crystallizing protectant or bulking agent upon heating from ambient temperature to 300
C. As temperature increases, the sample
first undergoes a glass transition, followed by crystallization of the
protectant or bulking agent and melting of the crystals. As temperature increases further, several exothermic reactions could occur,
including oxidation, cross-linking, and decomposition. Crystallization and melting are not always observed for many low-moisture
samples, depending on the composition of freeze-drying formulations. However, glass transition, exothermic reactions, and decomposition are usually detectable.
DSC analysis not only provides the qualitative information as
shown in Figs. 1 and 2, it can also be used for quantitative measurements, such as water transport across cell membrane during extracellular freezing, the kinetics of crystallization and phase separation
in viscous liquids, the effect of annealing treatments in frozen
systems, molecular dynamics of freeze-dried products, as well as
kinetics of reactions and decomposition, etc. However, calorimetric
analysis has its limits. If the events do not involve thermal changes,
DSC analysis is not applicable. There are also difficulties in the
correct identification of the origin for some thermal events in
heterogeneous, complex biological samples.
2 Materials
1. A differential scanning calorimeter with a refrigerant or liquid
nitrogen cooling system.
2. A computer with the analytical software installed.
3. Hermetic aluminum crucibles (pans and covers, 20–30 μL).
4. Sample encapsulating press.
5. Indium (99.9999%, Standard Reference Material 2232
certified by National Institute of Standards and Technology),
melting temperature 156.75
C, melting enthalpy 28.53 J/g.
6. An analytical microbalance (accuracy at 0.1 mg for regular use
and at 0.01 mg for calibration).
7. Purge gas of purified nitrogen or helium.
3 Methods
3.1 DSC Verification
A calorimeter needs to be calibrated regularly for the accuracy of
measurements. It is always a good practice to verify the accuracy
before use. The SRM-2232 indium is commonly used as thermometric standard.
DSC Analysis of Thermophysical Properties
289
C. As temperature increases, the sample
first undergoes a glass transition, followed by crystallization of the
protectant or bulking agent and melting of the crystals. As temperature increases further, several exothermic reactions could occur,
including oxidation, cross-linking, and decomposition. Crystallization and melting are not always observed for many low-moisture
samples, depending on the composition of freeze-drying formulations. However, glass transition, exothermic reactions, and decomposition are usually detectable.
DSC analysis not only provides the qualitative information as
shown in Figs. 1 and 2, it can also be used for quantitative measurements, such as water transport across cell membrane during extracellular freezing, the kinetics of crystallization and phase separation
in viscous liquids, the effect of annealing treatments in frozen
systems, molecular dynamics of freeze-dried products, as well as
kinetics of reactions and decomposition, etc. However, calorimetric
analysis has its limits. If the events do not involve thermal changes,
DSC analysis is not applicable. There are also difficulties in the
correct identification of the origin for some thermal events in
heterogeneous, complex biological samples.
2 Materials
1. A differential scanning calorimeter with a refrigerant or liquid
nitrogen cooling system.
2. A computer with the analytical software installed.
3. Hermetic aluminum crucibles (pans and covers, 20–30 μL).
4. Sample encapsulating press.
5. Indium (99.9999%, Standard Reference Material 2232
certified by National Institute of Standards and Technology),
melting temperature 156.75
C, melting enthalpy 28.53 J/g.
6. An analytical microbalance (accuracy at 0.1 mg for regular use
and at 0.01 mg for calibration).
7. Purge gas of purified nitrogen or helium.
3 Methods
3.1 DSC Verification
A calorimeter needs to be calibrated regularly for the accuracy of
measurements. It is always a good practice to verify the accuracy
before use. The SRM-2232 indium is commonly used as thermometric standard.
DSC Analysis of Thermophysical Properties
289