Research and Development of Reference Materials for the Phase Transition Temperature of Pentane, Hexane, and Octane Using Secondary Thermometry

Until recently, the metrological assurance of measuring instruments for thermal analysis (synchronous thermal analyzers, mechanical analyzers, differential scanning calorimeters, Calvet calorimeters, thermophysical installations, and the like) in terms of measuring phase transition temperatures in the negative temperature range (from -150 to 0 °C) was carried out using resistance thermometers.

However, the design features of measuring instruments for thermal analysis limit the possibilities of their application. Such limitations include the high risk of damaging the measuring cell when attempting to place a resistance thermometer inside the measuring instrument. If the resistance thermometer is too close to the cell walls of the measuring instrument, temperature gradients occur. The limitations listed above, among others, have necessitated the development of reference materials.

The aim of this work is to validate pentane, octane, and hexane as candidate materials for reference materials for phase transition temperature, traceable to the State Primary Standards of the unit of temperature. The procedure for measuring phase transition temperatures (melting temperatures) was carried out using secondary thermometry with a first-class standard resistance thermometer. When determining the certified value of the reference material, the uncertainty contributions from the heterogeneity of the initial materials were evaluated, and the short-term and long-term stability of the materials were investigated.

The obtained metrological characteristics of the studied candidate reference materials for phase transition (melting) temperature are as follows: the range of permissible certified characteristics of the phase transition (melting) temperature for pentane is from -133 to -127.0 °C; for hexane – from -98.0 to -92.0 °C; for octane – from -60.0 to -54.0 °C. A comparison of the certified values of the developed reference materials for melting temperature with reference melting temperature values showed that the certified characteristics of the proposed reference materials agree within ± 0.2 °C; the differences are mainly due to the chemical purity of the substances.

As proof of the applicability of the secondary thermometry method, a set of reference materials for phase transition temperatures of the approved type OPG SO UNIIM has been released. As a result, testing laboratories will be able to establish and control the calibration dependence of thermal analysis measuring instruments, to validate measurement procedures (methods), and to monitor the accuracy of measurement results for the phase transition temperatures of metals, metal salts, metal oxides, polymer materials, and organic and inorganic substances.

1. Belenky AM, Bursin AN, Ulanovsky AA, Chibizova SI. Temperature measurement: science or art? In: Thermal engineering and computer science in education, science and production: Collection of reports of the X All-Russian Scientific and Practical Conference of Students, Postgraduates and Young Scientists (TIM’2022) with international participation, 19–20 May 2022, Yekaterinburg, Russia. Yekaterinburg: UrFU; 2022. P. 32–53. (In Russ.). https://elar.urfu.ru/handle/10995/119259.

2. Pearce J, Kjeldsen H, Nielsen J, Müller I, Krause C, Sutton G et al. Thermometry with embedded SI traceability for industrial applications. The European Physical Journal Conferences. 2025;323:07001. https://doi.org/10.1051/epjconf/202532307001

3. Hay B. A brief history of the thermal properties metrology. Measurement. 2020;155:107556. 10.1016/j.measurement.2020.107556

4. Nepomiluev AM, Kazantsev VV, Shipitsyn AP. Development of reference materials for thermodynamic properties: metrological support of measurements in the field of thermal analysisand calorimetry in Russia. Measurement Standards. Reference Materials. 2019;15(3):15–22. (In Russ.). https://doi.org/10.20915/2077 1177 2019 15 3 15 22

5. Sabbah R, Xu-wu An, Chickos JS, Planas Leitão ML, Roux MV, Torres LA. Reference materials for calorimetry and differential thermal analysis. Thermochimica Acta. 1999;331(2):93–204. https://doi.org/10.1016/S0040–6031(99)00009-X

6. Boyko B. Differential scanning calorimetry in the study and control of drugs, new devices and methods. Dual Technology. 2010;4(53):56–60. (In Russ.).

7. Mehczel JD, Prime RB. Thermal analysis of polymers: fundamentals and applications. New Jersey: John Wiley & Sons; 2009. 688 p.

8. Akhkiamova AA, Abukaev AF, Melnikov AP, Komov EV, Rulev II, Ivanov DA. Nanocalorimeter and Raman microscope combination technique to study polymorphic transition processes in pharmacy materials. Plasticheskie massy. 2024;(2):36–38. (In Russ.). https://doi.org/10.35164/0554 2901 2024 02 36 38

9. Schick C, Zhuravlev E, Androsch R, Wurm A, Schmelzer Jürn WP. Influence of thermal prehistory on crystal nucleation and growth in polymers. In: JWP Schmelzer. Glass. Selected Properties and Crystallization. Berlin, Boston: De Gruyter; 2014. P. 1–94. https://doi.org/10.1515/9783110298581.1

10. Melnikov A, Rodygin A, Grafskaya K, Anokhin D, Ivanov D. High temporal resolution nanocalorimetry and its combination with microand nanofocus X-Ray diffraction for study of functional nanostructured materials. Nanoindustry. 2016;8(70):60–66. (In Russ.). https://doi.org/10.22184/1993–8578.2016.70.8.60.66

11. Sanders GHW, Roberts CJ, Danesh A, Murray AJ, Price DM, Davies MC et al. Discrimination of polymorphic forms of a drug product by localized thermal analysis. Journal of Microscopy. 2000;198:77–81. https://doi.org/10.1046/j.1365–2818.2000.00709.x

12. Kumar A, Singh P, Nanda A. Hot stage microscopy and its applications in pharmaceutical characterization. Applied Microscopy. 2020;50:2–11. https://doi.org/10.1186/s42649 020 00032 9

13. Kazartsev YaV, Korchagina EN, Solovev IV. Melting point certified reference materials for organic substances: development perspectives. Measurement Standards. Reference Materials. 2023;19(1):29–40. (In Russ.). https://doi.org/10.20915/2077 1177 2023 19 1 29 40

14. Merkulov VA, Yagudina RI, Serpik VG. Global pipeline of innovative medicinal products: a narrative review. Bulletin of the Scientific Centre for Expert Evaluation of Medicinal Products. Regulatory Research and Medicine Evaluation. 2024;14(1):14–28. (In Russ.). https://doi.org/10.30895/1991 2919 2024 14 1 14 28

15. Diomina NB. Modern aspects of suppositories manufacturing. Drug development & registration. 2016;2(15):60–69. (In Russ.).

16. Kiseleva TY, Ivanenko IP, Kostenko OV, Yakuta EV, Ilyushin AS, Kovaleva SA et al. Application of differential scanning calorimetry to study the resistance of UHMWPE-based composite materials to electron irradiation. Zhurnal fizicheskoi khimii. 2021;95(5):678–685. (In Russ.). https://doi.org/10.31857/S0044453721050174

17. Zhorin VA, Kiselev MR. Melting and crystallization of high-density polyethylene mixed with organic acids and acid–base indicators after plastic deformation at high pressures. Zhurnal fizicheskoi khimii. 2021;95(7):987–993. (In Russ.). https://doi.org/10.31857/S0044453721070311

18. Greengrass MA. Thermal study on crystallisation & phase transitions of PA6 by DSC: technical report. 2021. 31 p. Available from: https://www.researchgate.net/publication/335082996 [Accessed 26 Juny 2026].

19. Gavrichev KS. Precision calorimetry in the kurnakov institute of general and inorganic chemistry of the Russian Academy of Sciences (IGIC RAS): brief review. Zhurnal Neorganicheskoi Khimii. 2020;65(5):609–612. (In Russ.). https://doi.org/10.31857/S0044457X20050098

20. Riddle JL, Furukawa GT, Plumb HH. Platinum resistance thermometry. U. S. National Bureau of Standards Monograph, 1973.

21. Pearce JV, Veltcheva RI, Large MJ. Impurity and thermal modelling of SPRT fixed-points. AIP Conference Proceeding. 2013;1552(1):283–288. https://doi.org/10.1063/1.4819554

22. Large MJ, Pearce JV. A phase-field solidification model of almost pure ITS 90 fixed points. International Journal of Thermophysics. 2014;35:1109–1126. https://doi.org/10.1007/s10765 014 1685 2

23. Vasil’ev EV, Ignatov AA, Kalinin MI, Markin LD. Investigation of the reproducibility of melting and freezing curves for tin in a miniature cell. Izmeritel’naya Tekhnika. 2018;5:55–60. (In Russ.).

24. Vihareva NA, Belavina DE. Creation of a miniature ampule of a reference point for the attestation of liquid thermostats. Intere’kspo Geo-Sibir’. 2020;7(1):45–49. (In Russ.). https://doi.org/10.33764/2618–981X 2020 7 1 45 49

25. Lopardo G, Bertiglia F, Braccialarghe G, Florio M, Girard F, Giraudi D et al. Supercooling effect in miniature gallium phase transition cell. Advanced Engineering Materials. 2025;27(7):2402763. https://doi.org/10.1002/adem.202402763

26. Brodnikov AF, Safronov AN, Vinokurov AS. A Small-sized technical device for reproducing & transmitting a temperature scale. Kompetentnost’ / Competency (Russia). 2024;7:50–55. (In Russ.). https://doi.org/10.24412/1993 8780 2024 7 50 54

27. Liu YuS, Cai J, Meng S, Ren J. The effect of metal quantity on the temperature plateau time. Journal of Physics: Conference Series. 2023;2554:012004. https://doi.org/10.1088/1742–6596/2554/1/012004

28. Huang H, Cai W, Mao Y, Wan K, Wen Y, Han Y et al. A study on miniaturized in-situ self-calibrated thermometers based on Ga and Ga-Zn fixed points. Sensors. 2024;24(17):5744. https://doi.org/10.3390/s24175744

29. Wang P-y, Li T, Pan J, Ling Z-q, Diao F-G, Sun J-p et al. Reproducibility and assignment of phenol temperature fixed point. International Journal of Thermophysics. 2024;45:7. https://doi.org/10.1007/s10765 023 03299 8

30. Liu Z, Li T, Li Y, Sun J, Chen L, Li M et al. Development and precise determination of temperature fixed point based on n-Tetradecane. Measurement Science and Technology. 2026;37(9):095006. https://doi.org/10.1088/1361–6501/ae425c