Optimization of the operating conditions using factorial designs for determination of uranium by inductively coupled plasma optical emission spectrometry

Abstract

A critical evaluation of the determination of uranium by inductively coupled plasma optical emission spectrometry was performed using factorial designs (23) involving the factors: acid concentration, radio frequency power and nebulizer gas flow rate. All of the experiments in this study were made for five emission lines, in the presence of nitric and hydrochloric acid. The results demonstrated that, between nitric and hydrochloric acid, the determinations in the presence of nitric acid were most sensitive. The factorial design showed that the nebulizer gas flow rate was the most significant among the factors studied for the five emission lines. Calcium in concentrations of 10 mg L−1 was observed to cause suppression of the emission intensity for some lines. Iron (at least up to 10 mg L−1) did not interfere in the emission intensity of uranium across the five lines studied. Another experiment evaluated simultaneously the effect of 13 other elements, and the results demonstrated that these elements did not affect the emission intensity of uranium for the lines chosen. The optimized method, using the line at 385.957 nm, allows the determination of uranium with limit of quantification of 31 μg L−1 and precision expressed as RSD lower than 2.2% for uranium concentrations of either 500 or 1000 μg L−1. The accuracy was confirmed by analysis of two laboratory reference materials. The developed method was applied to the determination of uranium in an industrial effluent collected from uranium-producing mine in Caetite City, Brazil. The sample was analyzed by inductively coupled plasma mass spectrometry ICP-MS, and the observed recovery was satisfactory.