Radiometric trace analysis of lead with diethyldithiocarbamate and 204T1

Two methods for the determination of submugram amounts of lead are described. (A) Lead is selectively extracted with carbon tetrachloride from an alkaline solution containing exccss diethyl-dithiocarbamatc (DDC) and cyanide. Traces of DDC arc back-extracted. The lead in the DDC complex is exchanged with ²⁰⁴Tl and the amount of ²⁰⁴Tl in the organic layer acts as a measure for the lead. The limit of sensitivity is 0.1 mg; the standard deviation is 11% (for 0. 1μg). Bismuth and thallium interfere; their influence can be accounted for with the help of EDTA, however. (B) Excess cyanide is added to the alkaline sample solution and lead is exchanged selectively with ²⁰⁴Tl by shaking with a CHCl₃ solution containing ²⁰⁴T1(DDC)₁. As the process is not 100% effective (with a reasonable excess of the thallium complex) isotope dilution with ²¹⁰Pb is also carried out. The amount of ²⁰⁴Tl in the aqueous layer acts as a measure for the exchanged lead. The limit of sensitivity is 0.05 μg and the standard deviation is 12% (for 0.05 μg). Bismuth and thallium must be removed in advance, e.g. by anion exchange.