Direct determination of ultratraces of thallium in water by flow-injection-differential-pulse anodic stripping voltammetry

A direct method for the determination of thallium concentrations on the order of 10(-11) M was developed. Long deposition times (up to 2 h) performed in the flow system with circulation of the analyte ensured the necessary preconcentration. A large volume sample (100 ml) was used to prevent depletion of thallium during deposition. The flow-through cell of a wall-jet type with the mercury film electrode based on an epoxy resin impregnated graphite was used. The detection limit of the method is 2 ng l(-1) at 90 min preconcentration). A spike of 0.05 M EDTA was found to be an effective preservative for fresh water samples. Numerous examples of determinations of thallium in tap water and river water are given.