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Extraction-Spectrophotometric Study on the Vanadium(V) – 2,3-Dihydroxynaphtalene – Tetrazolium Violet – Water – Chloroform System
Abstract
The system vanadium(V) - 2,3-dihydmxynaphtalene (DHN) - tetrazolium violet (TV) - water - chloroform was studied. The composition of the ternary ion-associate complex was established and the optimum conditions for extractive-spectrophotometric determination of vanadium were found.Beer's law was obeyed up to 1.7 mug cm-3 vanadium(V) with a molar absorptivity coefficient of 1.5x104 l mol-1 cm-1. The limit of detection and limit of quantification were calculated to be 0.17 mug/ml and 0.57 mug/ml, respectively. The effect of foreign ions was examined.
A liquid-liquid extraction-chromogenic system for vanadium(IV, V) containing 2,3-dihydroxynaphtahlene (DN), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), water and chloroform was studied in detail. When the vanadium is in the oxidation state of IV, the extracted species are aggregates containing three 1:2:1 (V:DN:TTC) ion-pair units composed of triphenyltetrazolium cations (TT⁺) and chelate anions {[VIVO(DN)(DNH)]⁻ (I) and/or [VIV(OH)(DN)2]⁻ (II)}. When the initial oxidation state of vanadium is V and the DN concentration is high, vanadium(V) is reduced by DN to a lower oxidation state, V(IV). However, at low DN concentration, vanadium(V) can enter the organic phase as a part of an ion-pair consisting of TT⁺ and [VVO2(DN)]⁻ (III). The ground-state equilibrium geometries of the anions I, II, and III were optimized by quantum chemical calculations using BLYP/6-31++G⋆. The following characteristics were determined under the optimum conditions for VIV extraction: absorption maximum λmax = 333 nm, molar absorptivity ε333= 2.1x10⁴ dm³ mol⁻¹ cm⁻¹, Sandell’s sensitivity SS = 2.4 ng cm⁻², and fraction extracted E = 98%. The conditional extraction constant was calculated by two independent methods. The calibration graph was linear in the range 0.1-3.1 μg cm⁻³ (R²=0.9994) and the limit of detection was 0.03 μg cm⁻³.
The formation of a new ternary ion-associate complex of vanadium(V) with 2,3-dihydroxynaphthalene and iodonitrotetrazolium
chloride with a composition ratio of 1:2:1 is reported. The complex is quantitatively extracted from water into chloroform.
The molar absorptivity (ɛ) of the extract at λ
max=340 nm is 2.5 × 104 dm3/mol cm, and Beer’s law is obeyed for concentrations ranging from 0.1 to 0.9 µg/cm3 V(V). The following constants are determined: the extraction constant, the association constant, the distribution constant,
and the recovery factor. The effects of foreign ions and reagents are studied. A selective and sensitive method is developed
for determination of vanadium in steels.
The formation and extraction of ion-associate complexes between the vanadium(V)-4-(2-thiazolylazo)resorcinol (TAR) anionic
chelate and the cations of some mono-and ditetrazolium salts {3-(4,5-dimethyl-2-thiazol)-2,5-diphenyl-2H-tetrazolium bromide
(Thiazolyl blue, MTT), 3-(2-naphtyl)-2,5-diphenyl-2H-tetrazolium chloride (Tetrazolium violet), 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium
chloride (Iodonitrotetrazolium chloride), 3,3′-[3,3′-dimetoxy(1,1′-biphenyl)-4,4′-diyl]-bis[2,5-diphenyl-2H-tetrazolium] chloride
(Tetrazolium blue chloride) and 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride]
(Nitro blue tetrazolium chloride)} have been studied. The optimum extraction conditions have been found. The composition of
the V-TAR-monotetrazolium and V-TAR-ditetrazolium complexes extracted into chloroform has been determined to be 1:2:3 and
2:4:3 respectively. The extraction, distribution and association constants, and the recovery factors have been calculated.
The relationship between the molecular weight of tetrazolium cations, and the association constants of their complexes has
been discussed. The special behavior of the tetrazolium cations, containing-NO2 groups has been noticed. The effects of foreign ions and reagents on the extraction of vanadium with TAR and the best tetrazolium
salt-MTT have been studied. A sensitive, selective, simple and fast method for the determination of vanadium has been developed.
The system vanadium(V)–pyrogallol (Pg)–iodonitrotetrazolium chloride (INT)–H2O–n-butanol has been studied. The composition of the extracted complexes has been established by applying various methods. The formulas of the complexes formed as well as chemical equations of the running reactions are suggested. An attempt is made to explain the processes. Under the optimum extraction conditions, the dominating vanadium species is established to be vanadium(V) : Pg : INT = 1 : 2 : 3. With low INT concentrations, vanadium(IV) complexes are extracted. The effect of 29 diverse ions on the extraction of vanadium(V) is studied.
Owing to the toxic and essential nature of vanadium in biological systems, there has been considerable interest in the determination of its content in different kinds of samples. Among several analytical techniques for the determination of vanadium, spectrophotometric methods are very popular due to their simplicity and low-cost instrumentation. Various attempts have been made to modify these methods in order to improve their sensitivity and selectivity. This review shows recent developments in the spectrophotometric determination of vanadium and highlights those which can be used for speciation analysis of this element.
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Ternary complexes of vanadium(V) with 4-nitrocatechol and neotetrazolium chloride. Extraction-spectmphotometric study
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Khlm., 1980, 18,23-35
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