Differential pulse polarographic determination of lead (II) in complex materials after adsorption of its trifluoroethylxanthate-cetyl-trimethylammonium ion-associated complex on microcrystalline naphthalene or on trifluoroethylxanthate-cetyltrimethyl

摘要

Lead(II) is adsorbed as lead trifluoroethylxanthate (TFEX)-cetyltrimethylammonium (CTMA) ion pair complex on microcrystalline naphthalene quantitatively in the pH range 4.50-10.50. In the absence of cetyltrimethylammonium as the counter ion, the adsorption is only 80%. Lead(II) is desorbed with HCl and determined with a differential pulse polarograph. Dissolved oxygen is removed by adding 3 ml of 4% NaBH_4 solution. Alternatively, lead(II) can be quantitatively adsorbed on TFEX-CTMA-naphthalene adsorbent packed in a column at a flow rate of 1-2 ml min~(-1). Well defined peak has been obtained in this medium at -0.40 V versus S.C.E. Cyclic voltammetric, differential polarographic and D.C polarographic studies indicate that lead(II) has been reduced reversibly in a two-electron reduction under these conditions. The detection limit is 0.20 mug ml~(-1) at the minimum instrumental settings (signal-to-noise ratio = 2). Linearity is maintained in the concentration range 0.5-16.40 mug ml~(-1) with correlation factor of 0.9997 and a relative standard deviation of +- 1.07%. Various parameters such as the effect of pH, volume of aqueous phase, flow rate and the interference of a large number of metal ions and anions on the determination of lead(II) have been studied in detail to optimize the conditions for its trace determination in various standard alloys, standard biological materials and environmental samples.