Flow injection on-line spectrophotometric determination of thorium(IV) after preconcentration on XAD-4 resin impregnated with oxytetracycline

Abstract

A very sensitive, selective and simple flow injection time-based method was developed for on-line preconcentration and determination of thorium(IV) at micro g L–1 levels in environmental samples. The system operation was based on thorium(IV) ion retention at pH 4.0 in the minicolumn at a flow rate of 15.2 mL min–1. The trapped complex was then eluted with 3.6 mol L–1 HCl at a flow rate of 4.9 mL min–1. The amount of thorium(IV) in the eluate was measured spectrophotometrically at 651 nm using arsenazo-III solution (0.05 % in 3.6 mol L–1 HCl stabilized with 1 % triton X-100, 4.9 mL min–1) as colorimetric reagent. All chemical, and flow injection variables were optimized for the quantitative preconcentration of metal and a study of interference level of various ions was also carried out. The system offered low backpressure and improved sensitivity and selectivity. At a preconcentration time of 60 s and a sample frequency of 40 h–1, the enhancement factor was 97, the detection limit was 0.25 μg L–1, and the precision expressed as relative standard deviation was 1.08 % (at 50 μg L–1), whereas for 300 s of the preconcentration time and a sample frequency of 10 h–1, the enhancement factor of 357, the detection limit (3σ) of 0.069 μg L–1 and the precision of 1.32 % (at 10 μg L–1) was reported. The accuracy of the developed method was sufficient and evaluated by the analysis of certified reference material IAEA-SL-1 (Lake Sediment) and spiked water samples.