VOLTAMMETRIC DETERMINATION OF NITRATE WITH A MODIFIED CARBON-PASTE ELECTRODE

A method for the voltammetric determination of nitrate in drinking wat er is presented. Nitrate exerts a catalytic effect on the reduction an d reoxidation of thallium (1 <-- --> 0) in cyclic and differential pul se voltammetry leading to a peak enhancement. Nitrate can be preconcen trated together with tetrachlorothallate(III) from hydrochloric acid s olutions onto a carbon paste electrode modified with a liquid anion ex changer (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 whe n applying anodic differential pulse voltammetry. Mechanical regenerat ion of the electrode surface is necessary after each measurement. The interference of other anions and the influence of methodical parameter s are investigated. The applicability of this method for the determina tion of nitrate in drinking water is demonstrated. A concise overview on the electroanalytical techniques for the quantitative determination of nitrate is also presented.