Comparison and combination of spectroscopic techniques for the detection of counterfeit medicines.

During this study, Fourier transform infrared spectroscopy (FT-IR), near infrared spectroscopy (NIR) and Raman spectroscopy were applied to 55 samples of counterfeit and imitations of Viagra and 39 samples of counterfeit and imitations of Cialis. The aim of the study was to investigate which of these techniques and associations of them were the best for discriminating genuine from counterfeit and imitation samples. Only the regions between 1800-400 cm(-1) and 7000-4000 cm(-1) were used for FT-IR and NIR spectroscopy respectively. Partial least square analysis has been used to allow the detection of counterfeit and imitation tablets. It is shown that for the Viagra samples, the best results were provided by a combination of FT-IR and NIR spectroscopy. On the other hand, the best results for the Cialis samples were provided by the combination of NIR and Raman spectroscopy (1400-1190 cm(-1)). These techniques not only permitted a clear discrimination between genuine and counterfeit or imitation samples but also the distinction of clusters among illegal samples. This might be interesting for forensic investigations by authorities.