Cation chromatography Quaternary ammonium ions

As mentioned above ion-pair partition is automatically involved in chromatography of anionic solutes on dynamically coated phases using long chain quaternary ammonium ions. The possibility of ion-pair partition of cationic solutes, however, has not been investigated and problems might occur due to the apparent possibility of ion-pair formation between the counterion and surfactant ions, as well as the solute in question. A dynamic modification of the support surface (alumina), using... 

The use of suppressors in ion chromatography of quaternary ammonium compounds can be of advantage. These are ion exchange membranes that introduce hydroxide ions instead of the counterion present in the analyte. This simplifies the mixture and enhances the electrolytic conductivity of the sample. The effluent of the suppressor may be nebulized and subjected to field-assisted evaporation, yielding a cloud of ions suspended in the gas phase, which can be introduced into an MS analyzer designed for work at atmospheric pressure. Both the molecular weight and the structure of the quaternary cations can be determined by this method419. 

In the field of cation analysis, ion-pair chromatography is the preferred method for the separation of amines of all types. While short-chain aliphatic amines (C3 to C3) and some smaller aromatic amines [39] can also be separated on surface-sulfonated cation exchangers, ion-pair chromatographic applications have been developed for the separation of structurally isomeric amines, alkanolamines, quaternary ammonium compounds, arylalkylamines, barbiturates, and alkaloids. 

In the field of surface-active cations, ion-pair chromatography is predominantly applied to the analysis of quaternary ammonium compounds, pyridine, pyrrolidine, and piperidine quatemisates, and for sulfonium, phosphonium, ammonium, and hydrazin-ium salts. 

The most commonly used resins are gel type sulfonated cation exchangers or anion exchangers with a quaternary ammonium functional group. The exchange capacity of the resins used is generally higher than those used for ion chromatography. The resins may be either styrene-divinylbenzene copolymeric beads or polyacrylate beads. The diameter of the beads should be small and uniform. Resins with a 5 pm bead diameter are now available. 

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