Interfering effects of different substances existing in environmental matrix on As determination by stripping voltammetry

Abstract

This paper evaluates the effects of the interferents on the method of determination of the As species through stripping voltammetry, using as a working electrode the dropping Mercury electrode. The interferents found in the determination of As through the voltammetric methods can be classified in three categories: the metallic ions which can form intermetallic compounds with As (Cd) that are accumulated on the hanging Mercury electrode; compounds with tensioactive properties which can be absorbed on the surface of the electrode or which can absorb As on their surface; compounds which can determine complexes or precipitates with As (Fe, Zn, Mn). The effected studies led to the following results: iron interferes in the correct evaluation of the result at concentrations higher than 13000µg/l, concentration corresponding to a As(III):Fe 1:4200 ratio; zinc presents interferences over 5000 µg/l values corresponding to a As(III):Zn ratio of 1:1700; the interference of Cadmium is very strong over 150 µg/l values; the tensioactive compounds over 500 µg/l concentrations, corresponding to a As(III) ratio: the tensioactive compounds of 1:167 completely block the determination of arsenic species. The samples were submitted to the UV digestion and then cysteine was added in order to determine the total arsenic, but the results were totally unsatisfactory; mangan proved not to have interference effects even over concentrations of 30mg/l. following these results, as well as the previous studies, we came to the conclusion that the method can be successfully applied on surface and drinking waters or on waters with low metal concentrations, as well as on waters with a reduced organic charge.