Study of the complexation chemistry and speciation of thallium for on-line preconcentration with immobilised quinolin-8-ol

Abstract

The effects of various buffering reagents and pH conditions were investigated by flame atomic absorption spectrometry to optimise complexation of T13+ with quinolin-8-ol (8-Q), immobilised on controlled-pore glass beads in a 5-cm column. As Tl3+ is a softer acid than the other trivalent cations of the Group III elements, the effects of the buffers are different from those observed previously for Al3+, Ga3+ and In3+. A mixed buffer of 0.1 mol l−1 acetate and 0.1 mol l−1 ammonium chloride at pH 10 proved most successful, although 0.1 mol l−1 maleate was also satisfactory over a pH range of 4–10. As thallium normally exists as Tl+ in solution, an oxidation method was developed to convert the ions to Tl3+, which is more efficiently complexed by 8-Q. Addition of 1–10 μl of bromine per 100 ml of sample was sufficient to oxidise Tl+ without heating. Excess bromine was removed by addition of phenol. With a flow-rate of 6 ml min−1, the detection limit of Tl3+ is 3 ng ml−1, for a 3-miri preconcentration time. The enrichment factor under these conditions is 55 and the characteristic concentration is 2 ng ml−1. The major ions in sea water did not interfere with Tl3+ preconcentration and the tolerable limits of Fe3+, Cu2+ and Al3+ are high enough to permit analysis of river and sea waters. The method was applied successfully to the determination of thallium in potassium-enriched table salt. It was also shown that the concentrations of Tl+ and Tl3+ in a solution can be derived using the described procedure, allowing speciation of inorganic thallium.