Improving SPE Disk Extraction Technology for US EPA Wastewater Method 625.1

Significance of the topic

US EPA Method 625.1 is a cornerstone analytical protocol for monitoring semivolatile organic pollutants in wastewater to ensure compliance with the National Pollutant Discharge Elimination System. Reliable, high-throughput sample preparation is critical for protecting human health and aquatic ecosystems by accurately quantifying hundreds of regulated contaminants.

Objectives and study overview

The study demonstrates the performance of a mixed-mode SPE disk (One-Pass disk) automated on the Biotage Horizon 5000 platform, coupled with a Fast Flow Disk Holder and carbon cartridge, for extraction according to EPA 625.1. Key goals included verification of calibration standards, initial demonstration of compliance (DOC), and evaluation of matrix spike and duplicate recoveries across representative analytes.

Methodology and instrumentation

Solid-phase extraction of one-liter wastewater samples employed:

• Mixed-mode SPE One-Pass disk in a Fast Flow Disk Holder to prevent particulate clogging.
• Carbon cartridge for retention of volatile nitroso and light-end compounds.
• Automated processing on Biotage Horizon 5000 (formerly SPE-DEX 5000).
• DryDisk membrane drying and DryVap in-line evaporation to 1 mL for extract concentration.
• GC/MS analysis (Agilent 6890 GC/5975 MS) with Zebron ZB-Semivolatiles column under splitless injection and a temperature program from 45 °C to 318 °C.

Main results and discussion

Calibration verification recoveries for >80 target analytes consistently fell within EPA 625.1 acceptance ranges (60–140 % for most compounds) across multiple checks. Initial demonstration of capability (DOC) showed average recoveries of 45–120 % with relative standard deviations <10 %, meeting precision limits. Matrix spike (MS) and duplicate (MSD) recoveries across 60+ analytes yielded relative percent differences <15 % and recoveries within prescribed criteria, confirming robust performance in realistic wastewater matrices.

Benefits and practical applications

The disk SPE approach offers:

• Reduced solvent consumption and waste versus cartridge SPE.
• High flow-through rates with minimal clogging using particulate shielding.
• Seamless automation improving throughput and reproducibility.
• Compatibility with extensive analyte panels (up to 364 compounds).
• Enhanced laboratory safety through enclosed, in-line drying and evaporation.

Future trends and potential applications

Advances may include further miniaturization of disk formats, integration with online LC-MS workflows, development of novel sorbent chemistries for emerging contaminants, and real-time data processing with AI-driven quality control. Such innovations will continue to streamline EPA 625.1 compliance and expand monitoring capabilities in environmental laboratories.

Conclusion

The combination of mixed-mode SPE disks, automated processing, and efficient in-line drying/evaporation meets all EPA 625.1 performance requirements. This workflow enhances laboratory productivity, reduces solvent usage, and maintains high analytical rigor for comprehensive wastewater monitoring.

Reference

• Method Update Rule, Federal Register, US EPA, February 19 2015, pp. 8946–8952.
• US EPA Method 625.1 Revision (December 14 2014), Office of Science and Technology, EPA.