Abstract: A superhigh sensitive spectrophotometric method has been developed for determinationof trace molybdenum, based on the formation of a complicated ion-associated complex ofmolybdenum with ethyl rhodamine B (ERB) and thiocyanate in the presence of polyvinylalcohol (PVA₁₂₄).Cu²⁺ was used to catalyze the reduction of Mo(Ⅵ) to Mo(Ⅴ) carriedout by thiocyanate in Mo(Ⅴ)-SCN^--basic dye system.The ion-associate exhibits maximumabsorption at 580nm, its apparent molar absorptivity is 5.6×10⁶ L·mol^-1·cm^-1.Beer's law isobeyed for 0～0.3μg/25mL of Mo(Ⅵ).The reaction mechanism has been discussed.The method has been used for the determination of trace Mo in water and in leaching solutionof Maifan stone with satisfactory results.

Key words: superhigh sensitive colour reaction, molybdenum, ethyl rhodamine B, spectrophotometry