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.

---

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.

---

---

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

Spectrophotometric determination of iron after separation of its 9,10-phenanthrenequinone monoximate on microcrystalline naphthalene

A sensitive and selective spectrophotometric method has been developed for the determination of iron as Fe(II) or Fe(III) using 9,10-phenanthrenequinone monoxime (PQM) as the complexing agent. Fe(II) and Fe(III) react with PQM to form coloured water insoluble complexes which can be adsorbed on microcrystalline naphthalene in the pH ranges 3.7–6.2 and 2.0–8.4, respectively. The solid mass consisting of the metal complex and naphthalene is dissolved in DMF and the metal determined spectrophotometrically by measuring the absorbances Fe(II) at 745 nm and Fe(III) at 425 nm. Beer's law is obeyed over the concentration range 0.5–20.0 g of iron(II) and 20–170.0 g of Fe(III) in 10 ml of DMF solution. The molar absorptivities are 1.333 × 10⁴ 1 · mole^–1 · cm^–1 for Fe(II) and 2.428 × 10³1· mole^–1 · cm^–1 for Fe(III). The precision of determination is better than 1%. The interference of various ions has been studied and the method has been employed for the determination of iron in various standard reference alloys, bears, wines, ferrous gluconate, human hair and environmental samples.     

Sorption–Desorption Photometric Determination of Trace Iron in Sodium, Potassium, and Ammonium Thiocyanates Using Polyurethane Foams

A reagent-free sorption photometric method for determining trace iron(III) in alkali-metal and ammonium thiocyanates was developed. The method consists in the adsorption of iron(III) thiocyanate complexes on polyurethane foams at pH 2–3 followed by the desorption of complexes with acetone and a measurement of the absorbance of solutions. The analytical range for iron was 0.5–20 g in a 0.2–2.5-g portion of salt. The determination limit and relative standard deviation were 2 × 10^–5% and 20–30%, respectively (n= 3; P= 0.95). The specific feature of the determination is that an additional photometric reagent is not introduced in the solution of the salt to be analyzed, because thiocyanate, that is, the matrix component of the test sample, acts as such a reagent.     

Stability constants of iron(III) borate complexes

The ultraviolet absorbance data from experiments conducted at constant pH and total iron concentration but variable B(OH)₃ concentration were used to determined the stability constants of FeB(OH) ₄ ²⁺ and Fe[B(OH)_{4 2} ⁺ at 25°C and an ionic strength of 0.68. The estimates obtained were *₁ = 1.0 ± 0.2 × 10^–2 and *₂ = 2 ± 1 × 10^–5, respectively (uncertainties are two times the standard error of the estimates). A calculation of the extent of iron(III) borate formation in ocean water at pH 8.2 shows that iron(III) borates are not a significantly large component of iron(III) speciation in seawater.     

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.

---

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.

     

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.

---

Bestimmung von Mikromengen Eisen durch Hydroxamatharz-Colorimetrie

     

Spectrophotometric determination of microquantities of Carbidopa using the Carbidopa-iron(III)-phenylfluorone ternary complex in micellar medium

Summary A new analytical method for the spectrophotometric determination of Carbidopa (CBDA), either in pure form or in tablets is described. The method is based on a ternary complex formation between CBDA, iron(III) and phenylfluorone (Phfl) in the presence of Tween 20 as a surfactant. At the optimum pH 9.55, the ternary complex shows an absorption maximum at =636 nm, with an apparent molar absorptivity of 1.098×10⁵ l mol^–1 cm^–1 and a Sandell's sensitivity of 2.22 ng cm^–2. The solution of the ternary complex obeys Beer's law in the concentration range of 0.1–3.0 ppm of CBDA. The correlation coefficient was found to be r=0.9999. Results obtained by application of the proposed method and the B.P. 1988 official one were in good agreement and a statistical comparison by means of the Student's t-test as well as by the variance ratio F-test shows no significant difference between the two analytical methods.     

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.     

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.     

Application of a bismuth film electrode to the voltammetric determination of trace iron using a Fe(III)–TEA–BrO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> catalytic system

A sensitive catalytic voltammetric method for determining trace iron at a bismuth film electrode (BiFE) is described. The method is based on the cathodic reduction of the Fe(III)–triethanolamine (TEA) complex to Fe(II). It has been proved that the addition of KBrO₃ causes rapid oxidation of Fe(II) and TEA, and therefore results in a large increase in the analytical signal from Fe(III) when TEA is placed in alkaline solution. When TEA was present in the solution, operating the BiFE under optimized conditions yielded a stable catalytic voltammetric response for iron, with high sensitivity (0.88 A M^–1), good precision (RSD=3.9%) and a low detection limit (7.7×10^–9 M), obtained without any preconcentration procedure. Possible interferences from the coexisting ions and surface-active substances were investigated. Finally, the method was applied with satisfactory results to the determination of iron in certified reference river water samples.     

Spectrofluorimetric determination of trace amounts of Tb(III) using acetylacetone in ethanol solution

Summary The spectrofluorimetric determination of terbium(III) in ethanol (95%) solution of acetylacetone (3×10^–4 mol/l) was studied. Intensive fluorescence of terbium(III) (=545 nm) was observed after excitation of the system (=310 nm). The method proposed is satisfactory for the determination of terbium(III) in the range of 4 to 40 ng/ml (2.5×10^–8 to 2.5×10^–7 mol/l). The effect of other rare earths, common metal ions and anions upon the intensity of the fluorescence emitted by terbium(III) is discussed.

---

Spektrofluorimetrische Bestimmung von Tb(III)-Spuren mit Acetylaceton in Ethanollösung

     

Spectrophotometric determination of trace amounts of iron(III) by extraction of mixed-ligand iron-tartrate-purpurin or iron-NTA-purpurin complex

Summary Spectropbotometric Determination of Trace Amounts of Iron(III) by Extraction of Mixed-Ligand Iron-Tartrate-Purpurin or Iron-NTA-Purpurin Complex A selective method is described for the determination of microgram amounts of iron(III) by means of its reaction at pH 9.0 with purpurin (1,2,4-trihydroxyanthraquinone) and tartrate or NTA and extraction into methyl isobutyl ketone. The molar absorptivity of the 112 iron(III)-auxiliary ligand-purpurin complex is 4.8×10⁴ 1·mole^–1·cm^–1 at 595 nm. Beer's law is obeyed from 0.05 to 0.25 ppm of iron in the aqueous phase. Procedures for determination of iron in tartrate or NTA medium, and fluoride-tartrate-NTA medium are given. The method is suitable for determining iron in Zn metal, W metal, NTA, drinking water, wines, urine and tartrates.     

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.

---

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.

     

Flow-Injection Methods for Determining Europium in Mixtures of Lanthanides(III)

Possible approaches to the flow-injection determination of europium(III) in the presence of other lanthanides are studied. One of the approaches is based on the direct amperometric detection of europium(III) in a flow-injection system with a glassy-carbon electrode at a potential of –0.85 V (against a saturated calomel electrode). The linear calibration range is 5.0 × 10^–5–5.0 × 10^–4M of europium, and the limit of detection is 1.8 × 10^–5M (2.8 g/mL). The throughput capacity is 90 h^–1for a sample volume of 600 L. Another approach involves the online reduction of europium(III) to europium(II) in a flow Jones mini-reductor filled with amalgamated zinc, followed by the spectrophotometric detection of europium(II) using redox reactions between europium(II) and iron(III) in the presence of 1,10-phenanthroline, molybdophosphoric acid, or Methylene Blue. In the latter case, the calibration curve is linear in the range 0–5.0 × 10^–6M europium(III), the limit of detection is 9.0 × 10^–8M (0.014 g/mL). The throughput capacity is 180 h^–1for a sample volume of 200 L. The performance parameters of the proposed flow-injection methods are estimated using the analysis of artificial mixtures and dissolved samples of samarium(III) oxide and lanthanum(III) fluoride containing europium impurities as an example.     

Spectrophotometric and derivative spectrophotometric study of the reaction of palladium (II) and rhodium (III) with 5-(3,4-methoxyhydroxybenzylidene)rhodanine and cationic surfactants

Spectrophotometric and derivative spectrophotometric methods for the determination of Pd(II) and Rh(III) are proposed. Pd(II) forms with 5-(3,4-methoxyhydroxybenzylidene)rhodanine [3,4-MHBR], in the absence and presence of cetylpyridinium bromide [CPB], 14 binary and 134 ternary complexes having molar absorptivities of 5.77 × 10⁴ and 7.46 × 10⁴ M ^–1cm^–1 at 525 and 530 nm, respectively. Rh(III) forms a 14 complex with 3,4-MHBR in the presence of cetyltrimethylammonium bromide [CTAB], which gives a maximum absorbance at 445 nm with a molar absorptivity of 5.13 × 10⁴ M ^–1cm^–1. Derivative spectrophotometric methods are employed for the determination of Pd(II) and Rh(III) at ng ml^–1 levels utilizing these complexes. Under the optimum conditions the calibration lines for Pd(II) and Rh(III) determination fit the equations d⁴ A/d⁴ = 1.10 × 10⁶ [Pd] – 0.018 (r = 0.9967) and d⁴ A/d⁴ = 2.25 × 10⁶ [Rh] + 0.03 (r = 1.0426) and have detection limits of 5.6 and 1.2 ng ml^–1, respectively. The influences of experimental variables and foreign ions are studied. The methods are free of interference from most common metal ions and anions. The results of the analysis of some synthetic mixtures of Pd(II) and Rh(III) are reported.     

Spectrophotometric determination of iron in aluminium metal and some non-ferrous alloys

A new, sensitive and selective spectrophotometric method is suggested for the determination of traces of iron(III) based on complex formation with hematoxylin in presence of cetyltrimethylammonium bromide (CTAB). Addition of CTAB shifted the absorption maximum of the iron-hematoxylin complex from 630 to 640 nm and increased its molar absorptivity from 9.88 × 10⁴ to 1.16 × 10⁵ 1·mol^–1·cm^–1. The method adhered to Beer's law up to 0.4 and 0.2 g/ml of iron in presence and absence of CTAB, respectively. The corresponding values of Sandell's sensitivity were 0.5 and 0.6 ng·cm^–2. The effect of reagent and surfactant concentrations, pH and standing time were investigated. EDTA, tartrate and sodium fluoride were used as masking agents for most of the interfering ions. The method was successfully used for the determination of iron in aluminium metal and some non-ferrous alloys.     

Studies on the voltammetric behaviour of salicyl fluorone and gallium-salicyl fluorone complex

In the NH₄Cl supporting electrolyte, within the pH range from 1 to 5, an irreversible adsorptive reducing wave of salicyl fluorone(SAF) was obtained. The electrode process was verified as follow: On the surface of mercury electrode, the adsorption of SAF obeys Frumkin isotherm.In 0.2 mol/l potassium hydrogen phthalate/HCl buffer solution, at pH 3.0, the sensitive adsorptive complex wave of Ga-SAF was obtained by linear sweep voltammetry. The composition of the electroactive complex was determined as Ga:SAF = 11. The peak height of the complex is proportional to the concentration of Ga(III) in the range of 1.5 × 10^–9 to 6.0 × 10^–7 mol/l, the detection limit is 1.0× 10^–9 mol/l. The proposed method has been applied to the determination of gallium content in aluminium alloys.     

Analytical separation of antimony(III) from bismuth(III), lead(II), gallium(III), thallium(III), tellurium(IV) and tin(IV) with cyanex 302

A method is proposed for the separation of antimony(III) (100–400 g) from bismuth(III), lead(II), gallium(III), thallium(III), tellurium(IV) and tin(IV) from an aqueous solution of pH 0.5–1.5 using 8×10^–3–1×10^–2 mol dm^–3 cyanex 302 dissolved in toluene as an extractant. The antimony is stripped from the cyanex phase with water and determined spectrophotometrically with iodide. Various experimental parameters are optimized and the probable 13 stoichiometry of the extracted species is evaluated. The method is applicable to the analysis of alloys and pharmaceutical samples. The separation and determination take only 20 min.     

On the mechanism of racemisation of dichlorobis(ethylenediamine)-metal chlorides [metal = cobalt(III) or chromium(III)] in the solid state

Summary In the solid state l-cis-[M(en)₂Cl₂]Cl [M=cobalt(III) or chromium(III)] undergoes thermal racemisation smoothly at 158 °C without anycis-trans interconversion. The values of k_rac, H and S are 6 × 10^–6s^–1, 218 kJM^–1 and 156.1 JK^–1M^–1 for the cobalt(III) complex and 3.5 × 10^–5s^–1, 229.7 kJM^–1 and 197.9 JK^–1M^–1 for the chromium(III) complex, respectively. The results are only in accord with a rhombic twist mechanism of the type originally proposed by Ray and Dutt for [M(AA)₃] complexes.     

Determination of Ionol by Voltammetry and Coulometric Titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10^–4 to 1.0 × 10^–2 M (RSD = 9%) and from 3.0 × 10^–5 to 4.0 × 10^–3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10^–4 and 1.0 × 10^–5 M, respectively. The detection limit in coulometric titration was 20 g/mL.