Ion-exchange in Analytical Chemistry: Problems and Prospects

An analysis is made of some of the practical problems of ion-exchange chromatography. A comparison is made with gas—liquid chromatography and this leads to the suggestion that improvements can be made in the monitoring system and in the selection of eluents for specific separations. The need for a general purpose gradient elution apparatus is stressed. Some theoretical aspects of several factors which affect, in particular, the tailing of elution peaks are examined. The desirability of presenting ionexchange data in the form of complete isotherms is underlined and the type of information that can be derived from such isotherms is indicated by reference to some typical examples of uni-bivalent exchange isotherms. A plea is made for international cooperation in the compilation and collection of such data and in its interpretation in the design of analytical ion-exchange separations. The early outstanding successes of ion-exchange in the separations of lanthanides1, trans-uranic elements2 and amino acids3 led to hopes that ion-exchange would provide a powerful analytical tool. Indeed many papers have been written on the analytical applications of ion-exchange as well as someuseful books4. Nevertheless, the early hopes have not been fully realized and it might even be considered that ion-exchange is tending to be replaced as a separations technique by gas—liquid chromatography or by solvent extraction. It is also to be noted that, with the development of instrumental techniques, such as atomic absorption and x-ray fluorescence spectroscopy, separation of the components of a material before analysis is often no longer necessary. Such developments are welcome ones, but they do call into question the status of ion-exchange as an analytical technique. It is clear that, in such circumstances, an analytical separation process is likely to be of use only if it can be coupled to an automatic detection and recording process—as is the case with gas—liquid chromatography. So far ion-exchange has lacked the auxiliary instrumentation that is available in gas—liquid chromatography. A fraction collector connected to an ion-exchange column enables the components of a mixture to be collected separately, but it still leaves the work of analytical determination to be done. By contrast, the detector of a gas—liquid chromatographic column is usually connected to a chart recorder and thus automatically provides a permanent analytical record. Ion-exchange chromatography needs an equally efficient