CARBON-PASTE ELECTRODES PLATED WITH A GOLD FILM FOR THE VOLTAMMETRIC DETERMINATION OF MERCURY(II)

Carbon pastes of different compositions were tested as supports for go ld film electrodes. A paste containing highly-viscous silicone oil as a binder was found the most suitable. Experimental conditions were opt imized in order to develop a differential pulse anodic stripping volta mmetric method for the determination of mercury in water samples. In a supporting electrolyte containing HNO3 (0.1 mol/L), KCl (0.02 mol/L) and tetrachloroaurate(III) for in situ plating with a gold film, the r esponse of Hg was found to be linear in a concentration range from 1x1 0(-9) up to 2.5x10(-7) mol/L (0.2-50 mu g/L; accumulation potential +0 .2V (vs. Ag/AgCl); accumulation time 30 s-5 min) with a detection limi t of about 2.5x10(-10) mol/L (50 ng/L) after accumulating for 30 min. Reliability of the method depended mainly on the concentration of Au-I II in the electrolyte which had to be chosen adequately, with respect to the concentration level of Hg-II in the sample. Interferences from some ions with the determination of mercury were also studied. The met hod was tested on both model and real samples and the results agreed w ell with those obtained by reference determinations.