Identification of Pesticide Residues in Essential Oils by QuEChERS Extraction and GC/MS Analysis

Importance of the Topic

Essential oils are widely used in pharmaceutical, cosmetic, aromatherapy, and food applications. Citrus peel, which concentrates in essential oils, can accumulate pesticide residues applied during cultivation. Regulatory limits and consumer demand for organic authenticity drive the need for sensitive and reliable analytical methods to ensure product safety and quality.

Study Objectives and Overview

This study aimed to develop and validate a rapid, straightforward QuEChERS-based extraction and clean-up procedure coupled with GC/MS analysis for the determination of 26 pesticide residues in lemon essential oil. The method targets detection limits in the 60–150 ppb range with high reproducibility.

Methodology and Instrumentation

The optimized workflow consists of the following steps:

• Weigh 3 g of lemon essential oil in a centrifuge tube.
• Add internal standard (if required) and vortex to mix.
• Introduce 12 mL water, 10 mL acetonitrile (ACN), and 2 mL hexane to facilitate phase separation.
• Add EN-buffered QuEChERS extraction salts; shake and centrifuge.
• Discard the upper hexane/oil layer; transfer ACN extract to AOAC dispersive-SPE tubes for fats and pigments.
• Vortex, centrifuge, and collect the cleaned ACN fraction for GC/MS analysis.

Used Instrumentation

• Gas chromatograph: Agilent 7890A.
• Mass spectrometer: Agilent 5975C MSD.
• Column: HP-5MS Ultra Inert (15 m × 0.25 mm × 0.25 µm).
• QuEChERS kits: SampliQ EN extraction (p/n 5982-5650) and AOAC dispersive-SPE for fats and pigments (p/n 5982-5421).
• Centrifuges: Centra CL3R and Eppendorf microcentrifuge.

Results and Discussion

Comparison of EN-buffered versus AOAC (acetate) extraction salts demonstrated superior cleanup with EN salts, yielding lower matrix interference and a reduced interference bump around 10 min retention time. Method performance was evaluated at low (60 ppb), mid (200 ppb), and high (800 ppb) spiking levels. Key findings include:

• Average recoveries ranged from approximately 65 % to 110 % for most analytes at low QC levels, with reproducibility (RSD) below 5 % for major pesticide classes.
• Chlorinated pesticides exhibited lower recoveries (e.g., heptachlor ~28 %).
• Addition of 2 mL hexane improved phase separation and reduced late-eluting matrix components.

Benefits and Practical Applications

The combined QuEChERS EN extraction and AOAC dispersive clean-up offers a fast, cost-effective solution for multi-residue pesticide analysis in essential oils. The method minimizes sample preparation time, provides robust reproducibility, and achieves regulatory-relevant detection limits, making it suitable for quality control in food, cosmetics, and pharmaceutical industries.

Future Trends and Potential Applications

Advancements may include:

• Automation of QuEChERS workflows to increase throughput.
• Application of high-resolution or tandem MS to enhance selectivity.
• Extension to other essential oil types and complex natural product matrices.
• Integration of miniaturized dispersive SPE sorbents to reduce solvent use.

Conclusion

A streamlined QuEChERS extraction with EN buffering, followed by targeted d-SPE cleanup and GC/MS analysis, delivers sensitive, reproducible detection of 26 pesticides in lemon essential oil. The method satisfies performance criteria for recovery, precision, and sensitivity, representing an effective approach for residue monitoring in essential oil products.

References

No external literature references were provided in the source material.