Your PFAS TOP Assay Produced a Result.
But Was the Oxidation Complete?
The Total Oxidizable Precursor (TOP) Assay can reveal PFAS precursor content that may not be captured by conventional targeted analysis. For complex environmental matrices, however, monitoring oxidation efficiency is an important part of analytical confidence.
Why Use the TOP Assay?
Targeted LC-MS/MS methods quantify defined PFAS analytes, but environmental samples can also contain oxidizable PFAS precursors outside the routine target list.
The TOP Assay converts many of these precursors into measurable terminal perfluoroalkyl acids and compares PFAS profiles before and after oxidation.
The Critical Question: Did Oxidation Work?
Incomplete oxidation can lead to incomplete precursor conversion and potentially underestimate the oxidizable precursor burden.
This becomes particularly important in complex matrices where sample components can consume oxidant or otherwise influence reaction efficiency.
A robust TOP Assay therefore benefits from a process control that indicates whether oxidation performed as expected in the individual sample.
Stable Isotope-Labeled Oxidation Surrogates
A newly published multi-laboratory study evaluated stable isotope-labeled PFAS compounds as oxidation-monitoring surrogates for the TOP Assay.
↓ TOP oxidation
Loss of labeled precursor
+
Formation of labeled oxidation product
↓ LC-MS/MS
Evaluate oxidation performance
Because the surrogate is isotopically labeled, it can be distinguished from native PFAS while experiencing the oxidation conditions within the same sample.
Why Matrix-Specific Monitoring Matters
A single oxidation protocol does not necessarily guarantee identical performance across water, wastewater, soil extracts and other environmental matrices.
Matrix composition and oxidant demand can influence precursor conversion.
An oxidation-monitoring surrogate can therefore provide a practical QC indicator for determining whether oxidation conditions require further optimization.
CIL Oxidation Monitoring Surrogate Standards
CLM-11722-1.2
Perfluoroheptanesulfonamide (PFHpSA), 5,6,7-¹³C₃, 99%
100 µg/mL in MeOH · 1.2 mL
CLM-11723-1.2
Sodium perfluoro-n-heptanoate (PFHpA), 5,6,7-¹³C₃, 99%
100 µg/mL in MeOH · 1.2 mL
CLM-11724-1.2
Perfluoro-n-nonanoic acid (PFNA), 7,8,9-¹³C₃, 99%
100 µg/mL in MeOH with 4 molar equivalents NaOH · 1.2 mL
TOP Assay QC Checklist
✓ Oxidation-surrogate recovery
✓ Precursor conversion
✓ Oxidation-product formation
✓ Matrix-dependent oxidation performance
✓ Oxidant sufficiency
✓ Native PFAS background
✓ Internal-standard recovery
✓ Method blanks and batch QC
Need Standards for PFAS Analysis?
Dana Bioscience can help source native PFAS standards, stable isotope-labeled internal standards, TOP Assay oxidation-monitoring surrogates and reference materials for environmental PFAS workflows.
Share your analytes, analytical method, sample matrix and required concentration, and we can help identify suitable standards.
Discuss Your PFAS Workflow →