Determination of Lead and Cadmium in the Presence of Quercetin–5’–sulfonic Acid by Adsorptive Stripping Voltammetry with a Hanging Mercury Drop Electrode and a Nafion–coated Mercury Film Electrode

The use of a hanging mercury drop electrode (HMDE) and a glassy carbon electrode modified with Nafion–Hg (NHgFE) to determine Pb(II) and Cd(II) by adsorptive stripping voltammetry in the presence of quercetin–5’–sulfonic acid (QSA) is reported. With a HMDE it is possible to determine Pb(II) and Cd(II) individually because the peak current of Pb–QSA is maximum at pH 6.1 (Epeak –0.50 V), while the peak current of the Cd–QSA complex is maximum at pH 8.9 (Epeak –0.66 V). The linear calibration curves ranged from 0.5–40.0 μg L –1 for Pb(II) and 0.5–45.0 μg L –1 for Cd(II). The detection limits (3) were estimated to be around 0.3 and 0.1 μg L –1 and the relative standard deviations were 2.0 and 1.7 % at the 9.4 μg L –1 level of Pb(II) and Cd(II) with 30 s of accumulation (n=7) (CQSA 2.7 μmol L –1 ; Eads –0.10 V). On the other hand, it is found that with the prepared Nafion– mercury film electrode Pb(II) and Cd(II) can be analyzed simultaneously at pH 6.1 (Epeak –0.55 V, – 0.73 V). The detection limits were 0.2 μg L –1 for both metal ions, with a linear range until 18.0 μg L –1 . The methods were validated using synthetic sea water (ASTM D665) spiked with several metal ions, and reference material for measuring of elements in water (TMDA–61) and waste waters (SPS–WW1). Finally, the method was successfully applied to the determination of Pb(II) and Cd(II) in tap water after UV digestion.