Sub μg/L Level Analysis of Chlorinated Pesticide and Herbicide Analysis in Water by GC/μECD using Agilent J&W DB-35ms Ultra Inert and DB-XLB columns

Importance of the Topic

Chlorinated pesticides and herbicides pose risks to human health and ecosystems due to their persistence and potential to contaminate water supplies at trace levels. Regulatory agencies require monitoring at sub microgram per liter concentrations to ensure safe drinking water quality and compliance with environmental directives.

Objectives and Study Overview

This study aimed to develop and validate a sensitive and reliable method for simultaneous extraction and determination of 37 chlorinated pesticides and herbicides in water at levels below established maximum contaminant thresholds. A dual column gas chromatography electron capture detection GC/ECD approach was evaluated using primary analysis on a nonpolar column and confirmatory analysis on a less polar column. The method also incorporated rapid liquid solid extraction to concentrate analytes from liter scale water samples.

Methodology and Instrumentation

An automated sample preparation system was used to prepare calibration solutions and fortify water samples. One liter of water was spiked with surrogate standards and acidified to pH 2. Residual chlorine was removed via sodium sulfite. An Agilent SPEC C18AR liquid solid extraction disk retained analytes during vacuum assisted loading at 75 to 100 milliliters per minute. Disks were conditioned with ethyl acetate and methanol and dried before elution with organic solvents. Extracts were dried over sodium sulfate and concentrated to one milliliter in centrifugal evaporators. GC analysis employed an Agilent 7890A equipped with dual micro ECD detectors. Effluent was split to a primary DB 35ms UI column for quantitation and a DB XLB column for confirmation. Helium served as a carrier gas and nitrogen makeup gas for the detectors. An inert inlet liner and deactivated flow path minimized adsorption and degradation of active analytes.

Key Results and Discussion

Chromatograms of a 50 nanograms per milliliter standard demonstrated baseline separation of all target analytes within 23 minutes. Calibration over 1 to 100 nanograms per milliliter yielded correlation coefficients above 0.993 on both columns, confirming linear detector response. Spiked reagent water at 0.01 micrograms per liter was clearly detected with sharp peak shapes, and no interferences were observed in blank extractions. Analysis of a tap water sample fortified only with surrogates showed no pesticide residues at calibrated levels, indicating suitability for routine monitoring. The large diameter disks reduced extraction times to around 10 minutes per sample while maintaining high recovery of trace compounds.

Benefits and Practical Applications

This workflow achieves reliable sub microgram per liter detection of a broad range of chlorinated agrochemicals in water with regulatory compliance. Automation of sample preparation reduces manual error, solvent consumption, and turnaround time. Dual column confirmation enhances confidence in analyte identification, supporting environmental monitoring and quality assurance programs in drinking water analysis laboratories.

Future Trends and Applications

Emerging directions include coupling ultra inert columns with mass spectrometry for improved selectivity, integrating on line solid phase extraction for further productivity gains, and miniaturizing sample processing to lower solvent usage. Advances in detector technology and data processing are expected to enhance sensitivity and simplify compliance with evolving environmental regulations. Adaptations of this method to other complex matrices such as soils and biological samples may broaden its utility.

Conclusion

The presented GC/ECD method combining automated liquid solid extraction with dual column analysis on ultra inert and selective stationary phases delivers robust quantitation of chlorinated pesticides and herbicides at trace levels. High linearity, efficient sample throughput, and dual column confirmation make it a powerful tool for environmental laboratories tasked with safeguarding water quality.

Instrumentation Used

• Agilent 7890A gas chromatograph with dual micro electron capture detectors
• Agilent 7683B autosampler
• Agilent SPEC liquid solid extraction manifold and C18AR disks
• Agilent DB 35ms UI 30 meter by 0.32 millimeter id 0.25 micrometer column
• Agilent DB XLB 30 meter by 0.32 millimeter id 0.5 micrometer column
• Labconco CentriVap centrifugal concentrator

Reference

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