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Strategic implementation of liquid chromatography time of flight mass spectrometry (MS) & tandem MS for rapid screening of pesticide residues in fruit and veg. - PS2541

Description
A PSD funded a pilot project (PS2528) to assess the potential advantages of liquid chromatography - time of flight mass spectrometry (LC-TOF-MS) for screening samples of food for pesticide residues has recently concluded successfully. The project yielded information on the performance and ruggedness of LC-TOFMS and the advantages and disadvantages, compared to Liquid Chromatography coupled to tandem quadrupole mass spectrometry (LC-MS/MS).

LC-MS/MS is an established technique for the determination of trace concentrations (µg/kg) of pesticide residues in foods. One of the disadvantages of the ‘targeted` pesticide approach using LC-MS/MS is the inability to detect any `non-targeted` pesticides that are present in the sample but not a predefined list . This is because the operation of LC-MS/MS systems requires the mass of each pesticide to be programmed into the acquistion method. By contrast, LC-TOFMS acquires exact mass data across the entire mass range of interest and thus, does not require pre-programming with a pre-defined list of pesticides. As a consequence there is increasing interest in the use of TOFMS to overcome the limitation of the scope of methods based on the use of LC-MS/MS. Any pesticide that is soluble in the extraction solvent, compatible with the chromatographic conditions and gives sufficient detector response will be detected using TOFMS. Thus, a major advantage of TOFMS compared to LC-MS/MS is the potential to screen a much larger number of pesticides in a single analysis.

The results from the `proof of principle` pilot project (PS2528) demonstrated the capability of UPLC (ultra performance liquid chromatography)-TOFMS to reliably detect pesticides, with different physico-chemical properties, at adequately low concentrations (around 10 µg/kg); samples were extracted using the `generic` QuEChERS (Quick, Easy, Cheap, Effective and Robust) acetonitrile method. Results were compliant with EU Pesticide Method Validation Guidelines for 48 (76 %) of the pesticides tested at 10 µg/kg in grape matrix. The analysis was rapid (<10 minutes per MS run) and the TOFMS system proved extremely robust. These findings are confirmed by reports in the literature (1,2) and information from the Commity Reference Laboratory (3). Further funding is required to realise the potential advantages of implementing LC-TOFMS for screening pesticides in the UK monitoring programme.

The results of PS2528 show that a small number of pesticides are not amenable to `generic` UPLC-TOFMS conditions. The inference is that comprehensive LC-MS screening analyses will require parallel analysis of the same extract using both UPLC-MS/MS and UPLC-TOFMS (or equivalent). Those pesticides not amenable to UPLC-TOFMS could be determined by UPLC-MS/MS along with pesticides expected to occur as residues (to provide additional confirmation of identity). Before such an approach could be implemented an evaluation of a large number of pesticides (probably around 400) using both UPLC-MS/MS and UPLC-TOFMS is required to optimise the distribution of pesticides between TOFMS and LC-MS/MS. A current project (PS2537) is assessing the performance of UPLC-MS/MS for the analysis of 200 pesticides. This new proposal would evaluate the performance of those 200 pesticides, plus an additional 200 pesticides using TOFMS. The additional 200 pesticides which could include `biopesticides` (e,g. streptomycin, azadirachtin) and relevant metabolites (included in recent pesticide legislation) currently not included in the PRC programme. The longer term objective is to use UPLC-MS/MS and UPLC-TOFMS together to analyse around 350 analytes in a single extract. If achievable at realistic costs, (dependent on analytical quality control criteria and data handling considerations) this would have significant benefits for the UK Pesticides Residues Committee (PRC) monitoring programme i.e.

i) A significant improvement in the scope of the PRC UK monitoring programme
ii) A reduced risk of false negative results (residues not detected due to incomplete target compound lists), including the non- detection of the misuse of pesticides
iii) Improved consumer risk assessments
iv) Improved value for money (more pesticides per unit cost)


References
1) Juan F. Garcia-Reyes et al; Comprehensive screening of target, non-target and unknown pesticides in food by LC-TOF-MS, TrAC Trends in Analytical Chemistry (2007), 8, p828-841.
2) Imma Ferrer et al; Multi-residue pesticide analysis in fruits and vegetables by liquid chromatography-time-of-flight mass spectrometry, J.Chrom A., 1082 (2005) 81-90.
3) A. Fernndez-Alba - Oral presentation at the 1st latin American Pesticides Residues Workshop (LAPRW 2007), Brasil.
Objective
A PSD funded a pilot project (PS2528) to assess the potential advantages of UPLC-TOF-MS in the context of screening samples for the UK monitoring programme on pesticide residues in foods has recently concluded. To build on the success of the pilot project by developing UPLC-TOFMS methodologies for use in the PRC monitoring programme further funding is required. The requirement for additional funding was identified at the start of the pilot project. The results of the pilot project indicate that truly comprehensive monitoring of LC amenable pesticides will require complementary analyses using both UPLC-TOFMS and UPLC-MS/MS. Therefore it is proposed to align this proposed UPLC-TOF extension project with a concurrent project on UPLC-MS/MS. This would optimise the use of resources required for the procurement of pesticide reference standard materials and subsequent preparation of pesticide standard solutions, which have a short lifetime (usually <1 year). If possible the UPLC conditions will be kept the same for both TOFMS and MS/MS to enable transfer of the methods from one system to the other and to reduce the need for repeat optimisation of chromatographic conditions.

This LC-MS proposal, will assess the LC-TOFMS performance for the analysis of the same 200 pesticides currently being evaluated by LC-MS/MS in project (PS2537). This evaluation will take place in year 1. In the second year, an additional 200 pesticides will be evaluated using LC-TOFMS. The longer-term objective is to use LC-MS/MS and LC-TOFMS together to analyse a total of approximately 350 analytes in a single extract. If achievable at realistic costs, (dependent on analytical quality control criteria and data handling considerations) this would have significant benefits for the UK Pesticides Residues Committee (PRC) monitoring programme


The Specific Objective of this project is:

To attempt to implement a strategic approach based on the use LC-TOFMS and LC-MS/MS, for the screening/quantification of 350 or more pesticides in a single extract, by the end of March 2010.
Project Documents
• Final Report : Strategic implementation of liquid chromatography time of flight mass spectrometry (MS) & tandem MS for rapid screening of pesticide residues in fruit and veg   (855k)
Time-Scale and Cost
From: 2008

To: 2009

Cost: £148,614
Contractor / Funded Organisations
Central Science Laboratory
Keywords
Agriculture and Food Chain              
Analysis              
Analytical Chemistry              
Food Safety              
Mass Spectrometry              
Monitoring              
Pesticide Residues              
Public Health              
Residues Testing              
Fields of Study
Pesticide Safety