Synergetic catalytic effect of molybdate and tungstate on the hydrogen peroxide-iodide system and its analytical applications

The synergetic catalytic effect of molybdate and tungstate on the hydrogen peroxide-iodide system has been studied by using the I−3-starch complex as the indicator with a stopped flow injection technique. The degree of the synergetic effect was expressed by the proposed concept of a synergetic catalytic coefficient, D. The deviations from additivity of absorbance outside certain concentration ranges in the previous procedures could be compensated for by introducing the synergetic coefficient in the simultaneous measurement of a binary mixture with the stopped flow injection method. The linear concentration ranges could thus be extended by compensation, to 0–1.1 μg/ml for Mo and 0–2.0 μg/ml for W, in comparison to 0-0.6 μg/ml for Mo and 0-0.8 μg/ml for W as obtained with the procedure in which no compensation was applied, and the sensitivities also have been improved. The molybdenum and tungsten content in steel and simulated samples was determined, and the recoveries and relative standard deviations were 97.3–102.8% and 2.1–2.9%, respectively, for molybdenum, and 96.5–102.1% and 2.3-3.4% for tungsten.