Differential Scanning Calorimetry

1. PRESENTED BY – SMRUTI RANJAN MASANTA
M.PHARM(1ST YR)
PHARMACOLOGY

2. Content
 Introduction
 History
 Principle
 DSC curve
 Type of DSC
 Application
Differential Scanning Calorimeter

3. Introduction
 Differential scanning calorimetry (DSC) is one of the
thermo-analytical techniques in which the amount of
heat required to increase the temperature of a sample
and reference are measured as function of
temperature. Both the sample and reference are
maintained at nearly the same temperature
throughout the process.
 Only a few mg of material is required to run the
analysis. DSC is most often used because of its speed,
simplicity and availability.[1]

4. History
 The technique was developed by E.S. Watson and M.J.
O'Neill in 1962, and introduced commercially at the
Pittsburgh Conference on Analytical Chemistry and
Applied Spectroscopy in 1963.

5. Principle
 DSC is a technique for measuring the energy necessary to
establish a nearly zero temperature difference between a
sample and an inert reference, as the two specimens are
subjected to identical temperature regimes in an
environment heated or cooled at a controlled rate.
 When a sample undergoes phase transition, more or less
heat will need to flow to it than to the reference (empty
pan) to maintain both at the same temp.
 Whether more of less heat must flow to the sample
depends on whether the process is exothermic or
endothermic.[1]

6. Exothermic transition
 If sample release heat during phase transition, then
reaction is exothermic. Less energy is needed to
maintain sample and reference at same temp.[3]
 E.g.-
Crystallization
Degradation
Oxidation
Curing
Polymerization

7. Endothermic transition
 If a sample absorbs heat during phase transition then
reaction is endothermic. More energy is needed to
maintain sample and reference at same temp.[3]
 E.g.-
Melting
Boiling
Sublimation
Vaporization

8. DSC Curve
 The result of a DSC experiment is a curve of heat flux
versus temperature or time. This curve can be used to
calculate enthalpies of transitions, which is done by
integrating the peak corresponding to a given transition. [1]

9.  The enthalpy of transition can be expressed using
equation:
ΔH=KA
Where, ΔH = enthalpy of transition,
K= calorimetric constant,
A= area under the peak
 Calorimetric constant varies from instrument to
instrument and can be determined by analyzing a
material of known enthalpies of transition.
 Area under the peak is directly proportional to heat
absorbed or evolved by the reaction. Height of the
peak is directly proportional to rate of the reaction.[1]

10. Factors Affecting DSC Curve
 Instrumental factors
 Furnace heating rate
 Recording or chart speed
 Furnace atmosphere
 Geometry of sample holder/location of sensors
 Sensitivity of the recording system
 Composition of sample containers
 Sample characteristics
 Amount of sample
 Nature of sample
 Sample packing
 Solubility of evolved gases in the sample
 Particle size
 Heat of reaction
 Thermal conductivity [1]

11. Types of DSC
 Two basic types of DSC instruments: power compensation
and heat-flux.
 Heat flux DSC:
 In heat flux DSC, difference in heat flow into sample and
reference is measured with (linear) change in sample
temperature.
 In heat flux DSC, we can write the total heat flow dH/dt as,
dH/dt = Cp dT/dt + f (T,t)
Where : Dh/Dt - DSC Heat Flow Signal, Cp - Sample Heat Capacity =
Sample Specific Heat X Sample Weight, DT/Dt - Heating Rate, F(t,t) -
Heat Flow (That Is Function Of Time at an Absolute Temperature).[4]

12.  Sample holder - sample and
reference holders are connected by a
low resistance heat flow path. The
material with which the sample
holder is made may be aluminium,
stainless steel, platinum.
 Sensors - temperature sensors are
thermocouples.
 Furnace - same block is used for
sample and reference.
 Temperature controller -
temperature difference between
sample and reference is measured. A
metallic disc made of constantan
alloy is the primary means of heat
transfer. Sample and reference sit on
raised constantan discs. Differential
heat flow to sample and reference is
measured by thermocouples which
are connected in series, located at
the junction of constantan disc and
chromel wafers. With this, it is
possible to achieve heating or
cooling rates of 100˚c /min to 0˚c.[4]
Heat flux DSC

13.  Power Compensation DSC:
 In this, sample and reference
heated by separate heaters to keep
same temperature, as temp is
changed linearly. These heating
units are quite small, allowing for
rapid rates of heating, cooling.
 Sample holder - it is made up of
aluminium, platinum or stainless
steel.
 Sensors - platinum resistant
sensors are generally used.
Separate sensors are used for are
used for sample and reference
cells.
 Furnace - separate blocks of
furnace are used for sample and
reference cells.
 Temperature controller -
differential thermal power is
supplied to heaters to maintain
the temperature of the sample and
reference at the programmed
value.[4]
Power Compensation DSC

14. Application
 Determination of Heat Capacity-
 It is used to determine heat
capacity, when we start heating two
pans, the computer will plot
difference in heat output of two
heaters against temp. and this is the
heat absorbed by substance against
temp.
 The heat flow is heat (q) supplied
per unit time (t), whereas, The
heating rate is temperature increase
(ΔT) per unit time (t).
 Heat flow= q/t
 Heating rate = ∆T / t
 By dividing heat flow (q/t) by the
heating rate (ΔT/t).
 (q/t ) / (∆T / t) = q/ ∆T= Cp = heat
capacity.[1]

15.  Glass transition
temperature:
 When heating a sample
at a certain temperature
plot will shift downward
suddenly. Which means
more heat flow and heat
capacity increase
because of glass
transition. (It is a
reversible transition in
amorphous material
from a hard, brittle state
into molten rubber like
state).[1]

16.  Crystallization:
 When polymers fall into
these crystalline
arrangements, they give off
heat. This drop in the heat
flow appear as a big peak in
the plot of heat flow vs.
temperature.
 The temperature at the
highest point in the peak is
usually considered to be the
polymer's crystallization
temperature(Tc). Also, the
area of the peak can be
measured, which tells us the
latent energy of
crystallization of the
polymer.[1]

17.  Melting:
 If polymer is heated past its
Tc, eventually reach another
thermal transition, called
melting. When polymer's
melting temperature is
reached(Tm). the polymer
crystals begin to fall apart,
that is they melt. It comes
out of their ordered
arrangements and begin to
move around freely that can
be spotted on a DSC plot.
 The heat which polymer give
off when crystallized is
absorbed when reached at
Tm.[1]

18.  Drug analysis:
 DSC is widely used in the pharmaceutical and polymer
industries. For polymers, DSC is a tool for studying
curing processes, which allows the fine tuning of
polymer properties.[2]
 General chemical analysis:
 Melting-point depression can be used as a purity
analysis tool. This is possible because the temperature
range over which a mixture of compounds melts is
dependent on their relative amounts. Consequently, less
pure compounds will exhibit a broadened melting dip
that begins at lower temperature than a pure
compound.[4]

19. Reference:
1) Kodre KV, Attarde SR, Yendhe PR, Patil RY, and Barge VU,
Differential Scanning Calorimetry: A Review, Research
and Reviews: Journal of Pharmaceutical Analysis ,
Volume 3, Issue 3, July-September, 2014.
2) Thermal Methods. In: Chatwal GR, Anand SK.
Instrumental Methods of Chemical Analysis. Fifth
Edition: Himalaya Publication House, 2002. Pg.no.2.701
2.749-2.751
3) Schick C, Differential Scanning Calorimetry(DSC) of
semicrystaline polymers, Analytical and Bioanalytical
Chemistry, November 2009, 395:1589-1611.
4) www.sciencedirect.com