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Updated: Aug 16, 2026

Application and Methodology of the Non-destructive 19F Time-domain NMR Technique to Measure the Content in Fluorine-containing Drug Products
Published on: August 22, 2017
1H, 13C, 15N NMR analysis of sildenafil base and citrate (Viagra) in solution, solid state and pharmaceutical dosage
Iwona Wawer1, Maciej Pisklak, Zdzisław Chilmonczyk
1Department of Physical Chemistry, Faculty of Pharmacy, Medical University of Warsaw, Banacha 1, 02097 Warsaw, Poland. wawer@pluton.farm.amwaw.edu.pl
Abstract:
Sildenafil citrate (SC) (Viagra) and sildenafil base in pure form are easily and unequivocally characterized by multinuclear NMR spectroscopy. Analysis of chemical shifts indicates that: (i) N6-H forms intramolecular hydrogen bonds, (ii) N25 is protonated in the salt and (iii) intermolecular OH...N hydrogen bonds involving N2 and N4 are present in the solid sildenafil citrate. 13C CPMAS NMR method has been proposed for the identification and quantitation of Viagra in its pharmaceutical formulations.
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