True Melting Point Determination

While pure compounds melt isothermally at constant pressure, their melting points are commonly reported as the range between the temperatures recorded by a heated capillary-type melting range measuring instrument at the onset and at the completion of melting of a sample as determined by a pharmacopeiac test protocol. Based on the use of a simple, low-cost version of this type of instrument, a procedure is presented and exemplified for determining the true “thermodynamic” melting points of pure compounds from such melting range data.