Spectrophotometric determination of tungsten(VI) with rutin

A new spectrophotometric method for the determination of microamounts of tungsten(VI) with rutin has been developed. The effect of a large number of foreign ions was investigated, and the separation and determination of tungsten in the presence of the interfering ions examined are presented.     

Substoichiometric determination of mercury with cetyltrimethylammonium bromide

A radiometric method based on substoichiometric isotope dilution analysis has been developed for the determination of mercury using cetyltrimethylammonium bromide (CTAB) as the substoichiometric reagent. The method is based on the extraction of mercury as an ionassociation complex of tetraiodomercurate(II) ion with a substoichiometric amount of CTAB in benzene. The calibration graph was found to be linear in the range 0–10 μg Hg (II) in the aqueous phase of 10 ml volume. A detection limit of 0.06 μg·ml⁻¹ could be achieved by the proposed method. The relative standard deviation of the method was found to be 3.0% and the method has been successfully applied to study the determination of mercury in various synthetic mixtures.     

Kinetic-spectrophotometric determination of molybdenum (VI) and tungsten (VI) in mixtures

A simple kinetic-spectrophotometric method is described for the determination of molybdenum(VI) and tungsten(VI) in mixtures, without prior separation. The method is based on the catalytic effect of molybdenum(VI) and tungsten(VI) on the oxidation of 2,4-diaminophenol dihydrochloride (DAP) by hydrogen peroxide in acidic medium. The reaction was followed spectrophotometrically by measuring the rate of change in absorbance with time at 500 nm. A partial inhibition in the catalytic activity of each catalyst, when the other one is present, at all ratios of Mo(VI) W(VI) mixtures studied was observed. On the other hand, the catalytic activity of tungsten(VI) dropped to zero whilst that of molybdenum(VI) decreased slightly, in the presence of citrate ions. Two sets of experiments were carried out, the first in the absence and the other in the presence of citrate, and the resolution of Mo(VI)/W(VI) mixtures was achieved by solving two simultaneous equations. Various molar ratios of Mo(VI) W(VI), at the 10^–6 M level, from 0.2 1 to 5 1 can be determined with satisfactory precision and accuracy. The selectivity of the method was investigated and the method was applied successfully to the determination of molybdenum and tungsten in each other's presence in steel.     

Sensitive spectrophotometric determination of molybdenum(VI) with Pyrogallol Red and cetyltrimethylammonium ions

Pyrogallol red in the presence of cetyltrimethylammonium bromide is proposed for the spectrophotometric determination of microgram amounts of molybdenum. The sensitivity of the color reaction between molybdenum and Pyrogallol Red has been greatly increased by the sensitizing action of cetyltrimethylammonium bromide (?_{600 nm} = 90,000). Beer's law is obeyed over the range 0.1–0.4 μg/ml of molybdenum. The composition of the complex may therefore be formulated as Mo:PR:CTA = 1:2:4.     

A new method for the voltammetric determination of molybdenum(VI) using carbon paste electrodes modified in situ with cetyltrimethylammonium bromide

Molybdenum(VI) is determined by anodic stripping voltammetry using a carbon paste electrode modified in situ with cetyltrimethylammonium bromide (CTAB). The preconcentration of molybdenum is performed by adsorption and reduction of ion-pairs of cetyltrimethylammonium and molybdenum(VI) oxalate at a potential of −0.4 V vs. the saturated calomel electrode (SCE). The supporting electrolyte contains 0.01 M oxalic acid and 0.075 mM CTAB. Differential pulse anodic stripping voltammetry exploiting the reoxidation signal is used for the determination of trace levels of molybdenum(VI). Linearity between current and concentration exists for a range of 0.5–500 μg 1⁻¹ Mo with proper preconcentration times; the limit of detection (calculated as 3σ) is 0.04 μg 1⁻¹ with an accumulation period of 10 min.     

Spectrophotometric determination of germanium with Catechol Violet and cetyltrimethylammonium bromide

A ternary complex between germanium, Catechol Violet (CV) and cetyltrimethylanunoniuni bromide is proposed for the determination of germanium. The stoichiometric ratio Ge:CV is 1:2. Beer's law is obeyed from 0.1 to 1.0 ppm of Ge. The method is highly selective. Interference from Sn(IV), Fe(III), Bi(III), Cr(VI), Mo(VI), V(V) and Sb(III) in mg amounts is eliminated by extracting the germanium into carbon tetrachloride from 9M HC1 and then stripping into water before the photometric determination.     

Spectrophotometric determination of thorium with Xylenol Orange and cetyltrimethylammonium bromide

The thorium-Xylenol Orange reaction sensitized by cetyltrimethylammonium bromide ( = 5.51 x 10(4) l.mole(-1).cm(-1)) is accompanied by a bathochromic shift from 570 to 600 nm. The system is more selective than the binary system, because the reaction pH is lowered from 4.0 to 2.5; Beer's law is obeyed for 0.04-4.00 ppm of thorium.     

Ultraviolet spectrophotometric determination of tungsten(VI) with ammonium 1-pyrrolidinecarbodithioate

A simple and rapid ultraviolet spectrophotometric method is proposed for the determination of trace amounts of tungsten(VI) with ammonium 1-pyrrolidinecarbodithioate (APDC). The method is based on measurement of the absorbance of the tungsten APDC complex in fairly concentrated hydrochloric acid medium; no extraction is required. The complex is formed at an initial acidity of 6M hydrochloric acid and has an absorption maximum at 250 nm. The high absorption of the reagent blank at 250 nm disappears on decomposition of excess of reagent by heating. Beer's law is obeyed over the range 0.43–3.2 ppm of tungsten(VI). The molar absorptivity of the complex is 4.5 × 10⁴ l.mole⁻¹ .cm⁻¹ at 250 nm. Tenfold amounts of aluminium, magnesium, calcium, cobalt, iron(II), lead, silver, sodium and titanium do not interfere in the determination of 50 μg of tungsten (VI).     

Spectrophotometric determination of microamounts of scandium with o-chlorophenylfluorone and cetyltrimethylammonium bromide

The reaction of scandium(III) with o-chlorophenylfluorone (o-CIPF) in the presence of cetyltrimethylammonium bromide (CTMAB) has been studied. In an acetate buffer at pH 4.4, a red-purple complex is obtained, with maximum absorption at 569 nm and a molar absorptivity of 1.31 x 10(5)1.mole(-1).cm(-1). The composition of the complex is found to be 1:2:2 Sc-o-CIPF-CTMAB. Beer's law is obeyed over the range 0-12 mug/25 ml scandium. The proposed method has been used for determination of trace scandium in tungsten ores after its prior separation by solvent extraction.     

Extraction-spectrophotometric determination of iron(II) by ternary complex formation with pyrocatechol violet and cetyltrimethylammonium bromide

A method for iron(II) determination based on reaction with Pyrocatechol Violet to form a 1:2 binary complex at pH 5-7 is described and has been extended to an extraction-spectrophotometric procedure for the determination of iron(II) by formation of the 1:2:2 iron(II)-Pyrocatechol Violet-cetyltrimethylammonium bromide ternary complex. The molar absorptivities of the binary and ternary complexes at 595 and 605 nm are 6.55 x 10(4) and 1.35 x 10(5)1.mole(-1).cm(-1), respectively. The method has been successfully applied to the determination of iron in felspar, Portland cement and sodium hydroxide.     

Spectrophotometric determination of molybdenum in steels with o-nitrophenylfluorone and cetyltrimethylammonium bromide

A method has been developed for determining microamounts of molybdenum(VI) in aqueous solution by means of the Mo-o-nitrophenylfluorone—cetyltrimethylammonium bromide system, in which micellar solubilization is applied. A red complex is formed in 0.2–0.6M hydrochloric acid medium. The sensitivity of the method is high, and the apparent molar absorptivity is 1.55 × 10⁵ l.mole⁻¹. cm⁻¹. The absorption peak of the complex appears at 530 nm. The colour of the complex develops quickly and is stable for more than 24 hr. The composition of the complex is Mo: o-NPF = 1:1, and the system obeys Beer's law in the range 0–10 μg of Mo per 25 ml. The method has been used for the rapid determination of molybdenum in alloy steels with satisfactory results.     

Reactions of tungsten(VI) and molybdenum(V) chlorides,and tungsten(VI) and molybdenum(VI) oxychlorides,with azoxybenzene

Reactions of W^VI and Mo^V chlorides with azoxybenzene yield ionic species of W^VI and Mo^VI oxychlorides in which the cation is a protonated azobenzene. The reaction between MoCl₅ or MoOCl₄ and azoxybenzene gives, after extraction with methylene chloride—ethanol mixture, the complex [trans-MoOCl₄(OC₂H₅)]^? [C₁₂H₁₀N₂H]⁺. In contrast, WOCl₄ reacts with azoxybenzene to give a stable non-ionic adduct in which the organic moiety is coordinated through its oxygen atom trans to the WO bond. Several complexes of substituted azoxybenzene having similar structures are described.     

Spectrophotometric determination of molybdenum with 7,8-dihydroxy-4-methylcoumarin and cetyltrimethylammonium bromide

The 1:2 complexes formed between molybdenum and 7,8-dihydroxy-4-methylcoumarin in the presence and absence of cetyltrimethylammonium bromide (CTAB) have been studied. The binary complex formed at pH 5.6-6.0 in the absence of CTAB exhibits an absortion maximum at 360 nm with a molar absorptivity of 5.1 x 10(4) 1.mole(-1).cm(-1). The complex formed at pH 4.8-6.0 in the presence of CTAB has a molar absorptivity of 1.32 x 10(5) 1.mole(-1).cm (-1) at 400 nm, the wavelength of maximum absorption. Optimum conditions for complex formation were investigated and a rapid, sensitive and relatively selective method for the determination of up to approximately 70% of Mo in diverse alloys and steels is described. Small amounts of zirconium and tungsten interfere.     

Spectrofluorimetric determination of niobium with morin enhanced by cetyltrimethylammonium bromide micelles

The effect of surfactants on the fluorescence of the niobium—morin system is described. Cationic surfactants strongly enhanced the intensity (e.g., cetyltrimethylammonium bromide (CTAB) gives an 80-fold increase), while anionic and non-ionic surfactants are without effect. The formation of 1:1 and 1:3 (Nb:morin) complexes is demonstrated spectrophotometrically. The conditional stability constants for these complexes in CTAB micelles are β₁ = (1.14 ± 0.01) × 10⁴ l mol^?1 amd β₃ = (5.66 ± 0.02 × 10¹⁰ l³ mol^?3. The micellar-enhanced fluorimetric method has a 1 μg l^?1 detection limit, and is highly selective. The r.s.d. for the determination of 50 μg l^?1 Nb is 3.5%.     

Simultaneous determination of molybdenum(VI) and tungsten(VI) and its application in elemental analysis of polyoxometalates

Spectrophotometric determination of molybdenum(VI) and tungsten(VI) with application of Artificial Neural Networks is proposed and it was applied for elemental analysis of solid polyoxometalates. Better results in comparison with previously those achieved by previous published method were demonstrated. MALDI-TOF Mass Spectrometry was tested for possible determination of molecular weight of polyoxometalates utilizing different matrices. Phenomena observed during desorption-ionisation processes are discussed. LDI-TOF MS was found to be suitable for the determination of Mo:W ratio in polyoxometalates as a rapid screening method to follow synthetic procedure.     

Anodic stripping voltammetric determination of titanium(IV) using a carbon paste electrode modified with cetyltrimethylammonium bromide

A method is described for the voltammetric determination of titanium(IV) using a carbon paste electrode modified in situ with cetyltrimethylammonium bromide. The cationic micellar surfactant adsorbs onto the electrode particularly at negative potentials, simultaneously preconcentrating titanium(IV) as the oxalate complex with reduction to titanium(III). Anodic stripping voltammetry exploiting reoxidation can be used for the determination of trace levels of titanium(IV). Linearity between current and concentration exists between 5 and 160 mug l(-1) Ti(IV) (preconcentration time 2 min). The limit of detection (calculated as 3sigma) is 0.1 mug l(-1), with a preconcentration time of 10 min.     

Simultaneous electrochemical determination of three sunscreens using cetyltrimethylammonium bromide

This paper proposes a methodology based on electrochemical reduction for the simultaneous determination of three sunscreen agents, namely 4-methylbenzylidene camphor (MBC), benzophenone-3 (BENZO) and 2-ethylhexyl-4-methoxycinnamate (EHMC) by differential-pulse polarography (DPP). The highest peak currents and optimal separation of reduction peaks were obtained by using a supporting electrolyte consisted of Britton-Robinson buffer-methanol (8:2) solution at pH 4.0 and cationic surfactant 3.0 x 10(-4)mol L(-1) cetyltrimethylammonium bromide (CTAB). The methodology was validated using four commercial sunscreen preparation as a sample and the results showed high recovery rates. The efficiency of the proposed methodology was demonstrated by comparing the results obtained by DPP with those obtained by the high-performance liquid chromatography (HPLC) method.     

Anderson-type heteropolyanions of molybdenum(VI) and tungsten(VI)

The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H₂O)_6-x(Mo₇O₂₄)]⁴⁻ [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo_6-xW_x,O₂₄H₆]⁴⁻, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo₆O₂₄H₆]⁴⁻ by the S₂O²⁻₈ ion in aqueous solution gave the Waugh-type [Ni(IV)Mo₉O₃₂]⁶⁻ polyanion, whereas the oxidation of [Ni(II)W₆O₂₄H₆]⁴⁻ gave no heteropoly compound.