.' [...]