SIMULTANEOUS DETERMINATION OF TITANIUM AND MOLYBDENUM IN NATURAL-WATERS BY CATALYTIC CATHODIC STRIPPING VOLTAMMETRY

A procedure is set out by which titanium and molybdenum can be determined simultaneously in freshwater using cathodic stripping voltammetry preceded by adsorptive collection of their complexes with mandelic acid. The voltammetric procedure to determine molybdenum in natural waters is optimized. The optimal solution composition includes 4 mM mandelic acid, 45 mM chlorate, and a pH of 1.9. The reaction is characterized by a peak at -0.48 V vs. Ag/AgCl owing to the electrochemical reduction of M(VI)-mandelate to Mo(V), the re-oxidation of Mo(V) by the added chlorate to Mo(VI) and the re-reduction of the thus generated Mo(VI) to Mo(V) at the electrode surface. Thus the reduction current is catalytically enhanced by the chlorate. The limit of detection of the procedure is 1.4 pM with an adsorption time of 60 s using a 10 ml aliquot of sample; this analytical limit can be lowered further if required by extending the deposition time. Titanium (peak at -0.95 V) and molybdenum can be determined simultaneously at pH 3.1. Measurements in lake waters reveal subnanomolar levels of these elements. The data illustrate the extraordinary sensitivity of cathodic stripping voltammetry for certain single-electron reduction steps which can be enhanced catalytically.