Analysis of Pesticide Residues in Citrus Oils by GCxGC-TOFMS with Minimal Sample Preparation

Importance of the Topic

Citrus essential oils are widely used in food, cosmetics, and fragrance industries. As these oils are extracted from the fruit peel, they are prone to pesticide contamination. Regulatory limits for pesticide residues continue to tighten worldwide, driving the need for reliable, sensitive analytical methods. Comprehensive screening techniques enable quality control, consumer safety assurance, and compliance with international trade standards.

Study Objectives and Overview

This work demonstrates a streamlined approach to detect, identify, and quantify multiple pesticide residues in citrus oils using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS). Key aims are to minimize sample preparation, achieve detection limits down to parts-per-billion, and reveal any non-target contaminants present in commercial orange and lemon oils.

Methodology

• Sample preparation involved spiking Florida midseason orange oil and California cold-pressed lemon oil with a mixture of pesticides at nominal concentrations (25–1000 ppb).
• A 200 µL aliquot of each oil was diluted in a vial insert and fortified with 20 µL of 2-fluorobiphenyl (internal standard).
• Calibration standards were prepared in commercial limonene over 10–1000 ppb to evaluate linearity and instrument response.
• Five replicate injections at 25 ppb assessed method precision and repeatability.

Used Instrumentation

• LECO Pegasus 4D GCxGC-TOFMS system
• Primary column: J&W DB-PONA (50 m × 0.20 mm × 0.50 µm) for boiling-point separation
• Secondary column: SGE BPX-50 (2 m × 0.10 mm × 0.10 µm) for polarity/aromatic selectivity
• Modulation period: 10 s with a 30 °C offset
• TOFMS acquisition range: m/z 29–390 at 100 spectra/s
• Splitless injection at 250 °C, helium carrier flow at 0.5 mL/min

Main Results and Discussion

• GCxGC provided high peak capacity, resolving pesticides from complex citrus oil constituents that coelute in one-dimensional GC.
• Calibration curves exhibited excellent linearity (r > 0.9999) across 10–1000 ppb.
• Precision for 25 ppb spikes ranged from 5 % to 20 % RSD. Background-corrected spikes maintained comparable repeatability.
• Non-target pesticides such as chinomethionate, fenpropathrin, bromopropylate, and tetradifon were identified in unspiked oils via spectral deconvolution.
• Two-dimensional separation improved ion-ratio reliability by isolating target analytes from interfering matrix ions.

Benefits and Practical Applications

• Minimal sample handling reduces labor and potential analyte loss.
• Comprehensive spectral acquisition allows retrospective screening of additional analytes.
• Detection limits below 25 ppb enable early warning of pesticide contamination.
• Robust separation minimizes false negatives and enhances confirmation confidence.
• Applicable to routine quality control in food, fragrance, and pharmaceutical sectors.

Future Trends and Potential Applications

• Extension to other essential oils, botanical extracts, and complex food matrices.
• Integration with tandem MS or high-resolution spectrometry for enhanced selectivity.
• Automation of data-processing using machine-learning algorithms for spectral deconvolution.
• Faster modulation technologies and shorter columns to reduce analysis time.
• Development of standardized GCxGC-TOFMS methods for regulatory monitoring and international trade.

Conclusion

GCxGC-TOFMS with minimal sample preparation offers a powerful platform for comprehensive pesticide residue analysis in citrus oils. The approach achieves low-level detection, reliable quantification, and identification of both target and unexpected contaminants. Its high resolution and full-scan capability support robust quality assurance and regulatory compliance in the flavor, fragrance, and food industries.