Investigation of the presence of sildenafil in herbal dietary supplements by validated HPLC method

A simple, fast, reliable high-performance liquid chromatographic (HPLC) method coupled with ultraviolet (UV) detector was developed and validated for the analysis of sildenafil (SDF) in herbal dietary supplements (HDSs). The isocratic chromatographic separation was achieved by a C18 reverse-phase analytical column 4.6 x 250 mm, 5 μm particle size, using acetonitrile, 10 mM phosphate buffer containing 0.1% triethylamine (65:35, v/v, pH 3.5) as a mobile phase. The mobile phase flow rate was 1 mL/min and the column temperature was 35°C. UV detector was set at 293 nm. A liquid-liquid extraction method further provided a simple and practical way to process HDSs containing SDF with a good recovery between 87.57-111.65%. The method showed linearity with an excellent correlation coefficient (r2>0.999). Also, it was specific and sensitive to the limit of quantification 6.46 ng mL-1. Intraday and inter-day method precision was ≤8.13 (RSD%). Intraday and inter-day method accuracy were between (-4.02) to 7.14 (RE%). The method was strong according to robustness test results obtained from UV detection, mobile phase buffer pH, column temperature and flow rates changes values. The described procedure has been found to be simple, fast, precise and feasible for routine adulteration analysis of SDF, especially in food control or toxicology laboratories. This method has been successfully applied to the 50 individual solid and liquid form HDSs. The results showed that the number of 37 out of 50 HDSs sample (represented 74%) examined contained SDF between 0.01 and 465.47 mg/g, 150.87±127.48 (mean±SD), which could lead to serious health problems might be fatal for consumers.