Improved Analysis of EPA Method 625 Using Large- Particle, Large-Pore Solid Phase Extraction (SPE)

Significance of the Topic

EPA Method 625 is a cornerstone procedure for monitoring semivolatile organic contaminants in water. Traditional liquid–liquid extraction (LLE) meets regulatory criteria but suffers from high solvent consumption, lengthy processing times, emulsion formation and variable recoveries, especially when samples contain particulates.

Study Objectives and Overview

This study evaluates an optimized solid phase extraction (SPE) protocol using large‐particle, large‐pore polymeric cartridges (Strata‐XL‐C) to replace LLE in EPA Method 625. The goals were to enhance extraction efficiency, reproducibility, throughput and reduce solvent use, glassware handling and labor.

Methodology and Instrumentation

The workflow includes sample acidification (pH 1–3), SPE cartridge conditioning (methanol, water), sample loading (500 mL–1 L at 10–12 mL/min), vacuum‐assisted drying, sequential elution with organic solvents, water removal via sodium sulfate cartridges, nitrogen‐assisted evaporation (TurboVap LV) to ~0.5 mL, and reconstitution in dichloromethane. Key instrumentation:

• 12‐position SPE vacuum manifold and vacuum pump
• Zymark TurboVap LV evaporator (Biotage) for gentle nitrogen drying
• Shimadzu GC-2010 Plus coupled to MSD detector
• Zebron ZB-SemiVolatiles capillary column (30 m×0.25 mm×0.25 µm)

Results and Discussion

Surrogate recoveries averaged 40–85 % for most analytes, with low recovery (~5 %) of highly polar N-nitrosodimethylamine due to partitioning losses during cleanup. GC-MS analyses achieved sharp, well-resolved peaks for acids, bases and neutrals in under 17 minutes, including critical isomer separations. An independent lab reported a 50–75 % increase in daily throughput (from ~20 to 30–35 samples), a 90 % reduction in solvent use (360 mL to 41 mL per sample), and significant decreases in glassware and manual steps.

Practical Benefits and Applications

This large-particle SPE approach delivers faster extractions, lower operational costs, improved data consistency and scalable formats for both laboratory and on-site sampling. Reduced solvent and consumable requirements support greener workflows and lower disposal burdens.

Future Trends and Opportunities

Continuing developments may include integration with automated SPE platforms, expansion to other pollutant classes, use of alternative green elution solvents, and deployment of field-portable SPE units for rapid environmental screening. Advances in polymeric sorbent design could further boost selectivity for emerging contaminants.

Conclusion

The optimized Strata-XL-C SPE protocol for EPA Method 625 offers a robust LLE alternative, delivering enhanced recovery, precision and throughput while reducing solvent, labor and glassware demands. Combined with a fast GC-MS run on a semi-volatile column, this method ensures reliable quantification of semivolatiles in varied water matrices.