Ion chromatography

A modern ion chromatography system

Ion exchange chromatography
AcronymIC, IEC
ClassificationChromatography
Other techniques
RelatedHigh performance liquid chromatography
Aqueous normal phase chromatography
Size exclusion chromatography
Micellar liquid chromatography

Ion chromatography (or ion-exchange chromatography) is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger.[1] It works on almost any kind of charged molecule—including small inorganic anions,[2] large proteins,[3] small nucleotides,[4] and amino acids. However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein.[5]

The two types of ion chromatography are anion-exchange and cation-exchange. Cation-exchange chromatography is used when the molecule of interest is positively charged. The molecule is positively charged because the pH for chromatography is less than the pI (also known as pH(I)).[6] In this type of chromatography, the stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it. Anion-exchange chromatography is when the stationary phase is positively charged and negatively charged molecules (meaning that pH for chromatography is greater than the pI) are loaded to be attracted to it.[7] It is often used in protein purification, water analysis,[8][9] and quality control. The water-soluble and charged molecules such as proteins, amino acids, and peptides bind to moieties which are oppositely charged by forming ionic bonds to the insoluble stationary phase.[10] The equilibrated stationary phase consists of an ionizable functional group where the targeted molecules of a mixture to be separated and quantified can bind while passing through the column—a cationic stationary phase is used to separate anions and an anionic stationary phase is used to separate cations. Cation exchange chromatography is used when the desired molecules to separate are cations and anion exchange chromatography is used to separate anions.[11] The bound molecules then can be eluted and collected using an eluant which contains anions and cations by running a higher concentration of ions through the column or by changing the pH of the column.

One of the primary advantages for the use of ion chromatography is that only one interaction is involved the separation, as opposed to other separation techniques; therefore, ion chromatography may have higher matrix tolerance. Another advantage of ion exchange is the predictability of elution patterns (based on the presence of the ionizable group).[12] For example, when cation exchange chromatography is used, certain cations will elute out first and others later. A local charge balance is always maintained. However, there are also disadvantages involved when performing ion-exchange chromatography, such as constant evolution of the technique which leads to the inconsistency from column to column.[13] A major limitation to this purification technique is that it is limited to ionizable group.[6]

  1. ^ Muntean, Edward (2022). Food analysis: using ion chromatography. De Gruyter STEM. Berlin Boston: De Gruyter. ISBN 978-3-11-064440-1.
  2. ^ Ngere, Judith B.; Ebrahimi, Kourosh H.; Williams, Rachel; Pires, Elisabete; Walsby-Tickle, John; McCullagh, James S. O. (10 January 2023). "Ion-Exchange Chromatography Coupled to Mass Spectrometry in Life Science, Environmental, and Medical Research". Analytical Chemistry. 95 (1): 152–166. doi:10.1021/acs.analchem.2c04298. ISSN 0003-2700. PMC 9835059. PMID 36625129.
  3. ^ "Ion-Exchange Equilibria", Ion-Exchange Chromatography of Proteins, CRC Press, pp. 121–158, 14 April 1988, doi:10.1201/b15751-8, ISBN 9780429173790, retrieved 13 October 2023
  4. ^ Singhal, Ram P. (1974). "Anion-Exclusion and Anion-Exchange Chromatography of Nucleotides". European Journal of Biochemistry. 43 (2): 245–252. doi:10.1111/j.1432-1033.1974.tb03406.x. ISSN 0014-2956. PMID 4838980.
  5. ^ Cite error: The named reference :0 was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference :5 was invoked but never defined (see the help page).
  7. ^ "Principles of Ion Exchange Chromatography". separations.us.tosohbioscience.com. Retrieved 1 May 2018.
  8. ^ "Handbook for Monitoring Industrial wastewater". Environmental Protection Agency (USA). August 1973. Retrieved 30 July 2016.
  9. ^ Da̧browski, A., Hubicki, Z., Podkościelny, P., & Robens, E. (2004). Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere, 56(2), 91-106.
  10. ^ Luqman, Mohammad, and Inamuddin (2012). Ion Exchange Technology II. Springer Netherlands. p. 1. ISBN 978-94-007-4026-6.
  11. ^ Fritz, James S. (1987). "Ion chromatography". Analytical Chemistry. 59 (4): 335A–344A. doi:10.1021/ac00131a002.
  12. ^ Siegel, Miles (May 1997). "Rapid purification of small molecule libraries by ion exchange chromatography". Tetrahedron Letters. 38 (19): 3357–3358. doi:10.1016/S0040-4039(97)00650-3.
  13. ^ Neubauer, Kenneth (November 2009). "Advantages and Disadvantages of Different Column Types for Speciation Analysis by LC-ICP-MS". Spectroscopy. Spectroscopy-11-01-2009. 24 (11). Retrieved 9 May 2016.