Determination of Dithiocarbamates in Residues by Liquid Chromatography with Selective Precolumn or Reaction-Detection Systems

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Abstract
Two liquid chromatographic methods have been developed for the selective determination of dithiocarbamate fungicides in residues. Thiram was detected at 435 nm as copper(II) dimethyldithiocarbamate after post-column complexation with Cu(II). The reaction takes place in a solid-state reactor which is packed with metallic copper. Due to the high detection wavelength possibly interfering compounds do not disturb the determination of thiram. In combination with on-line trace enrichment on C18-bonded silica detection limits in the low-ppb range can be obtained. Examples for the determination of thiram in soil and on apples and lettuce are shown. For ethylenebisdithiocarbamates such as maneb or zineb, a selective preconcentration system was developed. Nabam which is formed during extraction with EDTA is preconcentrated as an ion-pair on a C18-precolumn which is loaded on-line with cetrimide. Interfering apolar compounds are removed by adsorption on a C18 clean-up precolumn which is inserted in front of the preoncentration precolumn. With this set-up maneb and zineb could be determined in soil extracts without off-line clean-up steps at concentrations of 100 ppb.