![]() ![]() įigure 2: Mechanism of separation in IEX.Ī mix of undissociated, partially dissociated and fully dissociated analytes can be separated by ion exclusion chromatography (IEC), which also uses charged stationary phases (Figure 3). When separation is brought about by competitive interaction between the analyte ions and eluent ions for the oppositely charged sites on the stationary phase (Figure 2), the type of chromatography is called ion exchange chromatography (IEX). Ion chromatography (IC) broadly refers to the separation of ions and includes three distinct mechanisms, namely, ion exchange, ion exclusion and ion pairing. How does ion pair reversed phase chromatography differ to other types of ion chromatography? 1, 2 It is also referred to as ion interaction chromatography, as the reagent ion interacts with the stationary phase to regulate the retention of ions present in the sample. Consequently, this technique was called “soap chromatography” when it was introduced by Göran Schill in 1973. As these molecules have a polar head group and hydrophobic hydrocarbon chains, they resemble a soap (Figure 1). Ion pairing reagents are also known as ion pairing additives or hetaerons. IPC is used for the separation of polar organic acids, bases and zwitterions as well as inorganic ions. The pairs formed between the analytes and reagent ions behave like neutral, hydrophobic moieties that can be separated on C18 or C8 columns. These reagent molecules carry charges opposite to that of the analyte ions with which they are able to form electrostatic bonds. It involves modifying the polarity of the charged analytes through their interaction with an ion-pairing reagent that is added to the mobile phase. IPC is a type of ion chromatography that is used to separate hydrophilic or charged analytes on columns using reversed phase or “neutral” stationary phases that do not carry charges. ![]()
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