Precipitate coating on cellulose fibre as sorption medium for selenium preconcentration and speciation with hydride generation atomic fluorescence spectrometry

Abstract

Lanthanum hydroxide precipitate is for the first time coated onto cellulose fibre and serves as a novel sorption medium for separation and speciation of inorganic selenium. A micro-column packed with precipitate-layer-coated cellulose fibre is incorporated into a sequential injection system for selenite retention from a neutral aqueous solution, which is afterwards stripped with a NaBH 4–NaOH solution as eluent. The hydride generation is actuated by merging the eluate and hydrochloric acid downstream, followed by the detection with atomic fluorescence spectrometry. Total inorganic selenium is derived by pre-reduction of selenate and speciation is estimated by difference. The coated precipitate layer can be used for 150 runs for selenium sorption, offering a clear advantage over the conventional precipitation protocols where a large amount of precipitate is dissolved into a small volume of eluent which might interfere with the detection. With a sample volume of 1.0 mL, an enrichment factor of 9.7 and a detection limit of 9 ng L −1 are obtained in a linear range of 0.05–2.5 μg L −1. A sampling frequency of 24 h −1 is achieved along with a R.S.D. of 1.7% at 0.5 μg L −1 Se(IV). The procedure is validated by analyzing selenium in a reference material GBW 10010 (rice) and a human hair sample. It is further demonstrated by speciation of inorganic selenium in surface water samples by pre-reduction of selenate.