Determination of magnesium and calcium by ion chromatography with post-column reaction fluorescence detection

A method is presented for the determination of magnesium and calcium at trace levels. The metals are separated from each other and other eluting species by using an aqueous lactic acid eluent in conjunction with a low-capacity strong cation-exchange stationary phase. Once separated, the magnesium and calcium ions react with quinolin-8-ol-5-sulphonic acid to produce fluorescent species [γ(ex)=390 nm, γ(em)=510 nm]. The calibration graph is linear for at least three orders of magnitude for both magnesium and calcium with detection limits of 0.6 and 40 μg l-1, respectively. No interference was observed from other trace metals present and magnesium and calcium were successfully determined in a certified reference material (USEPA Trace Metals III).