Highly sensitive solid forms discrimination on the whole tablet of the active ingredients in quercetin dietary supplements by NMR crystallography approaches

• Non-destructive solid-forms determination by combined PXRD and ss-NMR is demonstrated on quercetin dietary supplements.
• Good sensitivity to small traces of other solid forms than indicated is shown on two quercetin commercial products.
• Methanol and ethanol solvates of quercetin were discovered and characterized by NMR crystallography.
• Desolvation to anhydrous quercetin of the both solvates was found.
• A consistent interpretation of the data in terms of quercetin solid form purity was obtained in the end.

Similarly to synthetic drugs, the exact crystalline form of active ingredients in solid formulations of dietary supplements may directly influence the dissolution rate, bioavailability, and stability of the final product, but this information is usually not provided by manufacturers. Working on the examples of two commercial quercetin dietary supplements a quick, reliable, and sensitive method is introduced for quercetin solid forms discrimination directly on the marketed products, without the need for prior sample preparation. It exploits the complementarity between solid-state Nuclear Magnetic Resonance (ss-NMR) and Powder X-Ray Diffraction (PXRD), which proved essential for performing a complete and accurate solid-state characterization of the two commercial products, and for obtaining new insights into the complex quercetin solid-forms landscape. The method can be readily generalized also to other dietary supplements based on bio-flavonoids/polyphenols.

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