This document discusses key parameters for differential scanning calorimetry (DSC) experiments. It describes how heating rate, cooling rate, and resolution impact experimental results. A higher heating rate increases peak height and width while decreasing resolution. Cooling rate is not as important but can be controlled or ballistic. Resolution depends on furnace mass, sensors, and response time and can be improved with helium purge gas. Sources of error include environmental conditions, instrument design, and sample characteristics like particle size and shape.

1. Differential Scanning
Calorimetry (DSC)
Parameters
D.THILAGAVATHI
M.PHARM 1ST SEMESTER
DEPARTMENT OF PHARMACOLOGY

2. Contents
Heating rate
Cooling rate
Resolution
Source of error

3. Heating rate
It is defined as the rate of heat transfer to the sample as well as reference
substance.
Heating rate is generally 10 or 20°C /min, but it is important to adjust the
heating rate with respect to compound used in the experiment.

4. Heating rate contd.,
Increase in heating rate influences various observations in thermogram, they are
1. The height magnitude and width of the melting peak increases
2. The melting transitions is observed at higher temperature
3. As the heating rate increased, the width of the melting transition increases,
so resolution is decreases.
4. The peak height increases, so the detection limit (the ability to differentiate a
transition above instrumental noise) is increases

5. Heating rate contd.,
Heating rate Resolution Sensitivity Experimental time
Increases Decreases Decreases Decreases
Decreases Increases Increases Increases

6. Cooling rate
Once the substance is heated up it is important to cool the same.
Here cooling rate does not play any essential role in experimental parameters,
but only to cool the substance at the end of the experiment.
Cooling is achieved by two ways
i. Controlled cooling
ii. Ballistic cooling

7. Cooling rate contd.,
Controlled cooling
Here a specific temperature change per minute is specified as a rate between -
0.1*C/min to- 50*C/min and should be maintained through out the experiment.
Ballistic cooling
In ballistic cooling where the sample is cooled as fast as possible. The ballistic
cooling rate of 400*C/min. For this, various cooling options such as forced air,
intracooler or liquid nitrogen cooling systems are available

8. Resolution
Resolution in DSC is defined as the ability of the DSC to separate or resolve closely
occurring thermal transitions.
Resolution is one of the important performance characteristics of the DSC
instrument
Resolution of the DSC depends upon its design properties such as mass of the
furnace, temperature measuring system (sensors) employed and the response time
of the cell

9. Resolution contd.,
The resolution of a DSC is also a function of the given experimental conditions which
includes
i. Purge gas
ii. Sample mass
iii. Heating rate
Enhance resolution can be obtained using a helium rather than a nitrogen, air or
oxygen purge, it is due to the higher thermal conductivity of helium when compared to
other purge gases.

10. Source of errors
Major source of errors includes
1. Environmental error
2. Instrumental error
3. Sample characteristic
Environmental error: The DSC technique is more sensitive to the gaseous environment
around the sample.
Static gaseous environment around the sample effectively decreases the error, whereas
dynamic gas environment has a chances of increase in error.

11. Source of error contd.,
Instrumental errors:
The geometry and the material used in the fabrication of the sample holder affects the
resolution, shape and size of the DSC peak.
Increase in heating rate leads to decrease in resolution.If the winding used in furnace is not
uniform, the base line is changed.
The heating rate has a great influence on the DSC curve.

12. Source of errors contd.,
Sample characteristic:
Particle size alters the peak area, it decrease with increasing particle size. Particle size also
influence the peak temperature.
Generally with increase in particle size, the peak temperature is shifted to higher values.
The shape of the sample has little effect on the quantitative aspects of DSC but has more effect
on qualitative aspects.
About 0.5 to 10mg is usually sufficient. Smaller sample enable faster scanning, give better shape
peaks with good resolution and provide better contact with the gaseous environment.