Improved Recoveries of Polycyclic Aromatic Hydrocarbons (PAHs) as Defined in EPA 550.1 and Simultaneous Removal of Humic Acids from Water Using Strata® PAH

Significance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are pervasive environmental contaminants arising from incomplete combustion of fossil fuels. Due to their carcinogenic, mutagenic, and teratogenic properties, regulatory agencies monitor PAH levels in water and food. Conventional solid phase extraction (SPE) methods outlined by EPA Method 550.1 use C18 sorbents but co-extract humic acids, leading to chromatographic interference and reduced analytical performance. Developing selective sorbents that improve PAH recovery while removing matrix impurities is critical for accurate, sensitive environmental analysis.

Objectives and Study Overview

This study evaluated Strata® PAH SPE sorbent for simultaneous extraction of 16 priority PAHs and removal of humic acids from water samples. Performance metrics were compared against the standard EPA 550.1 C18 sorbent. Key goals included:

• Assessing recoveries of all target PAHs
• Demonstrating humic acid elimination to improve chromatographic baseline
• Comparing results under identical extraction conditions

Methodology and Instrumentation

A 100 mL water sample spiked with a 100 µg/mL PAH mixture (75:25 water/acetonitrile) and a humic acid standard (1 mg/L) was processed through 1.5 g/6 mL Strata PAH SPE tubes. Conditioning, loading, washing, drying, and elution followed a defined protocol using dichloromethane, methanol, and water. Extracts were dried under nitrogen at 35 °C and reconstituted in solvent. Analysis employed two platforms:

• Gas chromatography-mass spectrometry (GC–MS) on a Zebron™ ZB-5ms column
• High-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) with an Agilent® 1200SL HPLC coupled to an AB SCIEX™ 4000 QTRAP® and a Kinetex® C8 column

Key Results and Discussion

Strata PAH delivered consistently higher recoveries for 15 of the 16 EPA-listed PAHs, with average recoveries often exceeding 90%, compared to 60–80% for C18. Naphthalene recovery was limited by volatility but improved when monitored using deuterated analogs. Chromatograms revealed a significantly lower background signal and cleaner baseline after humic acid removal, enhancing detection sensitivity. These improvements highlight the sorbent’s dual selectivity for hydrophobic PAHs and polar humic substances.

Benefits and Practical Applications

• Enhanced PAH recoveries increase accuracy and compliance with regulatory limits.
• Effective humic acid removal reduces matrix interference, leading to sharper peaks and lower detection limits.
• Simplified sample preparation streamlines throughput in environmental monitoring laboratories.

Future Trends and Applications

Advancements may include tailoring SPE sorbents for broader classes of contaminants, integrating nano-structured materials for enhanced selectivity, and coupling with ultra-high performance chromatography. Application of multi-modal sorbents could further eliminate diverse matrix interferences in complex samples. High-throughput SPE automation and on-line SPE–LC/MS workflows are expected to improve laboratory efficiency.

Conclusion

Strata PAH SPE sorbent offers a robust solution for extracting EPA-priority PAHs from water while selectively removing humic substances. The method surpasses traditional C18 protocols by delivering higher recoveries and cleaner extracts, enhancing sensitivity and reliability in environmental analysis.

References

1. Hodgeson, J. W., et al. EPA Method 550.1, July 1990.
2. International Humic Substances Society (IHSS) Suwannee River humic acid standard.
3. Wikipedia contributors. Polycyclic aromatic hydrocarbon; Humic acid.