Thermomicroscopy

Thermomicroscopy is the simultaneous characterization of a sample by optical methods as the sample is subjected to a controlled temperature 

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M. Kuhnert-Brandstatter, Thermomicroscopy in the Analysis of Pharmaceuticals, Pergamon Press, Oxford, 1971, pp. 37 42. 

Measurements of melting curves can be used to obtain very accurate evaluations of the melting point of a compound when slow heating rates are used. The phase transition can also be monitored visually, with the operator marking the onset and completion of the melting process. This is most appropriately performed in conjunction with optical microscopy, thus yielding the combined method of thermomicroscopy or hot-stage microscopy [7]. 

The nucleation of these decomposition processes was studied by means of thermomicroscopy on single crystal cleavage plates of calcite, magnesite, dolomite and smithsonite (Fig. 59). The shape of the nuclei was found to be different for these carbonates, which might be also of importance for the decomposition mechanism. The partial pressure of water vapor has a pronounced effect on the decomposition of transition metal carbonates such as ZnC03 and CdC03. The evolution of C02 is probably catalyzed in the presence of water vapor and shifted to considerably... 

Kuhnert-Brandstatter, M. (1971),Thermomicroscopy, in The Analysis of Pharmaceuticals, Pergamon, Oxford, pp. 37—42. 

K. Seefeldt, J. Miller, F. Alvarez-Nunez, N. Rodriguez-Hornedo, Crystallization pathways and kinetics of carbamazepine-nicotinamide cocrystals from the amorphous state by in situ thermomicroscopy, spectroscopy, and calorimetry studies, J. Pharm. Sci. 96 (2007) 1147-1158. 

Hipeaux, J. C., Born, M., Durand, J. R, Claudy, R, and Letoffe, J. M. 2000. Physico-Chemical Characterization of Base Stocks and Thermal Analysis by Differential Scanning Calorimetry and Thermomicroscopy at Low Temperature. Thermochim. Acta, 348,147-159. 

Solvates may be readily detected and desolvation may be readily distinguished from a phase change using thermomicroscopy. The appearance of turbidity within the crystal upon heating is a sign of solvent being driven off, but a much more conclusive test involves covering the crystal with silicone gel or paraffin oil, which trap the bubbles of released solvent, as shown in Fig. 4.6. 

By thermomicroscopy the sublimation behaviour may be readily studied and conditions (e.g. temperature, amount of sample) may be varied to achieve different habits and even different polymorphic modifications (Section 2.4.1) (Fig. 4.7). 

Recent descriptions of microscopy and thermomicroscopy applied to pharmaceutically important compounds, along with quite comprehensive references to standard texts on the fundamentals and apparatus of the technique may be found in Byrn et al. (1999) and Brittain (1999ft). 

Kuhnert-Brandstatter, M. (1982). Thermomicroscopy of organic compounds. In Comprehensive analytical chemistry, Vol. 16 (ed. G. Svehla), pp. 329-513, Elsevier, Amsterdam. [95, lOOf, lOlf, 102, 104]... 

Thermoptometry is defined as a family of thermoanalytical techniques in which an optical property of the sample is monitored against time or temperature, while the temperature of the sample, in a specified atmosphere, is programmed. Two established examples are thermomicroscopy (observation under a microscope) and thermoluminescence (1). Thermomicroscopy is also referred to as thermal microscopy, optical thermal analysis, hot-stage microscopy (HSM), or fusion methods. 

In 1971, Kuhnert-Brandstatter applied thermomicroscopy to an even narrower segment of chemical compounds, namely, organic compounds of medicinal benefit (20). Her research efforts characterized many polymorphic systems in the pharmaceutical industry. Tynan and Von Gutfeld developed a vacuum sample holder for use on an optical microscope. This accessory had the ability to characterize small samples in the 30 to 800 K temperature range (21). Schultze presented a design for a high-temperature microscope-differential thermal analyzer, which explored this role of the combination technique in the high-temperature research field (22). 

Significant work has been conducted using light intensity measurements studying the birefringence of photopolymers (84), development of a controlled-rate thermomicroscopy system for both reflected and transmitted light (85), and the study of inorganic materials for a pyrotechnic system (86). 

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