Use of the molybdenum–thiocyanate–rhodamine 6G ternary complex for spectrophotometric molybdenum determination without extraction

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A modified thiocyanate method without extraction by using rhodamine 6G as a secondary ligand was developed. Molybdenum in 1.0×10−2M HCl, after the addition of ascorbic acid, was heated for 10min in a 90°C water bath for reduction. Suitable amounts of glycerine, Triton X-100, rhodamine 6G solutions and 2+1 (v/v) 9M H2SO4+3M KHSO4 were added in this order. This solution was allowed to cool to room temperature and the absorbance at 570nm was measured against a reagent blank 45min after the addition of thiocyanate solution and the second aliquot of Triton X-100 solution. The complex was stable for at least 4h, the order of reagent addition was important, and thiocyanate should be in large excess. Beer’s law was obeyed over the range 0.9×10−6 to 1.1×10−5M Mo with the molar absorptivity being 1.1×105lmol−1cm−1. The R.S.D. for the determination of 0.7mgMol−1 was 1.83% (n=8). Possible interferences of various cations and anions on molybdenum determination were studied. The proposed method was applied to the determination of molybdenum in a dental alloy, Wiron 99.