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

Abstract

A modified thiocyanate method without extraction by using rhodamine 6G as a secondary ligand was developed. Molybdenum in 1.0 x 10(-2) M HCl, after the addition of ascorbic acid, was heated for 10 min in a 90degreesC 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 570 nm was measured against a reagent blank 45 min after the addition of thiocyanate solution and the second aliquot of Triton X-100 solution. The complex was stable for at least 4 h, the order of reagent addition was important, and thiocyanate should be in large excess. Beer's law was obeyed over the range 0.9 x 10(-6) to 1.1 x 10(-5) M Mo with the molar absorptivity being 1.1 x 10(5) 1 mol(-1) cm(-1). The R.S.D. for the determination of 0.7 mg Mol(-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. (C) 2003 Elsevier Science B.V. All rights reserved.