Selective determination of thorium in water using dual-wavelength β-correction spectrophotometry and the reagent 4-(2-pyridylazo)-resorcinol

Abstract

A simple, fast, low cost, and precise direct β-correction spectrophotometric method was developed for thorium determination in water. The method is based on the reaction of Th(IV) with 4-(2-pyridylazo)-resorcinol (PAR) in aqueous solution of pH 5–6 and measuring the absorbance of the resulting red-colored complex at λmax 497 nm. The effective molar absorptivity of the Th(IV)-PAR complex was 2.52 × 104 L mol−1 cm−1. Beer’s law and Ringbom plots were obeyed in the concentration range 0.04–2.0 and 0.07–1.2 μg mL−1 of thorium ions using β-correction spectrophotometry, respectively. The limits of detection and quantification of Th(IV) were 0.02 and 0.066 μg mL−1, respectively. The developed method was applied for the analysis of thorium in certified reference material (IAEA-soil-7), tap-, underground- and Red-sea water samples. The validation of the method was also tested by comparison with data obtained by ICP-MS. The method is convenient, less sensitive to common interfering species and less laborious than most of published methods. The statistical treatment of data in terms of Student t-tests and variance ratio f-tests has revealed no significance differences. The structure of the Th(IV)-PAR complex was determined with the aid of spectroscopic measurements (UV–Visible and Fourier Transform Infrared Spectroscopy).