VERMICULITE CLAY MINERAL AS AN EFFECTIVE CARBON-PASTE ELECTRODE MODIFIER FOR THE PRECONCENTRATION AND VOLTAMMETRIC DETERMINATION OF HG(II) AND AG(I) IONS

A vermiculite modified carbon paste electrode (VMCPE) was employed for the in situ preconcentration of traces of Hg(II) and Ag(I) via an ion -exchange route. Heavy metal ions were accumulated in Britton-Robinson (BR) buffer pH 7 for Hg(II) and pH 6 for Ag(I), and afterwards reduce d at -0.7 V vs. Ag/AgCl in the separate measurement solution (BR buffe r pH 5 + 0.05 mom NaNO3) prior to the anodic stripping square wave vol tammetric (ASSWV) detection. For Hg(II) ions, at 15 min accumulation, a linear range from 1.0 x 10(-7) to 8.0 x 10(-6) mol/L was obtained, w ith a 5.7 x 10(-8) mol/L limit of detection. The VMCPE response was li near for Ag(I) ions in the concentration range from 2.0 x 10(-7) to 8. 0 x 10(-6) mol/L, at 10 min accumulation with a corresponding limit of detection of 6.3 x 10(-8) mol/L. The relative standard deviation of t he analytical procedure including accumulation from a 5 x 10(-7) mol/L solution of Hg (15 min) or Ag(I) (10 min), electrolysis, ASSWV detect ion, regeneration and activation of the VMCPE, was 4% (n = 6). The opt imisation of the parameters for the application of the VMCPE in combin ation with ASSWV detection is presented and discussed.