Reliable detection of polymorphs and mixed phase crystal systems is an important area of investigation in the development of pharmaceutical (small molecule) ingredients. This work deals specifically with small molecular entities as distinguishable from large or macromolecules, which also are used as active pharmaceutical ingredients. The first manuscript describes a digital band-pass filter for removal of white noise in Powder X-ray Diffraction. The filter reduces the noise by 21% for a real PXRD diffractogram and 40% for a synthetic PXRD diffractogram while maintaining the integrity of diffraction intensities and diffraction angle positions. The solid phase form of an active pharmaceutical ingredient is a regulatory and a manufacturing (blending and mixing into the final drug product) concern. It is necessary to understand the stable and metastable forms of the solid. In the second manuscript the thermodynamic stability of Inosine was investigated using water solubility and differential scanning calorimetry. beta-Inosine was found to be the more stable polymorph at all temperatures below the melting point and alpha-Inosine was the metastable polymorph. The anhydrous forms of inosine form a monotropic pair. Active pharmaceutical ingredients usually have a variety of structural elements that promotes their biological activity. Different solid-state forms are often energetically similar and of low crystal symmetry. This combination of low symmetry and multiple solid forms presents a challenge to the available measurement technologies. In the third manuscript the detection limit of mixtures of a low symmetry polymorphic pair was investigated using Powder X-ray Diffraction. The detection limit of Powder X-ray Diffraction for a low symmetry binary polymorphic mixture was 0.5%. Phase mixing for instrument calibration was successful from 0.5 -- 20%. Single peak and whole pattern calibration was successfully performed.