Ribavirin - Detection of the melting range

As per USP <891>, the Melting Temperatures and EnthalpiesThe enthalpy of fusion of a substance, also known as latent heat, is a measure of the energy input, typically heat, which is necessary to convert a substance from solid to liquid state. The melting point of a substance is the temperature at which it changes state from solid (crystalline) to liquid (isotropic melt).melting point of a crystalline substance is correlated with the extrapolated onset temperature of the DSC curve, called melt onset temperature.

For ribavirin, this value – at 168.0°C – is in good agreement with the melting range (168.1 to 169.8°C, highlighted in red) which was determined for this pharmaceutical ingredient by means of the capillary method (e.g., in line with USP <741>). In the capillary method, detection of the melting range (interval between the beginning of melting and the complete transition into the liquid phase) takes place visually.  

The capillary method was carried out at heating rates of 1 to 1.5 K/min.
The conditions for the DSC measurements were: sample weight: 1.02 mg, heating rate: 10 K/min, nitrogen atmosphere, Al crucibles.