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) and carbaryl, two of the most commonly used carbamate insecticides in vegetable crops, is described. A pH indicator, chlorophenol red, is used as optical transducer of the inhibition of the enzyme acetylcholinesterase by the analytes. The biorecognition element is covalently immobilized onto controlled pore glass beads (CPG) and packed in a thermostatized bioreactor connected to a flow-through cell that contains CPG-immobilized chlorophenol 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 related to the carbamate concentration in the sample solution. The performance of the biosensor has been optimized using a flow injection system. The linear 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 detection limit (3 s) of the biosensor for propoxur (0.4 ng) is lower than that measured for carbaryl (25 ng). Reproducibility, stability and interference studies of the optical device are reported. The biosensor has been applied to the determination of propoxur in spiked vegetables (onion and lettuce) using ultrasound extraction, achieving recovery values between 93 and 95% for onion samples at the different concentration levels assayed.