Voltammetric determination of lead at chemically modified electrodes based on crown ethers

The feasibility of fabricating lead-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and 40%(v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The thus-formed electrodes were able to bind Pb(II) ions chemically, and gave better voltammetric responses than unmodified ones. The crown ethers studied and compared were 18-crown-6 and dibenzo-18-crown-6. With a 5% 18-crown-6 CME, Pb(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.02 ppm. It was possible to selectively pick up W(II) from a solution of several other ions at an open circuit through complexation. A simultaneous analysis of Cu(II) and Pb(II) was also attempted. By differential pulse anodic stripping voltammetry Pb(II) could be quantified over the range of 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Ag(I), Fe(III), Ca(II) and Mg(II) was also studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.