ABSTRACT
RATIONALE: Preparation of in-house reference materials (RMs) is an important aspect of light element stable isotope analysis. While some relevant information is available, there is as yet no clear set of guidelines available covering all aspects of in-house production and characterization of RMs. METHODS: To address this need, the experience of production of certified reference materials under accreditation to ISO 17034:2016 and ISO/IEC 17025:2017 has been distilled into guidance for production of in-house RMs that are fit-for-purpose. RESULTS: The guidance provided covers five areas: (i) planning; (ii) material considerations including preparation, packaging, and storage; (iii) measurements and assessments; (iv) value and uncertainty assignment; and (v) monitoring and use. CONCLUSIONS: In-house RMs prepared by following this guidance can be used to provide traceability to measurement results when used for normalization or for quality control and/or assurance purposes.
ABSTRACT
BACKGROUND: This paper describes the preparation, analysis and certification of four frozen human serum certified reference materials (CRMs) containing creatinine and the electrolytes calcium, lithium, magnesium, potassium and sodium. These materials have been prepared to give concentrations of these analytes that cover the currently accepted analytical range. METHODS: The analysis of the materials for certification purposes has been carried out using methodology traceable to primary standards, and which is acceptable as a reference method. The certification methods include liquid chromatography-mass spectrometry (LC-MS) with exact-matching isotope dilution calibration (EM-IDMS) for creatinine, inductively-coupled plasma optical emission spectroscopy (ICP-OES), ICP-MS and isotope-dilution inductively-coupled plasma mass spectroscopy (ID-ICP-MS) for the electrolytes. RESULTS: The uncertainties estimated for these certified values include a component from the characterization measurements, as well as contributions from possible inhomogeneity and long-term instability. The certified values have been corroborated by measurements obtained in a major UK External Quality Assessment scheme, which have, with the exception of the determination of creatinine at a particularly low concentration, given excellent agreement. CONCLUSIONS: The materials are intended for use by pathology laboratories and manufacturers of in vitro diagnostic (IVD) kits for validation of existing routine methodology to a traceable standard, which will promote harmonization between the different methods, instruments and IVD kits used in these laboratories.
