as more bivalent CrO4
2−
/Cr2O7
2− ions were
generated and the membrane was more negatively charged at higher
pH [39]. Since organic salt ions possess larger size, their separation
mechanism includes both size and charge effects. Wang et al. [17]
found that the retentions of two amino acids (L-phenylalanine and Laspartic
acid) by ES20 membrane were nearly 100% regardless of pH
values, indicating that the steric exclusion was dominant in this case.
While using ESNA2 membrane with a larger pore size, these two
amino acids showed totally different retention behaviors with increasing
pH, mainly resulted from their different charge performance.
Li et al. [40] also reported that L-glutamine and L-glutamate had
dissimilar rejection curves as a function of pH using NTR7450
membrane