Determination of fluoride ion in sea water by capillary type isotachophoresis after coprecipitation enrichment.

Abstract

New determination procedure of fluoride ion in sea water was developed with a capillary type isotachophoresis after coprecipitation enrichment by magnesium hydroxide. Using a capillary tube with 200mm in length and 0.5mm in inner diameter connected a PTFE tube with 80mm in length and 1.0mm in inner diameter, optimum electrolyte system was studied for the determination of fluoride ion. Fluoride ion could be determined successfully using the leading electrolyte containing 0.01 M histidine hydrochoride, 0.1 % Triton X-100 and the terminating electrolyte containing 0.01 M hexanoic acid. Effects of amount of sodium hydroxide solution for coprecipitating fluoride ion and of concentration of sodium hydroxide solution for washing precipitate on the recovery of fluoride ion were examined. As a result, a solution of 1.5ml of 1 M sodium hydroxide and 10-3 M sodium hydroxide solution were respectively found to be optimum for 50 ml of sample. One and a half milliliters of 1 M sodium hydroxide solution was added to 50ml of artificial sea water sample containing fluoride ion to enrich the ion with magnesium hydroxide. To prevent the interferences caused by anions of high concentration, centrifuged precipitate was washed with 10-3 M sodium hydroxide solution and dissolved by adding 1.3g of Dowex 50 W X8 ion exchange resin. The total volume was made to 5.0 ml with distilled water after filtration. A 50μl aliquot of the above solution was injected into the isotachophoresis apparatus. The linear working curve was obtained. The proposed method was applied to the determination of fluoride ion in the coastal sea water samples in Osaka Bay collected in April, 1984. The result obtained by the working curve method agreed closely with that obtained by the standard addition method.