Determination of Lead (II) and Cadmium (II) in Water Lily Stems by anodic Stripping Voltammetry using a Bismuth Film Electrode Modified with Mesoporous Silica Nanoparticles and Chitosan

Abstract

Lead and cadmium in the environment can be toxic to human beings, even at very low concentration. Therefore, quantitative determination of Pb(II) and Cd(II) is the great importance for quality of environmental and also health assessment. In this work, the preparation of ex-situ bismuth film on glassy carbon electrode modified with mesoporous silica nanoparticles (2 - 50 nm) and chitosan used as a working electrode was developed and evaluated for reliable quantification of Pb(II) and Cd(II) by anodic stripping voltammetry in water lily stem samples. This electrode is more environmentally friendly than the commonly used mercury working electrode. Moreover, the selected chitosan as strong adhesion reagent for silica nanoparticles coating is cheaper than Nafion. The resulting accumulated metals were stripped off by differential pulse anodic stripping voltammetry (DPASV) with optimized conditions of plating potential and plating time of bismuth film, concentration of chitosan, pH of 0.1 M HCl/KCl, deposition potential and deposition time of Pb(II) and Cd(II) detection, equilibration time, pulse amplitude and step potential. Under the optimum condition, the linear ranges were 2 - 40 μg/L for with the linear correlation coefficient (R2) of 0.998 for both Pb(II) and Cd(II) for 240 s deposition time. The limit of detection (LOD) and limits of quantification (LOQ) were obtained of 0.3 μg/L and 1.1 μg/L for Pb(II) and 0.1 μg/L and 0.4 μg/L for Cd(II), respectively. Relative standard deviations (%RSD) of 20 μg/L Pb(II) and Cd(II) determinations obtained from this method were 2.26 and 1.71%, respectively. The method has percentage recoveries for the determination of those metals in range of 93.3-101.9 for Pb(II) and 99.3-103.7 for Cd(II). Effect of interferences caused by cations commonly found in water lily, especially, Ca(II), Cu(II), Mg(II), Zn(II), Ni(II), Hg(II) and Fe(III) levels were investigated. Cu(II) interference in this method, which could improve the stripping peak signal of Pb(II) and Cd(II) and eliminate Cu(II), 0.01 mM of ferrocyanide added to the solution. This studied method was applied to determine Pb(II) and Cd(II) in water lily stem samples in Thale Noi were found in range of 0.00-0.29 mg/kg and 0.00-0.10 mg/kg, respectively, which lower than the guideline values of edible portions of plants (0.5 mg/kg for Pb(II) and 0.2 mg/kg for Cd(II)) given by the World Health Organization (WHO). This method was validated to the determine the Pb(II) and Cd(II) with ICP-OES and the results were tested by accuracy (t-Test). They were not significant difference at the confidence level of 95%.