Automated determination of Cu(II), Pb(II), Cd(II) and Zn(II) in environmental samples by square wave voltammetry exploiting sequential injection analysis and screen printed electrodes

This paper describes the development of a methodology for quantification of Cu(II), Pb(II), Cd(II) and Zn(II) in waters and sediments by anodic stripping voltammetry (ASV) automated by Sequential Injection Analysis (SIA) using a graphite screen printed sensor modified with mercury. Determinations were made by standard addition automated by the SIA system. The limits of detection and quantification were, respectively, 1.3 and 4.3 µg L−1 for Cu(II), 1.4 and 4.6 µg L−1 for Pb(II), 0.6 and 1.8 µg L−1 for Cd(II) and 4.2 and 14 µg L−1 for Zn(II). These limits were obtained for a sample volume of 1000 µL, flow rate of 10 µL s−1 (during the deposition step), and utilizing 3 flow reversals (volume of reversion=950 µL), totalizing a deposition time of 315 s. The potentiostat worked synchronically with the SIA system applying the conditioning potential of −0.1 V vs. pseudo reference of Ag (100 s), deposition potential of −1.0 V for Cu(II), Pb(II) and Cd(II) or −1,3 V for Zn(II), square wave frequency of 100 Hz, potential step of 6 mV and pulse height of 40 mV. For quantification of Zn(II) in sediment extracts, deposition of Ga0 on the working electrode was necessary to avoid the formation of intermetallic between Zn0 and Cu0. The accuracy of the method was assessed by spike and recovery experiments in water samples which resulted recovery rates near 100 % of the spiked concentrations. Recoveries of concentrations in the certified sediment sample CRM-701 undergoing the three steps sequential extraction procedure of BCR varied from 71.7 % for Zn(II) in the acetic acid extract to 112.4 % for Cu(II) in the oxidisable fraction, confirming that the standard addition approach corrected the matrix effects in the complex samples of sediment extracts.