Determination of trace vanadium in various waters by differential pulse adsorptive stripping voltammetry

Abstract

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...

Determination of Trace Vanadium by Adsorptive Stripping Voltammetry at a Carbon Paste Electrode

“…The composition of the V(V)-ARS complex was determined by the mole ratio method to be 1 : 2. It was found that Pc 1 decreased with increasing the V(V) concentration and disappeared nearly when the concentration of V(V) was higher than half that of ARS, and Pc 2 did not be affected by the addition of bromate, in contrast to the previous observations [2,5,9,10,11,13,14] where the response signal for the V(V) complexes was enhanced catalytically in the presence of bromate. Moreover, the peak potential (E p ) of Pc 2 shifted toward more negative values with increasing scan rate (u).…”

“…Different ligands, such as catechol [1 -2], 5-Br-PADAP [3 -5], solochrome violet RS [6], 2-(2-thiazolylaloz)-p-cresol [7], pyrogallol [8], cupferron [9 -10], 2,3-dihydroxynaphthalene [11] and chloranilic acid [12 -13], have been used for the adsorptive voltammetric determination of vanadium. Several of these procedures involve a catalytic enhancement of the response in the presence of bromate [2,5,9,10,11,13]. Although the sensitivities of these methods at a hanging mercury drop electrode are fairly high, the mercury is becoming rather controversial material.…”

Speciation and preconcentration of vanadium(v) and vanadium(iv) in water samples by flow injection-inductively coupled plasma optical emission spectrometry and ultrasonic nebulization

“…Since one of the routes of incorporation of V into the human body is water, [6][7][8] its determination in this type of sample is very important. The concentration of V in natural water is very low, [9][10][11] of the order of a few mg L 21 , hence powerful techniques are required and only a few of them show sufficient sensitivity.…”

Direct detection of ultra-trace vanadium (V) in natural waters by flow-injection chemiluminescence with controlled-reagent-release technology

“…Therefore determination of V (V) is receiving increasing attention in pollution studies. Since one of the routes of incorporation of V into the human body is drinking water (Hirayama et al, 1992;Rao et al, 1997;Sabbioni et al, 1996), its determination in these types of samples becomes very important. Since the concentration of V(V) in drinking water is very low (Greenbreg et al, 1975;Ahmed and Banerjee, 1995;Bermejo-Barrera et al, 1990), in the order of a few micrograms per liter, powerful techniques are required and only a few of them show sufficient sensitivity.…”