Hot Stage Optical Microscopy

HSOM involves the examination of sample under a microscope while the sample is subjected to temperature changes over a period of time. Differential scanning calorimetry (DSC) is one of the most common techniques used to characterize polymorphs, but more can be understood about the sample if analyzed by HSOM. Using PLM and a hot stage allows for the detection of changes in polarization during heating, melting point, sublimation, phase transformation, crystallization, desolvation, decomposition, and purity. If a sample contains more than one polymorph or chemical compound, some particles will be observed to melt at one temperature whereas others will melt at a different temperature. Many times, challenging problems commonly encountered in pharmaceutical development such as “extraneous peaks” appearing XRPD patterns of different lots of material can be solved with a HSOM approach. HSOM can also be used to differentiate and characterize polymorphs with extremely similar melting points or thermal events. Such samples might provide DSC data that are not distinguishable whereas HSOM can clearly indicate differences between the samples. HSOM can also be used in conjunction with infrared microspectroscopy to collect chemical composition information about different particles at different temperatures, enabling the detection and identification of polymorphs or degradation products.

Improved Pharma’s thermomicroscopy accessory for polarized light microscopes:

  • Linkam LTS420 hot stage with T95 Temperature Controller and LNP (liquid nitrogen pump).