Suitability of open system digestions for the determination of thallium in environmental samples

Abstract

Abstract The determination of thallium (T1) content in environmental samples is important because of the high toxicity of this metal. Fast and accurate analytical methods are required. Therefore, various open system digestion methods were investigated for the rapid determination of T1 in plant and soil samples. For soils, all procedures were tested by analysis of two National Institute of Standards and Technology (NIST) standard reference materials. For plant samples, the accuracy of the methods was evaluated using three digested materials, with and without a standard addition of 1 μg T1 on each one before digestion. Thallium was determined directly on digested solutions, without separation or preconcentration procedures and with two electrothermal atomic absorption spectrophotometers (ETAAS). Results showed that only one procedure was suitable. The method is based on the solubuization of sample by heating a solution made from 30% hydrogen peroxide (H2O2) and 65% nitric acid (HNO3). The procedure gave good agreement with the NIST certified concentration for soils and adequate recoveries for plant samples. No further hydrofluoric acid (HF) digestion was required on soils samples. Thallium concentrations numerically were higher but the increase was not significant. Volatility of T1 compounds was a drawback with the other digestion methods (aqua regia digestion, HNO3‐H2SO4 digestion and sample dry‐ashing at 480°C) where Tl losses occurred. After volumation in flasks, changes in Tl concentration in digested solutions were not detected during 10 days. The detection limit for the wet digestion method in 10% HNO3 is 60 ng TI/L which is adequate with other investigations.