Certification of Beryllium Mass Fraction in SRM 1877 Beryllium Oxide Powder Using High-Performance Inductively Coupled Plasma Optical Emission Spectrometry with Exact Matching

Abstract

High-performance inductively coupled plasma optical emission spectrometry (HP-ICP-OES) was used to certify the Be mass fraction in National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1877 Beryllium Oxide Powder. The certified value and expanded uncertainty expressed at a 95% confidence level is (0.3576 +/- 0.0024) g/g. To obtain best results, the Be mass fractions, Mn (internal standard) mass fractions, and matrix compositions of the calibration solutions were carefully matched to those of the sample solutions for each individual HP-ICP-OES analysis. This "exact matching" approach was used because experience at NIST has shown that it often affords improved accuracy and precision in HP-ICP-OES analysis. NIST has never published these observations. Due to the toxicity of BeO and the difficulty of containing the very fine powder material, sets of solutions for HP-ICP-OES analysis were prepared by laboratories collaborating with NIST who have the experience and equipment needed to work with the material safely. Each laboratory utilized a unique digestion protocol(s). After preparing the sets of solutions, the collaborating laboratories shipped them to NIST for HP-ICP-OES analysis. NIST provided the collaborating laboratories with solution preparation kits and spreadsheets to help establish traceability of the HP-ICP-OES results to the International System of Units (SI) and to allow exact matching to be accomplished. The agreement observed among the four individual Be mass fraction values determined from the sets of solutions prepared by the collaborating laboratories was 0.074% relative (1s of mean). The excellent agreement provides a measure of confidence in the robustness of each of the digestion procedures, as well as in the certified Be mass fraction value. The analytical benefits of using exact matching for this particular certification were investigated. Results show that exactly matching the matrix compositions of the standards to the samples for each HP-ICP-OES analysis was critical to obtaining the excellent agreement observed among the individual Be mass fraction values and also helped to minimize bias and uncertainty in the certified value. Unlike previous NIST studies, exactly matching the Be and Mn mass fractions of the standards to the samples for this particular certification appears to have had little effect on the data.