Eutectics and drug identification

As the eutectic temperature of a substance in mixtures with other compounds is, as a rule, different even when the other substances have the same melting point, this parameter can be used for identification purposes. Benzanilide 

Ternary eutectics are also possible. The binary eutectic points of three mixtures are as follows for aminophenazone-phenacetin 82°C for aminophenazone-caffeine 103.5°C and for phenacetin-caffeine IZS C. The ternary eutectic temperature of aminophenazone-phenacetin-caffeine is 81°C. In this mixture the presence of aminophenazone and phenacetin can be detected by the mixed melting point 

The possibility of determining eutectic temperatures of multicomponent mixtures has practical value in another respect. During tableting, for example, heat is generated in the punch and die and in the powder compact measurement of the eutectic temperature can give information on whether this rise in temperature is likely to cause problems of melting and fusion. 

The external shape of the crystal can be described in terms of its habit, which is affected by the rate of crystallisation and by the presence of impurities, particularly surfactants. The habit of a crystal is of pharmaceutical importance, since it affects the compression characteristics and flow properties of the dmg during tableting and also the ease with which the suspensions of insoluble dmgs will pass through syringe needles. 

Many drugs exist in several polymorphic forms. The various polymorphs of a dmg differ in the packing of the molecules in the crystal lattice or in the conformation of the molecules at the lattice sites. The different polymorphs have different physical and chemical properties and usually exist in different habits. The transformation between 

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