Differential-pulse polarographic determination of zinc and manganese in various pharmaceutical and biological samples after adsorption of their morpholine-4-carbodithioates on microcrystalline naphthalene

Abstract

A highly selective, sensitive, rapid and economical differential-pulse polarographic method was developed for the simultaneous determination of trace amounts of zinc and manganese in various standard alloys and pharmaceutical, biological and environmental samples after adsorption of their morpholine-4-carbodithioates on microcrystalline naphthalene in the pH range 4.1–9.0 for manganese and 6.5–10.2 for zinc. After filtration, the metal complexes are shaken with 10 ml of 1 mol l^–1 HCl and determined simultaneously using a differential-pulse polarograph. There is no need to remove naphthalene from the solution. Dissolved oxygen is removed by adding a few millilitres of 4% NaBH₄ solution. The detection limits are 0.06 ppm for Mn and 0.1 ppm for Zn (signal-to-noise ratio = 2). Linearity is maintained in the concentration ranges 0.06–10 ppm for Mn and 0.1–12 ppm for Zn with a correlation factor of 0.9997 and relative standard deviations of 0.95 and 0.81%, respectively. The characterization of the electroactive process included an examination of the degree of reversibility. Various parameters such as the effect of pH, volume of aqueous phase and interference of a number of metal ions on the determination of manganese and zinc were studied in detail to optimize the conditions for their simultaneous determination (based on the large difference in their E_p values) in various biological, pharmaceutical and environmental samples.