Capillary electrophoresis with immobilized quantum dot fluorescence detection for rapid determination of organophosphorus pesticides in vegetables

Based on the highly sensitive and selective fluorescence enhancement of water-soluble CdTe/CdS core-shell quantum dots (QD) by organophosphorus pesticides (OPs such as mevinphos, phosalone, methidathion and diazinon), a simple, rapid and selective method is developed using CE with QD/LIF detection (473 nm excitation/532 nm fluorescence) to determine OPs in vegetable samples. The method enables the use of a simple pretreatment procedure based only on solvent extraction and eliminates the use of a time-consuming SPE step. A novel procedure is developed to immobilize QD onto the inside capillary surface via the formation of a silane coupling mercaptopropyltrimethoxysilane network. Under optimized CE conditions, baseline separation for all four OPs was observed within 12 min. The CE-QD/LIF method was shown to have a detection limit from 50 to 180 mu g/kg, working ranges 0.1-30 mg/kg, recoveries 88.7-96.1% and repeatability (RSD, n = 3) 0.36-0.75% for migration time and 2.9-5.7% for peak height. For tomato samples, the detection limits were more than ten times lower than maximum residue levels specified by the Codex Alimentarius Commission for all four OPs investigated. The method thus satisfies the need for a simple, quick and selective method to determine residual OPs in complex vegetable matrix as required by the increasingly strict regulations for health protection introduced in recent years.