APPLICATIONS COMPENDIUM FOR AGILENT 7696A SAMPLE PREP WORKBENCH

Significance of the Topic

Accurate measurement of chlorinated pesticides and herbicides in drinking water at sub-microgram per liter levels is essential to safeguard public health and comply with regulatory limits set by the EPA and European Union. Trace analysis of these persistent, bioaccumulative contaminants requires highly efficient extraction, clean-up, and sensitive detection to ensure reliable monitoring.

Objectives and Overview

This study demonstrates an automated, high-precision workflow for the analysis of thirty-seven chlorinated pesticides and herbicides in water at concentrations down to 0.01 µg/L. Key goals included:

• Developing sub-µg/L detection using liquid-solid extraction (LSE) with Agilent SPEC C18AR disks.
• Automating sample preparation steps on the Agilent 7696A Sample Prep WorkBench to improve reproducibility and reduce solvent consumption.
• Implementing a dual-column GC/µECD approach—Agilent J&W DB-35ms Ultra Inert for primary analysis and DB-XLB for confirmation—to achieve robust identification and quantitation.

Methodology and Instrumentation

Sample Preparation:
The automated protocol on the Agilent 7696A WorkBench employed 47 mm SPEC C18AR disks to enrich analytes from a 1 L water sample. After pH adjustment and membrane filtration, disks were conditioned with ethyl acetate/methylene chloride and methanol, and then the sample was drawn through under vacuum. Elution was performed with 1:1 EtOAc:MeCl₂, followed by methanol and water rinses. The combined extracts were dried over anhydrous sodium sulfate, concentrated under centrifugal evaporation to 1 mL final volume, and transferred to GC vials.
Instrumentation:

• GC: Agilent 7890A with inert tee for dual flow to µECD detectors.
• Autosampler: Agilent 7683B.
• Primary column: J&W DB-35ms UI (30 m×0.32 mm, 0.25 µm).
• Confirmation column: J&W DB-XLB (30 m×0.32 mm, 0.5 µm).
• Carrier gas: Helium at 35 cm/s; splitless injection with 0.5 min purge.
• Detector: Dual µECD at 340 °C with 30 mL/min N₂ makeup.

Main Results and Discussion

The dual-column GC/µECD method achieved baseline separation of all target pesticides and herbicides in under 23 minutes. Calibration over 1–100 ng/mL (equivalent to 0.01–1 µg/L in water) delivered excellent linearity (r² ≥ 0.995). Fortified water samples at 0.01 µg/L showed recoveries within 80–110 % and relative standard deviations below 5 % for key analytes. The inert Ultra Inert column and inlet liner minimized analyte adsorption and improved peak shapes for late-eluting, thermally labile compounds such as endrin and DDT.

Benefits and Practical Applications

• High sensitivity: Sub-µg/L detection supports compliance with drinking water regulations.
• Enhanced reproducibility: Automated SPE and clean-up reduce analyst variability.
• Reduced solvent use: Miniaturized disk extraction and WorkBench automation lower waste.
• Rapid throughput: Complete GC analysis in under 25 minutes per run.
• Robust confirmation: Dual-column approach ensures reliable compound identification.

Future Trends and Applications

Advances in laboratory automation, such as coupling the 7696A WorkBench with low thermal mass GC ovens or tandem mass spectrometry detectors, will further accelerate analysis and enhance selectivity. Integration of real-time data analytics and remote monitoring can streamline environmental surveillance. Miniaturized sample preparation and on-site portable systems may enable faster field testing of water quality in remote locations.

Conclusion

The described workflow combines automated sample preparation on the Agilent 7696A WorkBench with dual-column GC/µECD to deliver precise, sensitive, and high-throughput analysis of chlorinated pesticides and herbicides in water at sub-µg/L levels. This approach meets stringent regulatory requirements while improving laboratory efficiency and sustainability.

References

• 1 WHO. Environmental Health Criteria 8: Aldrin and Dieldrin; 1979.
• 2 Mañas, F.M., et al. Endocrine Disruption by Chlorinated Pesticides, Environ. Sci. Technol. 2018.
• 3 U.S. EPA Method 508.1: Determination of Pesticides in Drinking Water by GC/ECD.
• 4 Council Directive 98/83/EC on the Quality of Water Intended for Human Consumption.