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Practical approaches to the analyses for pesticide residues in essential oils

by Sandra M. Garland, Prof. Robert C. Menary, NW Davies and Garth S. Oliver

July 2004

RIRDC Publication No 04/109  RIRDC Project No UT-36A

Introduction
Many papers have been published detailing methods for the analysis of pesticide residues in matrices such as water and vegetables. The detection of analytes in essential oils, however, has specific problems associated. The chemical properties of the active ingredients of many pesticides, such as polarity and retention behaviour in chromatography media, are often very similar to those observed for components of essential oils.

Clean-up, or rather the limited applicability of standard pre-concentration steps, presents as the greatest limitation. The greater majority of commercially produced, solid phase extraction columns are designed to trap low levels of pesticide residues from large quantities of water. Even in the analysis of vegetables, an aqueous phase is the predominant matrix from which pesticides are absorbed. Essential oils are usually a complex mixture of medium polarity and non-polar extracts of plant material concentrated to as little as 5% of the source material. Development of an analytical methodology for any one contaminant can be achieved, but the pre-concentration of a number of pesticide residues within one screen is problematic.

For the great majority of pesticides, the structure and chemical properties of the active ingredient confer physical properties, such as polarity, solubility and elution characteristics which can be used as a predictive indicator for their behaviour in clean-up methodology involving chromatography. The components which present as the most likely to co-extract with essential oils are, by the nature of their extractability, the most difficult to separate from the matrix and the most likely to interfere with the analysis, having similar behaviour in liquid partition and chromatographic methodologies. This manual is designed to provide an overview of the applicability of the analytical technology generally available, to the detection of analytes.

Methodologies are designed based on the chemical type of the active ingredient. The Manual can be read in conjunction with reports on four RIRDC projects detailing the development of analytical techniques for the determination of pesticide minimum residue limits in essential oils: UT-8A, UT-13A Publication No 98/123, UT23A Publication No 04/023 and UT-36A Publication No 04/104

 

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