Direct determination of gallium in bauxite employing ICP OES using the reference element technique for interference elimination

Abstract

The determination of gallium in bauxite samples using inductively coupled plasma optical emission spectrometry (ICP OES) is complicated because aluminum in high concentrations interferes strongly in this analysis. This paper proposes a direct method for the determination of gallium in bauxite samples by ICP OES employing the reference element technique for correction of aluminum interference. The experimental parameters: hydrochloric acid concentration used for preparation of gallium standard solutions and bauxite samples, nebulizer flow rate and RF power were optimized by multivariate technique. Firstly, a factorial design was performed for preliminary evaluation. Afterward, a Box–Behnken design was also performed for determination of the critical conditions for these factors. Box–Behnken design is a chemometric technique that in the last years has been often used for optimization of analytical methods. The procedure proposed using the established conditions (in presence of yttrium and/or scandium as reference element) allows the determination of gallium with limits of detection and quantification of 0.0006 and 0.0019 mg L− 1 and precision expressed as relative standard deviation of 4.37 and 1.78% for bauxite samples with gallium content of 21.00 and 36.00 mg Kg− 1. For sample mass of 0.20 g the limits of detection and quantification are 0.042 and 0.140 mg Kg− 1, respectively. The accuracy of the method was evaluated and confirmed using standard reference materials of alumina and marine sediment. The method proposed was applied for the determination of gallium in five bauxites, having yttrium and scandium as reference element, being that the sample preparation was done employing microwave-assisted digestion. The gallium content in the five samples varied from 19.70 to 100.59 mg Kg− 1. These concentrations are in agreement with the data reported by literature.