The Analysis of Pyrethroids using the AT-Column Concentrating Technique

Importance of the Topic

Pyrethroid insecticides are widely used in agricultural and public health applications. Their analysis at trace levels requires sensitive and robust methods. The AT-column concentrating technique coupled with GC-MS offers a powerful solution for handling labile and high boiling point compounds with minimal matrix interference and low carryover.

Objectives and Study Overview

This work aimed to demonstrate the application of the AT-column large volume injection approach for quantitative analysis of cyfluthrin, alpha-cypermethrin and flumethrin in dichloromethane. Key goals included ensuring reproducible peak shapes, achieving low detection limits and verifying absence of carryover between injections.

Methodology and Instrumentation

The method involved direct injection of 100 microliter samples under AT-column conditions. Solvent vapors were selectively vented while analytes were focused on the head of a capillary column prior to GC temperature programming. Critical instrumental setup included:

• ATAS Optic 2-200 programmable injector with AT-column kit in large volume mode
• HP 5890 gas chromatograph coupled to HP 5971 mass selective detector
• HP5-MS capillary column, 30 m x 0.25 mm i.d., 0.25 micrometer film thickness

Typical injector parameters featured split vent flow at 120 ml/min, initial liner temperature of 43 C, solvent venting until threshold reached, followed by rapid temperature ramp to 300 C. GC oven programming comprised an initial hold at 56 C then multi step ramps to 195 C and 280 C and a final bake at 300 C. Detection was performed in selected ion monitoring mode.

Main Results and Discussion

The method delivered high precision with relative standard deviations of 2.95 percent for alpha-cypermethrin and 5.35 percent for flumethrin based on standardisation to cyfluthrin. No carryover was observed in blank injections following high concentration samples. Required detection limits of 4 micrograms per liter were readily achieved for all three pyrethroids. Chromatograms showed well resolved peaks without peak tailing or matrix interferences.

Benefits and Practical Applications

• Minimal method optimisation required for complex mixtures of sticky and thermally labile compounds
• High sample throughput due to rapid solvent venting and short GC cycles
• Robust performance with negligible carryover enhances reliability for routine environmental analysis

Future Trends and Opportunities

Advancements may include integration with high resolution mass spectrometry for improved selectivity, automation of solvent vent timing through smart software algorithms and extension of the AT-column approach to polar pesticides. Coupling with multidimensional GC could further enhance separation of complex pesticide residues.

Conclusion

The AT-column large volume injection technique provides a sensitive, precise and carryover-free method for analysis of pyrethroids in organic solvents. Its ease of use and compatibility with standard GC-MS systems make it well suited for environmental monitoring and quality control laboratories.

Reference

• Nicholas D Application Note No 065 The Analysis of Pyrethroids using the AT-Column Concentrating Technique GL Sciences BV