Simultaneous Determination of Lead and Cadmium in the Presence of Morin by Adsorptive Stripping Voltammetry with a Nafion-Ionic Liquid-coated Mercury Film Electrode

Abstract

This work describes the use of nafion coated with the ionic liquid 1–ethyl–3–methylimidazolium trifluoromethanesulfonate ([EMIM]F3MSO3) on a mercury film electrode (NILHgFE) for simultaneous determination of Pb(II) and Cd(II) by adsorptive stripping voltammetry in the presence of morin. Morin forms complexes with a metal:ligand stoichiometry of 1:1 with Pb(II) and of 1:2 with Cd(II). Electrodes were coated with nafion and [EMIM]F3MSO3 or 1–butyl–3–methylimidazolium tetrafluoroborate or 1–butyl–3–methylimidazolium hexafluorophosphate, obtaining higher peak currents with the former. Variables like concentration of ionic liquid (CIL) on the electrode, pH, morin concentration, adsorption potential (Eads) and adsorption time (tads) were optimized. The best experimental parameters were: CIL = 2.6 mol L–1; pH = 2.9; Cmorin = 1.1 μmol L–1; Eads = –0.3 V and tads = 60 s. The linear calibration curves ranged up to 16.0 μg L−1 for Pb(II) and Cd(II) with synthetic solutions; however, with real and certified samples linear range was up to 50.0 μg L−1 for Pb(II). The detection limits (3σ) were 0.12 μg L−1 for Pb(II) and 0.13 μg L−1 for Cd(II). The relative standard deviation was 2.0 % (n=7) for a solution containing 4.9 μg L−1 Pb(II) and Cd(II). The method was validated by determining Pb(II) and Cd(II) in reference material for measuring elements in water (TMDA–61) and waste water (SPS–WW1). Finally, the method was successfully applied to the determination of Pb(II) and Cd(II) in tap water after UV digestion.