title: Near-infrared spectroscopy for cocrystal screening. A comparative study with Raman spectroscopy.
abstract: Near-infrared (NIR) spectroscopy is a well-established technique for solid-state analysis, providing fast, noninvasive measurements. The use of NIR spectroscopy for polymorph screening and the associated advantages have recently been demonstrated. The objective of this work was to evaluate the analytical potential of NIR spectroscopy for cocrystal screening using Raman spectroscopy as a comparative method. Indomethacin was used as the parent molecule, while saccharin and l-aspartic acid were chosen as guest molecules. Molar ratios of 1:1 for each system were subjected to two types of preparative methods. In the case of saccharin, liquid-assisted cogrinding as well as cocrystallization from solution resulted in a stable 1:1 cocrystalline phase termed IND-SAC cocrystal. For l-aspartic acid, the solution-based method resulted in a polymorphic transition of indomethacin into the metastable alpha form retained in a physical mixture with the guest molecule, while liquid-assisted cogrinding did not induce any changes in the crystal lattice. The good chemical peak selectivity of Raman spectroscopy allowed a straightforward interpretation of sample data by analyzing peak positions and comparing to those of pure references. In addition, Raman spectroscopy provided additional information on the crystal structure of the IND-SAC cocrystal. The broad spectral line shapes of NIR spectra make visual interpretation of the spectra difficult, and consequently, multivariate modeling by principal component analysis (PCA) was applied. Successful use of NIR/PCA was possible only through the inclusion of a set of reference mixtures of parent and guest molecules representing possible solid-state outcomes from the cocrystal screening. The practical hurdle related to the need for reference mixtures seems to restrict the applicability of NIR spectroscopy in cocrystal screening.
authors.affiliation: Department of Pharmaceutics and Analytical Chemistry, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Allesø
authors.forename: Sitaram
authors.initials: S
authors.lastname: Velaga
authors.forename: Amjad
authors.initials: A
authors.lastname: Alhalaweh
authors.forename: Claus
authors.initials: C
authors.lastname: Cornett
authors.forename: Morten A
authors.initials: MA
authors.lastname: Rasmussen
authors.forename: Frans
authors.initials: F
authors.lastname: van den Berg
authors.forename: Heidi Lopez
authors.initials: HL
authors.lastname: de Diego
authors.forename: Jukka
authors.initials: J
authors.lastname: Rantanen
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry; D003460:Crystallization; D007213:Indomethacin / Q000737:chemistry; D012439:Saccharin / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013059:Spectrum Analysis, Raman; D014961:X-Ray Diffraction
chemical_list: D001224:Aspartic Acid; D012439:Saccharin; D007213:Indomethacin