Reproducible Recoveries of Pesticides from Fruits and Vegetables

Food & BeverageReproducible Recoveries of Pesticides from Fruits and VegetablesUsing Supel™ QuE QuEChERS and an Ascentis® Express RP-Amide HPLC ColumnLC-MS/MS methods are become very popular for the analysis of pesticides in fruits and vegetables. This is due to their ability to resolve many analytes of varying functionality. However, care must be taken during sample preparation to minimize unwanted matrix components (pigments, sugars, organic acids, fatty acids, etc.) from ending up in the final extract. The presence of these non-target compounds will cause ion suppression in the MS/MS, reducing system sensitivity. The “QuEChERS” (Quick, Easy, Cheap, Effective, Rugged, and Safe) method, employing dispersive SPE, was introduced in 2003 (1), and subsequently promulgated (2,3). This technique is now the standard for the extraction and cleanup of pesticides from fruits and vegetables.ExperimentalA group of 30 compounds was selected, representing pesticides, acaricides, insecticides, and fungicides. Four calibration curves of five points from 0.01-0.2 µg/mL were prepared, each curve using acetonitrile extracts of a different food as the solvent. The foods were pear (a sugar matrix), kiwi (an acid matrix), lettuce (a chlorophyll matrix), and maize flour (a cereal matrix). Triethylphosphate was used as an internal standard. Each of the 20 calibration standards were analyzed using LC-MS/MS with an Ascentis Express RP-Amide column. Figure 1 shows the calibration curve for ethoprophos.The RP-Amide column was selected instead of a traditional C18 column because it provides increased selectivity for polar compounds, especially those that can act as a hydrogen-bond donor. Additionally, this column uses a stationary phase with an embedded polar group (EPG) that is 100% aqueous compatible, so was better suited to the mobile phase conditions used for analysis.Several food samples were homogenized and split into several replicates, with some spiked prior to extraction. All samples and spiked samples were then processed according to the extraction and cleanup steps specified in the EN 15662 method. As suggested in the method, frozen samples were used to avoid overheating when MgSO4 is added during the extraction step. After the final cleanup step, all extracts were analyzed with LC-MS/MS using the same operating conditions as the calibration standards. Figure 1. Ethoprophos Calibration Curve (prepared in lettuce extract)Results & DiscussionRecovery and RSD data was tabulated for all spiked samples, and is presented in Table 1 alongside data found in the EN 15662 method. The observed recovery data is comparable to the data found in the published method. Of note is that the observed RSD data is most often a substantial improvement over the method data. These observations testify that an Ascentis Express RP-Amide column is a valid alternative to a C18 column for this application.The Ascentis Express RP-Amide column exhibited great robustness, reproducible peak shapes, and excellent resolution. In fact, more than 1500 samples were injected before the column was removed from service.References1. Anastassiades, M; Lehotay, S. J.; Stajhbaher, D.; Schenck, F. J. Fast and easy multiresidue method employing acetonitrile extraction/partitioning and “Dispersive Solid-Phase Extraction” for the determination of pesticide residues in produce. J. AOAC Int. 2003, 86, 412-431.2. EN15662:2008, Foods of plant origin - Determination of pesticide residues using GC-MS and/or LC-MS/MS following acetonitrile extraction/partitioning and cleanup by dispersive SPE - QuEChERS-method.3. AOAC Official Method 2007.01, Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate.0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200Analyte Conc. / IS Conc.0.00.20.40.60.81.01.21.41.6Analyte Area / IS AreaFood & BeverageOXL11543-513822/T4121301102©2012 Sigma-Aldrich Co. LLC. All rights reserved. SAFC, SIGMA-ALDRICH and SUPELCO are trademarks of Sigma-Aldrich Co. LLC, registered in the US and other countries. Solutions within is a trademark of Sigma-Aldrich Co. LLC. FLUKA is a registered trademark of Sigma-Aldrich GmbH. Supelco and Fluka brand products are sold through Sigma-Aldrich, Inc. Purchaser must determine the suitability of the product(s) for their particular use. Additional terms and conditions may apply. Please see product information on the Sigma-Aldrich website at www.sigmaaldrich.com and/or on the reverse side of the invoice or packing slip.Order/Customer Service (800) 325-3010 • Fax (800) 325-5052 Technical Service (800) 325-5832 • sigma-aldrich.com/techserviceDevelopment/Custom Manufacturing Inquiries (800) 244-1173Safety-related Information sigma-aldrich.com/safetycenterWorld Headquarters3050 Spruce St. St. Louis, MO 63103(314) 771-5765sigma-aldrich.comEnabling Science to Improve the Quality of LifeVisit our Food and Beverage/Pesticides resources,sigma-aldrich.com/food-pesticidesFeatured and Related ProductsDescription Qty. Cat. No.Supel QuE QuEChERS ProductsCitrate/Sodium Bicarbonate Extraction Tube, 12 mL 50 ea. 55237-UCitrate Extraction Tube, 12 mL 50 ea. 55227-UZ-Sep+ Cleanup Tube, 12 mL 50 ea. 55296-UPSA/C18/ENVI-Carb™ Cleanup Tube, 12 mL 50 ea. 55286-UPSA/C18 Cleanup Tube, 12 mL 50 ea. 55229-UPSA/ENVI-Carb Cleanup Tube 1, 12 mL 50 ea. 55230-UPSA/ENVI-Carb Cleanup Tube 2, 12 mL 50 ea. 55233-UPSA Cleanup Tube, 12 mL 50 ea. 55228-UEmpty Centrifuge Tube, 50 mL 50 ea. 55248-UAscentis Express HPLC Columns, 2.7 µm particlesRP-Amide, 15 cm x 2.1 mm I.D. 1 53914-URP-Amide, 10 cm x 2.1 mm I.D. 1 53913-URP-Amide, 7.5 cm x 2.1 mm I.D. 1 53912-UAscentis Express Guard Columns, 2.7 µm particlesHolder 1 53500-URP-Amide Cartridge, 5 mm x 2.1 mm I.D. 3 53514-UAnalytical Reagents and SolventsAmmonium Formate, >99.0% 17843Formic Acid Solution, 50% in Water 09676Methanol, LC-MS CHROMASOLV® 34966Water, LC-MS CHROMASOLV 39253Table 1. Recovery/RSD DataCompound% RecObserved% RecEN 15662% RSDObserved% RSDEN 15662Abamectine b1a NH4 95.4 - 5.0 -Abamectine b1b NH4 92.5 - 17.6 -Acetamiprid 98.6 97 12.2 13Aldicarb 107.7 85 5.9 23Azoxystrobin 97.9 95 4.3 14Buprofezin 97.3 95 2.6 6Carbendazim 83.7 91 7.9 12Carbofuran 100.7 99 3.3 11Ciromazine 29.7 - 6.2 -Clothianidin 106.0 - 13.9 -Cyazofamide 101.3 90 9.3 17Cyprodinil 101.5 93 13.1 14Difenoconazol 97.6 97 5.9 12Dimetoate 100.5 96 16.7 11Ethoprophos 96.5 99 3.0 8Etofenprox 82.9 94 6.1 12Fenexamide 74.5 93 11.2 19Fenpropimorph 107.3 100 4.7 11Fenpyroximate 91.6 95 6.5 12Flufenoxuron 91.7 96 5.4 17Imidacloprid 105.3 102 5.4 18Methiocarb 90.8 - 6.6 -Methomyl 98.5 99 5.1 18Pimetrozine 36.8 - 5.1 -Pirimicarb 103.8 95 5.7 11Rotenone 102.6 - 4.6 -Setoxydim 71.9 - 4.4 -Spinosad A 108.6 - 10.8 -Spinosad D 93.4 - 4.1 -Spiroxamine 89.5 90 4.2 17Tebufenozide 88.1 - 9.9 -Thiabendazol 86.1 101 6.5 12Thiametoxam 105.6 97 8.6 20Including products from