Inhibition-based determination of metrifonate in liquid and solid samples using the triple integration chemical hydrolysis-pervaporation-enzymic derivatisation

An innovative continuous flow approach consisting of the triple integration of chemical hydrolysis, analytical pervaporation and enzyme inhibition-bas ed reaction for the determination of metrifonate is presented. The method i s based on chemical degradation of the pesticide, a separation step consist ing of analytical pervaporation of its volatile metabolite and inhibition a ction of this on the acetylcholinesterase catalysis. The subsequent derivat isation reaction is a two-step reaction involving choline oxidase (ChOD) an d horseradish peroxidase (POD) with fluorimetric detection (lambda (ex) = 3 10 nm and lambda (em) = 415 nm) of the dimer formed by the action of hydrog en peroxide. The efficiency of the inhibitory effect was increased using an open-closed Row system. Applied to liquid samples, the method has a linear determination range of 0.0025-0.15 g l(-1) (n = 8, r = 0.9993) with a prec ision, expressed as RSD, of 3.2-6.7% and a sampling frequency of 3 h(-1). W hen applied to solid samples the method shows a linear determination range of 0.0026-0.13 g kg(-1) (n = 5, r(2) = 0.9981, RSD 2.7-7.7%) and a sampling frequency of 2 h(-1). The approach has been applied to the determination o f metrifonate in natural water and spiked soil samples with recoveries rang ing between 94.3 and 107.8% for liquid samples and between 86.5 and 99.6% f or solid samples. (C) 2001 Elsevier Science B.V. All rights reserved.