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Ion Exchange Chromatography

Techniques Equilibration of the stationary phase is needed in order to obtain the desired charge of the column. If the column is not properly equilibrated the desired molecule may not bind strongly to the column.

"Weak" and "Strong" Ion Exchangers A "strong" ion exchanger will not lose the charge on its matrix once the column is equilibrated and so a wide range of pH buffers can be used. "Weak" ion exchangers have a range of pH values in which they will maintain their charge. If the pH of the buffer used for a weak ion exchange column goes out of the capacity range of the matrix, the column will lose its charge distribution and the molecule of interest may be lost. However, weak ion exchangers are often preferred over strong ion exchangers due to their greater specificity. In some experiments, the retention times of weak ion exchangers are just long enough to obtain desired data.

Examples of functional groups of Strong ion exchange resins are Quaternary Ammonium (Q), which is an anion exchanger, and Sulfonic Acid (S), which is a cation exchanger. These types of exchangers can maintain their charge over a pH range of 0-14. Examples of functional groups of Weak ion exchange resins include Diethylaminoethyl (DEAE), which is an anion exchanger that can maintain its charge over the pH range of 5-9, and Carboxymethyl (CM), which is a cation exchanger that can also maintain its charge over the pH range of 5-9.