Extractive spectrophotometric determination of dimethoate with molybdate and Methylene Blue by a flotation–dissolution method

Abstract

A sensitive extraction spectrophotometric method based on flotation–dissolution is described for the determination of trace levels of the organophosphorus pesticide dimethoate. Dimethoate is converted into a molybdophospho complex by reaction with ammonium molybdate in sulfuric acid medium. The complex floating on the interface of the aqueous and organic layers along with Methylene Blue as an ion associate is separated and dissolved in acetone. The colour system obeys Beer's law in the range 0.02–0.16 µg ml^–1 of dimethoate. The molar absorptivities of the system calculated in terms of phosphorus and dimethoate are 1.5 × 10⁵(±100) l mol^–1 cm^–1 and 1.08 × 10⁶(±100) l mol^–1 cm^–1, respectively. The standard deviation and relative standard deviation were 0.006 µg ml^–1 and 3.2%, respectively. The method was satisfactorily applied to the determination of dimethoate in water, soil and plant materials.