Evaluation of standard measurement uncertainty from method validation data for the ICP-OES determination of Nb, Ta, Fe, Mn, Ti, Sn, Zr, and W in niobite-tantalite samples

Abstract

A procedure is described for the evaluation of standard measurement uncertainty from validation data by the GUM “bot-tom-up” approach for the determination of Nb, Ta, Fe, Mn, Ti, Sn, Zr, and W in niobite-tantalite (columbite-tantalite) mineral samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Sample preparation was carried out by fusion using a phosphate salt mixture. The method was validated using a single laboratory approach by assessing analytical performance characteristics like specificity, linearity, range, accuracy, and precision. The method showed good specificity and no spectral interferences were observed for all elements determined. Relative standard deviation (RSD) values ranging from 0.9 to 8.3% were obtained for the repeatability studies with values ranging from 2.5 to 14.3% for the intra-lab reproducibility studies. Accuracy was established by application of the method to two niobite-tantalite certified reference materials (CRMs) and also by comparison of the results obtained for a niobite-tantalite sample by the present method with those obtained by an alternate method. The validated method was applied to the determination of Nb, Ta, Fe, Mn, Al, Ti, Sn, Zr, and W in selected niobite-tantalite samples from India. The measurement uncertainty (MU) associated with the quantitative determination of Nb, Ta, Fe, Mn, Ti, Sn, Zr, and W in a typical niobite-tantalite sample was evaluated using the GUM “bottom-up” modelling approach. The MU results were compared with those obtained using the Horwitz equation and an uncertainty budget presented in this paper.