Dispersive liquid-liquid microextraction based on the solidification of a floating organic droplet for simultaneous analysis of diethofencarb and pyrimethanil in apple pulp and peel

A method for analysis of diethofencarb and pyrimethanil in apple pulp and peel was developed by using dispersive liquid-liquid microextraction based on solidification of a floating organic droplet (DLLME-SFO) and high-performance liquid chromatography with diode-array detection (HPLC-DAD). Acetonitrile was used as the solvent to extract the two fungicides from apple pulp and peel, assisted by microwave irradiation. When the extraction process was finished, the target analytes in the extraction solvent were rapidly transferred from the acetonitrile extract to another extraction solvent (1-undecanol) by using DLLME-SFO. Because of the lower density of 1-undecanol than that of water, the finely dispersed droplets of 1-undecanol collected on the top of aqueous sample and solidified at low temperature. Meanwhile, the tiny particles of apple cooled and precipitated. Recovery was tested for a concentration of 8 mu g kg(-1). Recovery of diethofencarb and pyrimethanil from apple pulp and peel was in the range 83.5-101.3%. The repeatability of the method, expressed as relative standard deviation, varied between 4.8 and 8.3% (n = 6). Detection limits of the method for apple pulp and peel varied from 1.2-1.6 mu g kg(-1) for the two fungicides. Compared with conventional sample preparation, the method has the advantage of rapid speed and simple operation, and has high enrichment factors and low consumption of organic solvent.