ABSTRACT
This chapter describes a variety of tools for the indirect estimation of total fluorine content. It focuses on the total oxidizable precursor (TOP) assay, which, if used appropriately, can provide estimates of the potential of unknown precursors in a sample to transform into stable and persistent perfluorinated alkyl acids (PFAAs) in the environment. There are multiple approaches to assessing total fluorine in a sample, each with different and complementary applications. Particle-induced gamma emission uses protons to stimulate the formation of gamma rays from molecules. The adsorbable organic fluorine (AOF) technique uses the relatively uncomplicated technique of hydropyrolysis combustion ion chromatography to measure organofluorine compounds adsorbed on a polystyrene-divinylbenzene-based activated carbon. The TOP assay, developed by E. F. Houtz and D. L. Sedlak, takes a different approach to estimating unknown PFAS contributions. While sometimes overlooked in discussions around the quality of TOP data, the underlying analytical procedure is a significant contributor to data quality.
