Polymer-based reversed-phase columns

Polymer C18 Column ODS-A 120A Silica Based Reverse Phase Column... 

The pore structure of most cross-linked polystyrene resins are the so called macro-reticular type which can be produced with almost any desired pore size, ranging from 20A to 5,000A. They exhibit strong dispersive type interaction with solvents and solutes with some polarizability arising from the aromatic nuclei in the polymer. Consequently the untreated resin is finding use as an alternative to the C8 and Cl8 reverse phase columns based on silica. Their use for the separation of peptide and proteins at both high and low pH is well established. 

An example of the efficacy of the resin phases used as an alternative to a conventional silica based reverse phase is shown in figure 12 where the separation of the three tocopherols are shown separated on the Cl 8 Polymer Column and The ODA-A 120A silica gel based columns. The columns were 15 cm long, 4.6 mm i.d., operated at a flow rate of 0.5 ml/min at 30°C with a mobile phase of 98% methanol/2% water. 

It is seen that the polymer resin does not have the same retentive capacity as the conventional reverse phase column and thus, will not exhibit the same resolution or the equivalent loading capacity. Nevertheless, the polymer column will function over a wide range of pH whereas the silica based columns will be restricted to operating within a pH of 4.0 to 8.0 at the most. 

The most popnlar system is a reversed phase column (Cl8), on a silica base column. However, the use of C18 on a polymer-based column has been reported to provide better resolution, especially for the separation of complex anthocyanin mixtures containing acylated pigments. - Polymer-based columns also show better stability at low pH operating conditions. 

Polystyrene/divinylbenzene-based ion-exclusion columns are also offered by Hamilton Co. (Reno, NV, USA) under the trade name PRP-X300. This is a 10-pm material with an exchange capacity of 0.2 mequiv/g [4], It is obtained by sulfonation of PRP-1, a macroporous PS/DVB polymer with reversed-phase properties. Fig. 4-2 shows the separation of various organic acids on this stationary phase. Dilute sulfuric acid was used as the eluent. The much higher retention of succinic acid compared to acetic acid reveals that the retention of organic acids is chararcterized, apart from reversed-phase effects, by the formation of hydrogen bonds. 

Additives in polymers were identified by solvent-elimination based coupling of reversed-phase column liquid chromatography(LC) and FTIR spectrometry. A spray-jet interface was used to deposit the effluent from a narrow-bore LC column on a zinc selenide window. The deposited additives were analysed by FTIR transmission microscopy, yielding identification limits in the low-nanogram range. High-quality IR spectra were obtained for components present in PVC and PP samples. 

Polymer-based mixed-mode columns are commercialized under the trade name Thermo Scientific Dionex OmniPac (Thermo Fisher Scientific, Waltham, MA, USA). They allow separations based on ion-exchange, ion-pair, reversed-phase, and ion-suppression interactions, depending on the type of eluent. Any combinations of these interactions, at the same time or in succession, can also be employed to separate analyte species. 

Mohammad, J, Jaderlund, B., and Lindblom, K., New polymer-based prepacked column for the reversed-phase liquid chromatographic separation of peptides over the pH range 2-12, J. Chromatogr. A, 852, 255, 1999. 

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