DETERMINATION OF ANTIMONY IN SEAWATER BY CATHODIC STRIPPING VOLTAMMETRY

The method proposes to determine subnanomolar levels of antimony in freshwater and seawater by cathodic stripping voltammetry preceded by adsorptive deposition of complexes with catechol. Dc-polarographic and cyclic voltammetric experiments indicated that the complex of catechol with Sb(III) is adsorbed prior to the scan, and is reduced to Sb(0) in a single reduction step. The optimized analytical conditions include a catechol concentration of 0.002 M and pH 6. The deposition potential is selected at -1.0 V. rather than at a more positive potential, in order to eliminate interference by uranium in seawater by including an amalgamation step in the preconcentration procedure. This is followed by a re-oxidation period of 20 s at -0.2 V to allow amalgamated Sb to become re-oxidized and form an adsorbed layer of Sb(III)-catechol complexes. The scan is then initiated in a negative direction using a linear sweep of 50 mV/s. The limit of detection lies near 0.2 nM Sb with a deposition time of 3 min, whereas the sensitivity can be increased by extending the deposition time. Interference by copper, lead and cadmium is eliminated by adding EDTA to the solution. Both Sb(III) and Sb(V) can be determined with identical sensitivity. © 1987