VOLTAMMETRIC DETERMINATION OF NITRATE WITH A MODIFIED CARBON-PASTE ELECTRODE

A method for the voltammetric determination of nitrate in drinking water is presented. Nitrate exerts a catalytic effect on the reduction and reoxidation of thallium (1 <-- --> 0) in cyclic and differential pulse voltammetry leading to a peak enhancement. Nitrate can be preconcentrated together with tetrachlorothallate(III) from hydrochloric acid solutions onto a carbon paste electrode modified with a liquid anion exchanger (Amberlite LA2) under open circuit conditions. After reduction of the TI(III) to Tl(0) at the electrode surface at a potential of -1.2 V (vs. SCE), the increase of the reoxidation current of Tl(0) to Tl(I) by nitrate is exploited for analytical purposes. Linearity between current and concentration exists for 0.5 to 60 mug . mL-1 nitrate when applying anodic differential pulse voltammetry. Mechanical regeneration of the electrode surface is necessary after each measurement. The interference of other anions and the influence of methodical parameters are investigated. The applicability of this method for the determination of nitrate in drinking water is demonstrated. A concise overview on the electroanalytical techniques for the quantitative determination of nitrate is also presented.