Abstract
Color reaction between tungsten and tiron was studied for a quantitative determination of tungsten. Tungsten reacts with tiron to give a stable complex, which has an absorption maximum at 313 mμ. Beer's law is obeyed over the concentration up to 0.02 mg W per ml. Molar extinction coefficient at 313 mμ is 7.6 × 103. The complex develops within 30 minutes at pH 5 and is stable for a day, showing 1 : 1 molar ratio of tungsten to tiron. Many ions interfere except for Mg2+, Mn2+, Co2+, As3+, Cl- and SCN- ions, but they can effectively be separated from tungsten by an anion-exchange in sulfate media.
Most of them can be removed from the ion-exchange column by elution with 0.07 M (NH4)2SO4-0.025 M H2SO4 solution, while Mo6+, Th4+, Zr4+ and U6+ retains strongly on the column.
Tungsten is then recovered by passing 0.5 M NaC1-0.5 M NaOH solution down the column and subjected to the direct determination with tiron.
