Modification of EPA Method 608 for Automated Solid-Phase Extraction (SPE) of Wastewaters and Surface Waters Using the Thermo Scientific Dionex AutoTrace 280 SPE Instrument

Importance of the Topic

Wastewater and surface water analysis for trace organic contaminants, such as organochlorine pesticides and PCBs, is critical for environmental monitoring and public health protection. Automated solid-phase extraction (SPE) streamlines sample preparation, reduces manual handling, and improves reproducibility. Adapting EPA Method 608 with an automated SPE platform addresses challenges posed by high particulate loads in wastewaters, enabling reliable extraction of hydrophobic contaminants from complex matrices.

Objectives and Study Overview

This study presents a modified workflow for EPA Method 608 employing the Thermo Scientific Dionex AutoTrace 280 SPE system. Key goals include:

• Demonstrating automated handling of high-particulate water samples without cartridge clogging.
• Comparing surrogate recoveries and analyte extraction efficiency with traditional liquid-solid methods.
• Establishing a robust protocol for routine environmental analysis of wastewater and surface water.

Methodology and Instrumentation

Sample Pretreatment and Surrogates:
500 mL of river or wastewater sample was spiked with tetrachlorometaxylene (TCMX) and decachlorobiphenyl (DCB) as surrogates, and with target analytes at known concentrations. 2.5 mL of methanol was added to aid in analyte solubilization.
Automated SPE Procedure:
The AutoTrace 280 system processed up to six samples in parallel using 6 mL C18 SolEx cartridges packed with 0.5 g sorbent. The sequence included:

• Cartridge conditioning (methanol and water).
• Sample loading at controlled flow rates, with automated gas drying of the bed.
• Elution with ethyl acetate and dichloromethane fractions.
• Use of a “Blocked Shocker” sub-program to overcome cartridge clogging by forcing solvent through with positive pressure.

Analytical Detection:
Extracts were concentrated to 1 mL and analyzed by capillary gas chromatography coupled to electron capture detection (GC/ECD) or mass spectrometry (GC/MS) using dual 30 m columns (Rtx-CLPesticides and Rtx-CLPesticidesII). Internal standard (dibromooctofluorobiphenyl) monitored instrument performance.

Main Results and Discussion

Surrogate Recoveries:
In tests with Iowa river water (70 mg/L suspended solids), average recoveries were 55–125% for TCMX and DCB, with relative standard deviations below 20%. Cedar River water (64 mg/L solids) yielded similar performance. Clogging events occurred in a minority of channels; application of the Blocked Shocker program recovered analytes without significant loss.
Analyte Performance:
Alpha-, beta-, gamma- and delta-BHC isomers, heptachlor, aldrin, endrin, DDT and metabolites exhibited recoveries generally between 40–125%, meeting EPA method quality criteria. Lower recoveries (<50%) for some highly hydrophobic compounds highlighted the importance of efficient cartridge conditioning and elution.
Clogging Management:
The AutoTrace 280’s positive-pressure syringe pump allowed recovery from plugged cartridges. Subsequent processing on a fresh cartridge and solvent combination ensured complete analyte transfer, preserving data integrity.

Benefits and Practical Applications

The automated SPE workflow reduces hands-on time and human error, increases sample throughput, and provides consistent recoveries in the presence of suspended solids. Laboratories performing QA/QC, environmental compliance, or research on organic pollutants can adopt this method to enhance efficiency and data reliability.

Future Trends and Potential Applications

Advances in automated SPE may include multimode sorbents for broader analyte coverage, real-time clogging detection with adaptive flow control, and integration with on-line GC or LC systems. Coupling automated SPE with high-resolution mass spectrometry could enable trace-level screening of emerging contaminants in complex water matrices.

Conclusion

The modified EPA Method 608, implemented on the Thermo Scientific Dionex AutoTrace 280, delivers a robust automated SPE solution for wastewater and surface water analysis. Surrogate and analyte recoveries meet regulatory standards, and automated clogging mitigation ensures reliable operation in high-particulate samples.

Reference

• Larabee-Zierath D. Automated Solid-Phase Extraction of Wastewaters Using the Thermo Scientific Dionex AutoTrace 280 SPE Instrument. Application Brief 875, Thermo Fisher Scientific; 2013.