Diffrential scanning calorimery (dsc) ppt

Presented by: Pooja s Bansude
M.pharm first year
Department of Pharmaceutics
Dattakala college of Pharmacy, swami11/12/2019 1

CONTENS:
 Introduction to Thermal Analysis
 Differential scanning calorimetry
 History of DSC
 Principle of DSC
 Typical DSC curve
 Instrumentation
 Errors in DSC
 Advantages
 Disadvantages
 Applicatons
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Thermal method of analysis
DEFINATION:
Thermal method of analysis: comprise
a group of techniques in which a
physical property of a substance is
measured as a function of
temperature while the substance is
subjected to a controlled temperature
programme.
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Different Techniques of Thermal
methods of Analysis.
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History of DSC:
The technique was developed by E.S.
Watson and M.J. O'Neill in 1960, and
introduced commercially at the Pittsburgh
Conference on Analytical Chemistry and
Applied Spectroscopy in 1963.
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Thermal transitions
Low-molecular-weight materials change their physical state as
the temperature increases; at the melting point they change
visibly from a crystal to a liquid, and at the boiling point from a
liquid to a vapor. Each true phase transition is defined
thermodynamically by a marked change in the enthalpy.
However, since changes in enthalpy can only be determined
with expensive instruments, other methods are generally
employed to determine the transition temperatures.
For example, in organic chemistry melting points are measured
via the formation of the liquid state in the melting-point tube.
This method can be used for the determination of the melting
point
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Principle:
 The sample and reference are
maintained at the same temperature,
even during a thermal event in the
sample.
• The energy required to maintain zero
temperature difference between the
sample and the reference is measured.
• During a thermal event in the sample, the
system will transfer heat to or fro from
the sample pan to maintain the same
temperature in reference and sample
pans.
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Block diagram of DSC
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Intsrumentation:
 There are two types of Instruments or DSC
systems commonly used:
1) Power-compensation DSC
2) Heat-flux DSC
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DSC Instruments:
HEAT FLUX DSC
 Sample holder:
platinum, aluminum and
stainless Steel.
 Sensors: Temperature
sensors.
Usually thermocouples
which are same for both
sample and reference.
 Furnace: one block for
both reference and
sample cell.
POWER COMPENSATION DSC
 Sample holder :
platinum, aluminum and
stainless steel pans.
 Sensors: platinum
resistance
thermocouple.
Separate sensors and
heaters for both
reference and sample.
 Furnace: separate block
for both reference and
sample cell
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HEAT FLUX DSC
 The sample and the reference cells are heated at
a constant rate and thermocouples are used to
detect the temperature difference between
sample side and the reference side using single
large mass furnace
• The large single furnace which acts as an infinite
heat sink to provide or absorb heat from the
sample.
• The dynamic sample chamber is the environment
of the sample pan compartments and the purge
gas.
• Nitrogen is the most common gas , but alternate
inert gas is helium or argon
• When using an oxidative atmosphere air or
oxygen are the gases of choice
• The heat flux DSC is based on the change in the11/12/2019 11

referen
Instrument
fig. Heat flux DSC
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POWER COMPENSATION DSC
 Introduced in the early1960s.
• It was developed by Perkin Elmer USA. It directly
measures heat flow between sample side and reference
side using two separate , low mass furnaces.
• This individual furnaces use different amount of power to
maintain a constant change of temperature between
sample and the reference and the advantages here
include faster heating and cooling , and better
resolution.
• This type of cell, with two individually heated with
platinum heater monitors the difference between the
sample and reference .
• Platinum resistance thermometers track the temperature
variations for the sample and reference cells.
• Holes in the compartment lids allows the purge gas to
enter and contact the sample and reference .
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Instrument
Fig. Power compensated DSC
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Sampling:
 Accurately-weigh samples (~3-20 mg)
• Small sample pans (0.1 mL) of inert or
treated metals (Al, Pt, Ni, etc.)
• Several pan configurations, e.g., open,
pinhole, or hermetically-sealed (airtight)
pans
• The same material and configuration
should be used for the sample and the
reference
• Material should completely cover the
bottom of the pan to ensure good
thermal contact 11/12/2019 15

Small sample masses and low heating rates increase
resolution
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Reference material
An inert material like alumina is generally used. An
empty pan with lid is also used if the sample
weight is small.
• With sample weight it is necessary to use
reference material , because the total weight of
the sample and its container should be
approximately the same as the total weight of the
reference and its containers .
• The reference material should be selected so that
it posses similar thermal characteristics to the
sample .
•Most widely used reference material is alpha
alumina
Keiselguhr is another reference material normally
used when sample has a fibrous nature
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Typical DSC curve
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DSC Scan of Polyethylene Terephthalate: Heat Flow versus Temperature

Factors affecting DSC curve
1-Instrumental factors
a- Furnace heating rate
b- Recording or chart speed
c- Furnace atmosphere
d- Geometry of sample holder/location
of sensors
e- Sensitivity of the recoding system
f-Composition of sample containers
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Cont…
2-Sample characteristics
a- Amount of sample
b- Nature of sample
c- Sample packing
d- Solubility of evolved gases in the
sample
e- Particle size
f- Heat of reaction
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Advantages:
 Rapidity of the determination
 Small sample masses
 Versatility
 Simplicity
 Applicable
 Study many types of chemical
reactions
 No of Need calibration over the entire
temperature for DSC
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Disadvantages:
 Relative low accuracy
 Not be used for overlapping reactions.
 Difficulties in test cell preparation in
avoiding evaporation of volatile
Solvents
 Does not detect gas generation
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APPLICATIONS
Purity determination of sample directly
• Detection of polymorphism
• Quantification of polymorph
• Detection of meta stable polymorph
• Detection of isomerism
• Stability / compatibility studies
• Percentage crystallinity determination
• Lyophilisation studies
• Finger printing
• Choosing better solvent
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Cont…
 Liquid crystals
 Oxidative stability
 Safety screening
 Drug Analysis
 General chemical analysis
 Food science
 Polymers
 Metals
 Protein analysis
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References:
 P. J. Elving & I. M. Kolthoff, Chemical analysis, Vol. 19, P134,
1964.
 Wang L, Wang B, Lin Q. Demonstration of MEMS-based
differential scanning calorimetry for determining thermodynamic
properties of biomolecules. Sensor Actuat B-Chem 2008;134:953–
958
 Masri MS, Reuter FW, Fiedman M. Interaction of wool with metal
cations. J Appl Polym Sci 1974;18:675–681
 Hohne G, Hemminger W, Flammersheim H-J. Differential
Scanning Calimetry: An Introduction for Practitioners. Berlin,
Germany: Springer-Verlag, 1996 .
 Instrumental methods of analysis- Willards,7th edition, CBS
Publications ;237-332.
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