INDIRECT DETERMINATION OF THE SUM OF CHELONS IN DRINKING-WATERS AND GROUND-WATERS BY ANODIC-STRIPPING VOLTAMMETRY

The complexing ligand EDTA can be determined as its complex with bismu th by indirect anodic stripping voltammetry down to 0.1 mu g/L without a concentration step. Interfering copper and excess bismuth have to b e removed by cation exchange, although in presence of these metals EDT A can be determined down to 0.5 mu g/L only. If NTA, EDTA, and DTPA ar e present simultaneously, the accumulation curves for the correspondin g bismuth-complexes can overlap, preventing a separate determination o f the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also d ominates in surface-waters. Thus it seems to be sufficient to determin e the sum of the three chelons as EDTA (index- of bismuth-complexation ) using suitable electrochemical conditions.