2,3,7-Trihydroxyfluorones immobilized on cellulose matrices in test methods for determining rare elements

It was shown that 2,3,7-trihydroxyfluorones immobilized by adsorption on cellulose matrices can be used as reagents for the test determination of Mo(VI), Ti(IV), Ge(IV), Hf(IV), Nb(V), Ta(V), W(VI), Bi(III), V(IV), and Zr(IV). The change of the protolytic and complexing properties of trihydroxyfluorones immobilized on cellulose matrices was considered in comparison to corresponding properties in a solution. It was found that the reactions of trihydroxyfluorones with rare elements on cellulose matrices and in a solution exhibit similar effects upon the addition of cetylpyridinium. These effects are the bathochromic shift of the absorption maxima of the reagents and their complexes with analytes and the extension of the range of optimum acidity for complex formation. The complexation of salicylfluorones with the titanium(IV) in solution and on cellulose paper was studied by IR spectrometry. Phenylfluorone immobilized on a mixed-fiber cloth as used in test determinations of (mg/L) 0.05–5 Ti(IV), V(IV), Hf(IV), Nb(V), and Mo(VI); 0.01–5 Ge(IV) and Zr(IV); 0.05–1 Bi(III) and W(VI); and 0.1–5 Ta(V) by the color intensity of the indicator matrix after passing through 20 mL of a test solution. It was shown that phenylfluorone immobilized on cellulose paper can be used to determine (mg/L) 0.05–50 Ti(IV), 0.5–1000 Ge(IV), 0.5–500 Zr(IV), 5–200 Bi(III), 0.1–50 Mo(VI), 0.1–1000 V(IV), 0.1–100 Nb(V), 0.1–800 Hf(IV), 1–100 Ta(V), and 1–800 W(VI) by the length of the colored zone of a test strip after it was brought into contact with a test solution.     

Determination of niobium in pyrochlore ore by differential pulse polarography

A differential pulse polarographic method has been developed for the quantitative determination of niobium in pyrochlore ore. One-step polarographic curves were obtained in 0.01 mol L(-1) EDTA as supporting electrolyte. Analytical curves indicated that response was linearly dependent on Nb(V) concentration between 1.6 and 8.6 mg L(-1) in the pH range 2-5. The system is quasi-reversible and controlled by diffusion in 0.01 mol L(-1) EDTA as supporting electrolyte; the electrode process involves one-electron reduction of Nb(V) to Nb(IV). The results obtained so far for niobium in pyrochlore ore were comparable with those obtained by X-ray fluorescence determination. Ions such as Fe(III), Cr(III), As(III), Cu(II), Ni(II), Co(II), Mn(II), Sn(IV), Zn(II), V(V), Ta(V), W(VI), Ce(IV), and Ti(IV) did not interfere. Possible interference from Pb(II) can be avoided by complexation with the supporting electrolyte in the pH range 3.5 to 4.6; Mo(VI) ions can be tolerated when their concentration is one-tenth that of Nb(V).     

Simultaneous determination of titanium and molybdenum in steel samples using derivative spectrophotometry in neutral micellar medium

A simple, selective and sensitive spectrophotometric method has been developed for the individual and simultaneous determination of Ti(IV) and Mo(VI) using resacetophenone p-hydroxybenzoylhydrazone (RAPHBH) in presence of Triton X-100, without any prior separation. Beer's law is obeyed between 0.13-1.2 microg mL-1 and 0.18-1.90 microg mL-1 concentration of Ti(IV) and Mo(VI) at 455 nm and 405 nm, respectively. The molar absorptivity and Sandell's sensitivity of the coloured complexes at pH 3.0 are 3.1x10(4) L mol-1 cm-1, 4.2x10(4) L mol-1 cm-1, and 1.6 ng cm-2, 2.3 ng cm-2 for Ti(IV) and Mo(VI), respectively. The stoichiometry of the complexes were found to be 1:2 and 1:1 (metal:ligand) for Ti(IV) and Mo(VI), respectively. These metal ions interfere with the determination of each other in zero-order spectrophotometry. The first derivative spectra of these complexes permitted a simultaneous determination of Ti(IV) and Mo(VI) at zero crossing wavelengths of 500.0 nm and 455.0 nm, respectively. The effect of foreign ions in the determination of Ti(IV) and Mo(VI) were investigated. The proposed method has been successfully applied for the determination of titanium and molybdenum in standard alloy steel, mineral and soil samples.     

Test determination of titanium(IV) and germanium(IV) in waste and natural waters in the presence of each other

It was demonstrated that trihydroxyfluorones immobilized on cellulose matrices can be used as the reagents for the rapid determination of titanium(IV) and germanium(IV). A high retention of trihydroxyfluorones on cellulose paper (78–98%) and strong chemically stable mixed fabric (74–97%) makes it possible to use these materials for the immobilization of the reagents. Mixed fabric (viscose with cotton) with immobilized phenylfluorone was used for the test determination of 0.05–5 mg/L titanium(IV) and 0.01–5 mg/L germanium( IV) by the color intensity of the reaction zone of the indicator matrix after passing 20 mL of the analyzed solution through it. A test procedure was developed for the determination of 1–200 mg/L titanium(IV) and 0.5–1000 mg/L germanium(IV) by the length of the colored zones of the test strips sealed in a polymer film. The time of the analysis is 10–15 min. The relative standard deviation of the results of the determination of germanium( IV) and titanium(IV) is no higher than 30%.     

Consecutive sorption of molybdenum(VI) and chromium(VI) from a single sample onto fiber materials filled with an anion exchanger and their solid-phase determination with phenylfluorone and diphenylcarbazide

We have considered the possibility of the sorption-spectrometric determination of molybdenum(VI) with phenylfluorone and chromium(VI) with diphenylcarbazide from a single sample by consecutive sorption from different media onto fiber materials filled with an AV-17 anion exchanger. The dependences of analytical signals of molybdenum and chromium on the sorption conditions (pH of the initial solution, NaCl concentration, sizes of the support disc, agitation time) have been studied in the batch mode. The conditions of analytical signal registration have been determined and the analytical ranges have been established (0.01–0.06 μg/mL for Cr and 0.02–0.2 μg/mL for Mo). It has been demonstrated that molybdenum and chromium can be determined at their ratios from 1: 1 to 5: 1 from a single sample after chromium sorption from 0.1 M HCl and molybdenum sorption at pH 4 by diffuse-reflection spectroscopy or visual test. The selectivity of molybdenum and chromium determination in the presence of interfering ions has been studied.     

Adsorptive stripping voltammetry determination of molybdenum(VI) in water and soil

A differential pulse stripping voltammetry method for the trace determination of molybdenum(VI) in water and soil has been developed. In 0.048M oxalic acid and 6 x 10(-5)M Toluidine Blue (pH 1.8) solution, Mo(V), the reduction product of Mo(VI) in the sample solution, can form a ternary complex, which can be concentrated by adsorption on a static mercury drop electrode at -0.1 V (vs. Ag/AgCl). The adsorbed complex gives a well-defined cathodic stripping current peak at -0.30 V, which can be used for determining Mo(VI) in the range 5 x 10(-10)-7 x 10(-9)M, with a detection limit of 1 x 10(-10)M (4 min accumulation). The method is also selective. Most of the common ions do not interfere but Sn(IV) and large amounts of Cu(2+), Ag(+) and Au(3+) affect the determination.     

Calculation of the detection limit in chemical test methods of analysis based on the principles of planar chromatography

Microsoft Office Excel and CorelDraw Graphics Suite were used for the statistical treatment of experimental data in the chemical test methods of analysis. A simple and available method for calculating the detection limit was demonstrated by the example of test systems for determining molybdenum(VI), bismuth( III), and titanium(IV). The use of Pantone Hexachrome Coated enabled us to construct calibration curves for the main color intensity of the reaction zone on the indicator matrix as a function of analyte concentration. The approximation of experimental data using the Microsoft Office Excel software was considered; it eliminated the complicated and laborious calculation of the coefficients of approximation equation and the correlation coefficient. It was found that, for the studied test systems, the detection limit was close to the determination limit. In the use of test strips, the detection limit for Mo(VI) and Bi(III) was 0.04 and 1.0 mg/L, respectively, and in the determination of Mo(VI) and Ti(IV) using a test facility, it was 0.03 and 0.02 mg/L, respectively.     

Fabrics and papers modified with analytical reagents for the test determination of selenium(IV) and tellurium(IV)

It is shown that Malachite Green and Crystal Violet immobilized on viscose fabrics can be used as reagents for the rapid determination of selenium(IV) and tellurium(IV). Selenium is determine by the color intensity of ion associates formed by the reagents with the triiodide ion formed upon the reduction of selenium(IV) with potassium iodide and tellurium, by the color intensity of reagent ion associates with telluromolybdic heteropoly acid. The analytical ranges for selenium and tellurium(IV) were 0.005–0.5 and 0.01–0.1 mg/L upon passing 20 and 100 mL of a test solution through the indicator matrix, respectively. The duration of analysis does not exceed 15–20 min. The relative standard deviation is 50%. Test strips were proposed for determining 0.1–100 mg/L selenium(IV) and 1–1000 mg/L tellurium(IV) by the length of the colored zone. The determination of selenium(IV) is based on the oxidation of 4-nitrophenylgydrazine to its diazonium salt and salt interaction with naphthylamine chemically immobilized on paper with the formation of a red azo compound. The determination of tellurium(IV) is based on its reaction with Bismuthol II immobilized on a paper.     

The separation of W(V) from HCl-KSCN medium on polyurethane foam sorbents for its spectrophotometric determination in steels and silicates

A simple procedure for selective sorption of tungsten is described. The method involves reduction of W(VI) to W(V) with tin(II) chloride (2%, w/v) at 8-9M hydrochloric acid, formation of the W(V)-SCN complex with 0.2M KSCN and its sorption on polyurethane foam within 20 min. The sorbed complex is then eluted with acidified acetone (1 ml of 1M hydrochloric acid and 8 ml of acetone) followed by addition of 1 ml of 0.1M KSCN to the eluent. The method has been applied to the spectrophotometric determination of tungsten in steels and silicates by measuring the absorbance of the eluted solution at 400 nm. Beer's law is obeyed for the range 0.1-12 mug W/ml. Other elements, e.g., Co(III) (50 mug/ml), Cu(II) (10 mug/ml), Ti(IV) (20 mug/ml), V(V) (10 mug/ml) and Mo(VI) (0.5 mug/ml) have no effect on the method. Interference of copper, up to 100 mug/ml has been eliminated by masking with thiourea and that due to molybdenum by prior separation with thioglycollic acid on PUF. The method has been verified with standard samples.     

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.     

Combination collectors in adsorption colloid flotation for multielement determination in waters by neutron activation

A method is described for the collection of small amounts of both anions and cations in water samples by adsorption colloid flotation with a combination collector, prior to quantitation by neutron activation. In the presence of 20 mg of iron(III) and 2 ml of 0.1 M ammonium pyrrolidinedithiocarbamate, As(V), Cd(II), Co(II), Cu(II), Hg(II), Mo(VI), Sn(IV), Sb(III), Te(VI), Ti(IV), U(VI), V(V) and W(VI) are quantitatively collected from 1 -l samples at a pH 5.8 ± 0.1; sodium dodecyl sulfate and sodium oleate are used as surfactant. Recoveries for all the elements tested are greater than 90%. Results for a number of elements in sea waer and an NBS water standard, SRM 1643a, are given.     

Test determination of molybdenum(VI) with the use of phenylfluorone immobilized on a cellulose cloth

It was demonstrated that phenylfluorone immobilized on a cellulose cloth matrix can be used as a reagent for the test determination of molybdenum(VI). Phenylfluorone was immobilized on a mixed fiber cloth (viscose with cotton), which provides high retention of the reagent (97%) and exhibits chemical stability and mechanical strength. The selectivity of the reaction was studied. A test procedure was developed for the determination of 0.05–5 mg/L molybdenum(VI) in natural waters (RSD < 40%); the time of analysis is 10–15 min.     

Study of the titanium-phenylfluorone complex formed in the presence of Triton X-305 and emulsifier OP

A highly sensitive method for the spectrophotometric determination of titanium with phenylfluorone (PF) in the presence of Triton X-305 and emulsifier OP has been developed. In acid medium (pH 1.4-2.2) Ti(IV) forms red-violet complexes with PF, Triton X-305 and OP. The complex exhibits maximum absorption at 540 nm. The molar absorptivity is 1.63 x 10(5) 1.mole(-1).cm(-1). The Ti:PF ratio in the complex is 1:2. Beer's law is obeyed in the titanium concentration range 0-0.2 microg/ml in the final solution. Fluoride and EDTA interfere. The method has been used for the rapid direct determination of microamounts of Ti(IV) in soils and cereals with satisfactory results.     

Generation of bis(dithiolene)dioxomolybdenum(VI) complexes from bis(dithiolene)monooxomolybdenum(IV) complexes by proton-coupled electron transfer in aqueous media

Electron transfer oxidation reaction of bis(dithiolene)monooxomolybdenum(iv) (Mo(IV)OL(x)) complexes is studied as a model of oxidative-half reaction of arsenite oxidase molybdenum enzymes. The reactions are revealed to involve proton-coupled electron transfer. Electrochemical oxidation of Mo(IV)OL(x) yields the corresponding bis(dithiolene)dioxomolybdenum(vi) complexes in basic solution, where the conversion of Mo(IV)OL(dmed) supported by a smaller electron donating dithiolene ligand (1,2-dicarbomethoxyethylene-1,2-dithiolate, L(dmed)) to Mo(VI)O(2)L(dmed) is faster than that of Mo(IV)OL(bdt) with a larger electron donating dithiolene ligand (1,2-benzenedithiolate, L(bdt)) under the same conditions. Titration experiments for the electrochemical oxidation reveal that the reaction involves two-electron oxidation and two equivalents of OH(-) consumption per Mo(IV)OL(x). In the conversion process of Mo(IV)OL(x) to Mo(VI)O(2)L(x), the five-coordinate bis(dithiolene)monooxomolybdenum(v) complex (Mo(V)OL(x)) being a one-electron oxidized species of Mo(IV)OL(x) is suggested to react with OH(-). Mo(V)OL(x) reacts with OH(-) in CH(3)CN or C(2)H(5)CN in a 2?:?2 ratio to give one equivalent Mo(IV)OL(x) and one equivalent Mo(VI)O(2)L(x), which is confirmed by the UV-vis and IR spectroscopies. The low temperature stopped-flow analysis allows investigations of the mechanism for the reaction of Mo(V)OL(x) with OH(-). The kinetic study for the reaction of Mo(V)OL(dmed) with OH(-) suggests that Mo(V)OL(dmed) reacts with OH(-) to give a six-coordinate oxo-hydroxo-molybdenum(v) species, Mo(V)O(OH), and, then, the resulting species undergoes successive deprotonation by another OH(-) and oxidation by a remaining Mo(V)OL(dmed) to yield the final products Mo(IV)OL(dmed) and Mo(VI)O(2)L(dmed) complexes in a 1?:?1 ratio. In this case, the Mo(V)O(2) species are involved as an intermediate in the reaction. On the other hand, in the reaction of Mo(V)OL(bdt) with OH(-), coordination of OH(-) to the Mo(V) centre to give a six-coordinate Mo(V)O(OH)L(bdt) species becomes the rate limiting step and other intermediates are not suggested. On the basis of these results, the ligand effects of the dithiolene ligands on the reactivity of the bis(dithiolene)molybdenum complexes are discussed.     

Spectrophotometric study and extraction of niobium(V) complexes with catechol and its derivatives as ion-pairs with quaternary ammonium ions: Application to the separation of niobium from other refractory metal ions

The reactions of niobium(V) with catechol and several substituted derivatives were studied. Optimal conditions for colour development in the niobium(V)-catechol system are: pH 6.7–8.0, and heating at 85° for at least 6 min; the wavelength of maximal absorption is 365 nm, and the molar absorptivity is 1.02·10⁴. Catechol derivatives require lower temperatures and develop colours with niobium(V) in neutral or slightly acidic solutions. The best of the derivatives studied were 3-methyl-catechol and 4-chlorocatechol. Extraction of the ion-pairs formed between niobium-(V)-catechol and different quaternary ammonium ions, was studied with representative solvents. Similar studies were made on other refractory metal ions, i.e., Ti(IV), V(V), Mo(VI) and W(VI), under the optimal conditions for the reaction with niobium(V). Separations of binary (1:1) mixtures of niobium(V) with Ti(IV), V(V), Mo(VI) or W(VI) at the 5·10^-5M level were shown to be possible under the predicted conditions.     

Extractive photometric determination of vanadium(V) as thiocyanato and azido mixed-ligand complexes with N-hydroxy-N-p-chlorophenyl-N'-(2-methyl-4-chlorophenyl) benzamidine hydrochloride

Ternary systems involving thiocyanate or azide (X) and N-hydroxy-N-p-chlorophenyl-N'-(2-methyl-4-chlorophenyl)benzamidine hydrochloride (HOAm) are used for the extraction-photometric determination of vanadium(V) as a VOX(2)(OAm)HOAm complex. A strong synergistic effect is observed. Mn(II), Cr(III), Ti(IV), Zr(IV), Mo(VI) and W(VI) do not interfere. The method has been applied to standard steel samples.     

Indirect cerimetric determination of gold at the milligram level

Summary A rapid volumetric method has been worked out for the indirect determination of 0.25–2.5 mg of gold in presence of many common ions. It is based on the reduction of gold(III) to metal with excess of cobalt(II) in the presence of 1,10-phenanthroline at pH 3 and 50°, and estimation of the unreacted cobalt(II) in the filtrate by visual, potentiometric or biamperometric titration with standardized cerium(IV) sulphate solution. It has been found that there is no interference from Ni(II), Pb(II), Zn(II), Cd(II), Mn(II), Mg(II), Ca(II), Al(III), Cr(III), Ti(IV), V(V) and W(VI). Interference due to Pd(II) and Ag(I) can be eliminated. Fe(III), Cu(II), Mo(VI), Hg(II) and Pt(IV) interfere, even present in small amounts.

---

Zusammenfassung Ein schnelles maßanalytisches Verfahren zur indirekten Bestimmung von 0,25–2,5 mg Gold in Gegenwart vieler Ionen wurde ausgearbeitet. Es beruht auf der Reduktion zu metallischem Gold mit überschüssigem Kobalt(II) in Anwesenheit von 1,10-Phenanthrolin bei pH 3 und 50°. Die Rückbestimmung des unverbrauchten Kobalts im Filtrat erfolgt durch potentiometrische oder biamperometrische Titration mit Cer(IV)sulfat. Ni(II), Pb(II), Zn(II), Cd(II), Mn(II), Mg(II), Ca(II), Al(II), Cr(III), Ti(IV), V(V) und W(VI) stören nicht. Eine Störung durch Pd(II) oder Ag(I) kann man ausschalten. Fe(III), Cu(II), Mo(VI), Hg(II) und Pt(IV) stören auch in geringen Mengen.

     

Fluorescence quenching method for determination of trace tungsten in environmental samples with dibromohydroxyphenylfluorone

A highly sensitive and selective fluorescence quenching method has been developed for the determination of trace tungsten in environmental samples using dibromohydroxyphenylfluorone (DBHPF) as an emission reagent. In the presence of 0.04?mol/L of sulphuric acid and acetyltrimethylammonium bromide, tungsten(VI) reacts with DBHPF to form a 1?:?3 red complex within 5.0?min. In order for the DBHPF–tungsten(VI) complex to form, the fluorescence intensity of the reagent solution was quenched linearly by adding 0.1 to 1.0?µg of tungsten(VI) in 25?mL of solution. This was measured at 528?nm with excitation at 495?nm. In this work, a standard addition method was investigated and used for sample analysis. The decrease in fluorescence intensity of the reagent solution (ΔF) was linear for 0?～?0.9?µg of tungsten(VI) in 25?mL of solution, and the detection limit (3?s) of the standard addition method was found to be 0.012?ng/mL of tungsten(VI). The effects of various metal and nonmetal ions were studied in detail. The experiments clearly showed that most foreign ions can be tolerated in considerable amounts; in particular, 50-fold Mo(VI), V(V), Zr(VI) and Ti(IV) do not interfere, and the selectivity of the proposed method is better than other previously described methods. Moreover, the method proposed here is very stable and simple, the fluorescence intensity of the solution can remain almost unchanged for 2.0?h at room temperature, and the method has been used successfully to determine tungsten in environmental samples.     

Consecutive thin-layer chromatographic separation of Zr(IV), Hf(IV) and many other ions on silica gel in nitric acid-hydrogen peroxide media

The thin-layer chromatographic (TLC) behaviour of 64 ions including Zr(IV) and Hf(IV) has been surveyed on systems composed of silica gel and of nitric acid and nitric acid-hydrogen peroxide media. In the 0.5 mol 1(-1) HNO(3)-3% (w/v) H(2)O(2) solution, only Hf(IV) adsorbed very strongly, whereas Zr(IV) and many other ions showed no or weak adsorption. Stepwise development with diluted nitric acid and subsequently with nitric acid-hydrogen peroxide solution allowed the consecutive separation of three-component mixtures consisting of Zr(IV), Hf(IV) and one of many other accompanying elements, such as Mo(VI), Nb(V), Th(IV), Ti(IV), U(VI) and rare earths(III), to be conducted simply and effectively.     

Sorption-spectrometric determination of lanthanum in the presence of uranium and thorium with the reagent Arsenazo M on the solid phase of fibrous filled sorbents

The possibility of the determination of La(III) in the presence of U(VI) and Th(IV), a solid phase with the reagent Arsenazo M, was examined. It was demonstrated that the determination of lanthanum with Arsenazo M in 0.05 M HCl in the presence of 3-, 2-, 1-, and 10-fold amounts of U(VI), Th(IV), Zr(IV), and Ti(IV) is possible after sorption on polyacrylonitrile fiber filled an ion exchanger with iminodiacetate groups (PANV-ANKB-50). For sorption under the optimum conditions at pH 5, the detection limit of lanthanum is 0.01 μg/mL. The method for the determination of lanthanum was verified by the added-found method in the analysis of tap water. To decrease the matrix effect, it is recommended to perform sorption in the analysis of water at pH 2.5. In this case, the detection limit of La(III) is 0.02 μg/mL, RSD < 20%. The time of the analysis of 5 or 6 samples is no longer than 20 min.