Spectrophotometric determination of molybdenum (V) by extraction of its 2-(2'-furyl)-3-hydroxychromone complex

A simple method is described for the rapid spectrophotometric determination of molybdenum in synthetic and industrial samples containing 0.1 - 5% Mo. Molybdenum is reduced with ascorbic acid at room temperature in 1 mol·dm-3 H2SO4 and extracted with chloroform after adding 2-(2'-furyl)-3-hydroxychromone (FHC). The yellow colour of the 1:2 Mo-FHC complex is measured at 414 nm against a reagent blank. Beer's law is obeyed over the range 0-2.7 μg Mo cm-3 of solvent phase. The molar absorptivity and Sandell's sensitivity are 5.18 x 104 dm3 mol-1·cm-1 and 0.0018 μg Mo cm-2 respectively. Relative standard deviations are 0.2% for solutions and 0.5 - 1.5% for solid samples. Interference from tungsten and tin is removed by adding citrate and EDTA, respectively, while niobium and tantalum are masked by fluoride. Many elements such as V, Fe, Ti, U, Mn, Cr, Co, Ni, Re, Ru, Pt, Rh, Se, Au, Bi, Zr, Th, Ce, As and Al do not interfere even in large amounts, but antimony always interferes. Among the anions and complexing agents, only thiocyanate interferes seriously. (author)