Fluorometric determination of selenium in sea-water

2, 3-Diaminonaphthalene reacts with selenium(IV) to form a complex with greenish yellow fluorescence, which are extracted into organic solvents, such as cyclohexane, toluene etc., and was used as a sensitive reagent for the fluorometric determination of selenium. The authors have studied on the fluorometry of selenium with the reagent, and the method was adopted for analysis of selenium in sea-water. Fifty milliliters of conc. HCl and 20 mg of Fe3+ as FeCl3 solution were added to 5 l of sample sea-water, and pH of the solution was adjusted to 5.5 with ammonia. After a few hours 5 mg of Fe3+ and ammonia were added to the solution. This procedure was repeated. After being allowed to stand overnight, the precipitate was filtered and washed with water, then dissolved in 56ml of 6 N HCl. Three milliliters of 1 M sodium acetate solution was added to the solution and pH was adjusted to 1 by adding conc. HCl, and the total volume was made up to 30 ml. To remove Fe3+, the solution was poured into an ion-exchange colume [Dowex 50 WX8 (H-form), φ: 30 mm, height: 50 mm], and the column was eluted with 0.1 M sodium acetate solution (pH of the solution was adjusted to 1 with hydrochloric acid, flow rate =1.3 ml/min). The selenium, fraction of the eluant was evaporated to 10 ml. Five milliliters of 0.1% 2, 3-diaminonaphthalene solution, 0.5 ml of 0.1 M EDTA solution, and 0.5 ml of 0.1 M sodium fluoride solution were added to this solution, and pH of the solution was adjusted to 1 with hydrochloric acid or ammonia. The solution was diluted to 25 ml and heated at 50°C for 20min. After being cooled to room temperature, the solution was extracted with 10 ml of cyclohexane. The organic layer was separated and dehydrated by centrifugation, and the fluorescence intensity was measured at 520 nm (excitation : 375 nm) against the standard uranine solution (0.0625 μg/ml). In this procedure, the recovery of selenium was about 90%. Selenium contents in the sea-waters offshore of Misaki (Osaka Pref.), Yuasa and Uragami (Wakayama Pref.) were found to be 0.010.07 μg/l. The amounts of dissolved selenium and the particle size distribution of selenium in suspended matter were determined successfully by the present procedure.