Abstract
A rapid coprecipitation technique using gallium phosphate as a coprecipitant was investigated as a technique for preconcentration of thallium in its atomic absorption spectrometric determination. Gallium phosphate could coprecipitate thallium(III) quantitatively at pH 5. The precipitate which collected thallium(III) was centrifuged and then dissolved in nitric acid. The concentration of thallium(III) in the solution were measured by using electrothermal atomic absorption spectrometry; the concentration of gallium in the solution was also consecutively did by using flame atomic absorption spectrometry. The content of thallium(III) in the initial sample solution could be calculated based on the ratio of the amount of gallium in the final sample solution to that added to the initial sample solution. In the determination, an oxidation process using ammonium peroxodisulfate was required to oxidize thallium(I) to thallium(III) before the coprecipitation because thallium(I) was little coprecipitated with gallium phosphate. Since the rapid coprecipitation technique does not require any filtration and complete collection of the precipitate because the ratio of the recovery of thallium to that of gallium was almost constant regardless of the recovery of the precipitate, the operation for the preconcentration was simple, and the time required for the preconcentration was considerably shortened. The method was applicable to the preconcentration of at least 0.02-0.30 μg of thallium in 100 mL of tap and mineral water samples.
