ION
CHROMATOGRAPHY
Ion Chromatography can be used in a number of novel ways and employing the appropriate conditions can even be used to separate mixtures where the components are not ionic or do not normally produce interactive ions in aqueous solution. An example of this type of separation is the analysis of saccharide mixtures using ion exchange interactions. An illustration of such a separation is given. The saccharine are reacted with a borate with which saccharides readily forms complex anions. The procedure for making the complex is simply and is achieve by merely including a borate buffer in the mobile phase.
The column packing was a strong anion exchange resin designated as TSKgel Sugar AXG. It had a particle diameter of 10 m and contained quaternary ammonium ions as the ion exchange moiety. The column was 15 cm long, 4.6 mm in diameter and had a potential efficiency of about 7,500 theoretical plates. The mobile phase consisted of three borate buffer solutions which were used in a stepwise gradient. The first buffer solution was a 0.5 M borate buffer (pH 7.7), the second a 0.7 M borate buffer (pH 7.3) and the last a 0.7 M borate buffer (pH 8.7) and the flow rate was 4 ml/min.
The last example clearly broaches an decidedly different approach to the sample separation. It is just as feasible for the solutes to be modified to suit a particular phase system as it is to choose or modify a phase system to suit the solutes.
This emphasizes the wide range of variables and alternative approaches that liquid chromatography provides for the analyst. Before ending an example needs to be include that utilizes Micro-reticulated polystyrene gels as a stationary phase. Micro-reticulated polystyrene gels, as already discussed, are formed from cross-linked styrene-divinyl benzene polymers and can be manufactured with a wide range of different pore sizes. Due to their method of manufacture, the pore volume of the micro- reticulated polystyrene gels may be significantly lower than that of silica gel. Consequently, some gels may have neither the peak capacity nor the loading capacity normally experienced with silica. However, this is generally not a problem in analytical LC.
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