Characterization of water in methylcyclohexane as a certified reference material for determination of trace water content in liquids

To ensure the accurate measurement of the water content in various materials, certified reference materials (CRMs) which are traceable to the International System of Units (SI) are required. The National Metrology Institute of Japan (NMIJ) has developed a CRM, water in methylcyclohexane (0.02 mg g(-1)), for quality control of trace water analyses in liquids. The water content of the CRM was determined by coulometric Karl Fischer titration as a primary method of measurements. The traceability of the electric charge applied on the titration was ensured to realize metrological traceability of the certified value to the SI. The uncertainties due to the analytical method, homogeneity, and long-term and short-term stabilities were evaluated and reflected in the uncertainty of the certified value. The certified value of the CRM was 0.018 mg g(-1) and its expanded uncertainty, calculated using a coverage factor of k = 2, was 0.005 mg g(-1). The new CRM can be applied for the validation of measurement instruments and procedures used in analyzing trace water. The technical details of the characterization of water in NMIJ CRM 4229-a are described in this paper.