Separation of metal ions by capillary electrophoresis

A number of experimental parameters have been optimized for the separation of 26 metal ions, including alkali, alkaline earth, transition and lanthanide metal ions. Experimental parameters that were evaluated included nature of indirect-detection reagent, pH of electrolyte, concentration of complexing agent and nature of the surface of the capillary; unbonded and C₁ and C₁₈ bonded phases were studied. In addition the effect of internal diameter on linearity and signal-to-noise ratio was examined, and separation efficiency was determined for a variety of experimental conditions. Detection limits (signal-to-noise RATIO = 3) were ca. 1 μg/ml for the lanthanides, ca. 0.6 μg/ml for transition and alkaline earth ions and ca. 0.1–0.8 μg/ml for alkali metal ions. The average relative standard deviations of were 3.7, 5.1 and 2.5% on unbonded, C₁ and C₁₈ capillaries, respectively. Whereas conventional regression analysis suggested that the calibration curves were linear over the range of 1·10⁻⁵ to 4·10⁻⁴ mol/l, sensitivity plots showed that the results were actually linear to within 6% only over the range of 2.5·10⁻⁵ to 4·10⁻⁴ mol/l.