Direct determination of mercury in sea-water by anodic stripping voltammetry with a graphite electrode

Abstract

In recent determinations of mercury in sea-water, methods such as spectrophotometry [ 1, 21, atomic absorption spectrometry with cold vapour techniques as well as with flameless techniques [ 3, 41, and neutron activation analysis [4, 51 have been employed extensively in conjunction with various pm-treatment procedures. Because of the extremely low concentration of mercury in sea-water (usually a few to 100 ng Hg l-l), the sample size normally taken must be relatively large (O-5-5 1 or more) in order to achieve satisfactory accuracy. Anodic stripping voltammetry (asv.) has been applied to mercury determinations by Perone and Kretlow [ 6] and by Luong and Vydra [ 71, who used, respectively, a graphite electrode and a rotating glassy carbon electrode. The sensitivity of their methods seems to be too low for the direct analysis of sea-water. Allen and Johnson [8] , using a rotating system with a platinum ring and a glassy carbon disc, attained a detection limit of about 10 ng Hg 1-l in the sulfuric acid medium, but the applicability of this method to sea water has yet to be proved. An attempt to apply a.s.v. with the graphite electrode to direct measurements of mercury in sea-water has proved successful when a perchloric acid solution is used as the stripping medium. The procedure described below permits the determination of mercury concentrations as low as 5 ng Hg l-l, in 50-ml samples with minimum pre-treatment.