Analytical Sciences

Characterization of Certified Reference Material for the Quantification of Water in Bioethanol

Shinsuke INAGAKI, Masahiko NUMATA, Nobuyasu HANARI, Ryoko IWASAWA, Mayumi MATSUO, and Kenji KATO

National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan

The National Metrology Institute of Japan has issued a certified reference material of bioethanol (NMIJ CRM 8301-a) for the quantification of water, methanol, sulfur, and copper. This paper presents technical details for the characterization of the water in NMIJ CRM 8301-a. The characterization was performed using coulometric and volumetric Karl-Fischer (KF) titrations. To reduce moisture absorption, sample handling and KF titration were performed in a glove box under a dried nitrogen atmosphere. In addition, a rubber cap with a three-way valve was attached to the ampoule immediately after opening so as to minimize the influence of moisture. Sample aliquots were obtained using a gas-tight microsyringe through the valve, and injected into the KF cell as soon as possible. The certified value of water obtained from coulometric and volumetric KF titrations was 1.688 mg g⁻¹, and the expanded uncertainty (coverage factor, k = 2) was 0.028 mg g⁻¹. This CRM would be suitable for the monitoring of water in bioethanol and similar matrices.

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