Characterization of the thermal properties of powder particles using microthermal analysis

Purpose. Microthermal analysis is a recently introduced thermoanalytical technique whereby discrete regions of complex samples may be scrutinized at micron or submicron resolution. In this investigation, the novel use of the technique to study individual powder particles is described. Methods. A TA Instruments microthermal analyzer was used in local thermal analysis mode using a heating rate of 10°C/s. Powder samples of crystalline ibuprofen, spray-dried salbutamol sulphate, spray-dried and crystalline trehalose, and two polymorphic forms of indometacin were studied using differential scanning calorimetry as a supportive technique as appropriate. Results. The ibuprofen showed a probe position discontinuity corresponding to the melting point of the material. Spray-dried salbutamol sulphate showed a discontinuity corresponding to decomposition but not to the glass transition, whereas both crystalline and amorphous trehalose showed a single discontinuity corresponding to physical collapse of the material. Studies using the f and n forms of indometacin showed that the technique was able to distinguish between the two polymorphic forms. Conclusion. The study suggests that micro-TA may be used to assess interparticulate composition and homogeneity.