Microchip separations of transition metal ions via LED absorbance detection of their PAR complexes

Micellar electrokinetic chromatography was utilized in the electrophoretic separation of seven transition metal ions, colorimetrically complexed by 4-(2-pyridylazo)resorcinol (PAR) on a glass capillary electrophoresis microchip. Detection of the PAR metal chelates was demonstrated using a green light emitting diode (540 nm) and a miniature photomultiplier tube. Parameters investigated included the effect of buffer type, pH and surfactant concentration (sodium dodecyl sulfate, SDS) on the separation efficiency. The optimally determined background electrolyte contained 10 mM ammonium phosphate buffer (pH 7.5), 1 mM PAR to prevent kinetic lability problems and 75 mM SDS for enhanced resolution. The separation of seven transition metal ions, Co2+, V3+, Ni2+, Cu2+, Fe2+, Mn2+ and Cd2+, was achievable in under 65 s, with the resolution of each metal ion in excess of 1.60. Detection limits obtained ranged from 400 ppb for Ni2+ to 1.2 ppm for Mn2+.