Determination of 4 Polycyclic Aromatic Hydrocarbons in 3 Edible Oils by HPLC with Fluorescence Detection After Sample Pretreatment by Specific Enzymolysis

A portion (2.0 g) of edible oil sample (animal oil, vegetable oil or oil after use in frying) was mixed with 5 mL of pH 8.0 phosphate buffer solution and 0.2 g of lipase, and enzymolyzed for 2 h at (37±2)℃ under stirring. 1.0 g of K₂CO₃ and 5 mL of ethanol were added and mixed thoroughly to saponify the fat and to reduce emulsification of the solution during the following extraction. Four PAHs (BaA, BbF, BkF and BaP) in the solution after adding 5 mL of water were then extracted twice with n-hexane (15 mL for each extraction) by shaking for 5 min, and after centrifugation for 5 min, and the extracts of the upper phase were collected, combined and evaporated to dryness at 40℃. The residue was dissolved and diluted to 1.0 mL with acetonitrile. The solution was filtered through 0.22 μm filtering membrane and the filtrate was used for HPLC analysis under the intrumental working condition. Dikma Plus C₁₈ chromatographic column was used as the stationary phase, and mixtures of (A) water and (B) acetonitrile in various ratios were used as mobile phases in the gradient elution. Retentiom times of 9.3, 12.0, 12.6, 13.9 min were found for the 4 PHAs respectively. Fluorescence detection (FLD) was made in the HPLC determination, and values of intensity of the emission fluorescence of the 4 analytes were measured at the λ_em of 380 nm for BaA and at the λ_em of 406 nm for BbF, BkF and BaP. Standard curves for the 4 analytes were prepared with the mixed standard solution of the 4 PHAs added separately to the 3 oil samples as matrixes, giving same linearity range between 0.1 and 5.0 μg·L^-1. Values of detection limits (3S/N) found were same of 0.03 μg·kg^-1 for the 4 PAHs. Tests for recovery were made by standard addition method using the 3 oil samples as matrixes, and values of recovery found were all over 90.0%, and values of RSDs (n=5) found were all below 9.0%.