Nitrogen-14 Nuclear Quadrupole Resonance Spectroscopy: a powerful new analytical methodology for medicines authentication and counterfeit antimalarial analysis

We report the detection and analysis of a suspected counterfeit sample of the antimalarial medicine Metakelfin through developing Nitrogen-14 Nuclear Quadrupole Resonance (14N NQR) spectroscopy at a quantitative level. The sensitivity of quadrupolar parameters to the solid-state chemical environment of the molecule enables development of a technique capable of discrimination between the same pharmaceutical preparations made by different manufacturers. The 14N NQR signal returned by a tablet (or tablets) from a Metakelfin batch suspected to be counterfeit was compared with that acquired from a tablet(s) from a known-to-be-genuine batch from the same named manufacturer. Metakelfin contains two active pharmaceutical ingredients, sulfalene and pyrimethamine and NQR analysis revealed spectral differences for the sulfalene component indicative of differences in the processing history of the two batches. Furthermore, the NQR analysis provided quantitative information that the suspected counterfeit tablets contained only 43 ± 3 % as much sulfalene as the genuine Metakelfin tablets. Conversely, conventional nondestructive analysis by FT-Raman and FT-NIR spectroscopies only achieved differentiation between batches, but no ascription. HPLC-UV analysis of the suspect tablets revealed a sulfalene content of 42 ± 2 % of the labelled claim. The degree of agreement shows the power of NQR as a means of the non-destructive identification and content-indicating first-stage analysis of counterfeit pharmaceuticals.