1993 Volume 42 Issue 6 Pages 357-362
A simple and sensitive method for the determination of mecoprop (MCPP) in river and ground-water samples is described. This method is based on the reaction of potassium MCPP (MCPP-K) with 4-bromomethyl-6, 7-dimethoxy coumarine (4-Brmdmc) in the presence of 1, 4, 7, 10, 13, 16-hexaoxacyclooctadecane (18-crown-6) as a catalyst to form the Mdmc·MCPP ester, which is determined using a liquid chromatograph equiped with a fluorescence detector set at 346 nm (λex) and 434 nm (λem) and an HIA thermostat kept at 40°C using a column of Kaseisorb LC-ODS-300-5 (250×4.6 mm i.d.). The calibration curve for MCPP in the 0.12.0μg/reaction mixture range is linear and sufficiently reproducible for a quantitative determination. The procedure was as follows A 200-ml portion of the sample was passed through a Sep-Pak Ps-1 cartridge column (which was conditioned with 5 ml of a methanol-acetonitrile (1 : 1) solution and 25 ml of distilled water before use) at a flow rate of 10 ml/min. The column was eluted with 6 ml of acetonitrile at a flow rate of 1 ml/min. The elutate was transferred into a 15-ml test tube with a glass stopper, and the evaporated under reduced pressure at 55°C in a water bath. The residue was dissolved in 0.5 ml of a potassium hydroxide-methanol solution (0.1 mg/ml) (This step is taken to form MCPP-K), and then evaporated, as described above. Subsequently, 0.1 ml of a 4-Brmdmc solution (0.5 mg/ml) and 0.1 ml of 18-crown-6 solution (0.5 mg/ml) were added. After a reaction at 70°C with occasional shaking for 10 min in a water bath and cooling to room temperature, 20 μl of the reaction mixture was injected into the HPLC. The MCPP in the river- and ground-water samples was determined from the peak height at the retention time (13.5 min) on the chromatogram, and compared with a calibration curve. The average recoveries of MCPP added to the river water were 90.9, 91.9, 94.5, 93.0 and 92.0% at 0.5, 1.5, 2.5, 5.0 and 10.0 ppb levels, respectively ; the detection limit was 0.3 ppb. The RSD (n=4) of the values determined was less than 6%. The MCPP was not detected in twenty of the river- and ground-water samples. The Mdmc·MCPP ester was stable for at least 5 days if stored under appropriate conditions.
