The Analysis of Organophosphorous Pesticides by Large Volume Injection

Significance of the topic

Organophosphorous pesticides are widely used in agriculture but present analytical challenges due to their tendency to adsorb onto injector surfaces or degrade under heat. Reliable detection at trace levels in environmental waters is critical for regulatory compliance and ecosystem protection. Implementing large volume injection (LVI) with suitably inert components can greatly enhance sensitivity and data quality for these compounds.

Objectives and study overview

This study aimed to develop and validate a gas chromatographic method using large volume injection to detect a suite of organophosphorous pesticides in river water at sub-nanogram per liter levels. Key goals included minimizing thermal degradation and adsorption losses, extending the injection volume beyond conventional limits, and demonstrating robust performance for routine analysis.

Methodology

The analytical approach combined speed-programmed large volume injection with a programmable injector and an autosampler capable of precise flow control. A multi-capillary liner was heated to match solvent evaporation rate, preventing liquid buildup and breakthrough. A 60 μL injection volume was selected to achieve detection limits around 1 ng/L. The chromatographic temperature program was optimized for rapid separation of 23 target pesticides.

Used Instrumentation

• Optic 2-200 programmable injector with multi-capillary quartz-wool liner
• Gas flows: split 50 mL/min; vent 150 mL/min; purge 5 mL/min
• Programmable pressure: initial 10 psi to final 22 psi
• Temperature ramp: injector from 40 °C to 230 °C at 16 °C/s; GC oven from 70 °C hold 1.5 min, 22 °C/min to 200 °C, 0.8 °C/min to 220 °C, 30 °C/min to 300 °C hold 4 min
• CTC A200S large volume autosampler with 500 μL syringe and 60 μL injection volume

Main results and discussion

A 60 μL injection of fortified river water yielded clear, well-resolved peaks for 23 organophosphorous compounds, including diazinon, malathion and azinphos methyl. The inert multi-capillary liner avoided adsorption losses, and speed-programmed injection prevented liquid carryover. Quantitation down to 1 ng/L was achieved with excellent reproducibility, demonstrating the method’s suitability for trace analysis.

Benefits and practical applications

• Enhanced sensitivity due to large injection volume without breakthrough risk
• Improved inertness minimizes thermal degradation and adsorption of labile pesticides
• Speed-programmed injection enables routine, unattended operation
• Applicable to environmental monitoring, water quality assessment and regulatory compliance

Future trends and potential applications

Continued advancements may include integration with mass spectrometric detectors for improved selectivity, development of novel inert liner materials, automated multi-residue screening workflows, and portable systems for in-field monitoring. Coupling large volume injection with real-time data processing and chemometric tools could further enhance throughput and decision-making in environmental analysis.

Conclusion

The combination of a programmable injector with a multi-capillary liner and speed-controlled autosampler injection delivers robust, sensitive analysis of organophosphorous pesticides at sub-nanogram levels in water. This approach addresses adsorption and thermal degradation challenges, making it a valuable tool for routine trace-level pesticide monitoring.