Comparison of Ionization Techniques for the Analysis of Trace-Level Pyrethroid Insecticides by GC-MS/MS

Significance of the Topic

Pyrethroid insecticides are widely used in agriculture and household pest control and can persist in water, soil and sediment at trace levels. Reliable detection at sub-part-per-billion concentrations is essential to assess environmental impact, protect aquatic life and meet regulatory requirements.

Study Objectives and Overview

This study evaluates two ionization techniques electron impact (EI) and negative chemical ionization (NCI) on a Bruker EVOQ GC-TQ system for quantifying trace-level pyrethroids in complex matrices. Calibration range, detection limits and precision are compared in sewage outfall and ocean sediment extracts.

Methodology and Instrumentation

Instrumentation Used

• Bruker EVOQ GC-TQ triple quadrupole mass spectrometer
• Bruker 436 gas chromatograph with CP-8400 autosampler
• BR-5ms column 15 m x 0.25 mm id x 0.25 µm

GC Conditions

• Carrier gas helium at 1.0 mL/min
• Oven program 60°C (2 min), ramp 50°C/min to 150°C (1 min), then 5°C/min to 320°C (hold 3 min)
• Injection 2 µL pulsed splitless at 28°C in a 4 mm fritted liner

Ionization Parameters

• EI source temperature 250°C
• NCI source temperature 150°C reagent gas ammonia at 20 psi

Sample Preparation

• Ocean sediment extracted by accelerated solvent extraction at 125°C and 2000 psi in dichloromethane/acetone
• Sewage outfall extracted by continuous liquid-liquid extraction with dichloromethane
• Extracts concentrated to 1 mL without further cleanup

Main Results and Discussion

Calibration and precision

• EI mode linear from 0.1 to 50 ppb with average RSD 8.7% and r2 0.9995
• NCI mode linear from 1 to 5000 ppt with average RSD 9.8% and r2 0.9990

Detection limits

• EI/MS/MS IDLs 0.01 to 0.28 ppb (mean 0.1 ppb, RSD 10.6%)
• NCI/MS/MS IDLs 0.01 to 0.3 ppb (mean 0.04 ppb, RSD 6.1%)
• Selected compounds achieved 10 ppt detection (mean 2.6 ppt, RSD 9.2%)

Matrix effects

• EI analyses of sediment and sewage extracts showed elevated baselines and coeluting interferences for allethrin, cypermethrin and deltamethrin
• NCI analyses provided clear chromatograms, accurate ion ratios and acceptable recoveries in both matrices

Benefits and Practical Applications

• High specificity and sensitivity for trace pyrethroid monitoring in environmental samples
• Robust discrimination against complex matrix interferences
• Compliance with sub-part-per-billion regulatory reporting limits
• Suitability for routine QA/QC and research laboratories

Future Trends and Opportunities

Advances in GC-MS/MS technology may include hybrid ionization sources combining EI and NCI, automated high-throughput sample preparation, and integration with high-resolution mass analysis. Expanding the method to additional pesticide classes and real-time monitoring platforms can further enhance environmental surveillance.

Conclusion

Combining negative chemical ionization with tandem mass spectrometry delivers superior sensitivity, precision and resistance to matrix effects for low-level pyrethroid analysis. This approach supports reliable environmental monitoring and regulatory compliance.

References

• Pyrethroid pesticides in municipal wastewater A baseline survey of publicly owned treatment works facilities in California in 2013 James C Markle et al January 22 2014