Dodecylsulfate-coated monolithic octadecyl-bonded silica stationary phase for high-speed separation of hydrogen, magnesium and calcium in rainwater

Abstract The high-speed determination of hydrogen, magnesium and calcium ions by ion chromatography (IC) is demonstrated on a monolithic octadecyl-boned silica (ODS) column coated with lithium dodecylsulfate (Li-DS). This stationary phase, when used in conjunction with a 2 mM ethylenediamine and 0.1 mM Li-DS solution as eluent at pH 6.0, was found to be suitable for the rapid and efficient separation of hydrogen and magnesium and calcium in the order H + 2+ 2+ within 4 min at a flow rate of 4.0 ml/min. Under the conditions, linear calibration plots of conductivity versus concentration were obtained for the cations over about three orders of magnitude, and the detection limits were 1 μM for H + , 2 μM for Mg 2+ and Ca 2+ . Rainwater was analyzed directly using this IC system with satisfactory results.