A reliable and simple hybrid electrode is fabricated using carboxylated MWCNTs and PdNTs for the simultaneous determination of Ascorbic acid (AA), Dopamine (DA) and Uric acid (UA). The carboxylated MWCNTs and PdNTs are naturally reduced by a unique method. Physical characterization of the modified electrode which is represented as rMWCNTs-PdNTs/Gr, was carried out with the help of X-ray diffraction and electrochemical impedance spectroscopy techniques. The electrochemical properties of the developed sensor toward the detection of AA, DA and UA was examined using cyclic voltammetry, differential pulse voltammetry and Chronoamperometry. The modified electrode exhibits high sensitivity and selectivity with separation of AA, DA and UA anodic peaks at 117.5, 139.2 and 316.7 mV respectively. The response time of AA, DA and UA was found to be 2 s, 2 s and 3 s respectively. The low detection limit was observed at 0.175 μM for AA, 0.1802 μM for DA and 0.0360 μM for UA. The proposed electrode also shows stability and reproducibility.
o-Phenylenediamine has been used as a reagent to quantify nitrites= nitrates in a variety of sample matrices. The method is based on the cyclization reaction between o-phenylenediamine and nitrite in acid medium. The amine undergoes diazotization with nitrite in the presence of acid to form the diazonium ion, which subsequently cyclizes to yield yellowish orange benzotriazole at room temperature with an absorption maximum at 450 nm. The formed dye has been separated, purified, and characterized by IR, NMR, and spectroscopy techniques. The parameters of the reaction between amine and nitrite have been optimized. The effect of interfering ions on the determination of nitrites=nitrates has been described. The developed method has been applied for the determination of residual NO 2 gas present in the ambient air after fixing it as a nitrite ion using sodium arsenite as a trapping medium. The dye formed has been extracted into organic solvent to improve the detection limit during the measurement of low levels of ambient NO 2 in air. The method obeyed Beer's law in the concentration range 0-250 mg in aqueous medium and 0-50 mg in organic medium with molar absorptivity of 4.09 Â 10 4 L mol À1 cm À1 and 4.3 Â 10 4 L mol À1 cm À1 respectively. Nitrate is determined by reducing it to nitrite after passing through the copperized 3342 cadmium reductor column. The developed method has been applied to determine nitrite=nitrate levels in water, soil, and biological samples.
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