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Save time and improve sample preparation for pesticides in food

By Joan Stevens
Agilent SPE Applications Chemist

Multiresidue analysis of pesticides in fruits, vegetables, and other foods is the primary function of many regulatory, industrial, and contract laboratories throughout the world. Because of the wide variety of pesticides and complexity of food matrices, analysts must extract and clean up samples prior to analysis. To address the need for a rapid, efficient approach to multiclass, multiresidue pesticide analysis, Agilent offers simple kits that save time and ensure consistency.

The Agilent kits are based on the QuEChERS method, which was introduced by USDA scientists and significantly simplifies preparation of food samples for pesticide analysis. QuEChERS (pronounced “Catchers”), is an acronym for Quick, Easy, Cheap, Effective, Rugged and Safe. With the widely accepted QuEChERS method, you can prepare your food samples for pesticide analysis with just a few easy steps. Adding to this efficiency, prepackaged Agilent SampliQ QuEChERS Kits reduce labor and increase the reliability of the method.

Kits have wide applicability

Figure 1. QuEChERS sample preparation procedures minimize the number of sample preparation steps and the required solvent volumes and glassware. (Click here to see this image larger.)

Figure 2. Chromatogram of apple extract fortified at 10 ng/g shows plenty of sensitivity for pesticides at the regulated level. (Click here to see this image larger.)

Figure 3. Chromatogram of blank apple extract shows no interferences. (Click here to see this image larger.)

Figure 4. The recoveries and RSDs from the AOAC method, for dispersive SPE cleanup of 1 and 8 mL volumes of extract, demonstrate excellent results. (Click here to see this image larger.)

Labs use two versions of the QuEChERS method – the Association of Analytical Communities method (AOAC 2007.01) and the European Committee for Normalization method (EN 15662). The SampliQ QuEChERS Kits address both versions. Figure 1 illustrates the sample preparation procedures for the two versions.

The QuEChERS method uses a single-step acetonitrile extraction while salting out water from the sample to induce liquid-liquid partitioning. You remove an aliquot from the organic layer for further cleanup with dispersive solid phase extraction (dispersive SPE). After mixing and centrifugation, the upper layer is ready for analysis. Agilent offers separate extraction kits that you select based on your method and sample size, as well as a variety of dispersive SPE kits that you choose based on your method and the type of food you are analyzing. A standard operating procedure shows the kit selection process.

Recent Agilent Application Notes (5990-3937EN and 5990-3938EN) describe studies that used 16 pesticides to demonstrate the performance of Agilent SampliQ QuEChERS AOAC and EN buffered extraction kits, along with the AOAC and EN dispersive SPE kits for General Fruits and Vegetables. The pesticides represented nine different classes, including acidic, basic, neutral, base-sensitive, and acid-labile pesticides. The pesticides were extracted from apple, cleaned up, then analyzed by LC/MS/MS. The maximum residue limits (MRLs) of these pesticides are 10 ng/g or greater.

Take less time, get better results

The studies showed that the unique design of Agilent SampliQ QuEChERS Kits makes the whole procedure even faster and easier. An analyst can process 40 to 50 samples in just a few hours. Figure 2 shows the analysis of apple spiked at 10 ng/g with pesticides, and illustrates that all compounds were readily detected at this low level. The limits of quantitation (5 ng/g or 5 ppb) of the pesticides were lower than their regulated MRLs. Figure 3 shows a blank apple extract. The selectivity of the triple quadrupole LC/MS/MS in multiple reaction monitoring mode removed any interferences.

Excellent recoveries, even for difficult compounds

Agilent’s SampliQ QuEChERS salts and buffers are uniquely prepared in anhydrous packages. This allows addition after adding solvent to the sample, as specified in the original QuEChERS methodology. You avoid the need to add a food sample with a high percentage of water directly to the salts, which may create an exothermic reaction that can affect analyte recovery.

The recovery and precision results for two different extracted volumes are shown in Figure 4 for the AOAC method. To simplify the comparison, the graphs show the average recovery and precision for the three fortification concentrations for all pesticides. Base-sensitive pesticides such as dichlorfluanid and tolyfluanid showed excellent recoveries and relative standard deviations (RSDs); even the acid-labile pymetrozine showed acceptable recovery and RSD.

The QuEChERS method greatly simplifies the sample extraction and cleanup procedure for pesticide residues in fruits, vegetables, and processed products. The Agilent SampliQ QuEChERS Kits reduce labor costs and ensure high-quality, consistent results. Learn more by watching a demonstration video that shows each step of the QuEChERS method, and by downloading the Application Notes that describe these studies (5990-3937EN and 5990-3938EN).

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