Determination of thallium by inversion voltammetry

3 Determination of thallium by inversion voltammetry Maceration and extraction 

To a beaker containing 10 to 250 ml of the water sample add 2 ml cone. H2SO4 and 2 ml cone. HNO3 to oxidize organic substances, and subsequently evaporate the solution. If higher levels of organic substances are 

Evaporate the combined extracts to dry matter in a 50 ml beaker over a water bath. Oxidize this evaporation residue 1 to 2 times with a few drops of HNO3 fumans and again evaporate to dry matter. 

To determine thallium by inversion voltammetry, pick up the residue from the maceration process in the beaker with 20 ml of 0.05 m EDTA, expose to nitrogen and reduce cathodically on a dropping mercury electrode. The amalgam thus produced is subsequently dissolved anodically. The current-voltage curve is registered with a recording instrument. 

In many matrices, surface-active substances can hinder analysis by mechanically inhibiting access of the depolarizer to the electrode or by influencing electrode reduction during measurement. In addition to a fall in peak currents, a shift in peak potentials can frequently also be observed. A breakdown into several peaks is possible here with considerable distortion of the current-voltage curves. These disturbances are however eliminated by maceration. 

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