ANALYTICAL METHODS FOR TEA PESTICIDE RESIDUES

Abstract

Guidance methods are provided for analysis of residues of pesticides in tea and tea brew. These methods cover most of the pesticides used in tea. Method for analysis of organochlorines, organophosphates and pyrethroids in tea involves extraction of the prehydrated tea samples with acetone. The acetone extract is evaporated, dissolved in water and re-extracted into n-hexane. Further clean-up is done on adsorption column with neutral alumina (activity grade V) as adsorbent and hexane-acetone mixtures as eluting solvents. Pesticide concentrations in the cleaned-up tea extracts are determined using gas chromatograph with either Electron Capture Detector (ECD) or Nitrogen Phosphorous Detector (NPD). Method for Triazole residues in tea is slightly different from the one proposed for organochlorines, organophosphorous and pyrethroids. In this method after acetone extraction, re-extraction is into dichloromethane instead of n-hexane and in adsorption column chromatographic clean-up, the eluting solvent is a mixture of dichloromethane and hexane. Method for pesticide residue analysis in tea brew follows the same steps by starting from re-extraction (liquid-liquid partitioning) step. The proposed methods are derived out of experience on pesticide residue analysis in tea and need to be optimized and validated prior to implementation.