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A method is presented for determining the trace amount of chromium in aluminum. Aluminum is dissolved in sodium hydroxide containing hydrogen peroxide. The method is based on the catalytic activity of nitrate ions on the reduction of Cr( 111 )-triethylenetetraminehexaacetic acid (-'ITHA) complex. The sensitivity of this method is further improved by adsorptive preccncentration o f Cr(II1)-TTHA complex at a hanging mercury drop electrode (HMDE). The adsorbed complex is then reduced at a peak potential o f -1.28 V, and the peak height of Cr(II1) reduction is measured. The Cr(II1) formed at the electrode surface by the reduction of Cr(VI), which is present in the bulk solution, is immediately complexed by TTHA. This method is suitable for the determination of chromium at levels as low as 0.5 pg g-' (with about 25 mg o f sample) and a relative standard deviation of 15%.

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A sensitive voltammetric method is developed for the determination of trace amounts of vanadium in various water samples. The method is based on the preconcentration of the Vv-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) complex at a potential of -0.5 V (vs. Ag/ AgCI). The adsorbed complex is then reduced, producing a response with a peak potential of -0.8 V. The catalytic action of bromate ions on the reduction of the VV-5-Br-PADAP complex has also been investigated. The high catalytic currents obtained in presence of bromate ions are taken advantage of enhancing the sensitivity of the method. From the preliminary studies the optimal conditions for the determination of vanadium by differential pulse adsorptive stripping voltammetry have been established. The interference of various elements in this method has also been studied. The method of standard addition is employed in evaluating the concentration of vanadium in water samples. The determination limit is 20nglL and the RSD is 12% for vanadium concentrations of 500ng/L. Keywords: 5-Br-PADAF', Adsorptive stripping voltammetry, Catalytic currents, Vanadium(v) determinationThere is a great deal of current interest in the incidence of trace elements in the environment and the quantities to which man is exposed. Although health effects have been related to high exposures to specific trace elements, of equal concern is the possible chronic disease relationships to the uptake of more typical quantities from food, water and air. Epidemiological investigations indicate the importance of and the need to understand the nature, incidence, variability, and controlling factors for vanadium in trace waters. Aside from man's direct exposure to vanadium from drinking water obtained from natural fresh waters, both surface and subsurface and with various degrees of treatment, water can also be a source of vanadium for aquatic organisms and terrestrial edible plants, ultimately reaching man and foraging animals through their food chains. Vanadium is reported to be present in natural waters in various concentrations, from 0.3 to 2 ppb in seawaters to 1 to 6 ppb in municipal waters [1,2]. Most of the vanadium is present in waters as pentavalent vanadium. Several researchers have developed polarographic methods for the determination of vanadium. A DC voltammetric method was proposed for the determination of VO; in borate buffer. The limit of detection was 1. The limit of detection of these methods was reported to be lo-'' M for 2 min accumulation. Recently, another adsorptive stripping voltammetric method based on complexing vanadium with 5-Br-PADAP was also reported [7], where again the limit of detection was of the order of lo-'' M for 1 min accumulation and for an electrode (HMDE) surface area of 2.08mm' and a scan rate of 100 mV/s. This article describes a differential pulse adsorptive stripping voltammetric method for the ultratrace measurements of V in various water samples. The method involves the interfacial accumulation of the VV-5-Br-PADAP complex fo...

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