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ANALYTICAL CHEMISTRY, VOL. 51, NO. 9, AUGUST 1979
Separation of the Lanthanides on High-Efficiency Bonded Phases and Conventional Ion-Exchange Resins S. Elchuk and R. M. Cassidy" General Chemistry Branch, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario, KOJ 7J0, Canada
wide variety of metal ions. This limitation is perhaps the most important factor responsible for the slow development of inorganic HPLC. T h e solution of detection problems for inorganic anions is one of the main reasons why ion chromatography has gained widespread acceptance; however, it is unlikely that ion chromatography will prove useful for metal ion analysis (alkali and alkaline earth metal ions are possible exceptions) because of their strong binding to ion-exchange sites and their hydrolysis under the conditions used for detection. Atomic absorption spectrometry has been used for the detection of metal ions (9) but because of the specificity of atomic absorption, its usefulness is limited to speciation within groups, such as organometallics (10) or metal chelates (11). Detectors are available for monitoring radioactive eluates but find limited application to HPLC because of poor sensitivity and a narrow range of applicability. Many metal chloride complexes absorb in the UV region and this property has been used for the detection of a number of metal ions in strong hydrochloric acid media (12). The separation of metal ions as metal chelates with detection based on the UV-visible absorption of the ligand-metal ion complex is feasible (13-19) but unless the metal chelates are kinetically inert, this approach is susceptible to a number of problems as a result of chromatographic disruption of the ligand-metal ion equilibria. Detection after post-column reaction is presently the most attractive method available for inorganics; this technique has been used extensively by Fritz and co-workers (20,21). The potential of this technique as a sensitive, selective, and, a t the same time, universal detector, is apparent but to date this method has been applied only to medium to low resolution HPLC systems. This report is concerned with the combination of HPLC on microparticulate ion-exchange packings with detection after post-column reaction for the rapid separation and determination of small concentrations of metal ions. The lanthanide metal ions were chosen for this study since this group of metal ions is particularly difficult to separate by LC and thus should adequately test the efficiency of these packings. A number of methods for the ion-exchange separation of the lanthanides have been reported over the past few years (5,22-24) but these methods still require long separation times and/or give only partial resolution between neighboring lanthanides.
High-performance liquid chromatographic separations (
