Dispersive magnetic solid-phase extraction for synthetic PDE-5 inhibitors determination by high-performance liquid chromatography with tandem mass spectrometry

A dispersive magnetic solid-phase extraction (DMPSE) procedure has been developed to preconcentrate four synthetic phosphodiesterase type 5 (PDE-5) inhibitors (sildenafil, desmethylsildenafil, vardenafil and tadalafil) from different samples (human hair, energy drinks, lubricating gels and dietary supplements). The target compounds were isolated from the solid samples by solid-liquid extraction in basic aqueous medium and the extract was submitted to DMSPE using multiwalled carbon nanotubes/Fe3O4@polypyrrole (MWCNTs/Fe3O4@PPy). For this, 20 mg of the magnetic nanocomposite was added to 30 mL of sample solution/extract and vortexed for 10 min before proceeding to the desorption step using 1 mL of methanol. Analysis was carried out by liquid chromatography with tandem mass spectrometry using electrospray ionization and a triple quadrupole mass analyzer (LC-ESI-QqQ-MS/MS). Matrix-matched calibration was applied for quantification. Limits of detection ranged between 0.01 and 0.22 ng mL−1 for energy drinks and between 0.25 and 7.5 ng g−1 for hair, lubricating gels, and dietary supplements. Relative standard deviations in the 4.3–12.2% (n = 10) were obtained for repeatability studies. The trueness of the proposed method was studied by fortifying the samples at two concentration levels and recoveries in the 85–112% range were obtained. None of the PDE-5 inhibitors studied were detected in real samples.