Thallium determination at the single picomole per liter level by flow-injection differential-pulse anodic stripping voltammetry

The flow-injection differential-pulse anodic stripping voltammetric (FI-DP-ASV) procedure has been developed for the determination of thallium concentration of the order of the single pM. Due to the analyte preconcentration at the electrode, DPASV is among the leaders in competition for achieving a detection limit as low as possible. The enrichment factor can be easily regulated by the duration of the preconcentration time. A DPASV measurement in a flow-injection system enables the circulation of an analyzed sample and a medium exchange when preconcentration is completed. This approach ensures significant improvement of a background current. The measurements were performed in a cell of the wall-jet type containing the mercury film electrode. One hour preconcentration was used for the determination of the lowest thallium concentrations. The developed method provides the opportunity to determine thallium in real environmental samples at the single pM level with the detection limit equal to 0.25 pM and RSD equal to 8.2%. This is by more than one order of magnitude better than the lowest detection limit reported in the literature (5 pM). Additionally, the medium exchange resulted in the improvement of the measuring accuracy, which was evidenced by the application of a certified reference material.