Fiber optic monitoring of carbamate pesticides using porous glass with covalently bound chlorophenol red

An optical fiber biosensor for the determination of the pesticides propoxur (Baygon(R)) and carbaryl, two of the most commonly used carbamate insectic ides in vegetable crops: is described. A pH indicator. chlorophenol red, is used as optical transducer of the inhibition of the enzyme acetylcholinest erase by the analytes. The biorecognition element is covalently immobilized onto controlled pore glass beads (CPG) and packed in a thermostatized bior eactor connected to a flow-through cell that contains CPG-immobilized chlor ophenol red placed at the common end of a bifurcated fiber optic bundle. In the presence of a constant acetylcholine concentration, the colour of the pH sensitive layer changes and the measured reflectance signal can be relat ed to the carbamate concentration in the sample solution. The performance o f the biosensor has been optimized using a flow injection system. The linea r dynamic range for the determination of carbaryl and propoxur spans from 0 .8 to 3.0 mg l(-1) and from 0.03 to 0.50 mg l(-1), respectively. The detect ion limit (3 s) of the biosensor for propoxur (0.4 ng) is lower than that m easured for carbaryl (25 ng). Reproducibility, stability and interference s tudies of the optical device are reported. The biosensor has been applied t o the determination of propoxur in spiked vegetables (onion and lettuce) us ing ultrasound extraction, achieving recovery values between 93 and 95% for onion samples at the different concentration levels assayed. (C) 2000 Else vier Science S.A. All rights reserved.