1985 Volume 34 Issue 1 Pages 21-25
Simultaneous determination of tripolyphosphate, pyrophosphate, and orthophosphate ions in sea water was developed with a capillary type isotachophoresis applying coprecipitation enrichment method. Using a capillary tube with 200 mm in length and 0.5 mm in inner diameter, optimum pH of leading electrolyte was studied for the separation of 3 phosphate ions. The best result was obtained by using the leading electrolyte containing 0.01 M hydrochloric acid, histidine, and 0.1 % Triton X-100 (pH 4.0) and the terminating electrolyte containing 0.01 M hexanoic acid. To enhance sensitivity in isotachophoresis, a PTFE tube with 225 mm in length and 1.0 mm in inner diameter was connected to the capillary tube in order to increase the sample injection volume to 150 μl. The effects of migration current on the zone length and the analysis time were examined with the modified system. After the optimization of procedure, the migration current was adjusted at 100μA for about 18 min and then it was reduced to 25 μA. Under these conditions, low concentrations of tripolyphosphate, pyrophosphate, and orthophosphate ions could be determined successfully. A solution of 0.2 ml of 10 M sodium hydroxide was added to 200 ml of artificial sea water sample and phosphate ions were enriched by coprecipitation with magnesium hydroxide. To prevent the interferences of high concentration anions in isotachophoresis, centrifuged precipitate was washed with 10-3 M sodium hydroxide solution and dissolved by adding 2.0 g of Dowex 50 W X8 ion exchange resin. The total volume was filled up to 5.0 ml with distilled water after filtration. A 1.0 ml aliquot of that solution was passed through a lanthanum type ion exchange resin column to remove fluoride ion. A 150 μl aliquot of the treated solution was injected into the isotachophoresis apparatus. The linear working curves were obtained for the phosphate solutions of 100, 200, and 500 ml in volume. The proposed method was applied to the determination of phosphate ions in the coastal sea water samples in Osaka Bay collected in April, 1984. In the sea water samples, orthophosphate ion could be detected, while tripolyphosphate and pyrophosphate ions could not.
