Spectrophotometric determination of the soil fumigant: dazomet with copper(II)–neocuproine reagent

Abstract

A spectrophotometric method has been developed for the assay of dazomet, a soil fumigant effective for the control of nematodes, germinating weeds and soil fungi, using the copper(II)–neocuproine (2,9-dimethyl-1,10-phenanthroline) oxidizing reagent. A highly colored copper(I)–neocuproine chelate formed immediately in ammonium acetate–buffered solution a result of the redox reaction with dazomet, and its concentration measured from the absorbance at 453nm using a molar absorptivity of (3.35±0.15)×104lmol−1cm−1 for dazomet, the LOD for soil being 1–2ppm. Dazomet in commercial formulations (such as Basamit, BASF) and soil extract could be measured by the developed method which was rapid (color development took 5min), and cost-effective. The developed method was as precise as the CIPAC HPLC method (at 95% confidence level) using a nucleosil 100-5 C18 column with UV detection. The degradation of dazomet in different types of forestry soil, i.e. sandy, loamy and clay soils to which moisture and Basamit in recommended doses were applied, was followed kinetically using the developed procedure. The proposed method is much simpler than the US-EPA and CIPAC methods of dazomet assay, and is applicable to on-site colorimetry for field use (via retention of the colored copper(I)–neocuproine cation on an acidic cation exchanger) where rapid detection of dazomet residues and breakdown products is required. The method was not interfered with common soil ions and 1,3-dichloropropene (1,3-D), a fumigant used in combination with dazomet.