SPECTROPHOTOMETRIC DETERMINATION OF MANEB, ZINEB AND THEIR DECOMPOSITION PRODUCTS IN SOME VEGETABLES AND ITS APPLICATION TO KINETIC-STUDIESAFTER GREENHOUSE TREATMENT

A simple and accurate spectrophotometric method has been developed for the determination of Maneb, Zineb and their decomposition product, et hylene-thiourea (ETU), using 2,6-dibromoquinone chlorimide (DBQ) and 2 ,6-dichloroquinone chlorimide (DCQ). The method depends upon releasing the ethylenebis-dithiocarbamate (EBDC) moiety from Maneb and Zineb us ing ethylenediamine tetraacetic acid disodium salt as a solvent. EBDC then reacts with either DBQ or DCQ yielding a red colour with a maximu m absorption at 495 nm. ETU, on the other hand produces a yellow colou r with a maximum absorption at 385 nm. The method was successfully app lied to the determination of these compounds in cucumber and tomato fr uits grown in greenhouses. The percentage extraction of Maneb and Zine b from cucumber was 94.5% and from tomato was 89.2%. The disappearance of Maneb and Zineb sprayed on cucumber and tomato grown in a greenhou se followed first-order kinetics. The rates of disappearance of Maneb and Zineb were correlated to the rate of growth of cucumber and tomato .