Certification of water content in NMIJ CRM 4222-a, water standard solution 0.1 mg g−1, by coulometric and volumetric Karl Fischer titration

Abstract

The precise determination of water content is a very important issue and in high demand in many fields. To ensure precise and reliable measurements, certified reference materials (CRM) of water standards, whose concentrations are traceable to the International System of Units (SI), are required. The National Metrology Institute of Japan (NMIJ) has issued a CRM of water in mesitylene (0.1 mg g⁻¹) (NMIJ CRM 4222-a), with a very small uncertainty, for use in controlling the quality of analyses of trace water contents and confirming the validity of Karl Fischer (KF) titrators. This CRM is homogeneous, stable and low-hygroscopic under normal laboratory conditions; therefore, complex sample handling is not required. Characterization of the CRM was performed by coulometric and volumetric KF titrations. The certified value of the CRM (mass fraction of water) is 0.134 mg g⁻¹, and its expanded uncertainty is 0.004 mg g⁻¹ with a coverage factor of 2, and is metrologically traceable to SI. We describe the measurement procedures and assays of trace water contents with linkage to SI and the technical details of the characterization of water in NMIJ CRM 4222-a. The developed CRM is particularly suitable for the quality control and validation of coulometric KF instruments and will be valuable in analyzing trace water contents.