A COMBINED ION-EXCHANGE SPECTROPHOTOMETRIC METHOD FOR DETERMINATION OF MOLYBDENUM AND TUNGSTEN IN SEA WATER

A combined ion-exchange spectrophotometric method has been developed for the determination of molybdenum and tungsten in sea water. The two elements are adsorbed quantitatively on Dowex 1-X8 (SCN-form) from sea water adjusted to 0.1 M in hydrochloric acid and 0.1 M in ammonium thiocyanate. Molybdenum also can be concentrated quantitatively on Dowex I-X8 (Cl-form) from sea water acidified to 0.1 M. in hydrochloric acid and containing > 6% hydrogen peroxide. In both concentration procedures, molybdenum and tungsten are easily eluted with 0.5 M sodium hydroxide-0.5 M sodium chloride solution. The adsorption and desorption steps provide selective concentration for molybdenum and tungsten, so that molybdenum can be determined spectrophotometrically with dithiol. Tungsten is separated from molybdenum by anion-exchange on DEAE (Cl-form), and can be determined similarly with dithiol. A sea-water sample collected from the Pacific Ocean, off the coast of Kominato, Chiba, gave values of 9.5 ±0.1 μg mo l and 9.3 ±0.2 μg Mo l for the thiocyanate concentration and hydrogen peroxide concentration methods, respectively, with 1-l samples. Duplicate analyses of sea water from the same location as for molybdenum, gave values of 0.115 and 0.116 μg l for tungsten, on a 20-l sample basis. © 1969.