SIMPLIFIED STRIPPING POTENTIOMETRY METHODOLOGY - APPLICATION TO THE DETERMINATION OF LEAD IN WINE

Wine samples (120/muL) were pipetted into a 480 muL matrix modifying solution in a disposable Eppendorff tube. The modifying solution was comprised of hydrochloric acid, Hg(II), Ca(II), Al(III), Mn(II), 10% v/v Triton X-100, 25% v/v EtOH, and Bi(III) as an internal standard. The mixture was transferred to a novel sample rotation assembly, used in combination with a cylindrical combined glassy carbon working electrode and Ag/AgCl reference and counter electrodes, and analyzed for 3 minutes by means of stripping potentiometry (SP). The analytical procedure, including control of all instrumental parameters and evaluation of the results, was performed fully automated using a commercial stripping analyzer and accompanying software. Calibration was performed using two aqueous standards, and due to the use of the internal standard, the same calibration curve could be used indefinitely. The relative precision was estimated to 5% and the detection limit to 3 mug/L. Good agreement was obtained between the results obtained by the proposed method and those obtained by isotope dilution inductively coupled plasma-mass spectrometry (ICP-MS) in the analysis of four red and four white wine samples, ranging in lead concentration from 18 to 151 mug/L, with the maximum relative difference between the two techniques being 11.5%.