Study on the color reaction of tungsten (VI) with 2,3,7-Trihydroxy-9- [3,5-dibromo-4-(2,4-dihydroxy) phenylazo ]phenylfluorone

In the presence of mixed nonionic surfactant (Triton X-100 and Emulsifying ageneop), the photometric analysis properties of color reaction of 2,3,7-trihydroxy-9-[3,5-dibromo-4-(2,4-dihydroxy)Phenylazo]phenylfluorone (DBARPF)with tungsten(Ⅵ) were studied, and a new method was established to determine microquantity tungsten by spectrophotometry. In 0.32 mol/L hydrochloric acid medium, Tungsten (Ⅵ)reacted with DBARPF to form a complex with maximum absorption at 538 nm and an apparent molar absorptivity of 2.92×10~5 L·mol~(-1)·cm~(-1), Tungsten (Ⅵ)reacted with DBARPF to form a 1∶4 stable complex. It indicated the effect of chromogenic enhancement for color reaction was greatly produced by mixed micelle. Beer's law was obeyed in the range of 0-320 μg Tungsten (Ⅵ) per L. Most metal ions do not interfere with determination of tungsten (Ⅵ),and especially the interference of molybdenum (Ⅵ), which is similar to tungsten (Ⅵ) in chemical property. The method has been applied satisfactorily to the determination of tungsten in alloys steel samples.