Examining the Compositional Selectivity of Hydrocarbon Oxidation Products Using Liquid-Liquid Extraction and...

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Geochemistry

Background:

• Hydrocarbon oxidation products (HOPs) are polar, water-soluble byproducts of petroleum biodegradation.
• Accurate detection of HOPs is crucial for understanding petroleum contamination and biodegradation processes in groundwater.
• Current regulatory monitoring often uses liquid-liquid extraction (LLE), but its efficiency for HOPs is questionable.

Purpose of the Study:

• To evaluate the analytical limitations and compositional selectivity of LLE versus solid-phase extraction (SPE) for HOPs in groundwater.
• To compare the extraction efficiencies and biases of LLE and SPE for various HOP classes.
• To provide quantitative data on the performance of LLE and SPE for HOP analysis.

Main Methods:

• Groundwater samples from the Bemidji, MN, crude oil spill site were analyzed.
• Excitation-emission matrix (EEM) spectroscopy and PARAFAC modeling were used to characterize optical properties.
• Ultrahigh-resolution mass spectrometry (UHR-MS) was employed to identify and quantify extracted compounds.

Main Results:

• LLE selectively recovered aliphatic-like compounds but underrepresented polar oxygenated HOPs.
• SPE methods were more effective in isolating highly oxidized compound classes.
• LLE demonstrated lower precision and was less representative of polar HOPs, introducing analytical bias.

Conclusions:

• LLE introduces significant bias in the characterization of groundwater HOPs, particularly underrepresenting polar compounds.
• SPE provides a more comprehensive and accurate recovery of diverse HOPs compared to LLE.
• These findings have critical implications for refining long-term groundwater monitoring and site assessment protocols for petroleum contamination.