Rapid Determination of Pesticides in Spinach

Using Supel™ Sphere Carbon/NH2 and an SLB®-5ms GC ColumnHighly pigmented foods, such as spinach, require cleanup prior to analysis for pesticide residues. A dual-layer SPE tube containing graphitized carbon and aminopropyl on silica (NH2) is often used. • Carbon removes pigments and sterols• NH2 removes fatty acids, polar pigments, organic acids, and sugarsRemoving these matrix materials reduces interferences that can lead to ion suppression in LC-MS, inlet contamination in GC-MS, and column contamination for both techniques. Our Supel Sphere Carbon/NH2 SPE tube uses spherical materials for both the carbon and NH2 layers, providing fast, more consistent flows compared to tubes containing granular material. This allows gravity elution (instead of vacuum elution) to be applied to Supel Sphere tubes, resulting in more contact time between extracts and sorbents.ExperimentalExtraction and cleanup procedures derived from two published methodologies1,2 are summarized in Table 1. Unspiked and spiked (5 ng/g) spinach samples were prepared, and allowed to sit for 1 hour prior to extraction. After extraction, extracts were split for cleanup using Supel Sphere Carbon/NH2 SPE tubes or a traditional dual-layer SPE tube containing granular materials. Quantitation was done using matrix-matched standards. Results & DiscussionSupel Sphere Carbon/NH2 Dual-Layer SPE tubes:• Exhibit superior and more consistent flow• Remove as much background as traditional SPE tubes• Result in improved recovery and %RSD values for most pesticidesThe average time required for 25 mL of extraction solvent (75:25 acetonitrile:toluene) to be gravity eluted through each tube is displayed in Figure 1. The range (slowest and fastest) of the five replicates is depicted by the black vertical line. Average flow times for the granular materials were similar, while the Supel Sphere Carbon/NH2 time was 50% faster and had the best reproducibility.The average recoveries and %RSD values for three spiked samples after cleanup using Supel Sphere Carbon/NH2 and a traditional dual-layer SPE tube are presented in Table 2. As shown, values from Supel Sphere Carbon/NH2 extracts are similar or better for most analytes.GC-MS runs of extracts after cleanup shown in Figure 2 emphasize that the Supel Sphere Carbon/NH2 tube removes an amount of unwanted matrix comparable to that of traditional tubes. A cleaner background should translate to less instrument contamination, and thus, longer periods of acceptable GC-MS performance before system maintenance is required.References1. Multiresidue Method for Agricultural Chemicals by GC/MS (Agricultural Products), Analytical Methods for Residual Compositional Substances of Agricultural Chemicals, Feed Additives, and Veterinary Drugs in Food: Syoku-An No. 0124001; Department of Food Safety, Japanese Ministry of Health, Labour and Welfare: January 24, 2005.2. Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate. AOAC Official Method 2007.01.0.005.0010.0015.0020.0025.0030.00MinFlow Comparison TestSupel SphereCarbon/NH2Competitor A Competitor BFigure 1. Average Timed Gravity Elution of 25 mL Solvent (n = 5)Table 1. Extraction and Cleanup Procedure 1. Place 10 g of homogenized spinach (spike added if a spiked sample) and 10 mL acetonitrile into a 50 mL centrifuge tube (55248-U), then shake for 1 min 2. Add content of Acetate Extraction Tube (55234-U), then shake for 1 min 3. Centrifuge at 3200 rpm for 5 min 4. Transfer top layer to a 12 mL tube containing 1 g of anhydrous MgSO4 (63135) 5. Shake sample, then centrifuge at 3200 rpm for 5 min 6. Transfer 5 mL of sample to glass test tube and evaporate to 1 mL (at 40 °C) 7. Add 250 µL of toluene to sample 8. Condition Carbon/NH2 Tube (54283-U) with 10 mL of acetonitrile:toluene (75:25) 9. Add sample extract from step 7, start eluent collection immediately 10. Gravity elute tube with 20 mL of acetonitrile:toluene (75:25) and collect all eluentFood & BeverageRapid Determination of Pesticides in SpinachFood & BeverageOrder/Customer Service (800) 325-3010 • Fax (800) 325-5052 Technical Service (800) 325-5832 • sigma-aldrich.com/techservice Development/Custom Manufacturing Inquiries (800) 244-1173 Safety-related Information sigma-aldrich.com/safetycenterWorld Headquarters 3050 Spruce St. St. Louis, MO 63103 (314) 771-5765 sigma-aldrich.comEnabling Science to Improve the Quality of Life©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. Supelco brand products are sold through Sigma-Aldrich, Inc. Solutions within is a trademark of Sigma-Aldrich Co. LLC. SLB is a registered trademark of Sigma-Aldrich Co. LLC. Supel is a trademark of Sigma-Aldrich Co. LLC. FocusLiner is a trademark of SGE Analytical Science Pty Ltd. 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.OXM11544/ T4121311092Table 2. Average % Recovery (%RSD), n=3Analyte Supel Sphere Tube (Spherical Material)Traditional Tube (Granular Material)Trifluralin 81 (2) 78 (3)alpha-BHC 83 (1) 75 (10)Thiometon 81 (5) 75 (3)Hexachlorobenzene 43 (6) 55 (5)Simazine 82 (2) 81 (4)Quintozene 74 (8) 71 (6)gamma-BHC 84 (5) 80 (7)Tolclofos-methyl 83 (4) 80 (3)Heptachlor 72 (3) 69 (9)Malathion 83 (11) 90 (5)Metolachlor 83 (4) 82 (2)Chloropyrifos 84 (3) 70 (4)Endosulfan I 84 (8) 66 (11)Oxadiazon 79 (3) 83 (3)Ethion 81 (1) 79 (5)Triazophos 73 (1) 83 (2)4,4'-DDT 67 (3) 67 (4)Phosmet 81 (3) 82 (4)Methoxychlor 71 (4) 80 (3)Coumaphos 79 (2) 79 (3)Cyfluthrin isomer 66 (5) 71 (14)Cypermethrin isomer 88 (5) 72 (8)Deltamethrin 76 (7) 63 (36)Figure 2. Extracts of Spiked Spinach (full scan mode, same Y-axis) column: SLB-5ms, 20 m x 0.18 mm I.D., 0.36 µm (28576-U) oven: 70 °C (2 min), 15 °C/min to 325 °C (5 min) inj. temp.: Programmed, 60 °C (0.28 min), 600 °C/min to 325 °C (5 min) detector: MS, SIM mode carrier gas: helium, 1 mL/min constant injection: 10 µL LVI, PTV solvent vent, rapid injection speed; split vent flow: 100 mL/min (5 psi) until 0.28 min, 60 mL/min at 2.78 min liner: 4 mm I.D., split type, wool packed FocusLiner™ with single taper design10 20Min10 20Min10 20Min10 20Min10 20Min10 20MinSupel Sphere Carbon/NH2CompetitorFeatured and Related ProductsDescription Qty. Cat. No.Supel QuE QuEChERS ProductsAcetate Extraction Tube, 12 mL 50 55234-UCitrate Extraction Tube, 12 mL 50 55227-UCitrate/Sodium Bicarbonate Extraction Tube, 12 mL 50 55237-UEmpty Centrifuge Tube, 50 mL 50 55248-USupel Sphere SPE ProductsCarbon/NH2 Tube, 6 mL 30 54283-USLB-5ms Capillary GC Columns30 m x 0.25 mm I.D., 0.25 µm 1 28471-U30 m x 0.25 mm I.D., 0.50 µm 1 28473-U20 m x 0.18 mm I.D., 0.18 µm 1 28564-U20 m x 0.18 mm I.D., 0.36 µm 1 28576-UAnalytical Reagents and SolventsAnhydrous Magnesium Sulfate (MgSO4), =97% 250 Kg 63135-250G-FAcetonitrile, for pesticide residue analysis 34481Toluene, for pesticide residue analysis 34494Visit our Food and Beverage/Pesticides resources sigma-aldrich.com/food-pesticidesIncluding products from©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. 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.