Title: co-ions
Long Title: IUPAC Gold Book - co-ions
DOI: 10.1351/goldbook.C01141
Status: current

Definitions
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Definition (1)
Ions of low relative molecular mass with a charge of the same sign as that of a given colloidal ion.

Related Terms
- Ions: https://goldbook.iupac.org/terms/view/I03158
- colloidal: https://goldbook.iupac.org/terms/view/C01172
- relative molecular mass: https://goldbook.iupac.org/terms/view/R05271

Source
- PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 607 (https://doi.org/10.1351/pac197231040577)

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Definition (2)
In an ion exchanger, mobile ionic species with a charge of the same sign as the fixed ions.

Related Terms
- fixed ions: https://goldbook.iupac.org/terms/view/F02402
- ion exchanger: https://goldbook.iupac.org/terms/view/I03171

Source
- Orange Book, 2nd ed., p. 88 (https://media.iupac.org/publications/analytical_compendium/)

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Other Outputs
- html: https://goldbook.iupac.org/terms/view/C01141/html
- json: https://goldbook.iupac.org/terms/view/C01141/json
- xml: https://goldbook.iupac.org/terms/view/C01141/xml

Citation: Citation: 'co-ions' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.C01141
License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.
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Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.
Accessed: 2026-05-09T23:34:31+00:00