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Extraction-Spectrophotometric Determination of Vanadium in Catalysts with Azoderivatives of Resorcinol and Tetrazolium Salts
Abstract
Two sensitive extraction-spectmphotometric methods for determination of vanadium in catalysts of conversion of sulfur dioxide to sulfur trioxide have been developed. They are based on the ternary ion-association complexes of vanadium(V) with azoderivatives of resorcinol(4-(2-pyridy1azo)-resorcinol (PAR), 4-(2-thiazoly1azo)-resorcinol (TAR)} on the one hand and tetrazolium salts {tetrazol violet (TV), triphenyltetrazolium chloride (TTC)} on the other hand, respectively. The limit of direct application of the methods has been outlined - iron to vanadium mtio in the sample 0.4 to 1. The proposed methods were
applied to analyse used Monsanio LP - 110 and LP-120 catalysts and good results were obtained in terms of precision and accuracy.
... It is known that iron and all the mentioned metals form intensively coloured ternary and multicomponent complexes with 4-(2-pyridylazo)-resorcinol (PAR) and bulky organic compounds, such as quaternary ammonium, arsonium and phosphonium salts, tetrazolium salts, diphenylguanidine, xylometazoline hydrochloride, nitron, etc. Some of these complexes are of analytical importance and can be used for sensitive and low-coast extraction-spectrophotometric metal (M) determination and speciation; M = Zn(II) [1] Co(II) [2], Cu(II) [3], Nb(V) [4], V(IV,IV) [5,6], Cr(III) [7], etc. However, one of the typical problems arising during their application is the interference caused by Fe(II,III) in the sample [6][7][8][9]. ...
... Some of these complexes are of analytical importance and can be used for sensitive and low-coast extraction-spectrophotometric metal (M) determination and speciation; M = Zn(II) [1] Co(II) [2], Cu(II) [3], Nb(V) [4], V(IV,IV) [5,6], Cr(III) [7], etc. However, one of the typical problems arising during their application is the interference caused by Fe(II,III) in the sample [6][7][8][9]. There are several approaches to eliminate iron interference: a) separation; b) masking; and c) choice of suitable extractionspectrophotometric conditions. ...
Complex formation and liquid-liquid extraction were studied in a system containing iron(III), 4-(2-pyridylazo)resorcinol (PAR), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), water, and chloroform. The optimum conditions for iron(III) extraction from water to chloroform as an ion-association complex, (TT+)[Fe3+(PAR)2]−, were found: pH, concentration of the reagents and shaking time. The following key equilibrium constants were calculated: constant of association, constant of distribution and constant of extraction. Some analytical characteristics were estimated and the settings at which the extraction system doesn’t produce spectrophotometric signal were specified.
A system containing zirconium (IV), 4-(2-pyridylazo) resorcinol (PAR), 2,3,5-triphenyl-2H-tetrazolium chloride (TTC), acetate buffer, water and organic solvents was studied. The optimum conditions for zirconium (IV) flotation and spectrophotometric determination as an ion-association complex were found: flotation solvent (chloroform), shaking time (2 min), pH (6.0-6.1, acetate buffer), concentration of the reagents CPAR=2.8×10-4 mol L-1 and CTTC=2×10-4 mol L-1), sequence of their addition, dissolution solvent for the floated compound (dimethylsulphoxide) and its volume (4 mL). The molar ratio between Zr(IV), PAR and TTC in the floated compound was found to be 1:2:3. It could be regarded as an ion-associate between the triphenyltetrazolium cation (TT+) and an anionic chelate [Zr(OH)3–j(CH3COO)j(PAR)2]3– (most probably j=2 at the optimum conditions). The constant of association was calculated by two independent methods (Log b=12.8±0.2 and Log b=12.9±0.7). Some additional characteristics like conditional molar absorptivity, Sandell’s sensitivity, Beer’s law range, limit of detection, limit of quantification and relative standard deviation of the system for flotation-spectrophotometric determination of Zr(IV) were estimated. Beer’s law was obeyed for Zr(IV) concentrations up to 1.3 μg mL-1 at lmax=545 nm with a correlation coefficient of 0.9978. The conditional molar absorptivity was estimated to be e545=1.2×105 L mol-1 cm-1.
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.
Determination of vanadium at very low levels in impregnated alumina-based catalysts by neutron activation analysis is reported. A pre-irradiation separation of vanadium, based on methyl isobutyl ketone extraction, yields high decontamination factors for Mo and Al. The technique is simple, precise and quantitative; recoveries of 50 ng of vanadium are obtained with a precision better than 10%. Results obtained for standard reference materials were, on average, within 3% of the reported values. The procedure can be applied satisfactorily to catalysts, metals, alloys, and geological samples. Detection limits of 5 ng can be easily achieved.
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