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Evaluation of pressurised liquid extraction for the extraction of pesticides from dry commodities - PS2538

Description
Pesticide multi-residue methods are capable of detecting and quantifying more than 100 pesticides in a single analysis. However, some important ionic pesticides cannot be included into commonly used multi-residue methods. For example, glyphosate and glufosinate, two of the most widely used pesticides worlwide, are often excluded from monitoring programmes because of the difficulties and hence high cost associated with their detection and quantification.

The current Gas- Chromatography Mass Spectrometry GC-MS method for glyphosate and glufosinate (1) is not robust (matrix dependent), lacks sensitivity and is costly because of the need for exhaustive (repeat) extraction, ion exchange SPE clean-up and derivatisation prior to GC-MS. The efficiency of recovery of incurred residues of ionic pesticides such as glyphosate and glufosinate is also questionable using current extraction procedures. Improved methodology is required to ensure that future monitoring programmes remian valid and effective.

Oat based cereal products are proposed for inclusion in the UK Pesticides Residues Committee programme 2008. Results from previous monitoring of cereals and pesticide usage data indicate that the pesticide residues likely to occur with a high incidence include glyphosate and glufosinate. To avoid criticism these should be included in the 2008 programme subject to the availability of a suitable method.

A previous Defra funded project (2) concluded that the use of methods based on reversed-phase chromatography or ion-pair chromatography did not provide satisfactory results and that ion chromatography with post column suppression and MS/MS detection could be a better alternative. Unfortunately this technique was not evaluated at that time.

Therefore, this proposal aims to evaluate the capabaility of pressurised liquid extraction to provide efficient extraction of incurred residues, and ion chromatography MS/MS for the direct analysis of glyphosate and glufosinate without the need for derivatisation. If successful the potential to analyse other difficult ionic pesticides including ethephon, fosetyl aluminium, chlormequat and trinexapac will be assessed.

References

1) P. L. Alferness and L. A. Wiebe., Determination of glyphosate and (Aminomethyl) phosphonic acid in crops by capillary gas chromatography with mass selective detection; Collaborative Study, Journal Of AOAC International, Vol 84, No.3, 2001, 823-846.

2) The development of a Method for Residue Analysis of the Herbicide Glufosinate and its Metabolites, Laboratory of Government Chemist (2002) Report No FA25/R028/2002
Objective
The overall objective of the project is to develop more robust and more cost effective methods for the determination of ionic pesticides in the future PRC monitoring programme. The aim is to include as many ionic pesticides as possible into a single extraction. Quantification of all of the pesticides will require two chromatographic analyses, one for anions and one for cations.

1) The first objective is to develop and validate a method for the determination of glyphosate, glufosinate and their transformation products in cereal and cereal products (including cereal based baby foods). The target reporting limit for cereal/cereal products will be 0.1 mg/kg and the objective is to complete the method development to enable implementation, if required, in Q3 of the PRC 2008 programme. The target reporting limit for cereal based baby food will be 0.01 mg/kg.

2) The second objective is to validate the methodology for the determination of other ionic pesticides (e.g. ethephon, chlormequat, trinexapac and fosetyl aluminium) at 0.01 mg/kg in a range of food commodities to be agreed with PSD. For those compounds which prove to be successful the methods should be available for inclusion in the PRC 2009 programme.

3) The results will be presented in the final SID 5 report by the 1st November 2008

Project Documents
• Final Report : Improved methodology for the determination of ionic pesticides in dried food commodities   (341k)
Time-Scale and Cost
From: 2007

To: 2008

Cost: £51,426
Contractor / Funded Organisations
Central Science Laboratory
Keywords
Agriculture and Food Chain              
Analysis              
Analytical Chemistry              
Analytical Quality Control              
Food Quality              
Food Safety              
Mass Spectrometry              
Method Development              
Monitoring and evaluation              
Pesticide Residues              
Public Health              
Residues Testing              
Fields of Study
Pesticide Safety