Determination of Residual Amounts of Olaquindox in Aquatic Products by UPLC

Aquatic sample was minced, pulped and homogenized to a gruel-like state. A portion (5.00±0.05) g of the sample was taken and extracted twice with 12 mL and 8 mL of water at 60℃ for 10 min in each extraction. After centrifuging, the extracts were combined, decolorized and separated from some impurities by mixing with 9 mL of saturated borax solution and 3 mL of 300 g·L^-1 zinc sulfate solution. The mixture was centrifugated, and the supernatant was taken and passed through SPE column to have the analyte (OLA) adsorbed on the column. The column was rinsed with 5 mL of water which were discarded. Then the column was eluted with 10 mL of a mixture of methanol and ethyl acetate (10+90) to desorb OLA from the column. The eluate was collected and evaporated to near dryness by N₂-blowing at 50℃. The residue was dissolved with 1.0 mL of the mobile phase used in UPLC analysis, and the solution was used for UPLC separation and determination. BEH C₁₈ column was used as the stationary phase and a mixture of CH₃OH-H₂O (15+85) was used as mobile phase in the LC separation. UV detector was used in the detection at the wavelength of 380 nm. Linear relationship between values of peak area and mass concentration of OLA in the range of 0.150-50.0 mg·L^-1 was obtained, with detection limit (3S/N) of 30 μg·kg^-1. Recovery was tested by standard addition method, giving values of recovery ranged from 76.4% to 90.2%. Values of RSDs (n=5) were found in the range of 3.3%-9.0%.