Melting Point Certified Reference Materials for Organic Substances: Development Perspectives

Abstract

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.