A spectrofluorimemc method for the determination of chlorpyriphos in apples, based on the inhibition of the acetylcholinesterase enzyme (ACE), has been established. The method employs a non-fluorescent synthetic enzyme substrate (Indoxyl acetate), which is hydrolyzed by the enzyme to yield a highly fluorescent product. In presence of the inhibitor, the rate of formation of this fluorescent product is lowered The rate of change in the fluorescence is measured AF/At. (Xex =395 nm; h, = 470 nm). The simple spectrofluorimetric method described for the determination of chlorpyriphos in apple has a limit of detection of 13.68 pM with relative standard deviation of 7.1 %. The method was applied to chlorpyriphos added (28.5 and 57 pM) to apples with recoveries ranged between 107% and 91%.
2-Naphthyl acetate acts as a pro-enhancer of the luminol-H2O2-horseradish peroxidase reaction. Cholinesterase hydrolyses the bound acetyl group and produces 2-naphthol, and this compound is an enhancer of the chemiluminescent reaction. We studied the kinetics of chemiluminescent emission and the influence of 2-naphthyl acetate and cholinesterase enzyme concentrations. The cholinesterase concentration versus chemiluminescence intensity maximum was linear for cholinesterase between 0 and 181 microU/mL, with a detection limit of 8 microU/mL and a relative standard deviation of 9.5% (n = 3), for a sample containing 90.67 microU/mL of cholinesterase.
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