Broad range purity analysis by melting point depression using a singular feature common to all DSC purity scans

DSC purity assay by melting point between has had a limited range of less than several percent impurities. Step-mode heating techniques have increased the range to 6–8%. However, empirical corrections were used to linearize the purity slope of the van't Hoff plot, temperatures vs. reciprocal of fraction melted (1/F).A unique feature common to all dynamic purity scans has been discovered which matches a point on the non-linear van't Hoff plot to the heating rate. This point, or reciprocal of the melt fraction (1/F), occurs where the melting rate has attained maximum acceleration. The melting rate at this point is used as a tangential straight line projection from the curve to become a function of mole % impurity. The melting rate at maximum acceleration is independent of reference material, heating rate, sample size, thermal conductivity, or specific heat.Phenacetin, spiked with 50 mole % benzamide, has been measured to ±2 mole % at heating rate of 5 and 10°C min^?1; the restriction on upper detection limits is adequate resolution between preliminary eutectic events and the final melt. Impurities in indium, with a reported purity of 99.9999%, have been measured at 4 × 10^?5 mole % by this technique.