Necessity of establishing chemical integrity of polymorphs of drug substance using a combination of NMR, HPLC, elemental analysis, and solid-state characterization techniques: Case studies

Abstract

Polymorphism is a solid-state phenomenon; hence, solid-state techniques such as XRPD, DSC, and FT-IR are used for characterization. Many a time, only XRPD is used. These techniques ignore the most important aspects, i.e., chemical purity and the chemical integrity of the polymorph, which can be confirmed by techniques such as 1H NMR, HPLC, and elemental analysis. The aim of this article is to emphasize how techniques such as 1H NMR, elemental analysis, and HPLC purity in addition to other solid-state characterization techniques would help to prove that the drug really exists in different polymorphic forms. H1NMR, HPLC, and elemental analysis reveal the formation of different compounds and not polymorphs in the case of pioglitazone·HCl and glyburide. In the cases of irbesartan and ropinirole·HCl use of a single solid-state characterization technique such as XRPD is not enough for establishing the existence of different polymorphic forms. © 2013 American Chemical Society.