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Assessment of Stability of Pesticides During Sample Processing. Richard Fussell CSL York, UK e-mail: r.fussell@csl.gov.uk. Analytical Strategies for Pesticide Residues Analysis. Derivatisation. Oxidation. SAMPLING RECEIPT OF SAMPLES SAMPLE PROCESSING ambient / cryogenic / acid
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Assessment of Stability of Pesticides During Sample Processing Richard Fussell CSL York, UK e-mail: r.fussell@csl.gov.uk
Analytical Strategies for Pesticide Residues Analysis Derivatisation Oxidation SAMPLING RECEIPT OF SAMPLES SAMPLE PROCESSING ambient / cryogenic / acid EXTRACTION ethyl acetate / acetone / acetonitrile / SFE CLEAN-UP GPC / HPGPC / SPE / SPME DETECTION / QUANTITATION / CONFIRMATION Gas Liquid Chromatography Liquid Chromatography AED / ECD / NPD / FPD / MS / MS-MS FL / UV / DAD / MS / MS-MS REPORTS
Ambient Temperature Processing ‘Tomato purée
Sample Processing - Losses at Ambient Temperature • 1994 CSL reported rapid losses of chlorothalonil in lettuce • Subsequent investigations have indicated losses of a number of pesticides during sample processing at ambient temperatures: bitertanol dichlofluanid isofenphos captan dicofol tebuconazole captafol etridiazole tolylfluanid chlorothalonil folpet
Mechanisms for Losses during Sample Processing No single mechanism involved • nature, temperature, duration of processing • volatility e.g. fumigants, biphenyl, dichlorvos • hydrolysis (exposure to water) • Interaction with chemicals/enzymes released from plant cells • pH
Sample Processing - Implications of the Losses • Unlikely to cause an underestimate of consumer risk • MRL exceedances and misuse may not be detected ‘Cryogenic’ processing may help to minimise some of the losses and is used in the generation of registration data
‘Cryogenic’ Sample Processing - Temperature Conditions • Freeze Sample (-20°C) • Add ‘dry ice’ (-69°C) • Homogenise to produce a flowable powder (-25 to -30°C) samples must not defrost
Development of a ‘ Cryogenic’ Processing Protocol for Apples Protocol designed to reflect intended practice • whole fruit spiked prior to freezing • spiking at realistic levels (0.05 mg/kg) • 106 different pesticides assessed for stability • parallel method recoveries • extraction using ethyl acetate • measurement using GC-MS, GC-FPD, LC-FL
Spiking Procedure 250 µl of pesticides standard in ethyl acetate
Development of a ‘ Cryogenic’ Processing Protocol for Apples Protocol designed to reflect intended practice • whole fruit spiked prior to freezing • spiking at realistic levels (0.05 mg/kg) • 106 different pesticides assessed for stability • parallel method recoveries • extraction using ethyl acetate • measurement using GC-MS, GC-FPD, LC-FL
Sample Processing Protocol - Other Considerations • calculation of mass balance - sum of pesticides on filters, in mill washes and sample • chlorpyrifos-methyl employed as an internal deposition standard - assumed to be stable • duplicate analysis on 7 different days, duplicate injection (n=28)
‘Cryogenic’ Processing - Summary of Results • Uncorrected Data AQC - % mean recoveries 85-90%, %CVs 5-10% mass balance - 75 - 85%, %CVs 5 -10% (equates to loss of 0.5 - 1 µg of each pesticide) • CPM Corrected Data AQC & ‘Survival’ (processing recovery minus AQC recovery) very similar - % mean recoveries 97 - 102%, %CVs 2 - 5% • >90% survival for >100 pesticides • malaoxon only 80% survival
‘Cryogenic’ Processing - Notable Successes Survival (%) Pesticide Ambient ‘Cryogenic’ bitertanol 5 100 captan* 41 81 captafol* 62 95 dichlofluanid 46 90 folpet* 50 93 heptenophos 50 93 isofenphos 60 100 tolylfluanid 52 96
‘Cryogenic’ Processing - Future Work • Re-assessment of ‘problem’ pesticides in apples • Assessment of dodine, dithianon, dinocap and dithiocarbamates in apples • Assessment of stability of a wide range of pesticides in other commodities (carrots, lettuce, onions, oranges and a brassica)
‘Cryogenic’ Processing -CPM Corrected Data Pesticides with Poor AQC Pesticide Survival Recovery %CV acephate 62 7321 methamidophos 61 7317 omethoate 71 8116 chlozolinate 87 104 24 biphenyl 46 74 17 dichlorvos 54 8021 carbendazim* 80 93 13 thiabendazole* 82 93 13 (*not corrected) phosalone, pyrimethanil, chlorothalonil - AQC failures ethoxyquin, tebuconazole, n-methyl carbamates - not included
‘Cryogenic’ Processing - Future Work • Re-assessment of ‘problem’ pesticides in apples • Assessment of dodine, dithianon, dinocap and dithiocarbamates in apples • Assessment of stability of a wide range of pesticides in other commodities (carrots, lettuce, onions, oranges and a brassica)
‘Cryogenic’ Processing - Pros and Cons • Advantages • more accurate results • improved homogeneity of sample • lower costs if samples can be milled for dithiocarbamates • Disadvantages • more stress on the equipment • more stress on the operator (noise) Cryogenic Processing is being used for more commodities in the UK monitoring programme - But cryogenic Processing does not solve all problems
Sample Processing - Chlorothalonil in Onions • Complete loss during processing at ambient temperatures and 80-90% loss during cryogenic Processing - possible reaction with sulphur compounds • Add 2.2 M phosphoric acid prior to processing - at 1 mg/kg recovery = 105%, %CV = 6.8
Sample Processing - Further Information • ARC Hill et al - Effects of Sample Processing on Pesticide Residues in Fruit and Vegetables Principles and Practices of Method Validation 2000 Ed A Fajelj and A Ambrus, RSC, ISBN 0-85404-783-2 • R Fussell et al - Assessment of the Stability of Pesticides During Cryogenic sample Processing Part 1: Apples J. Agricultural & Food Chemistry, 2002, 50, 5, 441-448 • www.iaea.org/programmes/ri/uc.html
Acknowledgments • Alan Hill, CSL, UK • Pesticides Safety Directorate, UK • Pesticides Team, CSL, UK