Determination of Pesticides in Edible Oils

Challenges and Opportunities for Solid Phase Extraction
Poster Presentation

Prepared by D. Stevens, E. Ross, J. De-Alwis, S. Adams
Waters Corp., 34 Maple, Milford, MA, 01757, United States

Contact Information:; 508-369-8311


Detection of pesticides in edible oils, such as olive oil, has many challenges due to the complexity of the matrix, which is high in lipids. Sample cleanup is, therefore, crucial to ensure robust methodology. Traditional approaches to the cleanup of such high fat content samples have used a liquid-liquid extraction followed by gel permeation chromatography (GPC) cleanup. This technique is undesirable due to high solvent consumption and lengthy extraction and cleanup times. This poster presents an alternative, extraction and cleanup procedure optimized for the simple and reliable determination of multi-residue pesticides in edible oils by GC-MS/MS.
Edible oils were homogenized and spiked with known concentrations of pesticides. The extraction was optimized, evaluating more environmentally friendly options to the traditional defatting by hexane. This was followed by a simple pass through cleanup, eliminating the need for nonpolar solvents and lengthy GPC or SPE conditioning and washing. All extracts were run on GC-EI-MS/MS, in MRM mode, using a splitless injection of 1 µL. Validation was completed for olive oil in accordance with European guidelines (SANTE/11813/2017) evaluating sensitivity, selectivity, repeatability, accuracy and identification criteria so that limits of quantification were within the range of the maximum residue limits for the compounds of interest.
Alternative, time and cost effective approaches to GPC cleanup are routinely sought by laboratories. One approach becoming increasingly popular is the use of acetonitrile as an extraction solvent, either in a QuEChERS procedure or a solvent extraction, followed by SPE cleanup to remove lipids. However, when employing this approach in edible oils, poor recovery of some organochlorine pesticides is observed (27 to 101 %), many lower than the 70% acceptance limit required. The extraction optimized in this study yielded improved method recovery for representative pesticides, when compared to the traditional hexane and acetonitrile extraction procedures. The impact of the pass through cleanup step was also evaluated separately, where analyte recoveries were >70% for all analytes. While the overall method recovery demonstrated improved performance, additional investigations were conducted to improve the linearity and repeatability. An alternative type of calibration, namely procedural standards, was employed. This mode of calibration compensates for low extraction efficiency and matrix effects and showed excellent improvements in terms of accuracy and repeatability, where the method’s trueness ranged from 99.2 to 108.5 % for a selection of challenging organochlorine pesticides. Excellent linearity, over the calibration range of 0.005 to 0.1 mg/kg, was achieved for all pesticides with coefficients of determination > 0.995 with residuals <20%. The method’s accuracy, repeatability and bias was evaluated from the analysis of spikes at 0.01 mg/kg (n=5), 0.02 mg/kg (n=5) and 0.1 mg/kg (n=5). This optimized extraction, cleanup and GC-EI-MS/MS analysis was shown to be simple, quick, solvent friendly, reliable and fit for the routine determination of multi-residue pesticides in edible oils.