Operational speciation of thallium in environmental solid samples by electrothermal atomic absorption spectrometry according to the BCR sequential extraction scheme

Electrothermal atomic absorption spectrometry was applied to the determination of extractable Tl in soil, sediment and fly ash certified reference materials (certified only in total Tl content) following the application of the BCR sequential extraction scheme. Strong matrix interference due to the presence of chloride arising from the hydroxylamine hydrochloride reagent used for leaching the reducible phase was observed. Thermal programmes were optimised for atomisation of Tl from aqueous standards, matrix-matched standards with extractants and real extracts obtained after treatment using the above method. In order to efficiently stabilise Tl for its determination in the acid-soluble and oxidisable fractions, 8 µg Pd were needed as a matrix modifier. The depressive interference caused by chloride required the use of 8 µg Pd + 8 µg ascorbic acid for determination of Tl in the reducible and residual phases. Application of stabilised temperature platform conditions in conjunction with a transverse-heated atomiser and longitudinal Zeeman background correction allowed calibration to be performed with aqueous standards in the acid soluble and oxidisable phases, whilst the standard additions technique was mandatory in the reducible and residual phases in order to achieve accurate results. Low extractability of Tl was observed in most of the analysed samples, thus indicating a low mobility for this metal. Between-batch precision values were lower than 5%. The LOD of Tl when determined in BCR extracts was 0.05 mg kg−1.