EFFECT OF SODIUM DODECYL-SULFATE ON THE MEASUREMENT OF LABILE COPPER(II) SPECIES BY ANODIC-STRIPPING VOLTAMMETRY IN THE PRESENCE OF HUMIC-ACID

The addition of sodium dodecyl sulphate (SDS) was found to be advantageous in measuring uncomplexed labile copper(II) species in the presence of humic acid (HA) by anodic stripping voltammetry with a thin mercury film glassy carbon electrode. If HA is present in the solution, the anodic peak of labile copper(II) species is broadened because of the adsorption of HA on the electrode. However, by adding SDS, a sharp peak was obtained and the peak area increased by about 30% because the adsorption of HA on the electrode was prevented. This was verified by electrocapillary curves in which SDS rather than HA become strongly adsorbed on the electrode. Moreover, this method was applied to the evaluation of copper(II) complexing abilities (conditional stability constants and complexing capacities) of HA by copper(II) titration. The copper(II) complexing capacities of HA evaluated in the presence of SDS were 16% smaller values than those in the absence of SDS.