Development of the measurement procedure and certified reference material of water mass fraction in a mineral oil

Abstract

The necessity of developing certified reference materials (CRM) for the composition of mineral oil with a certified value of the mass fraction of water, traceable to the State Primary Standard of units of mass fraction and mass (molar) concentration of water in solid and liquid substances and materials GET 173–2017 is revealed proceeding from the review of standardized methods for determining the quality of mineral oils and approved types of reference materials (CRMs). Mineral hydraulic oil MIL-H-5606 of CONOSTAN series manufactured by SCP SCIENCE (Canada) was chosen as the CRM material to control the accuracy of the results of water determination in mineral oils using IR spectrometers. A procedure for reproducing the mass fraction of water in a mineral oil using a standard installation based on coulometric titration according to Karl Fischer method from the composition of GET 173–2017 has been developed. The relative expanded uncertainty (at k = 2) of measurement results of the water mass fraction in mineral oil is 7.1%. The requirements to the metrological characteristics of CRM were formulated: the interval of permissible certified values, the limits of the permissible values of the absolute error at P = 0.95, and the permissible value of the absolute expanded uncertainty at k = 2. The choice of the method of packaging and conditions of CRM storage were analyzed. Taking into account the consistency of the measurement results of the water mass fraction obtained by coulometric titration according to Karl Fischer method and using a Fluid Scan infrared spectrometer manufactured by Spectro Inc., USA, the applicability of CRMs for metrological support of express IR spectrometers was demonstrated.