Figure 3.

Relevance of the counterion in the transport of organic anions through an NF membrane. (a) Rejection of the cation and the anion after separation using commercial DuPont NF270 membranes, corresponding to the highest pH tested from the respective anion from Figure 2, thus ensuring Na⁺ as the main counterion. The different anions in solution influenced the Na⁺ retention. (b) Translation of the electroneutrality condition on the single solute feed and permeate samples from filtration experiments toward analytical techniques. 1:1 cation/anion analytical detection for sodium octanoate, sodium perfluorooctanoate, and sodium chloride solutions (no pH modification). Sodium was measured using ICP-MS, Octanoate was measured using TOC, perfluorooctanoate was measured using LC-MS/MS, and chloride was measured using ICP-MS.