Differential thermal analysis and differential scanning calorimetry. : Differential thermal analysis and differential scanning calorimetry. Aju S. Sam
1st yr. M.Pharm
Nehru College of Pharmacy. Thermal methods of analysis : Thermal methods of analysis Technique in which some physical parameters of the system is determined and recorded as a function of temperature. Differential thermal analysis (dta) : Differential thermal analysis (dta) Introduction:
Records the difference in temperature between a substance and a reference material against time or temperature .
Thermal changes due to fusion, crystalline structure inversions, boiling, decomposition, oxidation, reduction, destruction of crystalline lattice structure etc. are generally accompanied by rise or fall in temperature.
phase transitions, dehydration, reduction produce endothermic effects.
crystallization, oxidation produce exothermic effects. Slide 4: DTA curve:
Endotherms are plotted downwards and exotherms upwards. The temperature of the sample is greater for an exothermic reaction, than that of the reference; for endotherms the sample temperature lags behind that of the reference.
Area of the peak is proportional to the amount of reacting material. Slide 5: Factors Affecting DTA Curve: Slide 6: Instrumentation:
Sample and reference holder with temperature detector
Amplifier and recorder
Atmosphere control equipment for furnace and sample holder Slide 7: Applications:
Identification of substances
Identification of products
Analysis of biological materials
Inorganic and Organic chemistry. Differential scanning calorimetry(dsc) : Differential scanning calorimetry(dsc) Slide 9: Introduction:
Advantage of keeping the sample and reference at the same temperature and heat flow into sample and reference is measured.
Achieved by placing separate heating devices in the sample and reference chambers.
In DSC the heat flow is measure and plotted against temperature of furnace or time to get a thermogram.
Curve obtained in DSC is between dH/dt in mJ s-1 or mcal s-1 as a function of time or temperature. Slide 10: DSC curve:
The area under the peak is directly proportional to the heat evolved or absorbed by the reaction, and the height of the curve is directly proportional to the rate of reaction. Slide 11: Factors affecting DSC curve:
a) Furnace heating rate.
b) Recording or chart speed
c) furnace atmosphere
d) Geometry of sample holder/ location of sensors
e) Sensitivity of recording mechanism.
f) Composition of sample container.
2. Sample Characteristics:
a) Amount of sample
b) Solubility of evolved gases in sample.
c) Particle size
d) Heat of reaction
e) Sample packing
f) Nature of sample
g) Thermal conductivity. Slide 12: Instrumentation: Slide 13: Types of DSC instruments: Slide 14: Applications: Slide 15: Parameters measured by DSC:
Melting and boiling points
Crystallisation time and temperature
Heats of fusion and reactions
Specific heat capacity
Rate and degree of cure
Purity references : references H.H.Willard , L.L.Merrit Jr., J.A. Dean , F.A.Settle Jr., Instrumental Method of Analysis, Wadsworth Publishing company , USA, 1986.
Skoog, Douglas A., F. James Holler and Timothy Nieman, Principles of Instrumental Analysis. Fifth Edition. New York. 1998.
Gurdeep R Chatwal, Sham K. Anand., Instrumental Methods of Chemical Analysis. Fifth edition.2007