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Pharmacopeia vs. Thermodynamic
Melting Point Determinations
Application Note #3
Pharmacopoeia Melting Point
The procedural rules for melting point determinations are defined in the
pharmacopeias. The medical handbooks include minimum requirements for the
design of the melting point apparatus and for performing the measurements.
Automated melting point determination procedures are generally included. Very
often, the pharmacopeias also list special methods for difficult or unusual cases
of melting point determination.
Figure 1. Standard capillary tubes used in melting point determinations.
The pharmacopeias regard the capillary technique as the standard method for
melting point determination. In this method, thin glass capillary tubes containing
packed samples of the substance are introduced into a heating stand that is
continuously being heated up.
The capillary technique is the standard method used for melting point
determinations in most organic and pharmaceutical chemistry laboratories.
The procedures for melting point determinations in the pharmacopeias call for a
fixed rate of temperature rise in the "heating stand" (i.e. liquid bath and/or metal
block), typically between 0.2