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In the present paper, the electrochemical reduction of nitrite at a hemoglobin modified pencil lead electrode (Hb/PLE) is described. The electrochemical properties of nitrite were studied by cyclic voltammetry and chronoamperometry. Results showed that the hemoglobin film has an excellent electrochemical activity towards the reduction of nitrite. By using voltammetric and chronoamperometric methods, α, n α and n were calculated. Then the ability of the electrode for nitrite determination was investigated using differential pulse voltammetry. The electrocatalytic reduction peak currents were found to be linear with the nitrite concentration in the range from 10 to 220 µM with a detection limit of 5 µM. The relative standard deviation is 2 % for 3 successive determinations of a 100 µM nitrite solution. This modified electrode was successfully used for the detection of low amounts of NO2− in spinach sample and a spiked sample of tap water. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemically pretreated pencil graphite electrode (PGE) has been proposed for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of high levels of ascorbic acid (AA). The electrochemical pretreatment of PGE was achieved in phosphate buffer (pH 7) by the potential recycling between 1.5–2.0V/SCE for 100 cycles, and at the scan rate of 100mVs−1. The influence of electrochemical pretreatment of PGE on the separation of overlapped peaks of AA, DA and UA were studied and optimum conditions were suggested. Differential pulse voltammetry (DPV) was used for simultaneous determination of DA and UA in the presence of high concentrations of AA. The peak separation between DA and AA, and also between DA and UA was up to 260 and 160mV, respectively. The calibration curves were in the range of 0.15–15μM and 0.3–150μM for DA and UA in the presence of AA, respectively. The detection limits (S/N=3) were 0.033 and 0.12μM for DA and UA, respectively. The results reveal that pretreatment of the pencil graphite electrode surface not only improves its electrochemical catalytic activities towards the oxidation of DA and UA, but also resolves the overlapped oxidation peaks of AA, DA and UA into three well-defined peaks. The present method can apply for UA and DA determination in human serum and urine, and also for some commercial pharmaceutical samples without additional sample pre-treatment. [Copyright &y& Elsevier]