The thermophysical properties of gaseous fuel, including the calorific value and the Wobbe index, are one of its main properties for industrial use. The correctness of measurements of the volumetric energy of gas combustion is currently ensured by using sets of certified reference materials of the lowest volumetric energy of combustion based on pure gases: hydrogen, methane, ethane and propane GSO 11662–2020 / GSO 11665–2020 and gaseous mixtures GSO 11904–2022 / GSO 11907–2022 with metrological traceability to GET 16–2018. However, it becomes necessary to measure the gas relative density to air with established traceability to GET 18–2014 when determining the Wobbe index.

The purpose of this research is to improve the accuracy of the pycnometer method for measuring the density of gases for further development and creation of metrological assurance in the field of measuring the Wobbe index.

In the course of the research, an analysis of existing methods for determining the gas density was performed, as a result of which the pycnometer method set forth in GOST 17310–2002, GOST 34721–2021 was taken as the basis for the developed method. The uncertainty budget of gas density measurements was estimated using the pycnometer method. It has been established that the mass determination of the gas under study makes the greatest contribution to the total uncertainty. It was decided to increase the internal volume of the pycnometer and use a modified method for determining its volume to minimize the uncertainty.

An imitator of a pycnometer with an increased volume was manufactured in an original design to solve the task of developing a modified pycnometer method for measuring the gas density. A gravimetrically produced gaseous mixture of the following composition was chosen for testing the developed method: CO₂ –  40.22 mol. %, CH₄ –  rest.

The theoretical significance of the results obtained lies in approbation of a modified pycnometer method to improve the measurement accuracy of such a gaseous fuel property as the Wobbe index. In the process of developing a modified pycnometer method, the measurement algorithm was tested, the density values of the studied gas were obtained, and the uncertainty budget of density measurements was estimated.

The practical significance of the results of this research will expand the possibility of establishing metrological characteristics during the metrological assurance of Wobbe index analyzers, as well as apply the developed method in future accuracy control of the measurement results of the gas relative density to air.

The requirements for thermal analysis instruments are increasing in terms of increasing the measurement ranges and improving their accuracy due to the development of scientific and technological progress in the field of metrological supervision, chemical and pharmaceutical industries. The study of determining the melting point of organic substances is of particular relevance for the metrological support of the applied thermal analysis instruments and traceability to the base units of physical quantities.

The purpose of the research was to test the possibility of using organic substances on the basis of sodium acetate and sodium methanesulfonate as phase transition temperatures standards for candidate material to certified reference materials for phase transition temperatures (CRMs) traceable to the SI unit of the «temperature» value.

The procedure for measuring the phase transition temperatures (melting point) was performed by differential scanning calorimetry using an STA 449 F5 JUPITER thermal analyzer from the GET 173–2017 State Primary Standard. The determination of the CRM certified value was performed in accordance with GOST ISO Guide 35–2015, the contributions to the uncertainty from the heterogeneity of the starting materials were evaluated, and the short-term and long-term stability of the materials were studied.

The obtained metrological characteristics of the investigated batch of CRMs are as follows: the range of permissible certified characteristics of the melting point of the phase transition for anhydrous sodium acetate (328.35–330.35) °C, for sodium methanesulfonate (352.05–354.05) °C. Comparison of the certified melting point values of the developed CRMs with the reference melting point values presented in IUPAC showed that the certified characteristics of the CRMs are consistent within ±1.4 °C.

The theoretical significance of the obtained results lies in the proof of the possibility of applying the method of differential scanning calorimetry for the development of certified reference materials for phase transition temperatures (a set of TPKR CRMs) GSO 11928–2022/GSO 11929–2022.

The practical significance of the results obtained makes it possible to expand the possibility of establishing and controlling the calibration dependence of thermal analysis measuring instruments; certification of measurement procedures (methods) and accuracy control of the measurement results of the phase transition temperatures of metals, metal salts, metal oxides, polymeric materials, organic and inorganic substances.

The field of the melting point measurements of high-purity organic substances today includes a large number of measuring instruments used in the field of medicine, biology, and the production of perfumery and cosmetic products.

The purpose of the research is to identify the features and justify approaches to the development of melting point certified reference materials of organic substances provided with metrological traceability to the SI base measurement units «temperature» (°C).

The objectives of the research included justification of the choice of substances-candidates for CRMs; determination of the certification procedure for RMs; establishment of restrictions affecting the certification procedure; estimation of uncertainty for certified values of the melting point CRMs.

In the course of the research, a state analysis of metrological assurance in the field of melting point measurements was performed. An overview of the reference complex designed to measure the melting point and purity of organic substances in the range from +40 °C to +250 °C is presented, its functional diagram is given. The basic requirements for substancescandidates for CRMs are identified. The study presents the results of determining the melting point of benzophenone, benzoic acid, succinic acid, anthracene, and caffeine obtained by direct measurements of the phase transition temperature and by indirect measurements based on recording the moment of optical transparency of the substances under study. The results of interlaboratory comparisons on samples of the studied substances are presented, which made it possible to obtain reliable data on the temperature of the emergence of optical transparency at different heating rates. A method for reconciling the results is proposed; it consists in presenting the certified value of the melting point determined by the method of direct measurements of the phase transition temperature in the thermodynamic mode, as well as the certified values of the optical transparency temperature at various heating rates as additional characteristics of the substance in the passports of the developed CRMs. Research objectives for further work are formulated.

The theoretical significance of the results obtained lies in the development of theoretical and methodological approaches to the certification of melting point CRMs based on pure organic substances, which make it possible to improve the measurement accuracy in the field of thermal analysis at a higher quality level.

The article is devoted to the special aspects of application of a certified reference material as a basis for comparison as one of the main tools for ensuring traceability and accuracy control of the measurement results of mechanical properties.

In the course of the research, an analysis of the approach of theoretical principles based on GOST 34100.3–2017 / ISO/IEC Guide 98–3:2008 and GOST R ISO 21748–2021 calculation algorithms for evaluating measurement uncertainty was carried out. The methodology of application of the reference material for the mechanical properties of steel grade 20 GSO 11854–2021 for evaluating the uncertainty of the static tensile test results was considered.

It was established that evaluating the uncertainty of the static tensile test results to ensure the traceability of the result leads to the need to account the systematic component of the laboratory when calculating the uncertainty of test results, either as a correction or as a contribution to the standard total uncertainty. Two accounting options for the systematic component of the laboratory were proposed.

The practical significance of the research is the possibility of applying the model-based approach of theoretical principles based on GOST 34100.3–2017 / ISO / IEC Guide 98–3:2008 and GOST R ISO 21748–2021 calculation algorithms (Equation 1) when evaluating uncertainty according to clause 7.6 of GOST ISO/IEC17025–2019 by accredited laboratories.

The method of Raman spectroscopy (RS) is widely used for timely metrological support of technological lines of the industrial sector in the chemical, medical and pharmaceutical, food, as well as criminalistics and forensic examinations. The wide application of the Raman spectroscopy method requires the use of specific metrological support tools, namely, measures for calibrating Raman spectrometers and microscopes according to the spectrum shape (i. e. relative spectral sensitivity).

The purpose of the research was to develop prototype measures designed to calibrate Raman spectrometers and microscopes on a scale of relative intensities provided with metrological traceability to the SI base units.

Prototype measures were made from inorganic glasses based on an oxide matrix, each of the glasses was activated with metal ions selected to excite a broad fluorescence line with radiation at a given wavelength: 532 nm (manganese ions), 633 nm (bismuth ions) and 785 nm (chromium ions). Metrological characteristics were established for prototype measures, where the certified characteristic is the relative intensity of the reproduced fluorescence radiation. The maximum expanded measurement uncertainty of the relative fluorescence intensity at a coverage factor k = 2 was determined, which is 9.4 %, 5.2 % and 2.8 % for prototype measures designed to reproduce the relative fluorescence intensity when excited at wavelengths of 532 nm, 633 nm and 785 nm, respectively.

Certification of measures performed on the laser Raman confocal microscope Confotec NR500, which is part of the GET 196-2015 standard, allows establishing metrological traceability through the scale of relative intensities of the GET 8 6-2017 microscope, providing traceability to SI units of the “(light) energy flux” value. Thus, it is possible to find the spectral correction function for determining the Raman spectra traceable to the State Primary Standard GET 196-2015 for calibrated devices using certified measures.

The practical significance of the results of the research makes it possible to expand the possibility of establishing and monitoring the stability of the calibration characteristics of microscopes and Raman spectrometers, namely, it allows calibration on a scale of relative intensities.