Determination of heat of fusion of USP melting point standards by differential scanning calorimetry

The determination of heat of fusion by differential scanning calorimetry (DSC) in the pharmaceutical industry has increased considerably over the past decade. To better standardize the results provided by the industry, this Stimuli article is proposed to include heat of fusion values of USP melting point standards (MPS). Dried materials that had been gently pulverized were used in this investigation. The Heat of Fusion was measured using heating rates from 0.1°/min to 20.0°/min. The heating rate had no effect on the heat of fusion of USP Phenacetin MPS, whereas for USP Vanillin MPS it increased. No differences in melt onset values were observed on results gathered for four consecutive days on two different lots of USP Vanillin MPS, with standard deviation less than 0.050. The sample size used in the tests varied from 3-16 mgs and had no impact on the values. There is no significant difference between pulverized and non-pulverized values. Based on these results, USP will propose to include the heat of fusion (J/g) to some of the melting point standards. This information will be used for sensitivity calibration of the instruments and/or to check the accuracy of the sample measurements.