Separation of Free Metal Cations

Incorporation of a crown ether (18-crown-6) and some methanol in the BGE improve the separation of metal ions [9]. 

Some metal cations absorb sufficiently in the UV spectral range to be detected directly. By working at a sufficiently acidic pH hydrolysis is inhibited and an additional buffer does not need to be added. Sharp peaks were obtained for U02 in an aqueous HCl electrolyte with direct detection at 214 nm [10]. Uranium(V) had not been separated previously as the uranyl ion. 

Iron(III) initially gave a rather broad peak with some tailing at = 11.8 min when run in HQ at pH 2.4. However, a much sharper peak for iron(III) was obtained by increasing the chloride content of the capillary electrolyte to actually 66 mM and maintaining a 3- to 6-fold ratio of chloride in the electrolyte to that in the sample. An excellent separation of U02 and Fe was obtained. Several other metal ions were separated at low pH with direct detection including vanadium(IV) and (V), and VO2 [10], 

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