Determination of residual levels of metrafenone in lettuce grown under greenhouse conditions using gas chromatography with a micro-electron capture detector

The current study was carried out to detect metrafenone residues and estimate the half-lives in lettuce grown under greenhouse conditions using gas chromatography with a micro-electron capture detector. Metrafenone was applied in two and three doses (with a 7-day interval) to two different sites in Naju (distance between sites 1 and 2 = 6.5 km) in different seasons (spring and autumn). Samples were extracted with acetone and matrix components were purified using a silica solid-phase extraction (SPE) cartridge. The calibration curve over the concentration range of 0.02-5.0 mg/L was linear with a determination coefficient (R-2) = 0.9993. The limits of detection and quantification were 0.003 and 0.01 mg/L, respectively. Recoveries at two fortification levels (0.1 and 0.5 mg/kg) ranged from 78.5 to 113.3 % with a relative standard deviation <8 %. The calculated half-lives were 2.3 and 2.2 days and 4.9 and 5.0 days for the double and triple doses at sites 1 and 2, respectively. These results suggest that the method is effective and sensitive for the determination of metrafenone residues in field-incurred lettuce samples, and the difference in the reported half-lives is due to seasonal variation.