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 dete rmination 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 a s the stationary phase and water was used as the mobile phase. The mat rix ions, SO42-, Cl-, Na+, K+, Mg2+ and Ca2+ were initially eluted as ion pairs of Na+/K+-SO42-, Na+/K+-2Cl(-) and Mg2+/Ca2+-4Cl(-) before t he 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 separa tion of Br-. Bromide ions in sea water could be determined within 4.3 min by using this IC system (a zwitterionic column, 4.6 x 250 mm; a wa ter mobile phase, 1.0 ml/min; and 20 mu l of sample injection).