Preconcentration method for the determination of thorium in natural water by wavelength dispersive X-ray fluorescence spectrometry

The preconcentration of thorium from natural water and its determination directly by wavelength dispersive X-ray fluorescence spectrometry (WDXRF) were attempted. The first step consists of thorium preconcentration from slightly acid solutions on polyurethane foam (PUF) loaded with 2-etilhexylphosphonic acid (EHPA) reagent as solid phase. PUF held up to 50% (w/w) of the reagent and the preconcentration was maximum at the acidity of 0.25 mol(.)l(-1) hydrochloric solution. Sorption on PUF had fast kinetics and 4.0 and 10 mg(.)l(-1) detection and quantitation limits of thorium were achieved, respectively, as well as a R.S.D. of 4.2% at 21.7 mg(.)l(-1). This method was successfully applied to natural water analyses. The results were in good agreement with reference values of water samples at 95% confidence level.