The surface tension isotherms of soluble salts of per- and polyfluoroalkyl substances (PFAS) in electrolyte solutions are typically reported as functions of the PFAS concentration. However, for univalent salts and electrolytes, the Langmuir-Szyszkowski equation is a function of the mean ionic activity a*. Using previously reported data, we show that for salts of perfluorooctanoic acid (PFOA) or hexafluoropropylene oxide dimer acid (GenX™), use of a* rather than concentration provides a unified surface tension isotherm, independent of the electrolyte concentration. This suggests that the electrolyte dependence of the isotherm arises purely from its effect on PFAS activity, rather than an intrinsic surface property. This finding has important implications for the understanding of PFAS retention in saline unsaturated soils, and for PFAS extraction from saline waters by foam fractionation.

通常报告电解质溶液中全氟烷基物质和多氟烷基物质的可溶性盐（PFAS）的表面张力等温线是PFAS浓度的函数。但是，对于一价盐和电解质，Langmuir-Szyszkowski方程是平均离子活度a *的函数。使用先前报道的数据，我们表明，对于全氟辛酸（PFOA）或六氟丙烯氧化物二聚酸（GENX™），使用的盐一*浓度而不是浓度提供了统一的表面张力等温线，与电解质浓度无关。这表明等温线对电解质的依赖性完全来自其对PFAS活性的影响，而不是固有的表面性质。这一发现对于理解PFAS在盐渍不饱和土壤中的保留以及通过泡沫分馏从盐水中提取PFAS具有重要意义。