Automated Liquid-Liquid Extraction of PAH Compounds in Water

Importance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are persistent environmental pollutants found in water bodies as a result of industrial discharge, urban runoff and combustion processes. Accurate and efficient extraction of trace-level PAHs from water matrices is critical for environmental monitoring, regulatory compliance and risk assessment. Traditional liquid–liquid extraction methods consume large solvent volumes, increase laboratory costs and generate significant waste. Automation and microextraction technologies address these challenges by reducing solvent usage, improving reproducibility and shortening preparation times.

Goals and Study Overview

This application note investigates an automated liquid–liquid microextraction approach for isolating PAH compounds in water samples. Using EST Analytical’s FLEX Autosampler in liquid mode and a large volume programmable temperature vaporization (PTV) inlet on a gas chromatograph–mass spectrometer (GC–MS), the study aims to:

• Demonstrate method linearity and sensitivity from 0.5 ng to 200 ng on-column.
• Evaluate method detection limits (MDLs) and precision at low calibration levels.
• Compare extraction recoveries against direct injection of standards.

Methodology

Samples were prepared following the principles of USEPA Method 3511. A 40 mL water aliquot was spiked with surrogate standard and salted with sodium chloride. Dichloromethane (500 µL) was used as the extraction solvent. Automated shaking, centrifugation and transfer of the solvent layer were programmed in the FLEX Autosampler. Extracts were introduced to the GC–MS via a Titan XL LVI port operating under PTV solvent vent conditions. Calibration standards were prepared in the range of 0.5 ng to 200 ng on-column. Seven replicates at the lowest calibration level established MDLs, while replicate extractions at 50 ng determined precision and accuracy. A direct injection of a 50 ng standard provided a benchmark for recovery comparison.

Used Instrumentation

• Agilent 7890 GC with Titan XL large volume PTV inlet
• Restek Rxi-5 Sil MS capillary column (30 m × 0.25 mm × 0.25 µm)
• Agilent 5975 Inert XL mass selective detector
• EST Analytical FLEX Autosampler in liquid extraction mode with 250 µL syringe

Main Results and Discussion

The calibration curves exhibited excellent linearity (R² ≥ 0.998) across all 12 PAH analytes. MDLs ranged from 0.18 ng to 0.25 ng on-column. At the 50 ng level, relative standard deviations were below 6%. Automated extraction recoveries exceeded 109% in calibration recovery tests. When compared to direct injection, recoveries for all compounds remained above 75%, demonstrating efficient analyte transfer during the microextraction process. These results confirm that the automated procedure reliably concentrates PAHs with minimal variability and high throughput.

Benefits and Practical Applications

• Significant reduction in solvent consumption (500 µL per sample) lowers operational costs and environmental impact.
• Fully automated workflow minimizes manual handling and improves reproducibility.
• High sensitivity and low detection limits support trace-level environmental monitoring.
• Suitability for routine screening of water samples in environmental, industrial and regulatory laboratories.

Future Trends and Opportunities

Advances in microextraction may include further miniaturization, integration with on-line sample cleanup modules and adoption of greener solvents. Coupling automated extraction platforms with high-resolution mass spectrometry and data analytics will enhance selectivity and compound identification. Field-deployable microextraction devices offer potential for real-time monitoring in remote locations.

Conclusion

The automated liquid–liquid microextraction method using EST Analytical’s FLEX Autosampler and LVI–PTV–GC–MS yields robust, high-throughput isolation of PAHs from water with excellent sensitivity, reproducibility and minimal solvent waste. This approach is well suited for environmental laboratories requiring efficient and cost-effective trace analysis of semi-volatile organic pollutants.