A Novel Large Volume At-Column Concentrating Technique and its Applicability to Labile Pesticide Analysis

Significance of the technique

The analysis of trace and heat-sensitive pesticides is critical in environmental monitoring, food safety and quality control. Conventional large volume injections often risk thermal degradation or irreversible adsorption of labile compounds in packed liners. The novel at-column concentrating approach addresses these challenges by eliminating packing materials and enabling large sample volumes with minimal decomposition.

Objectives and study overview

This work aims to develop and evaluate an at-column concentrating large volume injection method for gas chromatography that improves sensitivity and preserves heat-sensitive analytes. The technique was benchmarked against traditional hot splitless, cold on-column and programmable temperature vaporizer (PTV) methods for eight pesticides.

Methods and instrumentation

The method uses an Optic 2-200 programmable injector fitted with a special unpacked at-column liner and a short deactivated fused-silica pre-column. Sample solvent is evaporated within a temperature gradient below its boiling point, vented through a side port, while analytes concentrate at the capillary inlet. A 30 m × 0.25 mm NB-5 analytical column (0.25 µm film) or thinner film column for labile compounds was coupled via press-fit connectors. GC analysis employed an HP5890 with HP5971 MSD. Standard reagents included n-alkanes C10–C30 and pesticides DEP, Bendiocarb, Carbaryl, Methiocarb, Endrin, p,p’-DDT, Iprodione and EPN in acetone.

Main results and discussion

Injector and oven temperatures were optimized at approximately 3 °C below and 10 °C above the corrected solvent boiling point, respectively, to ensure efficient solvent venting without sample loss. The technique proved linear for 10–100 µL injections, yielding up to 100-fold sensitivity gain with RSDs below 5 %. Various solvents including dichloromethane, hexane and ethyl acetate mixtures were successfully tested. Comparative experiments demonstrated that traditional PTV methods with packing caused significant pesticide degradation, whereas the at-column approach preserved all labile analytes even at 50 µL injection volumes.

Benefits and practical applications

• Enhanced sensitivity through large injected volumes
• Minimal thermal decomposition and adsorption loss
• Compatibility with diverse solvents and mixtures
• Suitable for automation and hyphenation in QA/QC laboratories

Future trends and potential applications

Further integration with tandem mass spectrometry, miniaturized GC systems and automated workflows could expand use in environmental trace analysis, metabolomics and pharmaceutical impurity profiling. Adaptation to microfluidic GC-MS interfaces and real-time field screening platforms offers promising avenues.

Conclusion

The at-column concentrating large volume injection method delivers reproducible, high-sensitivity analysis of heat-labile pesticides without the drawbacks of packed liners. Its versatility and robustness make it a valuable tool for modern analytical laboratories.

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