Redox-Reaction Products Of 4-Sulfo-2-(4'-Sulfonaphthalene-1'-Azo) Naphthol-1 With Ce(IV) - New Analytical Forms For Its Quantitative Determination

Abstract

The results of redox interaction of Ce (IV) with 4-sulfo-2-(4’-sulfonaphthalene-1’-azo) naphthol-1 (carmosine- KAN) in aqueous solutions (pH 1.75) have been presented. The destructive oxidation of CAS into two fragments (2-nitroso-4-sulfonaphthol-1 (L1) and 1-nitroso-4-sulfonaphthalene (L2)) is accampanied by reduction of Ce(IV) to Ce(III). It was found that an increase in the Ce(III) -L1 -L2 system acidity to pH ~ 11 leads to formation of the [Ce(III)(ОН)2·L1·2Н2О] complex. After acetonitrile is introduced to [Ce(III)(ОН)2·L1 ·2Н2О] – L2 system (up to 40 % by volume) self-organization of products involving CH3CN is observed. The resulting water-acetonitrile system becomes turbid, and after ~10 min phase separation is observed. Phase I contains a solvate {L2·(CH3CN)п } of «straw» color (360 nm) and phase II (lower layer) contains solvated complex {[Ce (III) (ОН) 2 ·L 1 ·(CH 3 CN) 2 ]·(CH 3 CN)n} of «blue» color (640 nm). The use of these solvates allows determination of Ce(IV) in the range 2.2 ч 50.1 μg/cm3 (y = 0.5526с + 0.0575, R2 = 0.9917, ε360 = 6.2·103) and 4.2 ч 84.0 μg/cm3 (y = 0.1862c + 0.0265, R2 = 0.9952, ε640 = 2.05·103), respectively. The revealed dependence was used for indirect (volumetric) determination of Ce(IV) (y = -0.7857c + 20.4440, R2=0.9988). The methods was tested on standard samples of mineral origin and herbal pharmaceutical preparations.