A reference installation based on thermo-gravimetric analysis with mass-spectrometric detection as a part of the state primary standard GET 173

The issue of assuring the traceability of the results of water determination in solid and liquid substances and materials is discussed. The stages of development and improvement, as well as composition of the State primary measurement standard of mass fraction and mass (molar) concentration of water in liquid and solid substances and materials (GET 173) are considered. The problems of the limited applicability of GET 173 in case of separation of water with different binding energies and impossibility of conducting qualitative analysis of non-water volatile compounds during heating of substances and materials are revealed. The results regarding upgrading of GET 173 due to incorporation of additional reference installation which implements the methods of thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and mass-spectrometry (MS) are presented. The composition and operating principle of the new reference unit are described. An algorithm for estimating the uncertainty of reproducing a unit mass fraction of water using this reference facility is presented and sources of the uncertainty are identified. The results of the experiment on determination of the lower limit of the reproduction range for a unit water mass fraction are presented. We also present the results of comparisons regarding determination of the water mass fraction in crystalline hydrates obtained using the improved State primary standard and high-precision installations of the metrological and leading sectorial research institutes of the European countries. The results of developing a certified reference material of water mass fraction in sodium molybdate dihydrate (Na₂MoO₄ · 2H₂O CRM UNIIM 10911–2017 intended for metrological support of measurement instruments and measurement procedures based on thermo-gravimetric method are presented. Additional possibilities which result from the introduction of a new reference installation into the state primary standard of GET 173 are disclosed: identification and the quantification of non-water volatile components, adjustment of drying regimes both in laboratory and process conditions, determination of water content as one of the main impurities in estimating mass fraction of the main component of high-purity substances.

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