Improved GC/MS Analysis of Tomato Pesticides with Agilent Deactivated Silica Tubing

Significance of the Topic

Multiresidue analysis of pesticide residues in food matrices such as tomatoes is critical to food safety and regulatory compliance.
Complex sample matrices can compromise chromatographic columns and impair quantitative accuracy for active compounds.
Implementing an inert guard column with highly deactivated fused silica tubing can extend column life, improve sensitivity, and maintain consistent results in GC/MS pesticide analysis.

Objectives and Study Overview

This study compares the performance of Agilent Ultimate Plus deactivated fused silica tubing as a guard column against a widely used competitor’s deactivated guard column in the analysis of tomato extracts processed via QuEChERS.
Key performance indicators include inertness, linearity, repeatability, stability, and the ability to protect the analytical column from matrix-induced contamination.

Methodology and Instrumentation

• Sample Preparation:
  Organic tomatoes homogenized, 10 g extracted with QuEChERS EN salts, acetonitrile extraction, dispersive SPE cleanup.
• Standards:
  Stock solutions (100 µg/mL) in acetonitrile, high-QC in toluene, calibration levels 10–500 ng/mL with internal standard triphenyl phosphate (100 ng/mL).
• Chromatography and Mass Spectrometry:
  
  • GC: Agilent 7890B with splitless injection; Agilent J&W HP-5ms UI column (30 m × 0.25 mm, 0.25 µm); guard column: 5 m × 0.25 mm deactivated FS tubing.
  • MSD: Agilent 5977A, EI mode, SIM, optimized temperatures and retention time locking.
  • Consumables: Ultra Inert liners and gold seals, UltiMetal Plus ferrules, unions and inlet fittings to ensure an inert flow path.

Main Results and Discussion

• Chromatographic Protection:
  Both guard columns prevented analytical column contamination, but the Agilent tubing showed fewer background interferences over multiple injections.
• Inertness and Peak Shape:
  Agilent Ultimate Plus tubing delivered sharper, more symmetric peaks, especially for polar and active pesticides (e.g., methamidophos, acephate, omethoate), reducing adsorption and tailing.
• Linearity:
  Calibration curves in tomato matrix (10–500 ng/mL) yielded R² > 0.99 for all analytes with both columns, with Agilent tubing showing marginally higher R² values for challenging compounds.
• Repeatability and Stability:
  Fifteen consecutive injections of a 50 ng/mL spiked sample produced lower RSDs for active pesticides with Agilent tubing (e.g., methamidophos RSD 5.9% vs. 6.7%; acephate 8.9% vs. 10.8%).

Benefits and Practical Applications

• Extended Column Life: Periodic trimming of guard tubing preserves the analytical column and reduces maintenance costs.
• Enhanced Sensitivity: Improved inertness minimizes analyte loss and enhances quantitation at trace levels.
• Operational Efficiency: Fewer source cleanings and chromatographic troubleshooting when analyzing complex matrices.
• Regulatory Compliance: Reliable performance for routine pesticide residue testing in food safety and quality control labs.

Future Trends and Opportunities

• Integration of backflushing with high-inert guard tubing to further protect column heads and accelerate analysis cycles.
• Development of advanced deactivation chemistries to broaden inert range for the most active pesticide classes.
• Adoption of high-resolution MS and tandem MS detection to improve selectivity and lower detection limits.
• Automation of sample preparation and in-line guard column monitoring for high-throughput testing laboratories.

Conclusion

Agilent Ultimate Plus deactivated fused silica tubing outperformed a leading competitor’s guard column in inertness, stability, and repeatability for pesticide analysis in QuEChERS tomato extracts.
The enhanced performance supports more robust and reliable GC/MS workflows, extending column lifetime and improving data quality in food safety testing.

References

• Anastassiades, M. et al. J. AOAC Int. 86 (2003) 412–431.
• Zhao, S.; Zhai, A. Agilent Application Note 5990-6323EN (2012).
• Zhao, L.; Wylie, P.; Stevens, J. Agilent Application Note 5990-4073EN (2012).
• Dang, N. A. Agilent Application Note 5991-5404EN (2014).
• Zou, Y. Agilent Application Note 5991-5914EN (2015).
• Meng, C.-K. Agilent Application Note 5989-6018EN (2006).