Quick determination of molybdenum in ferro-molybdenum by spectrophotometry with thiocyanate

A spectrophotometric method for determination of large amounts of molybdenum in ferro-molybdenum with ammonium thiocyanate has been studied in the present of iron perchlorate as a depressant and ascorbic acid as a reductant.Sample is dissolved in nitric acid and perchloric acid.After adding sulfuric acid and heating until the fumes of sulfuric acid to appear,the salt is dissolved in water.Mo(Ⅵ) in the solution is reduced to Mo(Ⅴ) by ascovbic acid in the present of iron perchlorate.Mo(Ⅴ) with ammonium thiocyanate forms a orange complex,of which absorbance can be measured at the wavelength of 460 nm.Molybdenum in three ferro-molybdenum standard samples is determined by the proposed method.The results compare favourably with the certified values,giving the RSD of 0.29%-0.35%(n=6).The analysis of samples can be completed within 50 min.