Determination of traces of iron with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse polarographic method for the determination of iron employing the catalytic maximum wave has been studied. A well-defined differential pulse polarographic peak for iron(III) in Britton-Robinson buffer solution containing 50 mol/l N-(2-hydroxyethyl) ethylenediamine N,N,N-triacetic acid (HEDTA) and 5 mmol/l KBrO₃ is observed in the potential range from +0.2 to –0.3 V vs. SCE. The peak current is very large compared to that of the Fe(III)/EDTA complex, being proportional to the concentration of iron(III) between 1.00×10^–8 and 3.58×10^–6 mol/l under optimum conditions. The relative standard deviations for 3.58×10^–7 mol/l and 1.79×10^–6 mol/l iron(III) were 1.38 and 0.54%, respectively (n=5), and the calculated detection limit was 5.2×10^–9 mol/l iron(III). The method has been applied to the determination of iron in fresh snow and rain waters.

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Spurenbestimmung von Eisen mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Das Verfahren beruht auf der Tatsache, daß in Britton-Robinson-Puffer (mit 50 mol/l HEDTA und 5 mmol/l KBrO₃) im Potentialbereich von +0,2 bis –0,3 V gegen SKE ein gut definierter puls-polarographischer Peak für Eisen(III) auftritt. Der Peakstrom ist im Vergleich zu dem des Fe(III)/EDTA-Komplexes sehr groß und ist unter optimalen Bedingungen im Konzentrationsbereich von 1,00·10^–8 bis 3,58·10^–6 mol/l der Eisen(III)-Konzentration proportional. Die relative Standardabweichung beträgt 1,38% bzw. 0,54% (n=5) für 3,58·10^–7 mol/l bzw. 1,79·10^–6 mol/l Fe(III). Die berechnete Nachweisgrenze liegt bei 5,2·10^–9 mol/l Fe(III). Das Verfahren wurde zur Eisenbestimmung in Schnee- und Regenwasser eingesetzt.

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This work was supported in part by a Grant-in-Aid for Scientific Research from Hokkaido-prefecture, 1982.     

The catalytic adsorptive stripping voltammetric determination of chromium with TTHA and nitrate

A sensitive voltammetric method is presented for the determination of trace amounts of total chromium (Cr(III) and Cr(VI)) in natural waters, employing the square wave mode. The method is based on the preconcentration of the Cr(III)-TTHA complex by adsorption at the HMDE at the potential of –1.0 V vs. Ag/AgCl. The adsorbed complex is then reduced producing a response with a peak potential of –1.29 V and the peak height of the Cr(III) reduction is measured. The catalytic action of the nitrate ions on the Cr(III)-TTHA reduction has been elucidated using cyclic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a.c. voltammetry and the potential range of adsorption was determined.Based on these investigations optimal conditions for the determination of the total chromium concentration in the range 155–2000 ng 1^–1 have been established. The determination limit is 15 ng 1^–1 and the RSD is 3.5% for chromium concentrations 200 ng 1^–1.The usefulness and wide scope of this method for reliable and highly sensitive chromium analysis down to the ultra trace levels existing in various types of natural waters is demonstrated by determinations of the total chromium content in lake, sea and rain water.     

Highly sensitive spectrophotometric determination of micro amounts of iron with chromai blue G and cetyltrimethylammonium chloride

Summary A ternary complex between iron(III), Chromal Blue G (C. I. 43835) and cetyltrimethylammonium chloride is proposed for the determination of iron (III). The stoichiometric ratio of iron (III) to Chromai Blue G is 13. Beer's law is obeyed from 0.04 to 0.4 ppm of iron; the molar absorptivity is 1.43×10⁵ l·mole^–1·cm^–1. The proposed method has been applied to the determination of iron in a magnesium alloy.

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Hochempfindliche spektrophotometrische Bestimmung von Mikromengen Eisen mit Chromctlblau G und Cetyltrimethylammoniumcblorid

Zusammenfassung Zur Bestimmung von Eisen(III) wird ein ternärer Komplex aus Eisen(III), Chromai Blue G (Farbindex 43835) und Cetyltrimethylammoniumchlorid vorgeschlagen. Das stöchiometrische Verhältnis Eisen(III): Chromal Blue G ist 13. Das Beersche Gesetz gilt von 0,04 bis 0,4 ppm Fe; der Extinktionskoeffizient ist 1,43×10⁵ l·mole^–1·cm^–1. Die vorgeschlagene Methode dient für die Bestimmung von Eisen in Magnesiumlegierungen.

     

Differential Pulse Stripping Voltammetry of Mercury(II) Ions at a Cylindrical Carbon-Fiber Microelectrode in the Presence of Au(III) Ions

The determination of Hg(II) ions in aqueous solutions containing Au(III) ions was studied using differential pulse stripping voltammetry at a cylindrical carbon-fiber (d= 30 m) microelectrode fabricated from a pitch at 2800°C. At the [Au(III)]/[Hg(II)] ratio higher than 25, the anodic voltammogram of mercury accumulated in the potential range from 0.2 to –0.2 V for 40–200 s exhibited a current peak at 0.62–0.72 V. The peak height and area were directly proportional to the concentration of Hg(II) in the range (1–1000) × 10^–10M. The results of determining Hg(II) in waters of different origin are reported.     

Electrochemical behaviour of persulphate on carbon paste electrodes modified with Prussian blue and analogous compounds

Summary Peroxodisulphate (persulphate) may be determined by direct current voltammetry (DCV) using carbon paste electrodes chemically modified with Prussian Blue, iron(III)-hexacyanoruthenate(II) or iron(III)-hexacyano-osmate(II). The determination is based on the exploitation of catalytic currents from the reduction of the modifiers. Best results are obtained for iron(III)-hexacyanoosmate(II) yielding a detection limit of 1 g O ₂ ^2– /ml (as persulphate) when using HCl (10^–2 mol/l) as supporting electrolyte and measuring in the DCV-mode. Electrodes doubly-modified with the osmium compound and a liquid anion-exchanger (Amberlite LA2) allow determinations of persulphate after preconcentration under open circuit conditions, in the presence of hydrogen peroxide and perborate, with a detection limit of 20 ng O ₂ ^2– /ml (as persulphate).     

Spectrofluorimetric determination of Ga(III) with 1-hydroxy-2-carboxyanthraquinone

Summary The fluorescent chelate formed between 1-hydroxy-2-carboxy-anthraquinone and gallium(III) at pH 3.9 has been studied spectrofluorimetrically in an ethanol-water mixture (70/30% V/V). A new method for the fluorimetric determination of gallium(III) is described. The fluorescence is monitored at 580 nm (wavelength of excitation 465 nm) and the range of application of the method is between 50 and 500 ng ml^–1. The stoichiometry of the complex has been found to be 11.

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Spektralfluorimetrische Bestimmung von Ga(III) mit 1-Hydroxy-2-carboxyanthrachinon

Zusammenfassung Ein neues Verfahren zur fluorimetrischen Bestimmung von Ga(III) mit 1-Hydroxy-2-carboxyanthrachinon bei pH 3,9 in wäßrigem Ethanol wurde ausgearbeitet. Die Fluoreszenz wurde bei 580 nm gemessen (Anregung bei 465 nm). Das Verfahren eignet sich für 50–500 ng/ml. Die Zusammensetzung der Komplexverbindung entspricht dem Verhältnis 11.

     

Photometric titrations of metal ions based on UV absorption of Bi(III)-EDTA

Summary The Bi-EDTA chelate absorbs strongly in the UV ( _max=263 nm;=10³ l. mole^–1. mm^–1) in a wavelength region where most other metal chelates, metal ions and EDTA absorb to a much smaller extent or not at all. Two applications of this phenomenon are described:the determination of Bi(III) at the 10^–5 M level in the presence of other metals, and the use of bismuth(III) as a back-titrant in the determination of traces of iron.

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Zusammenfassung Bi(III)-ÄDTA-Chelat absorbiert UV-Licht sehr stark ( _max=263 nm; =10³ l. Mol.^–1 mm^–1) in einem Wellenlängengebiet, wo andere Metallchelate, Metallionen und ÄDTA viel weniger stark oder gar nicht absorbieren. Zwei Anwendungen dieser Eigenschaft werden beschrieben. Als erste die Analyse von 10^–5-m Bi(III)-Lösungen in Anwesenheit anderer Metalle. Weiter die Anwendung von Bismuth(III) als Titrant bei der komplexometrischen Rücktitration von Eisenspuren.

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Part of this paper was presented at the VI. International Symposium on Micro-techniques, Graz, 7–11 September 1970, Austria. Mikrochim. Acta 1971/5     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Spectrophotometric Determination of Iron(III) After Separation by Adsorption of its 2-Thenoyltrifluoroacetone Complex on Microcrystalline Naphthalene

Summary A new spectrophotometric method for the determination of iron (III) after adsorption of its red TTA complex onto microcrystalline naphthalene has been developed. Iron(III) reacts with 2-thenoyltri-fluoroacetone in pH range 2.4–5.2 to form a water-insoluble 13 red complex which is easily adsorbed onto microcrystalline naphthalene from its acetone solution. The naphthalene mixture is separated, dried and dissolved in 10 ml dioxane. The red organic phase has a plateau around 480–500 nm while the reagent has no absorbance beyond 420 nm. The system obeys Beer's law over 20–120g iron(III) in 10 ml of dioxane solution or 0.4–2.4 ppm aqueous. The molar absorptivity of the complex species is 3.9×10³·l·mol^–1·cm^–1, while the sensitivity for Fe(III) extends to 1.43×10^–2 g cm^–2 for 0.001 absorbance. Samples containing 80g of iron gave a relative standard deviation of 1.23%. The effects of experimental variables such as pH, amount of reagents, shaking and digestion time, aqueous volume and diverse ions have been examined. The method has been applied to the determination of iron(III) in standard reference and environmental samples and results compared with other standard colorimetric procedures.

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Spektrophotometrische Bestimmung von Eisen(III) nach Adsorption seines 2-Thenoyltrifluoraceton-Komplexes an mikrokristallines Naphthalin

Zusammenfassung Eine neue spektrophotometrische Methode zur Bestimmung von Eisen (III) nach Adsorption seines roten TTA-Komplexes an mikrokristallines Naphthalin wurde ausgearbeitet. Fe(III) reagiert mit 2-Thenoyltrifluoraceton bei pH 2,4-5,2 unter Bildung eines roten, wasser-unlöslichen 13-Komplexes, der sich aus seiner acetonischen Lösung leicht an mikrokristallines Naphthalin adsorbieren läßt. Das Naphthalin-Gemisch wird abgetrennt, getrocknet und in 10 ml Dioxan gelöst. Die rote organische Phase hat ein Adsorptions-Plateau bei 480–500 nm, während das Reagens jenseits 420 nm nicht adsorbiert. Das System entspricht dem Beerschen Gesetz von 20–120g Fe(III) in 10 ml Dioxan-Lösung bzw. 0,4–2,4 ppm in wäßriger Lösung. Die molare Extinktion der Komplexverbindung beträgt 3,9× 10³l·mol^–1·cm^–1. Die Empfindlichkeit für Fe(III) entspricht 1,43×10^–2 g cm^–2 für 0,001 Absorptionseinheiten. Proben mit 80g Fe(III) zeigen eine rel. Standardabweichung von 1,23%. Die Wirkung variabler Versuchsbedingungen pH, Reagensmenge, Zeit, Volumen und diverse Fremdionen wurden geprüft. Das Verfahren wurde an Standardsubstanzen geprüft und seine Ergebnisse mit denen anderer kolorimetrischer Verfahren verglichen.

     

Trace determination of chromium in various water types by adsorption differential pulse voltammetry

Summary A new sensitive voltammetric method is presented for the determination of trace amounts of total chromium [Cr(III) and Cr(VI)] in natural waters. The method is based on the preconcentration of the Cr(III)-DTPA complex by adsorption at the HMDE at the potential of –1.0 V. The adsorbed complex is then reduced producing a response with a peak potential of –1.22 V and the peak height of the Cr(III) reduction is measured. The catalytic action of nitrate and bromate ions on the Cr(III)-DTPA reduction has been elucidated using cyclic voltammetry. The adsorption of chromium complexes at the HMDE was investigated using out-of-phase a. c. voltammetry and the potential range of adsorption was determined. Based on these investigations optimal conditions for the determination of the total chromium concentration in the range 20–2,000 ng/l have been established. The determination limit is 20 ng/l and the RSD is 5% for chromium concentrations 200 ng/l.The usefulness and wide scope of this new voltammetric method for reliable and highly sensitive chromium analysis down to the natural ultra trace levels existing in various types of natural waters is demonstrated by determinations of the total dissolved chromium content in river, lake, sea and rain water.

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Spurenbestimmung von Chrom in verschiedenen Wassertypen durch Adsorptions-Differentialpuls-Voltammetrie

Zusammenfassung Eine neue voltammetrische Methode zur Spurenbestimmung von Chrom [als Summe von Cr(III) und Cr(VI)] in natürlichen Gewässern wurde entwickelt. Die Methode beruht auf einer Anreicherung des Cr(III)-DTPA-Komplexes durch Adsorption an der hängenden Queck-silbertropfenelektrode beim Potential –1.0 V. Der adsorbierte Komplex wird anschließend im differentiellen Pulsmodus reduziert und die Peakhöhe beim Peakpotential –1.22 V gemessen. Die katalytische Wirkung von Nitrat- und Bromationen auf die Cr(III)-DTPA-Reduktion wurde mit der cyclischen Voltammetrie geklärt. Die Adsorption der Cr-Komplexe wurde zusätzlich mit der a.c.-Voltammetrie (kapazitive Komponente) untersucht und der Potentialbereich der Adsorption ermittelt. Aufgrund der Untersuchungen wurden die optimalen Bedingungen zur Chrombestimmung im Konzentrationsbereich 20–2000 ng/l festgelegt. Die Bestimmungsgrenze liegt bei 20 ng/l und die relative Standardabweichung beträgt 5% für Konzentrationen 200 ng/l. Die weite Anwendbarkeit der Methode für die zuverlässige und hochempfindliche Analyse von Chromspuren bis zu den natürlichen Ultraspurengehalten in verschiedenen Typen natürlicher Wässer wird an Beispielen der Analyse des gelösten Gesamtgehaltes von Chrom in Flußwasser, Seewasser, Meerwasser und Regenwasser aufgezeigt.

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Dedicated to Prof. Dr. H. Monien on the occasion of his 60th birthday

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Attached from Department of Chemistry of Warsaw University, Poland, within the scope of the joint research project on Eco-toxic Metals in the Environment     

Ion-pair adsorption film colorimetry of iron (III) in water samples and human serum

The anionic chelate of iron(III)-2,2-dihydroxyazobenzene (H₂L), [FeL₂]^–, formed 1 1 ion-pair with crystal violet cation (CV⁺), CV⁺ [FeL₂]^–, and was adsorbed on a surface of transparent polyvinyl chloride (PVC) film plasticized with di-n-octyl phthalate. Enrichment of the blue violet species of the ion-pair onto the transparent PVC film has enabled a highly sensitive and simple method for the determination of iron(III). The detection limits are 1 × 10^–8 mol dm^–3 (0.6 ppb) by spectrophotometry at 592 nm, and 4 × 10^–8 mol dm^–3 (2 ppb) by visual colorimetry. The method has been successfully applied to the determination of iron in water samples and human serum. No preparatory procedures for the separation of serum protein and other coexisting substances are required, since ion-pair adsorption process provides a new method to prevent interference of serum matrix.     

Flow procedure for ion-exchange preconcentration and on-line spectrophotometric determination of iron(III) as its thiocyanate complex

On-line ion-exchange preconcentration of iron(III) on a conventional cation exchange resin with spectrophotometric detection based on thiocyanate complexation is described. The calibration graph is linear over the range 0.01–0.2 g ml^–1 and the detection limit (3 ) is 6 ng ml^–1 for a 6-ml sample. No interference effects were detected. The recovery of iron from the resin is 95%. 12 samples h^–1 can be analysed.     

Determination of microamounts of iron by hydroxamate resin colorimetry

Summary A new, sensitive chelating ion-exchanger colorimetric method has been developed for the determination of iron at the g/l level in water, based on the direct measurement of light absorption of iron hydroxamate resin complex. In 0.2 N perchloric acid solution, iron could be rapidly, selectively and quantitatively absorbed on the hydroxamate resin. The calibration curve for iron(III) of a 25 ml solution was linear in the concentration range 8.00×10^–6 to 5.00×10^–5 M. For iron(III) with larger sample volumes, the relative detection limit was increased. Most of the metals interfered negligibly, such as Ca(II), Co(II), Cu(II), Ni(II) and Zn(II), except for higher concentration of lead(II) and mercury(II) when present at up to 400 times the concentration of iron(III). The effects of EDTA, glycine, thiourea, phosphate, nitrate and chloride on the retention of iron(III) were also examined. Only thiourea significantly influenced the retention of iron(III). The presence of sodium chloride even at a concentration of 3.5×10⁴ times that of iron(III) did not interfere at all.

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Bestimmung von Mikromengen Eisen durch Hydroxamatharz-Colorimetrie

     

Studies on the voltammetric behaviour of a 2-mercaptoimidazole containing carbon paste electrode: determination of traces of silver

The voltammetric behaviour of a 2-mercaptoimidazole (2-MI) containing carbon paste electrode was studied. When mixed to carbon paste as an electrode modifier, 2-MI can be reduced at negative potentials (–1 V vs. SCE), but it does not give a response in the potential range where Ag(0) is oxidized to Ag(I). Silver could be accumulated from 0.1 mol l^–1 acetate buffer onto a 2-MI modified carbon paste electrode without a potential applied; after medium exchange, it was reduced at –1 V vs. SCE in 0.1 mol l^–1 acetate buffer solution and determined by differential pulse anodic stripping voltammetry. With suitable preconcentration times, the detection limit was 0.1 g l^–1; a linear relation between current and concentration was found to exist within a range of 0.5 to 1000 g l^–1. In the presence of EDTA, common metal ions have no or only little effect on the voltammetric determination of silver.     

Determination of Ni and Co using 2-quinolinethiol by adsorptive voltammetry

Summary A new method for the simultaneous determination of cobalt and nickel has been developed by differential pulse adsorptive voltammetry using 2-quinolinethiol as chelate. A separation of the two peaks by 0.3 V was achieved, allowing the determination of the two metals in a wide range of concentrations. The influence of pH, nature of the supporting electrolytes, preconcentration time and applied potential was investigated. Pb, Cd, Fe, Zn and Cr do not interfere. The determination limits were 10^–8 mol/l for Co and 10^–9 mol/l for Ni. The method was applied to mussel tissues and wines.     

Determination of Iron in Natural and Drinking Waters by Stripping Voltammetry

A thick-film graphite-containing electrode modified with calomel was proposed for determining iron(III) by stripping voltammetry. Of the organic reagents under study, pyrocatechol was found to be the most sensitive in determining iron(III). The detection limit for iron(III) was 3.6 × 10⁻¹⁰ M (0.02 µg/L) at a preconcentration time of 30 s. The analytical signal from iron(III) was a linear function of its concentration in the range from 0.05 to 5 µg/L. A procedure for determining total iron in drinking and natural water was developed and certified.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 7, 2005, pp. 747–752.Original Russian Text Copyright © 2005 by Stozhko, Inzhevatova, Kolyadina.     

A new polymeric chromogenic reagent for dual-wavelength spectrophotometric determination of iron(III)

By condensing chitosan with 7-(4-formyl-phenylazo)-8-quinolinol-5-sulfonic acid (FPAQS), a new polymeric chromogenic reagent C-FPAQS has been synthesized and its properties investigated. In acidic media (pH 2.7), C-FPAQS reacts with iron(III) to yield an orange complex with a molar absorptivity of 2.8 × 10⁴ lmol^–1 cm^–1 at 420 nm, and in the meantime a negative peak at 524 nm. The apparent molar absorptivity (420–524 nm) obtained by dual-wavelength measurements is 7.9 × 10⁴lmol^–1cm^–1 which is about two times higher than that by single-wavelength measurements at 420 nm Beer's law is obeyed in the range of 0–0.8 g ml^–1 for iron(III). The developed method has been satisfactorily used to determine iron at the 0.03 to 3% (ww) level in a nylon-6 and in a soil sample. Compared to the corresponding low-molecular weight FPAQS and other chromogenic reagents, C-FPAQS has not only good sensitivity but also largely increased acid solubility and improved selectivity for iron, which may be explained by the incorporation of FPAQS into an acid-soluble polymer.     

Indirect spectrophotometric determination of chromium in aqueous samples with a novel chromogen ferene-TM

Summary An analytical procedure for the indirect determination of chromium at theg level in aqueous samples has been developed. It involves the use of a novel chromogen 3-(2-pyridyl)-5,6 bis(5-(2 furyl disulfonic acid))-1,2,4-triazine disodium salt (Ferene-TM), which forms an intensely blue tris chelate with iron(II) that absorbs at 593 nm with a molar absorptivity of 35,500 1 cm^–1 mol^–1. In an acidic system (pH1.0) chromium(VI) is reduced to chromium(III) in the presence of an excess of iron(II), which in turn decreases the absorption of the tris iron(II)-ferene-TM complex. The differential absorption data show a linear relationship for chromium(VI) in 0.01–1.0 ppm range. Many common cations and anions in micro concentration range do not influence the analytical response.

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Indirekte spektrophotometrische Bestimmung von Chrom in wärigen Lösungen mit dem neuen Farbreagens Ferene-TM

Zusammenfassung Ein Verfahren zur indirekten Bestimmung vong-Mengen Chrom in wäßrigen Proben wurde ausgearbeitet. Es beruht auf der Verwendung eines neuen Farbreagens 3-(2-Pyridyl)-5,6-bis(5-(2-furyldisulfonsäure))-1,2,4-triazin-dinatrium (Ferene-TM). Dieses bildet mit Fe(II) ein intensiv blau gefärbtes Tris-Chelat, das bei 493 nm eine molare Absorptivität von 35500 l· cm^–1·mol^–1 zeigt. Chrom(VI) wird bei pH 1,0 zu Cr(III) in Gegenwart eines Überschusses an Fe(II) reduziert, so daß die Absorption des erwähnten Tris-Chelates herabgesetzt wird. Die Absorptionswerte zeigen für 0,01 bis 1,0 ppm Cr(VI) ein lineares Verhältnis. Viele übliche Kationen und Anionen beeinflussen in Mikromengen das analytische Ergebnis nicht.

     

Spectrophotometric and titrimetric determination of gallium in minerals and ores using semimethylthymol blue

The composition, overall stability constant and molar absorptivity of the chelate of gallium(III) ion with semimethylthymol blue, SMTB, were determined spectrophotometrically in acetate buffer (pH 4.5–5). A violet Ga(SMTB) chelate was formed with logarithmic overall stability constant of 18.0±0.1 (I=0.1) and molar absorptivity of 4.25×10⁴l mol^–1cm^–1 (_max 580 nm). SMTB is proposed as a new reagent for the spectrophotometric determination of micro-molar amounts of gallium(III). The colour development depends on time, temperature, pH and buffer species. The interference of different cations, anions and organic acids on gallium(III) determination was also investigated. Beer's law was obeyed for 3.5–31.3 gGa(III)/25ml (0.14–1.25 g ml^–1). SMTB was used for the spectrophotometric determination of gallium in different grade minerals and ores and the results were of acceptable error and relative standard deviation. Comparison between the two suggested methods and atomic absorption spectrometry for Ga(III) determination was carried out.