Determination of thallium in soils by flame atomic absorption spectrometry

A method is described for the determination of Tl in soils by FAAS, involving extraction of Tl from 5 g of soil by digestion with HClO₄/HNO₃ followed by separation of the extracted Tl into 5 mL of diisopropylether from HBr solution, including Ce(SO₄)₂. Tl in the organic phase is determined by direct aspiration into the spectrophotometer. The percentage relative standard deviation (% RSD) for 5 replicate samples is about 1%. The detection limits (S/N = 3) of this method are 0.001 mg/L for aqueous solution and 0.02 mg/kg DW for soil, when 50 mL of soil solution corresponding to 2.5 g soil are used. The Tl concentration even of unpolluted soils can be determined. The method was shown to be unaffected by the presence of various ions in soil and was able to recover nearly 100% Tl added to soils. The arithmetic mean (range) of 18 Japanese unpolluted surface soils was 0.33 (0.10–0.56)mgTl/kg DW.