LC-MS/MS Determination of Sildenafil in Health Food with On-Line Solid Phase Extraction of Molecularly Imprinted Monolithic Column

A sildenafil molecularly imprinted monolithic column was prepared in a stainless steel tube mold by in situ polymerization with sildenafil as template molecule, lauryl methacrylate as functional monomer, ethylene glycol dimethacrylate as crosslinker, dimethylformamide and dodecanol as porogens, and azobisisobutyronitrile as the initiator. The sildenafil molecularly imprinted monolithic column was used as on-line solid phase extraction column. The health food sample of crushing uniform was extracted ultrasonically for 30 min with acetonitrile, and then centrifugated for 5 min at the speed of 8 000 r·min^-1. The supernatant was taken and the residue was extracted twice with acetonitrile. The supernatant was combined and evaporated to near dryness by N₂-blowing. The residue was dissolved and diluted to1.0 mL with acetonitrile. The above solution was filtered with 0.22 μm organic nylon film. LC-MS/MS was applied to the determination of sildenafil in the filtrate with on-line solid phase extraction of molecularly imprinted monolithic column. Zorbax SB C₁₈ chromatographic column was used as stationary phase, and the mixture of 0.1% (φ) formic acid solution and acetonitrile mixed in different ratios was used as mobile phase in gradient elution. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Linear relationship between values of peak area and mass concentration of sildenafil was kept in the range of 0.5-100.0 μg·L^-1, with detection limit (3S/N) of 0.15 μg·kg^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 93.5%-99.7%, with RSDs (n=6) of determined values in the range of 0.80%-2.1%.