Prepare Samples in Half the Time Using a Fraction of the Solvent with dSPE

By Michelle Misselwitz, Environmental Innovations Chemist, Julie Kowalski, Ph.D., Food Flavours and Frangrances Innovations Chemist, Mark Crawford, Applications Chemist, Michael Halvorson Ph.D., Senior Product Specialist, and Joan M. Stevens, Ph.D., Applications Manager

Simplify and speed up sample preparation with Resprep dSPE tubes. Here we show the extraction and clean-up of pesticide residues from olive oil samples—twice as fast as GPC, with only a fraction of the solvent required for conventional SPE.

Olive oil is considered a healthy fat source and is a staple in many recommended diets. However, concerns about potentially negative health effects associated with pesticide residues have increased consumer interest in testing. While organophosporus pesticides are currently used in olive orchards to control pests, organochlorine pesticides are still tested for as persistent organic pollutants (residues), even though they are no longer in commercial use. There are several existing methods for measuring pesticide residues in olive oil, all of which involve sample extraction and clean-up.1 The common goal of these methods is to remove lipids that are harmful to the analytical system.2 Efficient sample clean-up procedures are critical to maximizing sample throughput and minimizing labor and material costs. Here we demonstrate the efficiency of a dSPE clean-up procedure, as well as the capabilities of both method-specific and general purpose analytical columns.

Simple Procedure Uses Half the Time and Minimal Solvent

Sample extraction and clean-up can be accomplished with gel permeation chromatography (GPC), solid phase extraction (SPE), or dispersive solid phase extraction (dSPE) methods. However the dSPE method shown here is much less expensive than GPC (which requires specialized equipment) and uses substantially less solvent than comparable GPC or SPE methods (Table I).3 The method is simple to use and allows sample extraction and clean-up to be accomplished in half the time of other techniques (Table II).

Extraction and dSPE Clean-up for Pesticide Residues in Olive Oil Test sample: A 1.5mL sample of commercially obtained virgin olive oil was spiked with a standard organochlorine pesticide mix. The spiked sample was processed as follows. Dilute with 1.5mL hexane. Add 6mL of acetonitrile (ACN). Mix for 30 minutes on a shaker. Allow layers to separate (approximately 20 minutes), then collect the top (ACN) layer. Repeat the liquid-liquid extraction (steps 2-4) and combine both ACN extract layers. Place 1mL of the combined ACN extract in a 1.5mL tube containing 150mg magnesium sulfate and 50mg PSA. Shake the tube for 2 minutes. Centrifuge at 3,000 U/min. for approximately 5 minutes. Remove the top layer and inject directly into the gas chromatograph system.

Extracts were analyzed using both Rtx®-CLPesticides2 and Rxi®-5Sil MS columns (Figure 1). The Rtx®-CLPesticides2 column is a method specific column that resolves all compounds. The Rxi®-5Sil MS column is a general purpose column that has one coelution that can easily be extracted by a mass spectrometer detector (MSD). Only ?-BHC was not detected, a subject of further investigation, however either column can be used effectively. Recoveries of 70%-80% were obtained, levels comparable to conventional SPE—without the necessity of vacuum manifolds or high pressure systems. The GPC method attained recoveries of > 95%. However this method requires large amounts of solvent and takes over twice as long as other methods.

The dSPE method shown here is an efficient, cost-effective way to clean up chlorinated pesticide residues in olive oil. With good recoveries and minimal matrix interference, it is an easy way to reduce solvent usage, compared to conventional SPE, and is more cost-effective than GPC.

Table I: Resprep's dSPE method uses 42% and 89% less solvent than SPE and GPC methods respectively.

Table II: Cut extraction/clean-up time by 50% using a Resprep dSPE method.

Figure 1: Chlorinated pesticide residues in olive oil are easily separated on either Rtx®-CLPesticides2 or Rxi®-5Sil MS columns.

Compound Quant.ion Qual. ion 1 Qual. ion 2 *1. ?-BHC 219 181 109 2. ?-BHC 219 181 109 3. ?-BHC 219 181 109 4. ?-BHC 219 181 109 5. heptachlor 272 237 100 6. aldrin 263 293 220 7. heptachlor epoxide 263 237 81 8. ?-chlordane 272 237 65 9. ?-chlordane 272 237 65 10. endosulfan I 195 207 241 11. 4,4?-DDE 246 318 176 12. dieldrin 79 263 277 13. endrin 263 281 81 14. 4,4?-DDD 235 165 199 15. endosulfan II 195 207 - 16. 4,4?DDT 235 165 199 17. endrin aldehyde 67 250 345 18. endosulfan sulfate 272 229 239 19. methoxychlor 227 274 - 20. endrin ketone 67 317 281 *not present Column: A: Rtx®-CLPesticides2, 30m, 0.25mm ID, 0.20µm (cat.# RE11323) B: Rxi®-5Sil MS. 30m, 0.25mm ID, 0.25µm (cat.# RE13623) Sample: 10µg/mL Organochlorine Pesticide Mix AB # 3 (cat.# RE32415) in olive oil Inj.: 1µL, splitless (hold 0.5 min.), 3.5mm single gooseneck liner (cat.# RE20962 ) packed w/wool Inj. temp.: 225°C Carrier gas: helium, constant flow Flow rate: 1mL/min. Oven temp.: 140°C (hold 0.5 min.) to 268°C @ 20°C/min. to 290°C @ 3°C/min. to 330°C (hold 5 min.) @ 20°C/min. Det.: MS Transfer line temp.: 320°C Ionization: EI Mode: SIM GC_FF01043-44

REFERENCES

1. C. Lentza-Rizos, E.J. Avramides, Rev. Environ. Contam. Toxicol. 141 (1995) 111.
2. S. Cunha, S. Lehotay, K. Mastovska, J. Sep. Sci. 30 (2007) 620.
3. M. Crawford, M. Halvorson, J. Stevens, The Examination and Automation of GPC, SPE and QuEChERS Utilized in Extracting Pesticides from Olive Oil. HPLC 2008 poster presentation.