Identification of thioketone analogues of sildenfil using gas chromatography–mass spectrometry

Sildenafil analogues have been found adulterated in herbal preparations and food products that claim to have natural aphrodisiacs. In this study, a gas chromatography–mass spectrometry (GC–MS) assay was developed for the screening and identification of thioketone analogues of sildenafil. Thiopyrazolopyrimidine, a precursor or a cleavage product of thioketone analogue, exhibited characteristic fragment ions of m/z 328 and m/z 299 was found to be the best marker to screen the presence of general thioketone analogues. Identification by GC–MS assay was rapid and specific as all the studied thioketones showed characteristic mass fragmentations including their intact molecular ions. The developed GC–MS assay had successfully identified thiosildenafil, thiohomosildenafil and thiodimethylsildenafil in herbal preparation and food products.