Differential scanning calorimetry (DSC) measures the difference between the heat flow to the sample and the reference pan that flows undergo a controlled temperature program. Heat flow corresponds to transmitted power and is estimated in watts (W). The change in enthalpy after absorbing the energy is termed an endothermic reaction and when the sample releases the energy is termed an exothermic reaction.
The principle of Differential scanning calorimetry (DSC)
Differential scanning calorimetry (DSC) is a thermal analysis technique that measures the difference in heat flow between a sample and a reference as they are subjected to a controlled temperature program. The heat flow is measured in watts (W) and corresponds to the transmitted power. The change in enthalpy of the sample is determined from the heat flow curve. Endothermic reactions absorb heat, which is indicated by a negative heat flow. Exothermic reactions release heat, which is indicated by a positive heat flow.
Differential scanning calorimetry (DSC) is a thermoanalytical technique that measures the difference in heat flow between a sample and a reference as they are subjected to a controlled temperature program. The heat flow is measured in watts (W) and corresponds to the transmitted power. The change in enthalpy of the sample is determined from the heat flow curve. Endothermic reactions absorb heat, which is indicated by a negative heat flow. Exothermic reactions release heat, which is indicated by a positive heat flow.
DSC is an analytical technique to measure the heat released or absorbed over a range of temperatures during heating and cooling. Different thermal events are measured by DSC such as crystallization, the onset of oxidation, melting, cure reaction, and heat of transitions (i.e., enthalpy).
Pharmaceutical Applications of DSC
Differential scanning calorimetry (DSC) is widely used in the pharmaceutical industry to measure a variety of properties, including:
- Reaction kinetics: DSC can be used to measure the rate of chemical reactions, such as the degradation of a pharmaceutical.
- Melting and exothermic decompositions: DSC can be used to identify and quantify the melting point, glass transition temperature, and other phase transitions in materials.
- Glass transition temperature (Tg): DSC can be used to measure the glass transition temperature, which is the temperature at which a substance changes from a glassy state to a rubbery state.
- Specific heat capacity: DSC can be used to measure the specific heat capacity of a material, which is the amount of heat required to raise the temperature of a unit mass of a material by one degree Celsius.
- Compatibility: DSC can be used to test the compatibility of different materials, such as a drug and an excipient.
- Stability of samples: DSC can be used to assess the stability of samples over time, such as the stability of a pharmaceutical formulation.
- Effect of aging: DSC can be used to study the effect of aging on materials, such as the effect of aging on a pharmaceutical formulation.
- Impact of additives on crystallization: DSC can be used to study the impact of additives on the crystallization of a material, such as the impact of additives on the crystallization of a pharmaceutical.
- Characterization of the drug substance: DSC can be used to characterize the drug substance, such as the purity of the drug substance and the polymorphic form of the drug substance.
Differential scanning calorimetry (DSC) is a useful technique to identify the polymorphic form conversions of a drug substance. This is because DSC can be used to study the sample under different heating and cooling conditions, which can impact the polymorph formation.
The different thermal events that can be measured by DSC
DSC is used mainly to study the thermal stability of the sample. DSC is very useful in the characterization of drug substances and drug products. DSC is a speedy, simple, and consistent technique which allows fast estimation of polymorphic forms, pharmaceutical drug substance / excipient compatibilities, endotherms, and exotherms in the corresponding enthalpies of reaction.
Endothermic events: These events occur when the sample absorbs heat. Some examples of endothermic events include glass transition, melting, evaporation/volatilization, enthalpic recovery, polymorphic transitions, and decompositions.
Exothermic events: These events occur when the sample releases heat. Some examples of exothermic events include crystallization, cure reactions, polymorphic transitions, oxidation, decomposition, and freezing.
The calorimetric purity of a crystalline drug substance sample can also be measured by DSC. This is because the melting point of a pure sample is sharp and symmetrical, while the melting point of an impure sample is broader and less symmetrical. The presence of impurities can also lower the melting point of the sample. Therefore, DSC is a valuable tool for the characterization of drug substances, including the identification of polymorphic forms and the assessment of purity.
FAQ’s
DSC is widely used to measure reaction kinetics, melting and exothermic decompositions and glass transition temp, specific heat capacity, compatibility, stability of samples, the effect of aging, impact of additives on crystallization, and the characterization of the drug substance.
Differential scanning calorimetry (DSC) analysis helps to provide results for pharmaceuticals, chemicals, organic materials, food, plastics, petroleum products, polymers, and more.
Differential scanning calorimetry (DSC) is a thermoanalytical method in which the difference in the amount of heat required to increase the temperature of sample & reference is measured as a function of temperature and also the temperature is maintained the same for both sample and reference throughout the experiment.
References:
- Physical Characterisation of Pharmaceutical Solids, Edited by Harry G. Brittain,
- Various Aspects of The Estimation of Impurities in Drugs, Sdndor Gorog,
- Craig, D.Q.M., Reading, M. Thermal Analysis of Pharmaceuticals. Boca Raton, FL: CRC Press,
- Sestak, J. Thermophysical properties of solids. In: Svehla, G. ed. Comprehensive Analytical Chemistry: Volume XII, Thermal Analysis Part D. New York,
- Ford, J.L; Timmins, P. Pharmaceuticals Thermal Analysis – Techniques and Applications,
- Ahuja S and Scypinski S, Eds Handbook of Modern Pharmaceutical Analysis,
- Dean JA (1995). The Analytical Chemistry Handbook. New York: McGraw Hill, Inc. pp. 15.1–15.5.
- Pungor E (1995). A Practical Guide to Instrumental Analysis. Florida: Boca Raton. pp. 181–191.
- O’Neill MJ (1964). “The Analysis of a Temperature-Controlled Scanning Calorimeter”. Anal. Chem. 36 (7): 1238–1245.
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