Quantitation of Pesticides in Strawberries at Tolerance Levels Established by the US EPA

Significance of the Topic

Reliable monitoring of pesticide residues in food is critical for consumer safety and regulatory compliance. Strawberries, a high-value fruit with known sensitivity to environmental conditions, often require pesticide applications that can leave trace residues. Regulatory bodies such as the US EPA set maximum residue limits ranging from 10 to 25,000 ppb in strawberries. Achieving accurate quantitation across this wide concentration range demands robust, high-throughput analytical workflows capable of minimizing matrix interferences and instrument downtime.

Study Objectives and Overview

The primary goal of this work was to evaluate the performance of Agilent’s 8890 gas chromatograph coupled to 7000D and 7010B triple quadrupole mass spectrometers for quantifying incurred pesticides in commercial strawberry samples at or below EPA tolerance levels. Twenty-eight target analytes, including insecticides, fungicides, herbicides, and pesticide synergists, were selected based on prior screening with GC/MSD and GC/Q-TOF systems. The study assessed method linearity, sensitivity, and accuracy over a broad calibration range (1–10,000 ppb) and demonstrated the ability to detect both regulated and non-regulated compounds at reporting limits as low as 10 ppb.

Methodology and Used Instrumentation

Sample Preparation and Chromatography

• A QuEChERS extraction protocol was applied: 10 g of homogenized strawberries were extracted with acetonitrile and salt, followed by dispersive SPE cleanup.
• Pulsed splitless injection maximized analyte transfer and reduced thermal degradation; midcolumn backflush eliminated high-boiling matrix residues, shortening run times and maintenance.
• Retention Time Locking to a pesticide database ensured consistent retention times across columns and instruments.

Mass Spectrometry and Data Acquisition

• Dynamic MRM mode distributed dwell times automatically across up to eight transitions per analyte.
• The Agilent MassHunter Pesticide & Environmental Pollutant MRM Database provided ready-to-use quantifier and qualifier transitions.

Used Instrumentation

• Agilent 8890 Gas Chromatograph with multimode inlet (pulsed splitless).
• Agilent Purged Ultimate Union (PUU) and PSD pneum atics module for midcolumn backflush.
• Agilent 7000D and 7010B Triple Quadrupole GC/MS systems.
• Inert Extractor EI Source (7000D) and High Efficiency Source (HES) (7010B).
• HP-5ms UI columns (15 m × 0.25 mm, 0.25 μm).

Main Results and Discussion

Preliminary screening identified 37 pesticides or related compounds. Of these, 28 were reliably quantified across 12 strawberry samples using matrix-matched calibration. Linearity (R² > 0.99) was achieved up to 5,000 ppb for most analytes, with extended calibration to 10,000 ppb permitted for high-level pesticides. Boscalid (tolerance 4,500 ppb) showed excellent linearity from 1 to 10,000 ppb when a quadratic fit was applied. Acetamiprid (600 ppb tolerance) and thiamethoxam (reporting limit 10 ppb) were quantified accurately at their levels. The 7010B with the HES source delivered lower limits of quantitation and superior signal-to-noise ratios (S/N ~19.6 at 10 ppb for thiamethoxam) compared to the 7000D.

Benefits and Practical Applications

This workflow enables single-run quantitation of multiple pesticides across regulatory ranges, reducing the need for reanalysis. Pulsed splitless injection and midcolumn backflush enhance sample throughput and instrument uptime. Predefined MRM databases and dynamic MRM simplify method development, making the approach suitable for routine food safety testing and QA/QC laboratories.

Future Trends and Potential Applications

Advances in inlet design and temperature programming could further lower LOQs for thermo-labile compounds. Expanding MRM libraries and adopting high-resolution technologies may facilitate simultaneous screening of emerging contaminants. Integration with automated sample preparation and data processing will enhance throughput and support regulatory programs in diverse food matrices.

Conclusion

The Agilent 8890/7000D and 8890/7010B triple quadrupole GC/MS systems provide a robust, sensitive, and high-throughput solution for quantifying pesticide residues in strawberries at EPA tolerance levels. Combining pulsed splitless injection, midcolumn backflush, retention time locking, and dynamic MRM enables accurate measurements across a broad concentration range, supporting food safety laboratories in meeting regulatory requirements.

References

• Index to Pesticide Chemical Names, Part 180 Tolerance Information and Food and Feed Commodities. US EPA Office of Pesticide Programs, Dec. 2012.
• USDA PDP Database Search Application – User Guide. USDA AMS, Jan. 2019.