Influence of reactant adsorption on limiting currents in normal pulse polarography: Part III. Experimental illustration of some basic effects for the reduction of methylene blue and lead(II) in humic acids at the SMDE

Abstract

Experimental support is presented for the applicatility of our newly developed analytical theory [J. Electroanal. Chem., 135 (1982) 13; 162 (1984) 55] for NPP limiting currents influenced by reactant adsorption. For methylene blue the variation of the current with pulse duration was shown to correspond with an adsorbed monolayer of the dye being reduced at potentials more positive than the reversible half-wave potential. Drop time variation at high methylene blue concentration was utilized to find the maximum coverage (Г max=2.5×10 −10 mol cm −2), confirming the presence of a bilayer. On the whole, the agreement between theory and experiment is satisfactory. The reduction of lead(II) from humic acids solutions is used to verify the theoretically predicted enhancements (up to tens of percent) of the adsorption-influenced NPP limiting current as imposed by sphericity of the electrode.