Solid‐state13C NMR study of drugs: Aspirin

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Abstract
Natural abundance13C NMR spectra of different crystal habits of pure aspirin and several aspirin tablets in the solid state have been measured by using the combined techniques of high‐power decoupling, cross‐polarization and magic angle spinning. Solid‐state NMR of aspirin had excellent sensitivity compared with liquid‐state NMR, and the carbon signals were assigned using a modified pulse sequence to detect non‐protonated carbons. The solid‐state13C NMR spectra of two crystalline forms of aspirin were identical, suggesting that the origin of their difference is not polymorphic.The solid‐state13C NMR spectra of several commercial aspirin tablets, some of them containing buffer components, indicated that there were no interactions among the aspirin and the buffer components; only after dissolving the tablets and lyophilization did the13C NMR spectra of the dry lyophilized powders show strong interactions between aspirin and the buffer components.