Improved Purity Measurement Method of Organic Compounds Using Differential Scanning Calorimetry

A study was made of the calculation methods which give an accurate purity value when the purity is measured with a mixture which forms an eutectic mixture. It was revealed by a comparison of the purity values obtained by various measurement methods using DSC that those obtained by the stepwise method are more accurate than those obtained by other methods. Aiming to apply the advantages of the stepwise method to the dynamic method, the following improvements were made. The total heat of fusion was measured inclusive of the eutectic peak. To calculate the melt fraction, the total heat of fusion was regarded as extending up to the inflexion point at the end of the peak. Furthermore, the melt fraction was calculated assuming the heat up to each temperature to be the partial heat of fusion. A van′t Hoff plot was assumed starting with a point 5% below the principal component peak following the end of the eutectic mixture′s peak and ending at the inflexion point. An analysis using the improved method excludes any bias, and the obtained value was highly reliable. A 95mol% pure sample gave a measurement with an error within 0.5mol% or less.