Characterization of the thermal properties of powder particles using microthermal analysis.
OBJECTIVE
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 degrees 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 alpha and gamma forms of indometacin showed that the technique was able to distinguish between the two polymorphic forms.


CONCLUSIONS
The study suggests that micro-TA may be used to assess interparticulate composition and homogeneity.
Murphy
John R
JR
The School of Pharmacy, The Queen's University of Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, United Kingdom.
Andrews
Christopher S
CS
Craig
Duncan Q M
DQ
D000420:Albuterol / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002209:Caprolactam / Q000031:analogs & derivatives* / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004355:Drug Stability; D006361:Heating / Q000009:adverse effects*; D007052:Ibuprofen / Q000737:chemistry; D007213:Indomethacin / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011208:Powders / Q000737:chemistry*; D014199:Trehalose / Q000737:chemistry
D011108:Polymers; D011208:Powders; C009916:nylon 6; D002209:Caprolactam; D014199:Trehalose; D000420:Albuterol; D007052:Ibuprofen; D007213:Indomethacin