Simultaneous determination of copper, zinc and lead by adsorptive stripping voltammetry in the presence of Morin E. Shams a,∗ , A. Babaei b , M. Soltaninezhad b
Institute for Advanced Studies in Basic Sciences, Zanjan 45195-159, Iran b Department of Chemistry, Arak University, Arak, Iran
Received 24 November 2002; received in revised form 5 September 2003; accepted 15 September 2003
Abstract A sensitive and selective method for the simultaneous determination of copper, zinc and lead is presented. The method is based on the adsorptive accumulation of 2 ,3,4 ,5,7-pentahydroxyﬂavone (Morin) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. Optimal analytical conditions were found to be Morin concentration of 2.0 M, pH of 4.0, and an adsorption potential at −500 mV versus Ag/AgCl. With an accumulation time of 60 s, the peak currents are proportional to the concentration of copper, lead and zinc over the 1 to 60, 0.3–80 and 1–70 ng ml−1 range with detection limits of 0.06, 0.08 and 0.06 ng ml−1 , respectively. The procedure was applied to the simultaneous determination of copper, lead and zinc in some real and synthetic artiﬁcial real samples with satisfactory results. © 2003 Elsevier B.V. All rights reserved. Keywords: Copper; Zinc; Lead; Adsorptive stripping voltammetry; Morin
1. Introduction Lead, copper and zinc are environmental pollutant, which have been tested and assessed over the past few years from both the toxicological and the human health viewpoints. While slight quantities of zinc and copper are essential for normal physiological processes, their excess intake poses an important threat to human health. The maximum tolerable daily intakes for copper and zinc are 0.5 and 1.0 mg kg−1 body weight, respectively . Lead is widely distributed in nature and exhibits severe deleterious effects on human . In particular, it strongly affects the mental and physical development of children. The development of new methods for quantifying trace metals is required and challenged. In some common procedures for the determination of low concentrations of heavy metals a pre-concentration step is needed before performing determination. Most of the sensitive and selective methods recently available such as ICP–AES, ICP–MS, GF–AAS and NAA are too expensive to be used in routine analysis.
Corresponding author. Fax: +98-241-449023. E-mail address: email@example.com (E. Shams).
Stripping voltammetry (SV) comprises a variety of electrochemical approaches, having a step of pre-concentration onto the electrode surface prior to the voltammetric measurements. The major advantage of SV compared with direct voltammetric measurement and other analytical techniques is the pre-concentration factor. Anodic stripping voltammetry (ASV) that is the most popular stripping voltammetric technique is an effective technique for the determination of trace amounts of metal ions. Although anodic stripping voltammetry is a powerful tool for the determination of trace amounts of these three important elements but it suffer from some drawbacks. The main problem in the simultaneous determination of copper and zinc by ASV is the formation of intermetallic compound between copper and zinc. The Cu–Zn interference in ASV has been frequently noted [3–6]. The intermetallic compound is oxidized from mercury at the same potential as Cu, causing enhancement of the Cu stripping peak and depression of the Zn stripping response. This implies that simultaneous determination of these two species is not possible by common electroanalytical methods. Controlling the deposition potential so that only copper is deposited into the electrode can eliminate the zinc interference in copper analysis. The addition of Ga3+ to the
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