Differential Scanning Calorimetry (DSC)

 

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Differential Scanning Calorimetry (DSC) provides qualitative and quantitative information on the thermal properties of solid materials such as the melting and degradation temperatures, glass transition temperature, melt and crystallisation enthalpy, specific and latent heats, polymorphism, and purity of the materials.

DSC is used as an industrial quality control technique as it can establish sample purity and detect the presence of impurities in a drug formulation, for instance. It provides a wealth of information regarding both the physical and energetic properties of the substance.


DSC 4000

Applications & Properties Measured with Differential Scanning Calorimetry

Melting Range or Melting Point is defined as those points of temperature within which, or the point at which, the first detectable liquid phase is detected to the temperature at which no solid phase is apparent. DSC is an important technique for gauging purity of organic and pharmaceutical compounds. It is used to identify a sample, establish its purity, and determine the thermal stability of the sample.

An understanding of the degree of crystallinity for a polymer is important as crystallinity affects physical properties such as storage modulus, permeability, density and melting temperature.

Polymer crystallinity can be determined with DSC by quantifying the heat associated with melting (fusion) of the polymer. This heat is reported as Percent Crystallinity by normalizing the observed heat of fusion to that of a 100 % crystalline sample of the same polymer. As authentic samples of 100 % crystalline polymer are rare, literature values are often used for this value.

In pharmaceutics, the understanding of the phase transitions is necessary for characterising the amorphous and crystalline solid dispersions. Glass transition is the stage at which the substance changes it states from a glass-like form to a more elastic form.

The glass transition is due to the presence of amorphous structures in the sample. It is detected by DSC based on a step-change in molecular mobility that results in a step increase in heat capacity and heat flow rate.The physical and reactive properties of amorphous structure are significantly different at temperatures above and below Tg. It constitutes a parameter of high interest in the study of amorphous and semi-crystalline drugs since amorphous drugs are more bio available and soluble.

The processing of pharmaceutical materials is known to introduce small amounts of amorphous material, which can dramatically affect product stability, compatibility, processing and storage. It is thus critical that pharmaceutical scientists have the ability to accurately and precisely measure amorphous content, particularly at low levels.

The most common measurement of amorphous structure involves the analysis of the glass transition by DSC. It is important to examine both the size of the transition in heat flow or heat capacity units and the temperature (Tg) at which it occurs. The size of the transition provides quantitative information about the amount of amorphous structure in the sample, and the temperature identifies the point where there is a dramatic change in physical properties.

Specific surface area is typically described in units of m2/g and BET is the most common model for the calculation of surface area. One of the routine experiments carried out by the DVS is to calculate BET surface area of materials using organic vapors as probe molecules. The traditional BET determination includes nitrogen sorption under vacuum conditions. The DVS overcomes these limitations by using a range of organic probe molecules for sorption which can be carried out at ambient and varied temperatures as well as under ambient pressure or under vacuum. This has the advantage of calculating BET surface areas under real conditions, which is useful for material application.

Dynamic Vapor Sorption is a gravimetric technique used to measure the sorption properties of materials using water and organic vapors, used to characterise complex materials used in a range of industries.

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Pharmaceuticals

Personal Care

Chemicals

Environmental

Aerospace & Automotives

Energy Storage

Food and Beverage

Biomaterials
Coatings

Polymers/Plastics

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