Advances in thermal microscopy

Duncan Stacey reports on innovations in temperature- controlled imaging microscopy

Accurate, precise and reproducible control of temperature is vital in the manufacture of many products in the world today.

A material’s melting point, its glass transition temperature or the speed at which it is chilled will greatly affect its finished properties, lifetime in storage or finally in use.

The field of thermal analysis is well established in many fields. Scientists in the life sciences and pharmaceutical sectors still use traditional experimental and test protocols that use a light microscope and simple observations by the user. Imaging when combined with precise temperature control enhances the characterisation of materials. This provides information not only about the thermal properties of the material but also its morphological changes, such as size, shape and colour.

Thermal analysis in the pharmaceutical industry

Understanding the solid- state properties of active pharmaceutical ingredients (APIs) is extremely important as these have a direct effect on the manufacture, production and even the stability of the drug product, which can lead to changes in the quality and efficacy of the final product.

Differential scanning calorimetry (DSC) is used in almost every pharmaceutical lab. Combining thermal analysis with micro imaging using the Linkam Optical DSC450 provides additional information. Imaging can show changes in morphology and colour that can be correlated with the temperature and DSC signal. Once images have been captured, analysis techniques such as thermal analysis by structural characterisation (TASC) can be applied. TASC products are a family of techniques developed by Cyversa and commercialised by Linkam.

TASC analyses changes in the surface structure of samples such as crystalline materials. During heating crystals lose their surface structure as they melt.

Fig. 1(a) shows an image of a number of sucrose crystals in a DSC pan. Traditional DSC will provide a bulk signal from all crystals in the pan (red, Fig.1. (b)). However, as TASC is an image analysis technique (green, Fig. 1(b)), it is possible to analyse each crystal in the pan, making it an ideal technique for investigating sample inhomogeneity.

Freeze-drying for the pharmaceutical industry

Linkam stages have enabled the optimisation of freeze-drying for many life sciences, pharmaceutical and agrochemical applications. Freeze-drying is a method of processing a wet product into a dry solid product for stabilisation and storage purposes. Traditionally, freeze-drying processes had been developed by trial-and-error, hit-and-miss experimentation. However, with stricter regulatory requirements and higher value products, it is critical that techniques that are rapid, rigorous and reproducible are used.

Linkam’s FDCS196 (shown in Fig. 2) is designed to provide information about the freeze drying-related parameters of a product that is directly related to formulation and process development, most importantly the temperature at which a product undergoes collapse. Collapse, the loss of structure of a frozen product, causes potentially disastrous processing defects and must be avoided by ensuring the product is kept below its collapse temperature throughout primary drying.

The new FDVM system from Linkam complements the FDCS196, allowing freeze-drying protocols to be further refined by running the trials using industry-standard glass vials. The FDVM closely simulates the conditions found in industrial scale freeze-drying cabinets. By incorporating vials, the FDVM simulates large- scale industrial processes while minimising sample wastage.

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Duncan Stacey is with Linkam

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