Determination of the nateglinide polymorphic purity through DSC

It is well known that the control of the crystallization of drugs to ensure that only the approved and desired polymorph is present in the formulation is a crucial point of a preformulation study. In this regard, the aim of the present work is to devise a method for the quantification of the polymorphic purity of nateglinide in mixtures formed by polymorphs H and B. In order to achieve this goal, binary systems of known composition have been prepared and the melting peaks of both polymorphs have been recorded by differential scanning calorimetry. Experiments have determined that the method of preparation of the mixtures has to be carefully evaluated. Indeed it has been shown that grinding the samples induces transition from B to H form. Furthermore, it could be observed that the enrichment of the binary mixture with H form is caused by heating. Therefore, after having prepared the mixture without grinding stage, we propose a method to evaluate the content of H polymorph in mixture with the B one from the melting peak of B.