204 Determination of pesticide residues in grain by gel permeation chromatography/gas-liquid chromatography

Methods Type: Recommendations
Key data
Number: 204
Analyte: Pesticide Residues (Gel Permeation Chromatography/Gas-Liquid Chromatography)
Matrix: Grain
Year of Approval: 1998
Scope: The method is applicable to cereals and cereal foods and determines organohalogen, organophospate and synthetic pyrethroid residues in grain.
Principle: Ground cereal grain is extracted with acetone/methanol (1:1). Water is added beforehand in an amount that takes full account of the natural water content of the sample, so that during extraction the acetone : water ratio remains constant at 2:1. The extract is saturated with 3% sodium chloride solution and diluted with dichloromethane, resulting in separation of excess water. The evaporation residue of the organic phase is cleaned up by gel permeation chromatography on Bio Beads S-X3 (polystyrene gel) using a mixture of cyclohexane and ethyl acetate as eluant. The residue-containing fraction is concentrated and analysed directly by gas chromatography using a phosphorus selective detector for organophosphorus and electron-capture detector for organohalogen pesticides. For the analysis of synthetic pyrethroids by electron capture detection, a supplemental clean-up on silica or alumina (neutral) sep-pak is always necessary.

Reagents

All reagents shall be suitable for the analysis of pesticide residues.

  • Acetone
  • Dichloromethane
  • Ethylacetate
  • Cyclohexane
  • GPC eluting mixture: cyclohexane / ethyl acetate 1:1 v/v
  • n-Hexane
  • Pesticide standard solutions: 0.01-10 µg/ml (depending on detector sensitivity), in a suitable solvent
  • Glass wool, extracted exhaustively with aceton
  • Cotton-wool, extracted exhaustively with acetone
  • Bio Beads S-X3
  • Filter paper, 6 and 13,5 cm diameter, fast flow rate, extracted exhaustively with acetone

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