A case study for the provision of measurement traceability and measurement uncertainty for the South African reference materials

Abstract

The South African Reference Materials (SARMs) have traditionally been certified through interlaboratory studies involving reputable national and international laboratories. The ISO definition of a Certified Reference Material (CRM) has changed recently. In view of these changes re-certification of the SARMs with the use of primary methods to provide measurement traceability and complete evaluation of the uncertainties associated with the methods are urgently needed. The CSIR-National Metrology Laboratory of South Africa (CSIR-NML) has embarked on a project to re-certify some of the rock type South African Reference Materials (SARM 3 and 4) for selected trace elements using the primary method of isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). Analysis data published in the literature for these SARMs since their production and certification in 1978 was also collected and critically evaluated (data due to be published). Based on this work, new recommended values with associated expanded uncertainties are proposed for some trace elements of SARM 3 and SARM 4.