Analytical applications of mixed-ligand complexes: III. Vanadium(V)-xylenol orange reagent mixture for the spectrophotometric determination of traces of hydrogen peroxide

Vanadium(V) forms 2:1, 1:1, and 1:2 binary complexes with xylenol orange (XO). In slightly alkaline solution the formation of the complexes is almost instantaneous, whereas it takes a day for the equilibria to be reached at pH 4. On the action of hydrogen peroxide, both the 2:1 and the 1:1 complexes are transformed into mixed-ligand complexes, with 2:1:2 and 1:1:1 compositions, respectively. No intramolecular redox reaction takes place between XO and hydrogen peroxide. Peroxo complex formation can be used for estimation of hydrogen peroxide if the decrease in absorbance of the 576-nm band of the binary complexes is measured. The molar absorptivity decrease depends on the ratio $\text{[V(V)]}\text{[XO]}$ and the pH.     

Application of the vanadium(V)-xylenol orange reagent to the assay of serum glucose

The VXO reagent (mixture of V(V) and xylenol orange) provided in our earlier studies is found very useful for the colorimetric determination of traces of hydrogen peroxide. In this paper the reagent is successfully extended to the assay of glucose in serum by the combined use of glucose oxidase.The VXO reagent exhibited a characteristic absorption maximum at 582 nm, and the presence of glucose together with glucose oxidase led to a significant decrease in the absorbance of the reagent. A linear relation was found between the magnitude of the decrease and glucose concentration in the range of 5 to 400 mg/100 ml. The average recovery of glucose added in serum was 98.6% and the data were reliable with a coefficient of variation below 3.0%. A good correlation to the method by 4-aminoantipyrine-phenol was found: r = 0.970. Ascorbic acid and uric acid did not interfere with the assay.     

Spectrophotometric determination of traces of hydrogen peroxide with the Ti(IV)-xylenol orange and the Ti(IV)-chromazurol S reagents

The formation of mixed ligand complexes in Ti(IV)-xylenol orange (XO)-H₂O₂ and Ti(IV)-chromazurol S (CAS)-H₂O₂ systems was studied by spectrophotometry. The former system gave constant absorbance (λ_max = 562 nm) under the condition of [XO]/[Ti(IV)] = 1 in the pH 2–4 region. In the latter system, a distinct maximum at 557 nm was observed when [CAS]/[Ti(IV)] = 4 in the pH range of 4.5–5.2. In both cases, the absorbance at λ_max was stable for a long time and proportional to the concentration of hydrogen peroxide. From those facts, the usefulness of the mixtures of Ti(IV)-XO and Ti(IV)-CAS as the colorimetric reagents for the determination of hydrogen peroxide can be expected. The conditions for the use of the Ti(IV)-XO and the Ti(IV)-CAS reagents were examined in detail, and both reagents were found to be available for trace analysis of hydrogen peroxide with high sensitivity.     

Use of N-benzyl-2-naphthohydroxamic acid as a highly selective reagent for solvent extraction and spectrophotometric determination of vanadium(V)

N-Benzyl-2-naphthohydroxamic acid extracts vanadium(V) selectively and quantitatively into chloroform from 2-8.5M hydrochloric acid in the presence of Mo(VI), Zr(IV) and Ce(IV). The extraction takes place quickly and gives a stable reddish-violet extract which shows an absorption maximum at 505 nm with molar absorptivity of (5.34 +/- 0.05) x 10(3) 1.mole(-1).cm(-1). The optimum range for the determination is 2.2-7.4 ppm of vanadium(V) in the final solution. The method has been used for the determination of vanadium in steels.     

Tropoloae as a specific reagent for the determination of vanadium(V)

The blue colour developed on interaction of vanadium(V) with tropolone m 5.5-7.0N acid can be extracted into chloroform. The complex has an absorption maximum at 590 nm. Colour development is instantaneous and the extracted species is stable for 72 hr. Beer's law is followed in the range 1.02-14.25 ppm of vanadium. The molar absorptivity is 4.63 x 10(3)l.mole(-1).cm(-1). Most anions do not interfere. Of the 37 cations examined, only Ti(III), Ru(III), Pt(IV), Ir(IV), Mn(II), Ta(V) and Ce(III) were found to interfere. The interference due to these cations has been removed by masking them with EDTA.     

An improved technique for the spectrophotometric determination of nitrate with 2,4-xylenol

An improved method is proposed for the spectrophotometric determination of nitrate with 2,4-xylenol. The sample in aqueous (1.7 + 1 ) sulfuric acid is treated with 2,4-xylenol to produce 6-nitro-2,4-xylenol which is distilled into an ammoniacal water—isopropanol mixture. The intense yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. The distillation is done in a Parnas—Wagner Kjeldahl Semimicro distillation apparatus. The isopropanol keeps the excess of 2,4-xylenol in solution. Two procedures are described. In the first (applicable to samples containing alkali nitrates but no chloride, alkaline earth, or ammonium salts), the solution is evaporated to dryness, and (1.7 + 1) sulfuric acid and 2,4-xylenol in acetone are added. In the second (applicable to samples containing chloride, alkaline earth, or ammonium salts), concentrated sulfuric acid is added dropwise to a cooled aliquot and the 2,4-xylenol reagent is then added; if chloride is present, it must be removed by prior precipitation with silver sulfate. Nitrite shows a slight interference which depends on the amount of nitrate and nitrite present.     

Hydrazine sulphate as reagent for titrimetric determination of vanadium(V) and chromium(VI)

Conditions have been developed for the direct titration of vanadium(V) and chromium(VI) with hydrazine sulphate, barium diphenylaminesulphonate being used as indicator and osmium tetroxide as catalyst.     

Extraction and spectrophotometric determination of vanadium(V) with ferron

Various metal complexes of 7-iodo-8-hydroxyquinoline-5-sulphonic acid (ferron) were found to be selectively extracted into immiscible alcohols. Vanadium(V) is almost completely extracted into n-butanol in a single extraction from solutions which are 0.05 M in sulphuric acid. A sensitive and selective spectrophotometric method can be based on this extraction. Beer's law is obeyed up to 15.3 μg of vanadium per ml; the sensitivity of the color reaction is 0.011 μg of vanadium per cm² at 430 mμ. The interference of iron(III) can be eliminated by adding excess pyrophosphate. The extracted species appears to contain vanadium, ferron and n-butanol in the ratio 1:2:4.     

Extraction—spectrophotometric determination of traces of antimony as the ferroin—hexachloroantimonate(V) complex

The sparingly soluble scarlet precipitate formed by the interaction of ferroin and antimony(V) in strong hydrochloric acid medium is soluble in nitrobenzene. The composition of the complex is [Fe(phen)₃] [SbCl₆]₂. The percentage extraction into nitrobenzene, determined by tracer techniques, reaches a maximum (98%) at 8–9 M hydrochloric acid. The advantages of this procedure over those employing dyes as reagents are discussed. Antimony(V) can be determined in the range 2.5–24μg ml^-1. Interferences are described.     

An examination of chlorpromazine hydrochloride as indicator and spectrophotometric reagent for the determination of molybdenum(V)

Chlorpromazine hydrochloride (CPA) has been tested as indicator in the titration of molybdenurn(V) with cerium(IV)sulphate at room temperature in sulphuric acid medium. It gives a sharp, reversible colour change from colourless to dark-red at the equivalence point. Chlorpromazine hydrochloride also reacts in acidic media with thiocyanatomolybdenum(V) complexes forming an orange compound with the formula (CPA · H) [MoO(SCN)₄]. This reaction provides a sensitive method for spectrophotometric determination of molybdenum(V). Molybdenum(VI) is reduced with ascorbic acid in hydrochloric acid solution, and complexed with thiocyanate, and the complex formed is extracted with chlorpromazine hydrochloride in chloroform. The molar absorptivity is 1.6 × 10⁴ l mol^-1 cm^-1 at 465 nm. Beer's law is obeyed in the range 0.5–5.0 μg Mo ml^-1.     

Ethylisobutrazine hydrochloride as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V) and its application to vanadium-bearing minerals and alloys

Ethylisobutrazine hydrochloride is proposed as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V). It forms a red-colored species with vanadium(V) in 3.5–6.5 M phosphoric acid medium. An eight-fold molar excess of reagent is necessary for the full development of the color. The red species exhibits an absorption maximum at 518 nm with a molar absorptivity of 9.75 × 10³ liters mol⁻¹ cm⁻¹. Sandell's sensitivity is 5.2 ng cm⁻². Beer's law is obeyed over the range 0.1–6.2 ppm of vanadium(V) with an optimum concentration range of 0.4–6.0 ppm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration, and the interferences from various ions, are reported. The method has been used successfully for the determination of vanadium in ilmenite and vanadium steels that contain chromium, molybdenum, manganese, nickel, copper, tungsten, and titanium.     

Extraction equilibria and spectrophotometric determination of vanadium(V) with 4-nitrocatechol and the ion-pair reagent thiazolyl blue tetrazolium

The formation and liquid-liquid extraction of a yellow ternary complex of vanadium(V) with 4-nitrocatechol (NC) and the ion-pair reagent Thiazolyl Blue Tetrazolium ⨑ub;3-(4,5-dimethyl-2-thiazol)-2,5diphenyltetrazolium bromide, MTT⫂ub; with 1: 2: 3 stoichiometry (V: NC: MTT) was studied. The optimum extraction conditions (pH, concentration of the reagents, extraction time), spectrophotometric parameters of the extract and key constants (extraction constant, association constant, distribution constant) were determined. Beer’s law was obeyed for concentrations ranging from 0.12 to 1.2 μg/mL of vanadium(V) with a molar absorptivity of ɛ = 3.13 × 10⁴ L/mol cm at λ_max = 400 nm. The effect of diverse ions was studied and extraction-spectrophotometric procedures for determination of vanadium in catalysts and steels were proposed.     

2-(2-Thiazolylazo)-p-cresol as a spectrophotometric reagent for vanadium determination in the presence of ascorbic acid

The present work describes the use of 2-(2-thiazolylazo)-p-cresol (TAC) as a spectrophotometric reagent for vanadium determination. TAC reacts with vanadium(IV) in the presence of ascorbic acid, forming a red complex with absorption maximum at 525 nm. The following parameters were studied: complex stability, pH effect, amount of TAC, amount of acetate buffer, HEDTA effect, order of addition of reagents and Beer's law validity. TAC can be used for vanadium determination in the pH range 4.6–6.0, with molar absorptivity of 2.11 × 10⁴Lmole^–1 cm^–1 (at525nm). Beer's law is obeyed up to 2.0 g mL^–1. Many cation interferences can be easily eliminated by using HEDTA as a masking agent. Steel reference standards were used to test the proposed procedure and the accuracy and precision obtained were satisfactory.     

Extraction and spectrophotometric determination of vanadium(V) with 8-hydroxyquinoline

The extraction and spectrophotometric determination of vanadium (V) with oxine is investigated at higher acidities than described previously. Under these conditions, n-butanol and other alcohols are found to exert a synergic effect on the extraction of vanadium into benzene. In the presence of alcohol only a 6-fold ligand excess is needed for quantitative extraction in a single operation, the acidity of the aqueous medium being 0.05M with respect to sulphuric or phosphoric acid. The interference of iron(III) in the spectrophotometric determination of vanadium is suppressed by the addition of pyrophosphate. Beer's law is obeyed up to 14.0 mug of vanadium/ml and the sensitivity is 0.008 mug of vanadium/cm(2) at 390 mmu. The composition of the extracted species is found to be vanadium:oxine:n-butanol = 1:2:2.     

Simultaneous kinetic spectrophotometric determination of vanadium(V) and iron(III)

Vanadium(V) and iron(III) can be determined simultaneously at pH 2 and 25 degrees C by a single experiment using their kinetic effect on the oxidation of indigo carmine by bromate which goes through an induction period and then decreases in absorbance, at lambda(max), 612 nm. The rate of the color-fading of indigo carmine is proportional to the concentration of vanadium and is independent of the concentration of iron. The length of the induction period of the reaction is related to the concentration of iron and is independent of the concentration of vanadium. Concentrations of 0.3-2 (mug ml(-1)) vanadium(V) and 6-12 (mug ml(-1)) iron(III) were determined with mean relative errors of 2.7 and 1.6%, respectively. The interference effects of various cations and anions on determination of mixtures of vanadium and iron is reported. Application of the method to real samples and several mixtures of standard solutions are performed which gave acceptable results.     

Resorcinol as an analytical reagent for the spectrophotometric determination of uranium

A spectrophotometric study of the reaction of uranyl acetate and resorcinol shows that an orange-red coloured resorcinolate of composition 1:2 is formed. This colour reaction can be conveniently used for the spectrophotometric estimation of uranium at PH 4.72.     

Stopped-flow spectrophotometric determination of hydrogen peroxide with hemoglobin as catalyst

A rapid and sensitive method was proposed for the determination of hydrogen peroxide based on the catalytic effect of hemoglobin using o-phenylenediamine as the substrate. Stopped-flow spectrophotometric method was used to study the kinetic behavior of the oxidation reaction. The catalytic effectiveness of hemoglobin was compared with other four kinds of catalysts. The initial rate of the formation of the reaction product 2,3-diaminophenazine at the wavelength of 425 nm was monitored, permitting a detection limit of 9.2x10(-9) mol/l H(2)O(2). A linear calibration graph was obtained over the H(2)O(2) concentration range 5.0x10(-8)-3.5x10(-6) mol/l, and the relative standard deviation at a H(2)O(2) concentration of 5.0x10(-7) mol/l was 2.08%. Satisfied results were obtained in the determination of H(2)O(2) in real samples by this method.     

Propericiazine as a reagent for the spectrophotometric determination of ruthenium(III)

Propericiazine forms an orange-red species with ruthenium(III) immediately in 6–8 M phosphoric or hydrochloric acid or 4.5–5.5 M sulphuric acid. The absorption maximum is at 511 nm and the molar absorptivity is 1.1 × 10⁴ 1 mol^?1 cm^?1. Beer's Law is obeyed over the range 0.2–9.4 mg 1^?1 (optimum range 0.5–9.0 mg 1^?1). Interferences are described. The method is used to determine ruthenium in synthetic zinc–magnesium alloy and uranium alloy (fuel) solutions.     

p-Sulphobenzeneazo-4-(2,3-dihydroxy-5-chloropyridine) as a reagent for spectrophotometric determination of niobium(V)

Niobium reacts with p-sulphobenzeneazo-4-(2,3-dihydroxy-5-chloropyridine) to form an orange-red ML(2) complex having maximum absorbance at 485 nm in citric acid medium at pH 6.0 +/- 0.5. The reaction is slow at room temperature, but complete in 10 min at 60 degrees . The colour is stable for at least 16 hr. The system obeys Beer's law over the concentration range 0.5-8 mu/ml. The molar absorptivity is 5.26 x 10(3)l.mole(-1).cm(-1).     

Flow injection spectrophotometric determination of anionic surfactants using methyl orange as chromogenic reagent

A flow injection(FI) spectrophotometric method for the determination of anionic surfactants was developed on the basis of the competition for the cationic surfactant cetyl pyridine (CP+) chloride between the acidic dye methyl orange (MO) and anionic surfactants. In a pH 5.0 medium the cation of cetyl pyridine (CP+) reacts with dissociated methyl orange (MO-) to form an ion-associate complex, causing a blue shift of lambda(max) from 465 nm for MO- to 358 nm for the CP+ x MO- associate. The MO- in the ion-associate complex can be quantitatively substituted by such anionic surfactants as sodium dodecyl benzene sulfonate (DBS) or sodium lauryl sulfate (LS), leading to an increase in the absorbance measured at 465 nm. This increased absorbance value is proportional to the concentration of anionic surfactants. Various chemical and physical parameters for the FI spectrophotometric method were optimized, and interference-free levels were examined. At the optimized conditions, Beer's law was obeyed in the range 1.4 approximately 25 mg/L sodium DBS for an injected sample volume of 180 microL, and a detection limit of 0.22 mg/L for sodium DBS was achieved at a sampling rate of 90 h(-1). Eleven determinations of a 16 mg/L sodium DBS solution gave a RSD of 0.4%. The proposed method has successfully been applied to the determination of anionic surfactant concentration in waste water and in detergents.