Examination of Interferences in the Stripping Voltammetric Determination of Trimethyllead in Seawater by Polarography and Mercury-199 and Lead-207 Nuclear Magnetic Resonance Spectrometry

Detailed Investigations using polarography and pulse Fourier transform multlnuclear magnetic resonance spectrometry show that mercury(II) Ions react with trimethyllead cations In seawater and other aqueous media according to the equation Hg²⁺ + [(CH₃)₃Pb]⁺ → CH₃Hg⁺ + Pb²⁺ + 2CH_3·. This reaction may Invalidate proposed methods for determining trimethyllead by anodic stripping voltammetry at a glassy carbon electrode (In situ deposition of mercury) since mercury(II) Ions are added In relatively high concentrations to the sample solution as part of the analytical procedure. While stripping techniques at the hanging mercury drop electrode do not suffer from this kind of Interference, under oxygen-free conditions, transalkylation reactions at the electrode surface Interfere with the direct determination of [(CH₃)₃Pb]⁺ In the presence of Inorganic Pb(II) and double standard addition experiments are required to simultaneously determine both forms of lead. These experiments are Inherently Inaccurate and chromatographic or other separation techniques are recommended as a precursor for determining [(CH₃)₃Pb]⁺ In the presence of Inorganic Pb(II).