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 reduced at -0.7 V vs. Ag/AgCl in the separate measurement solution (BR buffer pH 5 + 0.05 mom NaNO3) prior to the anodic stripping square wave voltammetric (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, with a 5.7 x 10(-8) mol/L limit of detection. The VMCPE response was linear 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 the analytical procedure including accumulation from a 5 x 10(-7) mol/L solution of Hg (15 min) or Ag(I) (10 min), electrolysis, ASSWV detection, regeneration and activation of the VMCPE, was 4% (n = 6). The optimisation of the parameters for the application of the VMCPE in combination with ASSWV detection is presented and discussed.