Direct Determination of Cadmium Traces in Natural Water by Adsorptive Stripping Voltammetry in the Presence of Cupferron as a Chelating Agent

Abstract

A sensitive, simple and fast adsorptive stripping voltammetric procedure for trace determination of cadmium in natural samples containing high concentrations of surface active substances and humic substances has been developed. The method is based on adsorptive accumulation of the Cd(II)-cupferron complex onto a hanging mercury drop electrode, followed by the reduction of the adsorbed species by a voltammetric scan using differential pulse modulation. The detection limit was 3 10 À10 mol L À1 (33.6 ng L À1) with an accumulation time 30 s. The procedure was applied to the determination of Cd(II) in natural water samples without any pre-treatment with satisfactory results.Keywords: Cadmium, Determination, Adsorptive stripping voltammetry, Natural water, Organic matrix DOI: 10.1002/elan.201100357One of heavy metals of considerable environmental and occupational concern is cadmium [1]. Cadmium compounds are classified as human carcinogens by several regulatory agencies [2][3][4][5].Since the concentration of cadmium is extremely low in various natural samples, a sufficiently sensitive procedure for its reliable determination would be of great interest. Electroanalytical techniques such as stripping voltammetry are considered as powerful tools for trace metal determination [6,7]. The most widely used stripping voltammetric mode for determination of Cd(II) is an anodic stripping voltammetry (ASV) [8][9][10][11][12][13][14][15][16][17][18]. An alternative method for the determination of cadmium is based on adsorptive rather than electrolytic accumulation. Primary predominance of adsorptive stripping voltammetry (AdSV) over ASV is a potentiality to obtain lower limit detection. Only several procedures within the last 15 years have been reported for the determination of cadmium by AdSV using different complexing agents [19][20][21][22][23][24][25][26].This paper describes a novel adsorptive stripping voltammetric procedure for the determination of traces of cadmium in natural water in the presence of cupferron as a complexing ligand. Cupferron is a commonly used organic compound which can form stable complexes with many metal elements [27-31]. As it was proved in the paper [32], cupferron also forms a stable electrochemical active complex with Cd(II), but has never been used for voltammetric determination of cadmium so far.The AdSV is a very sensitive technique notably influenced by variables such as time and potential deposition, the concentration of the complexing agent (cupferron) and the pH value. Therefore, optimization of these parameters was performed.An acetate buffer was used as a supporting electrolyte and the influence of pH of supporting electrolyte on the stripping peak current of cadmium was studied in the range from 4 to 7. The experiments were performed using Procedure B (see Experimental). In acidic solution at a pH equal to 4 the peak was not observed. Next the peak current of cadmium increased as the pH of the buffer increased to 5.2 and then was almost stable up to pH 6.5.The effect of the cupf...

Simultaneous voltammetric determination of trace bismuth(III) and cadmium(II) in water samples by adsorptive stripping voltammetry in the presence of cupferron

“…In the second step, after sedimentation of resin, an appropriate volume of the sample was transferred to the voltammetric cell and standard measurement was performed. It was stated that, like Amberlite XAD-7 resin, as described in previous papers [12,13], XAD-16 resin also noticeably minimalizes the negative influence of organic substances. To study the influence of surface active substances on the analytical signal in the proposed procedure three types of surfactants, Triton X-100 (Fig.…”

“…This interfering effect was precisely studied in our earlier papers focused on Bi(III) and Cd(II) determination using cupferron as a complexing agent. Haw proved this interference can be efficiently minimized using an addition of Amberlite XAD-7 resin to the analyzed natural water sample before introducing them to voltammetric cell [12,13]. In this work the possibility of using an Amberlite XAD-16 resin for elimination of organic substances interferences was examined.…”

“…In order to keep the composition of the buffer constant when studying the effect of the pH, an acetate buffer was used. An acetate buffer as a supporting electrolyte was used on the basis of the literature data as the most suitable for both Bi(III)-cupferron and Cd(II)-cupferron complexes accumulation on the HMDE [12,13]. It is clear that the peak current of the Bi(III)-cupferron complex is almost stable from 3.0 to 5.5 and slowly decreases at higher values.…”

“…As it was described before even a bit of an organic substances concentration disturbs both bismuth and cadmium voltammetric signals [12,13]. In order to eliminate these interferences in the proposed procedure the additional step of mixing analyzed sample with Amberlite XAD-16 was effectuated.…”

“…For such measurements the choice of appropriate supporting electrolyte and most of all a suitable complexing agent is very important. Recently we proposed cupferron as a new complexing system for Bi(III) and Cd(II) adsorptive stripping determinations [12,13]. These works have been optimized by a selection of optimal conditions, such as the selection of the supporting electrolyte, pH, concentration of the cupferron as the complexing agent and accumulation potentials and time.…”