Optimizing the total oxidizable precursor (TOP) assay: enhanced PFAS quantification and analytical gap bridging in...

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Environmental Science

Background:

• Targeted analyses often fail to detect the full spectrum of per- and polyfluoroalkyl substances (PFAS).
• The Total Oxidizable Precursor (TOP) assay offers a broader detection approach for PFAS and their precursors.
• Optimization is needed to enhance the TOP assay's effectiveness across diverse environmental matrices.

Purpose of the Study:

• To optimize the Total Oxidizable Precursor (TOP) assay for improved detection of diverse PFAS and their precursors.
• To evaluate key factors affecting TOP assay performance, including temperature, sorption, oxidation, and reagent ratios.
• To assess the impact of solid-phase extraction (SPE) timing on assay sensitivity.

Main Methods:

• Optimized the TOP assay by evaluating temperature, sorption, oxidation, and reagent-to-organic compound ratios.
• Utilized spiked solutions and real environmental matrices (wastewater, sludge, compost, struvite).
• Assessed solid-phase extraction (SPE) efficiency before and after the oxidation step.

Main Results:

• Post-oxidation SPE significantly improved sensitivity, especially for low PFAS concentrations.
• The modified TOP Assay quantified 56 PFAS and precursors, with up to a 1000% increase in perfluoroalkyl carboxylic acids (PFCA).
• PFAS precursor oxidation efficiency ranged from 64% to 100% across liquid and solid samples under optimized conditions (K₂S₂O₈: 240 mM; NaOH: 600 mM; 2.5 mL).

Conclusions:

• The optimized TOP assay effectively quantifies a wider range of PFAS and their precursors in various environmental samples.
• The assay's adaptability and improved sensitivity provide more comprehensive insights into PFAS contamination.
• Further application to solid samples can enhance environmental PFAS contamination estimations.