the purge gas. Helium may be used to improve the resolution
between thermal events due to its better heat conductivity.
3. The refrigerant cooling system (RCS) can only reach to À40 or
À80
C. With liquid nitrogen cooling, the temperature can go
below À170
C.
4. DSC is applicable to solutions, viscous liquids, and solids or
powders. Heat transport properties of crucibles are affected by
the material type, design, and size, and a beginner may need to
consult more experienced users for advice to choose suitable
crucibles. Solid and powder samples sometimes do not make
good contact with the bottom of the crucibles and may need to
be pressed before testing for better heat transfer. Atmosphere,
moisture, and pressure may influence thermophysical changes
and thermochemical reactions of certain samples, and therefore
such samples may need to be prepared with sealable crucibles in
the environment of inert gases and/or under the right pressure
condition. Enough sample material should be added to allow
accurate measurement, but an oversized sample reduces the
resolution and often causes adjacent peaks that overlap. In
most situations, a sample size of 10–20 mg is suitable. For
measurements between room temperature and subzero temperature, 20–30 μL standard aluminum crimp sample crucibles
are a good choice. However, hermetic sample crucibles are
preferred for measurements above room temperatures to prevent the loss of moisture and/or volatiles. The loss of moisture
and/or volatiles causes the baseline drifting.
5. It is important to use the right temperature ramping program.
The cooling and heating rates affect both the position (temperature/time) of a thermal event and its magnitude (height or
area). In general, a faster rate results in larger peak area but is
more likely to deviate from the equilibrium condition due to
nonuniform heating. Similarly due to the oversize effect, rapid
scanning may also lead to a lower resolution and overlapping of
adjacent peaks. A slow rate can separate peaks better and measure more accurately but requires the instrument to have a
higher sensitivity. It should be noted that thermal events of
cryopreservation and freeze-drying solutions, as well as
biological materials, are not just thermodynamic events but
also kinetic events, i.e., time-dependent processes. Therefore,
the temperature/time ramping program must be carefully
designed to meet the requirements for specific measurements.
To measure the glass transition temperature (T
0
g ) of the freezeconcentrated amorphous domain for the freezing–drying process development, the cooling rate (ramp) at 0.5
C per min
from 0 to À80
C and the warming rate at 2
C per min are
sufficiently slow enough for accurate measurement.
DSC Analysis of Thermophysical Properties
301
between thermal events due to its better heat conductivity.
3. The refrigerant cooling system (RCS) can only reach to À40 or
À80
C. With liquid nitrogen cooling, the temperature can go
below À170
C.
4. DSC is applicable to solutions, viscous liquids, and solids or
powders. Heat transport properties of crucibles are affected by
the material type, design, and size, and a beginner may need to
consult more experienced users for advice to choose suitable
crucibles. Solid and powder samples sometimes do not make
good contact with the bottom of the crucibles and may need to
be pressed before testing for better heat transfer. Atmosphere,
moisture, and pressure may influence thermophysical changes
and thermochemical reactions of certain samples, and therefore
such samples may need to be prepared with sealable crucibles in
the environment of inert gases and/or under the right pressure
condition. Enough sample material should be added to allow
accurate measurement, but an oversized sample reduces the
resolution and often causes adjacent peaks that overlap. In
most situations, a sample size of 10–20 mg is suitable. For
measurements between room temperature and subzero temperature, 20–30 μL standard aluminum crimp sample crucibles
are a good choice. However, hermetic sample crucibles are
preferred for measurements above room temperatures to prevent the loss of moisture and/or volatiles. The loss of moisture
and/or volatiles causes the baseline drifting.
5. It is important to use the right temperature ramping program.
The cooling and heating rates affect both the position (temperature/time) of a thermal event and its magnitude (height or
area). In general, a faster rate results in larger peak area but is
more likely to deviate from the equilibrium condition due to
nonuniform heating. Similarly due to the oversize effect, rapid
scanning may also lead to a lower resolution and overlapping of
adjacent peaks. A slow rate can separate peaks better and measure more accurately but requires the instrument to have a
higher sensitivity. It should be noted that thermal events of
cryopreservation and freeze-drying solutions, as well as
biological materials, are not just thermodynamic events but
also kinetic events, i.e., time-dependent processes. Therefore,
the temperature/time ramping program must be carefully
designed to meet the requirements for specific measurements.
To measure the glass transition temperature (T
0
g ) of the freezeconcentrated amorphous domain for the freezing–drying process development, the cooling rate (ramp) at 0.5
C per min
from 0 to À80
C and the warming rate at 2
C per min are
sufficiently slow enough for accurate measurement.
DSC Analysis of Thermophysical Properties
301