OptiMelt Automated Melting Point System - Stanford Research ...

Appendix A Pharmacopeia vs. Thermodynamic Melting Points 83Step 3Use the Thermodynamic Correction Factor to calculate the thermodynamic melting pointof the sample from the measured clear points (eqn. 7). An agreement within the accuracyof measurement should be observed for all calculated thermodynamic melting points.An example of this calculation procedure is included below.ThermoCF Calculation ExampleIn order to demonstrate the simplicity of the calculation procedure described in theprevious section, a series of melts were performed on a phenacetin sample with rampingrates 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 °C/min.Figure 41 summarizes the results and shows the expected linear relationship between theclear point determinations and the square root of the ramping rate. The slope of thestraight line corresponds to a thermodynamic correction factor, ThermoCF= 1.9 forphenacetin samples.MPpharma vs. SQRT(ramp rate)138.5138137.5137136.5136135.5135134.5134133.50 0.5 1 1.5 2 2.5SQRT(ramp rate, [Celsius/min])Figure 41. “Clear point temperature vs. square root of ramping rate” for a phenacetin samplemelted at 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 ˚C/min. The slope of the straight line, ThermoCF=1.9, isprogrammed into the OptiMelt as the thermodynamic correction factor, ThermoCF, for thiscompound.Table 7 demonstrates the use of the thermodynamic correction factor to calculate thethermodynamic melting point of a phenacetin sample. In contrast to the clear pointOptiMelt Automated Melting Point System