Spectrophotometric determination of trace vanadium by means of flow injection analysis based on the catalytic oxidation of Bindschedler's Green leuco base by potassium bromate

A sensitive and simple method has been developed for the determination of trace vanadium by means of flow injection analysis based on the catalytic oxidation of Bindschedler's Green leuco base (4,4'-bis(dimethylamino)diphenylamine, BGL) by potassium bromate. A schematic diagram of the flow injection system is shown. The reagent solutions of BGL and potassium bromate in reservoirs A and B, respectively, were pumped out using a peristaltic pump into the manifold. A sample solution, 20 μl, was introduced into the carrier reagent solution via syringe loading sample injector. The introduced sample was then transported through the reaction coil (poly(tetrafluoroethylene), inner diameter 0.56 mm), and BGL was oxidized to Bindschedler's Green (BG) which showed a maximal absorbance at 725 nm. The absorbance of BG was monitored at 725 nm by spectrophotometer equipped with a flow-through cell (volume 200 μl, light path 5 mm), and was continuously recorded. Some factors that influence the flow injection system, pumping rate, reaction coil length, sample volume and sampling rate, were studied systematically. Under the conditions of BGL: 1.6 x 10-3 mol/l, potassium bromate: 6.4 x 10-2 mol/l, pH: 3.8 and temp.: 250C with pumping rate 1.6 ml/min and reaction coil length 5 m, a liner relationship was obtained between the peak height (absorbance) and the concentration of vanadium (IV) in the range of 0 -- 80 ppb. In this method, the detection time after sample injection was ca. 40 s, and a sampling rate of 60 samples/h was achieved. (author)