Low-molecular weight alcohols as colour stabilizers in the spectrophotometric determination of extracted molybdenum-thiocyanate species

Molybdenum(VI) was reduced to its pentavalent state by ascorbic acid in the hydrochloric acid medium. The diminishing orange-red colour of the unstable molybdenum(IV)-thiocyanate complex was stabilized by addition of low alcohols and by extraction either into chloroform or into butanol. Spectrophotometric measurements followed the extraction procedure. All the investigated systems obeyed Beer's law (lambda(max) = 465 nm), molar absorptivities covering the range from 1.40 x 10(4) to 3.1 x 10(4) l mol(-1) cm(-1), depending on the system type. Based on the equilibrium shift method, a reaction mechanism is proposed with MoO(NCS)(3) as the extracted spicies solvated by each of the alcohols added.