Determination of metal cations in microchip electrophoresis using on-chip complexation and sample stacking

A method for the determination of metal cations in aqueous solution using a monolithically integrated microfabricated (microchip) device which allows sample stacking, electrophoretic separation, and postcolumn derivatization is described. The metal cations are detected by UV laser-induced fluorescence following complexation with 8-hydroxyquinoline-5-sulfonic acid. To make use of electrokinetic stacking phenomena, the sample is added to a reservoir containing a low-conductivity buffer and is then introduced into a main separation channel using a gated injection scheme. The complexing agent is added downstream from the injection cross. For two model compounds, magnesium and calcium, detection limits were 0.5 and 18 ppb, respectively. The reproducibility for multiple injections was 1.5% relative standard deviation.