Electrochemical fluorination products (ECF):

PFAS manufactured by ECF, such as sulfonamide linked products almost always show oxidation products dominated by PFAS of corresponding perfluorinated carbon content.

Figure 4: Sulfonamide linked PFAS products

Other PFAS:

Replacement PFAS products including the perfluorinated Gen-X and PFEESA species did not exhibit degradation products included in traditional PFAS analytical suites and hence their presence may have been easily missed under legacy environmental monitoring projects. In contrast, polyfluoroether compounds in which complete substitution with fluorine does not occur (e.g., ADONA) have been reported to degrade under TOP-A conditions by other researchers.

Perfluoroethylcyclohexane sulfonate (PFECHS) belongs in the same chemical class as PFOS although can be distinguished from the better known perfluorinated sulfonic acids (PFSAs) by the presence of a cyclic perfluorinated moiety. Industrially it has been used as an erosion inhibitor in aircraft hydraulic fluid, but its inclusion in PFAS lists is relatively new. Under the experiment PFECHS did not degrade, and as for Gen-X and PFEESA, TOP-A would not have included contributions from PFECHS contamination.

6:2 FTAB has received attention recently due to its inclusion in AFFFs. Although it is a telomer based product and exhibits the characteristic distribution of PFCA products, it is distinctive because it is also a zwitterion.

Figure 6: Gen-X, PFEESA, PFECHS, 6:2 FTAB products
¹Improved Total Oxidizable Precursor Assay for Quantifying Polyfluorinated Compounds Amenable to Oxidative Conversion to Perfluoroalkyl Carboxylic Acids; Katerina Tsou, Edmund Antell, Yanghua Duan, Christopher I. Olivares, Shan Yi, Lisa Alvarez-Cohen, and David L. Sedlak. ACS ES&T Water 2023 3 (9), 2996-3003

ALS Australia’s TOP-A Services:

Since the emergence of PFAS as contaminants of concern, chemists have battled hard to devise analytical solutions. ALS provides analytical services for many of today’s prevailing solutions including TOP-A. Total oxidisable precursor assay is a useful technique, but caution is required with data interpretation. However, despite challenges associated with TOP-A, an understanding of degradation patterning can be helpful rather than hindering, for example, providing a way to infer manufacturing processes and hence PFAS sources (e.g., telomerisation vs ECF). New and emerging enhancements are also frequently being published on optimisation of TOP-A.

ALS Australia offers services for TOP-A in various matrices, and method codes and matrices are summarised below:

Our technical experts and customer services teams are here to discuss your PFAS needs including elucidation of the presence of PFAS ‘dark matter’ and assist with interpretation of TOP-A results as required.

If you have any questions relating to PFAS Screening, please contact:

Brisbane: ALSEnviro.Brisbane@alsglobal.com

Sydney: ALSEnviro.Sydney@alsglobal.com

Melbourne: ALSEnviro.Melbourne@alsglobal.com

Perth: ALSEnviro.Perth@alsglobal.com