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Olive oil is considered a healthy fat source and is a staple in many recommended diets. However, concerns about potentially nega-

tive 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.

The common goal of these methods is to remove lipids that are

harmful to the analytical system.

Efficient sample clean-up procedures are critical to maximizing sample throughput and minimiz-

ing 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 sub-

stantially less solvent than comparable GPC or SPE methods (Table I).

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).

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

Prepare Samples in Half the Time

Using a Fraction of the Solvent with dSPE

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.

By Michelle Misselwitz, Environmental Innovations Chemist, Julie Kowalski, Ph.D., Food Flavors, and Fragrances Innovations Chemist,

Mark Crawford*, Applications Chemist, Michael Halvorson Ph.D.*, Senior Product Specialist, and Joan M. Stevens Ph.D.*, Applications Manager

*Gilson, Inc.

• 12 •

2008 vol. 3

Food, Flavors & Fragrances

Table I

Resprep 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.

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.

1. Dilute with 1.5mL hexane.

2. Add 6mL of acetonitrile (ACN).

3. Mix for 30 minutes on a shaker.

4. Allow layers to separate (approximately 20 minutes), then

collect the top (ACN) layer.

5. Repeat the liquid-liquid extraction (steps 2-4) and combine

both ACN extract layers.

6. Place 1mL of the combined ACN extract in a 1.5mL tube

containing 150mg magnesium sulfate and 50mg PSA.

7. Shake the tube for 2 minutes.

8. Centrifuge at 3,000 U/min. for approximately 5 minutes.

9. Remove the top layer and inject directly into the gas

chromatograph system.

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