Spectrophotometric determination of molybdenum in sea water with 5-chloro-7-iodo-8-quinolinol

Abstract

5-Chloro-7-iodo-8-quinolinol was used for the spectrophotometric determination of micro amount of molybdenum in sea water after the preconcentration with organic coprecipitant. Effect of pH on the coprecipitation of molybdenum in phenolphthalein was examined using 99Mo as a tracer. Recovery of molybdenum was about 93% between pH of 2 to 4. Because the concentration of molybdenum in sea water is too low, it is preferable to reduce the volume of water sample to about one fifth by evaporation. No loss of molybdenum was observed by evaporation with the presence of a small amount of nitric acid. On the basis of these results water sample was analyzed with following procedure: Add 4 ml of nitric acid to 1 l of filtered sea water and evaporate to about 200 ml. Add 1 ml of 1% oxineacetic acid solution to the solution. After the pH of the solution adjust to 4.0, add phenolphthalein-ethanol solution (0.3 g/5 ml) and allow to stand over night. Collect the precipitate and dissolve in 10 ml of hot nitric acid. Add 5 ml of 60% perchloric acid to the solution and decompose organic matter by heating. After the pH of the solution adjust to 1.0, dilute to 25 ml with water. Extract molybdenum with 10 ml of 2.5 × 10-3 M 5-chloro-7-iodo-8-quinolinol-CHCl3 solution. Measure the absorbance of CHCl3 solution at 392 nm against the reagent blank. The overall recovery of molybdenum from sea water was about 89%. The content of molybdenum in surface sea water in the Pacific near the Ogasawara Islands and Yoron Island were found to be 10.4 and 9.8μg/l, respectively.