Matrix-Independent XRF Methods for Certification of Standard Reference Materials

Abstract

The Spectrochemical Methods Group of the Analytical Chemistry Division at the National Institute of Standards and Technology develops and applies matrix-independent methods for its certification of Standard Reference Materials® (SRM). Such methods are required to achieve accuracy, i.e., to minimize potential sources of analytical uncertainty. This paper delineates a matrix-independent method for X-ray fluorescence spectrometry that uses destructive sample preparation instead of matrix corrections. The method is based on borate fusion of samples and synthesis of calibration standards that closely mimic the complete composition of the fused samples. The method is described in detail and illustrated using recent work on cements and zeolites. A typical uncertainty budget is itemized and sources of uncertainty are discussed. Expanded relative uncertainties are 1 % or lower. The technique is applicable to major, minor and sometimes trace constituents. Excellent agreement is demonstrated with both a classical gravimetric method and instrumental neutron activation analysis.