Determination of sildenafil citrate adulterated in a dietary supplement capsule by LC/MS/MS

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was used to identify and quantify an adulterated substance, in a dietary supplement capsule. The capsule is claimed to be an extract of animal organs and traditional Chinese herbs and indicated for enhancing sexual activity. At first, the sample was extracted with 50% v/v methanol in water and the extract was injected directly into the LC/MS/MS with no separation and a full scan of positive ion eletrospray (ESI +) analysis was performed. The full scan mass spectrum was compared with the NLFD3/LM library created by Division 3rd of National Laboratories of Foods and Drugs for LC/MS/MS analysis. A sildenafil specific mass spectrum was matched indicating that the capsule may have been adulterated with sildenafil, the active ingredient of VIAGRA®. Furthermore, sildenafil was confirmed by carrying out a daughter ion scan and a parent ion scan. The daughter ion spectrum was compared with the NLFD3/LM library. A negative ion eletrospray (ESI -) analysis was performed for confirming the citrate salt in the capsule. The results indicated that the adulterated ingredient was sildenafil citrate. For quantitative analysis of the sildenafil citrate, multiple reaction monitoring (MRM) was performed. Pirenzepine 2HCL was used as the internal standard. A series of standards solution and sample solution with internal standard were analyzed by LC/ MS/MS. The analytical condition is as following: column: Cosmosil 5C18-AR, 4.6 x 150 mm; mobile phase:methanol:acetonitrile: 1% acetic acid (25:17:58); capillary voltage: 3 kV;cone voltage: 80 V; collision energy: 25 eV; source temperature: 120°C; desolvation temperature: 350°C. The detection limit was 40 ng/mL. An excellent calibration curve of sildenafil citrate was obtained with the γ 2 correlation coefficient of 0.9977. The RSDs of interday and intraday were between 7.56∼7.75% and 9.09∼11.25%, respectively. The analytical strategy and method is suitable for identification and measurement of sildenafil citrate adulterated in capsule. Amount of sildenafil citrate in the capsule was determined as 42.8 mg/capsule.