Comparison between DSC and TMDSC in the investigation into frozen aqueous cryoprotectants solutions.
OBJECTIVE
The influence of thermal parameters in the observation of thermal events and in the calculation of heat transformation in aqueous cryoprotectant solutions after freezing was investigated using conventional differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC), respectively.


METHODS
The systems under study were formed by pure water and diluted aqueous solutions of mannitol, trehalose, sucrose, sorbitol, and glycine. The influence of different combinations of frequency and amplitude was analyzed in heating-cooling and heating-iso TMDSC scans.


RESULTS
Trehalose, sucrose, and sorbitol present a lesser critical temperature of primary drying than other cryoprotectants studied. The calorimetric variables selection is crucial to detect or not the thermal events, or to detect so with different numerical values. Then, the values of the calorimetric parameters determined are different if measured in a mode of heating-cooling or heating-iso. The TMDSC method-1 used in this study employs a higher number of cycles in each thermal event. The use of Lissajous figures and the study of the C(p in-phase) signal evolution will allow us to understand the complexity of the events detected.


CONCLUSIONS
The comparative study of both techniques points to the selection of conventional or modulated technique depending on the type of system and the nature of the studied events.
Santoveña
A
A
Departamento de Ingeniería Química y Tecnología Farmacéutica, Facultad de Farmacia, Universidad de La Laguna, La Laguna, Tenerife, Spain. ansanto@ull.es
Piñero
M J
MJ
Llabrés
M
M
D002152:Calorimetry, Differential Scanning; D003451:Cryoprotective Agents / Q000737:chemistry*; D003460:Crystallization; D005615:Freezing; D005998:Glycine / Q000737:chemistry; D006358:Hot Temperature; D008353:Mannitol / Q000737:chemistry; D044367:Phase Transition; D012996:Solutions; D013012:Sorbitol / Q000737:chemistry; D013395:Sucrose / Q000737:chemistry; D044366:Transition Temperature; D014199:Trehalose / Q000737:chemistry; D014867:Water / Q000737:chemistry*
D003451:Cryoprotective Agents; D012996:Solutions; D014867:Water; D008353:Mannitol; D013012:Sorbitol; D013395:Sucrose; D014199:Trehalose; D005998:Glycine