1987 Volume 36 Issue 11 Pages 712-716
A new analytical procedure for bromide ion in seawater using capillary type isotachophoresis and a membrane separation unit for pretreatment, was developed. The unit is a double-tube structure, consisting of an inner microporous polytetrafluoroethylene (PTFE) membrane tube and an outer glass tube. Analytical procedure is as follows: A mixed solution of 10 ml of seawater sample, 0.3 ml of 9 M sulfuric acid and 0.7 ml of 0.02 M potassium permanganate is circulated through the outer glass tube for 20 min at a flow rate of 7 ml/min. The temperature of the membrane separation unit is adjusted to 40 °C. During the circulation, bromide ion in the sample solution is oxidized to bromine. The bromine permeates through the PTFE membrane and dissolves in 1.5 ml aliquots of a mixed solution of 10 ml of distilled water, 0.5 ml of 0.1 M acetic acid and 2.0 ml of 3% hydrogen peroxide placed in the inner PTFE tube as the reduced bromide ion. Then, 10 μl of the solution containing bromide ion is injected into an isotachophoresis apparatus equipped with a potential gradient detector and a 15-cm-long main column connected to a 20-cm-long precolumn. The leading electrolyte is a methanol solution containing 5 mM perchloric acid and 10 mM tris (hydroxymethyl) aminomethane. The terminating electrolyte is 10 mM sodium fluoride solution. The migration current is set at 200 μA for 18 min and then reduced to 50 μA. A linear working curve was obtained for artificial seawater samples containing up to 100 mg/l of bromide ion. The recovery of bromide ion was 42 ± 3%. The relative standard deviation of the method was 5.0% (n=7). The lower determination limit of bromide ion was 9.0 × 10-2 mg/l. The proposed method was applied to the determination of bromide ion in surface and bottom seawater samples collected around the coastal area of Osaka Bay. Sufficient recovery was obtained in the standard addition experiments.
