THE CATALYTIC ADSORPTIVE STRIPPING VOLTAMMETRIC DETERMINATION OF CHROMIUM WITH TTHA AND NITRATE

A sensitive voltammetric method is presented for the determination of trace amounts of total chromium (Cr(III) and Cr(VI)) in natural waters , employing the square wave mode. The method is based on the preconcen tration of the Cr(III)-TTHA complex by adsorption at the HMDE at the p otential of -1.0 V vs. Ag/AgCl. The adsorbed complex is then reduced p roducing a response with a peak potential of -1.29 V and the peak heig ht of the Cr(III) reduction is measured. The catalytic action of the n itrate ions on the Cr(III)-TTHA reduction has been elucidated using cy clic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a.c. voltammetry and the potential ra nge of adsorption was determined. Based on these investigations optima l conditions for the determination of the total chromium concentration in the range 155-2000 ng l-1 have been established. The determination limit is 15 ng l-1 and the RSD is 3.5% for chromium concentrations gr eater-than-or-equal-to 200 ng l-1. The usefulness and wide scope of th is method for reliable and highly sensitive chromium analysis down to the ultra trace levels existing in various types of natural waters is demonstrated by determinations of the total chromium content in lake, sea and rain water.