fixed ions

https://doi.org/10.1351/goldbook.F02402
In an ion exchanger, the non-exchangeable ions which have a charge opposite to that of the counter-ions.
Source:
PAC, 1993, 65, 819. 'Nomenclature for chromatography (IUPAC Recommendations 1993)' on page 854 (https://doi.org/10.1351/pac199365040819)