Chemical Fingerprinting of Counterfeits of Viagra and Cialis Tablets and Analogues via Electrospray Ionization Mass Spectrometry

Direct infusion electrospray ionization mass spectrometry (ESI-MS) is shown to provide an efficient technique for the investigation of polar composition of forensic tablets for male erectile dysfunction. ESI-MS fingerprinting of 41 commercial sildenafil samples (Viagra, Cialis, Lazar, Libiden, Maxfil, Plenovit, Potent 75, Rigix, V-50, Vimax, Pramil 75 and Pramil) and 56 counterfeit samples (Viagra and Cialis) were obtained. The spectra for the authentic Viagra tablets showed abundant ions exclusively corresponding to the sildenafil (SLD) molecule: [SLD + H] of m/z 475; [SLD + Na] of m/z 497; and [2SLD + H] of m/z 949. The spectra for commercial sildenafil samples also showed predominat SLD ions. Tablets of authentic Cialis showed mainly ions of m/z 343, 365 and 707 from the lactose molecule (the excipient); as well as a minor ion of m/z 390 corresponding to the active ingredient tadalafil (TAD) in its protonated form [TAD + H]. For counterfeit Cialis samples, however, normally TAD ions of much high abundances was observed, together with ions corresponding to sildenafil analogues such as those of m/z 489 (homosildenafil) and 505 (hydroxyhomosildenafil). Principal component analysis was applied to ESI-MS fingerprint data, placing samples according to their contents of active ingredients hence authentic and counterfeit samples are easily recognized.