Abstract
The complex formation in the vanadium(V)/4-(2-thiazolylazo)orcinol (TAO)/2,3,5-triphenyl-2H-tetrazolium chloride (TTC) liquid-liquid extraction-chromogenic system was studied. The chloroform-extracted complex has a composition of 2:2:2 under the optimum conditions (pH 4.8-5.2, extraction time 3 min, concentration of TAO 3.4 × 10(-4) mol dm(-3), and concentration of TTC 9.4 × 10(-4) mol dm(-3)) and could be regarded as a dimer (D) of two 1:1:1 species (S) presented by the formula (TT+)[VO2(TAO)]. The constant of extraction was calculated by two methods and some analytical characteristics were determined. The wavelength of maximum absorption (λmax), molar absorptivity (ελ) and fraction extracted (E) were found to be λ = 545 nm, ε545 = 1.97 × 10(4) dm(3) mol(-1) cm(-1), and E = 97.9%. The ground-state equilibrium geometries of the complexes S and D were optimized by quantum chemical Hartree-Fock calculations using 3-21G* basis functions. The bonding and interaction energies were calculated as well.
Highlights
Vanadium is a trace element with many industrial applications.[1]
Complexes with various reagents have been proposed for determination of vanadium.[5,6,7]
Among the complexes applied for vanadium LLEspectrophotometric determination and speciation of particular interest are these with participation of azocompounds (AC) and tetrazolium cations (TZ+).[5,6,9,10]
Summary
Vanadium is a trace element with many industrial applications.[1]. The recent interest in this element is related to the observed beneficial role of its compounds for different aspects of human health.[2,3,4] Complexes with various reagents have been proposed for determination of vanadium.[5,6,7] the concentration of its species in environmental and biological samples is often lower than the corresponding limits of determination. A classical approach to solve this problem and improve the method’s characteristics is to combine the instrumental method (e.g. spectrophotometry) with liquid-liquid extraction (LLE) – a simple technique for separation and preconcentration which does not require expensive equipment.[8]. Among the complexes applied for vanadium LLEspectrophotometric determination and speciation of particular interest are these with participation of azocompounds (AC) and tetrazolium cations (TZ+).[5,6,9,10] The following ACs were investigated as components of ternary V(V)-AC-TZ complexes: 4-(2-pyridylazo)resorcinol10–12, 4-(2-thiazolylazo)resorcinol,[13,14] and 4-(2-thiazolylazo)orcinol (TAO).[15] The obtained results show that the V(V):AC molar ratio in these complexes differs,[11,12,13,14,15] as a rule, from the typical 1:1 ratio established in the presence of other ion-association reagents (Table S1). The reason for this peculiarity is unclear and quantum-chemical calculations on V-AC-TZ ternary complexes have never been conducted
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