DEVELOPMENT OF A CHRONOCOULOMETRIC METHOD FOR THE DETERMINATION OF URANIUM AT TRACE LEVELS BY USING THE CATALYTIC NITRATE REDUCTION

The electroanalytical determination of uranium at trace levels was studied with the purpose of improving the sensitivity of the uranium-catalyzed reduction in the presence of nitrate on mercury electrode. Examination of the current dependence on time (chronoamperometry) revealed the advantage of measuring the current later and for a longer time interval than usual in pulse polarography. The uranium/nitrate system is particularly favorable in this sense because an intensification of the catalytic current with time is observed. The best signal-to-noise ratio was achieved using the technique of chronocoulometry. In this chronocoulometric catalytic determination (CCCD), analytical information was gathered, calculating the slope of the charge versus time curve during the period of 10 to 20 seconds after the application of the potential pulse and correcting it for the residual slope before the pulse. To establish the new analytical procedure, the effects of electrolyte composition, potential program, integration time, and blank correction were examined. A detection limit of 3 x 10(-10) M was attained, a power of ten lower than the sensitivity reported for the same catalytic determination by differential pulse polarography. An exploratory study of the combination of this procedure with preconcentration of uranium on the electrode allowed reduction of the detection limit by an additional order of magnitude.