Direct determination of bromide ions in sea water by ion chromatography using water as the mobile phase

A rapid and simple ion chromatographic (IC) method for the direct determination of bromide (Br−) in sea water was developed. A small amount of sea water was injected into a specific IC system where zwitterionic surfactants immobilized on octadecylsilica (ODS) surfaces were used as the stationary phase and water was used as the mobile phase. The matrix ions, SO2−4, Cl−, Na+, K+, Mg2+ and Ca2+ were initially eluted as ion pairs of Na+K+-SO2−4, Na+K+-2Cl− and Mg2+Ca2+-4Cl− before the ion pair Mg2+Ca2+-4Br− which contained the target ion (Br−). The retention interval between Mg2+Ca2+-4Br− and Mg2+Ca2+-4Cl− (the last eluted matrix ion pair) was long enough for the base-line separation of Br−. Bromide ions in sea water could be determined within 4.3 min by using this IC system (a zwitterionic column, 4.6 × 250 mm; a water mobile phase, 1.0 ml/min; and 20 μl of sample injection).