Robust Extraction and Clean-up Method for Analysis of Organophosphates, Synthetic Pyrethroids, Organochlorines, Diflubenzuron and Triflumuron on Raw Wool

Abstract

This report describes a robust method for the extraction of hydrophobic pesticides in raw wool and for clean-up of the extract prior to analysis. The pesticides covered by this method include organophosphates (OPs), synthetic pyrethroids (SPs), organochlorines (OCs) and the hydrophobic insect growth regulators (IGRs), diflubenzuron and triflumuron. In keeping with the original intention of Draft TM 59, the method described is not intended to be prescriptive; it simply seeks to provide guidance for the newer laboratories that are having problems with isolation of pesticides from the difficult wool wax matrix.

The procedures described remove the high molecular weight and polar materials that are encountered on raw wool, and produce relatively clean pesticide-containing fractions that can be chromatographed reliably and reproducibly. The methods can be performed manually and do not require specialised equipment. It is intended that laboratories will substantially modify the procedures to suit the equipment and supplies that they have on hand, and the analytes that they need to determine. As an example, quantitation of the analytes (with the exception of diflubenzuron and triflumuron) in this procedure is by gas chromatography (GC) using dual electron capture detector (ECD) and a phosphorous-specific thermionic specific detector (TSD). It is likely that most modern laboratories will already be using more selective mass spectrometry for the detection of most pesticides, however the tuning, set-up, selectivity and optimisation of these detectors is highly dependent on the brand and model of the detectors (and in some cases, different units), and is beyond the scope of this paper. It is possible that laboratories can operate both mass-selective detectors and TSD/ECD in parallel while they develop their own robust procedures.

The method described uses a mixture of hexane and ether to extract lipid material and hydrophobic pesticides from raw wool. The bulk of the high molecular mass wool wax is removed from the extraction solution using gel permeation chromatography (GPC), and a small silica gel chromatography column is used to isolate pesticides of different polarities into two different fractions. The more polar pesticides (the organophosphates) are analysed separately using suitable GC conditions with a specific TSD detector. The wool wax fraction containing the less polar pesticides is relatively free of interferences and can be analysed by GC with ECD, however a confirmatory analysis using a different GC column is strongly advised if the relatively non-specific ECD is used.

The more polar IGRs are thermally unstable under GC conditions, and they are analysed separately using a simpler solid phase extraction (SPE) clean-up with quantitation using high performance liquid chromatography (HPLC).

Citation

"Robust Extraction and Clean-up Method for Analysis of Organophosphates, Synthetic Pyrethroids, Organochlorines, Diflubenzuron and Triflumuron on Raw Wool", C.R. Nunn, L. Grundy, I.M. Russell, Report 04, Raw Wool Group, IWTO, Cairo Meeting, May 2006.