Comparison of surface techniques for the discrimination of polymorphs

Abstract

Nanoindentation and atomic force microscopy (AFM) are two surface techniques used to study mechanical and surface properties of solids. One area where these two approaches are not widely employed, however, is the discrimination of polymorphs, for which methods such as single crystal XRD, PXRD, spectroscopy, DSC and ss-NMR are more commonly used. The main advantage of the surface techniques is that a single micron-sized crystal is sufficient for analysis. Here we discuss the application of nanoindentation, AFM height imaging and force–distance measurements to distinguish two polymorphs of a pharmaceutical cocrystal containing caffeine and glutaric acid.