Development of extraction-spectrophotometric method of molybdate ions determination of in the antipyrine – sulfosalicylic acid – water system

The stratified system antipyrine - sulfosalicylic acid - water eliminates the use of toxic organic solvents, allows for the group extraction of macro- and micro-quantities of elements into a small volume (~ 2 ml) water-organic phase, in this phase many photometric reagents are easily dissolved. The extraction-spectrophotometric method for the determination of molybdate-ions with phenylfluorone has been developed. The optimal conditions for the formation of a colored compound with an organic reagent have been determined: light absorption maximums; optimal time for color development; photometric reagent amount, linearity range of the calibration graph. In optimal conditions for the complexation of phenylfluorone with MoO42- (λ = 526 nm, τ = 20 min, CR = 5·10-5 mol/l), a calibration graph is constructed. The Bouguer-Lambert-Beer’s law is fulfilled in the range from 10 to 60 μg Mo(VI)/20 ml. The molar coefficient of light absorption is calculated, which is 9.2∙104. The effect of interfering ions on the direct extraction-spectrophotometric determination of molybdate ions is studied. It is found that the determination of 50.0 μg of molybdenum(VI) does not interfere with: 5000 - fold molar excess of Ni(II), Co(II), Cr(III), Mn(II), Cd(II), Zn(II), Pb(II); 500 - fold molar excess of Re(VII); 1 - fold molar excess of In(III), W(VI).