Indirect spectrophotometric determination of chloride by solvent extraction as tris(1,10-phenanthroline)iron(II) thiocyanate

An indirect spectrophotometric method for the determination of small amounts of chloride in fresh waters is described. Chloride ions react with mercury(II) thiocyanate to liberate thiocyanate ions, which can be selectively extracted into nitrobenzene with tris(1,10-phenanthroline)iron(II) chelate cations. The red color (516 nm) of the organic phase measured against a reagent blank is proportional to the initial concentration of chloride ions in the aqueous phase. At least an equimolar amount of tris(1,10-phenanthroline)iron(II) chelate and a 3-fold amount of mercury(II) thiocyanate are needed; the optimal pH range is 1.5–3.5. Beer's law is obeyed over the concentration range of 0.8–5.6 10^-5 M of chloride. The color stability and the apparent sensitivity are better than those of the mercury(II) thiocyanate-iron(III) method. Large amounts of sulphate, phosphate, fluoride, carbonate, acetate, potassium, sodium, and ammonium ions had negligible or no effect ; bromide, iodide, cyanide, sulphide, and thiocyanate interfere.     

Determination of boron in high-purity silicon and trichlorosilane indirectly by measurement of cadmium in tris (1,10-phenanthroline) cadmium tetrafluoroborate

Summary An indirect method has been developed for the determination of boron in high-purity silicon materials, based on the reaction of tetrafluoroborate ion (BF ₄ ^– ) with tris(1,10-phenanthroline)cadmium reagent (Cd(Ph) ₃ ²⁺ ) to form the tris(1,10-phenanthroline)cadmium tetrafluoroborate (Cd(Ph)₃ · 2BF₄) ion-association complex, followed by spectroscopic or radiometric determination of the cadmium in the product complex. The optimal conditions for the separation of B from the silicon matrix, the transformation of B to BF ₄ ^– , the reaction of Cd(Ph) ₃ ²⁺ and BF₄ to Cd(Ph)₃ · 2BF₄, the separation of the complex from unreacted Cd(Ph) ₃ ²⁺ by solvent extraction have all been investigated in detail. Two methods, radio-reagent and GFAAS, have been used for the indirect determination of B in the complex. When the B content is plotted against the radioactivity of ¹¹⁵Cd(Ph)₃ · 2BF₄ in the organic phase, a linear relationship persists down to 20 ng; whereas the application of GFAAS to the determination of Cd in the complex, results in a determination limit of 5 ng for B. The limit of detection of this method is obviously decided by the blank value introduced by the contaminants from the reagents, container surfaces, etc. and, more seriously, by the incomplete separation of unreacted reagent Cd(Ph) ₃ ²⁺ from the complex. The method developed has been applied to the determination of B in various silicons.

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Indirekte Borbestimmung in hochreinem Silicium und Trichlorsilan durch Bestimmung des Cadmiums in Tris (1,10-phenanthrolin)-cadmiumtetrafluoroborat

Zusammenfassung Die empfohlene indirekte Borbestimmung beruht auf der Reaktion von Tetrafluoroboration (BF ₄ ^– ) mit Tris(1, 10-phenanthrolin)-cadmium-Reagens (Cd(Ph) ₃ ²⁺ ) zum Ionenassoziationskomplex Cd(Ph₃) · 2BF₄ und nachfolgender Bestimmung des Cadmiums (spektrometrisch oder radiometrisch) in diesem Komplex. Die optimalen Bedingungen zur Abtrennung des Bors von der Siliciummatrix, zur Umsetzung von B zu BF ₄ ^– , für die Reaktion zum Komplex sowie die Abtrennung des Komplexes von nicht umgesetztem Cd(Ph) ₃ ²⁺ durch Flüssigextraktion wurden im einzelnen untersucht. Radiometrie und Graphitofen-AAS wurden zur Bestimmung eingesetzt. Eine lineare Abhängigkeit des B-Gehaltes von der Radioaktivität des ¹¹⁵Cd(Ph)₃ · 2BF₄ wurde bis herab zu 20 ng festgestellt. bei Anwendung der Graphitofen-AAS ergab sich eine Nachweisgrenze von 5 ng B. Die Nachweisgrenze wird entscheidend beeinflußt durch eingeschleppte Verunreinigungen aus den Reagentien, Gefäßwänden usw., mehr noch durch die unvollständige Abtrennung nicht umgesetzten Reagenses vom Komplex. Das ausgearbeitete Verfahren wurde für die Borbestimmung in verschiedenen Si-Proben angewendet.

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Presented at the 9th International Symposium on Microchemical Techniques, Amsterdam, August 28–September 2, 1983     

Indirect complexometric determination of cadmium(II) using 1,10-phenanthroline as selective masking agent

An indirect complexometric method is described for the determination of cadmium(II), 1,10-phenanthroline being used as masking agent. Cadmium(II) in a given sample solution is initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. An excess of 1,10-phenanthroline is then added and the EDTA released from the Cd-EDTA complex is titrated with standard lead nitrate solution. Results are obtained for 1.5–57 mg of Cd with relative errors 0.90% and standard deviations 0.06 mg. Cu(II), Co(II), Hg(II), Ni(II), Zn(II), Pd(II), Tl(III), Au(III) and Sn(IV) interfere, but can be easily masked. The method is applied for the determination of cadmium in synthetic alloy solutions.     

Indirect spectrophotometric determination of palladium using 1,10-phenanthroline as reagent

Summary The spectrophotometric method for the determination of palladium is based upon the addition of a standard 1,10-phenanthroline solution to precipitate Pd(phen)Cl₂ and the determination of 1,10-phenanthroline concentration of the supernatant solution. The absorbancy readings were made in the absorption maximum at about 271 nm, in the concentration range of 10^–6 to 10^–5M 1,10-phenanthroline in 0.1 M hydrochloric acid and 0.1% hydroxylamine hydrochloride. For the phenanthroline system Beer's law is valid. Ions which either form with phenanthroline very strong complexes or interfere with the spectrophotometric determination of 1,10-phenanthroline must be absent. The method is simple, rapid, accurate and applicable to the macro and micro-determination of palladium in different systems. Standard deviation was found to be 0.085 ppm (in pure Pd solutions).

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Indirekte spektrophotometrische Bestimmung von Palladium mit 1,10-Phenanthrolin

Zusammenfassung Das Verfahren beruht auf der Fällung von Pd(phen)Cl₂ durch Zusatz einer bestimmten Menge Standard-1,10-Phenanthrolinlösung und spektrophotometrischer Bestimmung des Überschusses.Die Messungen werden bei dem Absorptionsmaximum bei etwa 271 nm und einer Konzentration von 10^–6M bis 10^–5M 1,10-Phenanthrolin in 0,1 M HCl und 0,1% Hydroxylaminhydrochlorid enthaltender Lösung durchgeführt. Das 1,10-Phenanthrolinsystem folgt dem Beerschen Gesetz. Ionen, die entweder mit 1,10-Phenanthrolin starke Komplexe bilden oder die spektrophotometrische Bestimmung von 1,10-Phenanthrolin beeinflussen, müssen abwesend sein. Die Methode ist einfach, rasch und genau und kann für Mikro- und Makrobestimmungen in verschiedenen Systemen angewendet werden. Die Standardabweichung beträgt 0,085 ppm (in reinen Pd-Lösungen).

     

The spectrophotometric determination of anions by solvent extraction with metal chelate cations. part XX : Trichloroacetic acid with tris(1,10-phenanthroline)iron(ii) chelate

Trichloroacetic acid can be extracted from an aqueous solution by nitrobenzene with tris(1,10-phenanthroline)iron(II) chelate, and can be determined spectrophotometrically by measuring the extract at 516 nm. The extracted species is probably [Fe(phen)₃].(CCl₃COO)₂. Beer's law is obeyed over the concentration range 1.0·10^-5–1.0·10^-4M trichloroacetic acid in aqueous solution. Large amounts of phosphate and sulfate and moderate amounts of chloride, acetic acid, and monochloroacetic acid do not interfere, equal amounts of dichloroacetic acid give a slight positive error     

Oxidation of phenol by tris(1,10-phenanthroline)osmium(III)

Outer-sphere oxidation of phenols is under intense scrutiny because of questions related to the dynamics of proton-coupled electron transfer (PCET). Oxidation by cationic transition-metal complexes in aqueous solution presents special challenges because of the potential participation of the solvent as a proton acceptor and of the buffers as general base catalysts. Here we report that oxidation of phenol by a deficiency of [Os(phen)(3)](3+), as determined by stopped-flow spectrophotometry, yields a unique rate law that is second order in [osmium(III)] and [phenol] and inverse second order in [osmium(II)] and [H(+)]. A mechanism is inferred in which the phenoxyl radical is produced through a rapid PCET preequilibrium, followed by rate-limiting phenoxyl radical coupling. Marcus theory predicts that the rate of electron transfer from phenoxide to osmium(III) is fast enough to account for the rapid PCET preequilibrium, but it does not rule out the intervention of other pathways such as concerted proton-electron transfer or general base catalysis.     

Liquid-liquid extraction and spectrophotometric determination of cadmium with 1,10-phenanthroline and thymol blue

A simple and highly sensitive extraction spectrophotometric method was developed for the determination of traces of cadmium. The method is based on the preconcentrative extraction of ternary-ion-association complex of cadmium—1,10-phenanthroline-thymol blue into chloroform and subsequent determination by spectrophotometry. The ternary ion associate is stable for 20 h and cadmium content as low as 0.1 g in 90 ml of sample can be determined. The method is precise and has been applied to the determination of cadmium in sea water, solder and high purity zinc and indium materials.     

Solvent extraction of anions with metal chelate cations-XVIII Spectrophotometric determination of maleic acid in the presence of fumaric acid by solvent extraction with tris(1,10-phenanthroline)iron(ii) chelate cations

A new colorimetric method is proposed for the determination of maleic acid. Among aliphatic dicarboxylic acids tested, maleic acid was found to be selectively extracted into nitrobenzene as the red ion-association complex (lambda(max) 516 nm) formed between the hydrogen maleate anion and the tris(1,10-phenanthroline)iron(II) cation. At least a 32-fold molar excess of tris(1,10-phenanthroline)iron(II) relative to maleic acid is needed and the optimal pH range is 3-5. A linear relationship is obtained over the concentration range 10(-5)-10(-4)M maleic acid. The relative standard deviation was 1.0 %. The colour intensity of the extract remains constant at room temperature for at least 24 hr. A large amount of fumaric acid, the trans-isomer of maleic add, is not extracted under the same conditions. This makes it possible to determine maleic acid in the presence of fumaric acid.     

Spectrophotometric determination of dissolved oxygen with tris(4,7-dihydroxy-1,10-phenanthroline)iron(II)

Tris(4,7-dihydroxy-1,10-phenanthroline)iron(II) reacts rapidly and quantitatively with dissolved oxygen in alkaline aqueous solution. In ammoniacal solution, the reaction is accompanied by the disappearance of the intense red colour of the iron(II) compound, which gives way to the pale gray, slightly-dissociated ion tris(4,7-dihydroxy-1,10-phenanthrolinefiron)(III). By measurement of the absorbance of a solution containing the ferrous compound before and after the injection of an oxygen-containing solution, the concentration of dissolved oxygen in the sample can be accurately determined in the range 1-20 ppm.     

Thermal racemization of tris(1,10-phenanthroline) chromium(III)

The thermal racemization of (+)₅₈₉-Cr phen₃(ClO₄)₃ has been examined under a variety of medium conditions. The racemization rate constant in water at 75°C, for example, is 8·5 × 10⁻⁵ sec⁻¹, with an energy and entropy of activation of 23·5 kcal mole⁻¹ and −10·9 e.u., respectively. The effect of acid, hydroxide, and various other added ions on the rate constant has been investigated, and the results compared with other tris-phenanthroline systems. An intramolecular twist process is considered the most probable mechanism of racemization.     

Transient bleaching of tris(1,10-phenanthroline) iron(II)

Absorption at the excitation wavelength recovers in a sub-nanosecond, two stage process following bleaching of tris(1,10-phenanthroline) iron(II) by a single picosecond pulse at 530 nm. Absorption coefficients and decay times suggest that a CT and a dd excited state are consecutively occupied before ground state repopulation.     

Indirect extraction—spectrophotometric method for the determination of traces of tin(II) by means of 4,7-diphenyl-1,10-phenanthroline

An indirect extraction-spectrophotometric determination of tin(II) is based on reduction of iron(III) and determination of the iron(II) formed with bathophenanthroline. Analysis is possible in strongly acidic samples even with large excesses of iron(III). The apparent molar absorptivity is 39,080 dm³ mol^-1 cm^-1 ; the limit of determination is 32 ng cm^-3 and the sensitivity is 64 ng cm^-3. Interferences are reported. The method is applicable to the determination of tin in samples soluble in non-oxidizing acids, and to the determination of tin in lead.     

Indirect determination of chloride as chromyl chloride by atomic-absorption spectrophotometry

Summary A method for the determination of chloride in aqueous solution by atomic-absorption Spectrophotometry is described. The chloride is converted into chromyl chloride, which is extracted into carbon tetrachloride and subsequently back-extracted and determined in a solution buffered with NH₄H₂PO₄/(NH₄)₂HPO₄. Calibration plots of the atomic absorption of the aqueous back-extracted phase at the chromium 425.4 nm resonance line are linear in the range 5–270g of chloride. The calibration graph can be obtained directly with aqueous solutions of Cr(VI). The proposed method can be applied directly to mineral and medicinal water samples.

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Indirekte AAS-Bestimmung von Chlorid als Chromylchlorid

Zusammenfassung Eine Methode zur Bestimmung von Chlorid durch Atom-Absorptions-Spektroskopie wurde entwickelt, deren Basis die Bildung von Chromylchlorid, dessen Extraktion mit Cl₄C und die anschließende Bestimmung des rückextrahierten Chroms in einer Lösung von NH₄H₂PO₄/(NH₄)₂HPO₄ ist. Das lineare Verhältnis zwischen Absorbanz und Chromkonzentration ermöglicht die Bestimmung des Chlorids im Bereich 5–270g; zur direkten Eichung dienten wäßrige Lösungen von Chrom(VI). Die vorgeschlagene Methode wurde für die Chlorid-Bestimmung in Mineral-und Medizinalwasser benutzt.

     

A new method for the spectrophotometric determination of pertechnetate with tris(1,10-phenanthroline)iron(II) ion

A new spectrophotometric determination of technetium has been developed by means of the solvent extraction of tris(1,10-phenanthroline)iron(II) ([Fe(phen)₃ ²⁺]) with pertechnetate into nitrobenzene. The concentration of technetium can be determined by measuring the characteristic absorbance at 516 nm (=11,700M^–1·cm^–1) in the organic phase. An important feature of the proposed method is that the concentration of pertechnetate can be determined without complicated processes such as the reduction of pertechnetate and the subsequent formation of a colored chelate.     

Indirect determination of iodate by atomic-absorption spectrophotometry

An indirect method for determination of trace iodate in certain high-purity chemicals by atomic-absorption spectrophotometry (AAS) is described. Iodate forms a stable ion-association complex [Hg(dipy)(2)](IO(3))(2) in neutral medium, which can be extracted into methyl isobutyl ketone with 99% efficiency. The extract can be analysed for mercury (and hence indirectly for iodate) by flameless AAS. The limit of detection for iodate by this method is 7.5 ng. Apparent recoveries of 92-112% have been obtained for spikes of 0.25-0.70 mug of iodate.     

Electrochemical behavior of 5-amino-1,10-phenanthroline and oxidative electropolymerization of tris[5-amino-1,10-phenanthroline]iron(II)

The electrochemical behavior of 5-amino-1,10-phenanthroline and tris[5-amino-1,10-phenanthroline]-iron(II) at carbon paste, glassy carbon, and platinum electrodes is reported. The iron complex undergoes electrochemically induced oxidative polymerization from acetonitrile solutions and the resulting polymers are very stable. Charge transport through the polymer films occurs with a charge transfer diffusion coefficient, D_ct, equal to 3.1 × 10⁻⁸ cm² s⁻¹ corresponding to an electron self-exchange rate of 5.2×10⁷M⁻¹ s⁻¹. The activation energy and the entropy change for the charge transfer diffusion process are (approximate values) 32.0 ± 0.12 kJ mol⁻¹ and −24.7 ± 0.4 J K⁻¹ mol⁻¹, respectively.     

Effect of solvent extraction on the atomic-absorption spectrophotometry in determination of ppM levels of cadmium with dithizone

Various organic solvents for cadmium dithizonate extraction have been examined for their suitability for subsequent absorption spectrophotometry. The solvents are discussed on the basis of their physical properties. Much enhanced sensitivity is achieved by use of a large aqueous phase/solvent volume ratio. Conditions for the determination of ppM levels of cadmium are described for nitrobenzene and n-butyl acetate as solvents. Dithizone and cadmium dithizonate are very stable in nitrobenzene. The extraction is completely quantitative over the pH range 3.5-10.0. Interference by diverse ions was studied, and their tolerance levels are given.