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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]

• Utilization of activated pencil lead electrode (APLE) for the first time in determination of gallic acid in food stuffs. • High catalytic activity of the APLE toward gallic acid oxidation. • Selective determination of gallic acid in the presence of high levels of ascorbic acid in the food stuffs using APLE. • Determination of gallic acid in sub-micromolar concentration range via adsorptive stripping (AdSDPV) using APLE. An electrochemical sensor for the determination of some polyphenolic compounds such as Gallic acid (GA) and Galloyl esters was developed using the activated pencil lead electrode (APLE). At first, a study has been made of the optimum conditions for electrochemical activation of the pencil lead electrode. Potentiodynamic and potentiostatic strategies were investigated for activation of the pencil lead electrode and the results show that the potentiodynamic pretreatment gives better performance toward measurement of the polyphenolic compounds. Electrochemical properties of GA were investigated using chronoamperometry and cyclic voltammetry; and some thermodynamic and kinetic variables such as α, n α , and D were calculated. Sensitive differential pulse voltammetry (DPV) technique was applied for the determination of Gallic acid and Galloyl esters in different samples. Enhanced oxidation peak currents of Gallic acid were observed at APLE when compared with non-activated PLE. The calibration graph has two linear ranges of 0.49–24.3 µM and 0.07–0.83 mM, and the obtained limit of detection for S/N = 3 was 0.25 µM. Adsorptive stripping differential pulse voltammetry (AdSDPV) was also conducted to determine Gallic acid and Galloyl esters in sub-micromolar concentration range. Using the AdSDPV method, the limit of detection was improved and calculated to be 5.2 nM. The proposed method was successfully applied for quantification of the total concentration of Gallic acid and Galloyl esters in a variety of real samples such as black and green tea, and mango juice samples, and desirable recovery values indicated the good accuracy of the developed sensor. [ABSTRACT FROM AUTHOR]