A microelectrode study of the mechanism of the reactions of silver(II) with manganese(II) and chromium(III) in sulphuric acid

The variation of the steady state limiting current for the Ag(I)/Ag(II) oxidation wave with the radius of the microdisc electrode, concentration and temperature has been used to probe the kinetics and mechanisms for the reactions of silver(II) with manganese(II) and chromium(III) in 10 mol dm⁻³ sulphuric acid. It is shown that the current density for the silver(I) mediated oxidation of manganese(II) is controlled by the diffusion of manganese(II) to the surface except for microelectrodes with radii below 5 μm. On the other hand, the current density for the mediated oxidation of chromium(III) is determined by the rate of the Ag(II)/Cr(III) reaction over a range of conditions. In contrast to the Ag(II)/water reaction, its kinetics can be fitted to a mechanism where the initial electron transfer from Cr(III) to the Ag(II) is the rate determining step.     

Selective detection of bismuth(III) and iron(II) ions with certain new reagents

Isoperthiocyanic acid (3-amino-5-thione-1,2,4-dithiazole) (I), tetraethylthiuram monosulphide ("Tetmosol") (II), eosin (III), and mercurochrome (IV) are used as new qualitative reagents for bismuth, III and IV are also used for detection of iron(II). A conc. sulphuric acid solution of I, or an acctone solution of II, when treated with bismuth in presence of potassium iodide, gives a deep red or reddish-orange precipitate, characteristic of bismuth. Bismuth in presence of III or IV gives a heavy and characteristically bright deeppink precipitate on addition of ammonia. With I, 1 mug of bismuth may be detected with a dilution limit of 1:50,000. Sb(III) and As(III) do not interfere in any of these tests. Iodides interfere only when I and II are used as reagents. Pb, Cu(II). and Fe(III) interfere with III and IV. I and II are also proposed as reagents for iodide; nitrites would interfere. III and IV, with iron(II) on addition of ammonia, produce a precipitate with highly intense green fluorescence. No other common cation [including Fe(III)] or anion interferes. The limit of detection is 3 mug ml .     

The spectrophotometric determination of vanadium after extraction as vanadium(III) ferronate by tribenzylamine

Vanadium(III) obtained by dithionite reduction of vanadium(V) can be extracted as its ferron complex with tribenzylamine in chloroform from 0.05 M sulphuric acid. Vanadium (0–5 μg ml^-1) is determined spectrophotometrically at 430 nm with a sensitivity of 0.0028 μg V cm^-2. Al(III), Co(II), Ni(II), Fe(II, III), Hg(II), Si(IV), Be(II), Mg(II), Ca(II), Sr(II), Ba(II), Cr(VI, III), W(VI), Zn(II), U(VI), Mn(II). Pb(II), Cu(II), Cd(II) and Th(IV) do not interfere; only Mo(VI), Ti(IV), Zr(IV). Bi(V) and Sn(II) interfere. A single determination takes only 7 min. The extracted complex is V^III (R-3H.TBA)₃ where R = C₉H₄O₄NSI. The method is satisfactory for the determination of vanadium in steels, alum and other samples without preliminary separations.     

Analysis of metal alloys by second-harmonic phase-selective a.c. voltammetry

Second-harmonic phase-selective a.c. voltammetry and second-harmonic a.c. anodic stripping voltammetry are shown to be particularly suitable for simultaneous determinations of elements having very close half-wave potentials (differences of <50 mV). The technique are applied to real matrices. Samples of standard materials BCS 207/2 Gunmetal, SRM 631 SPectrographic Zinc Spelter and SRM 899 (Nickel-base High-temperature Alloy) were digested with a sulphuric acid/nitric acid mixture; after dissolution, the samples were taken up in hydrochloric acid. After adjustment to 1 mol l^?1 HCl, the solutions were used directly for voltammetric measurements of Pb(II)/Sn (II), Sb(III)/Bi(III), Pb(II)/Tl(I) and In(III)/Cd(II) as appropriate. The confidence intervals of the experimental data were in agreement with the certified values for each element. Both the accuracy, expressed as percentage error, and precision, expressed as relative standard deviation, were better than 5%. The standard addition technique was found to improve the resolution of the a.c. voltammetric peaks even in the case of severe overlapping.     

Extraction of molybdenum(V) as its ferron complex with trioctylamine in chloroform from a sulphuric acid medium

A simple, rapid, and highly selective method for the separation of molybdenum from a large number of elements of analytical importance has been developed. The method is based on the extraction of a Mo(V)-ferron (7-iodo-8-hydroxyquinoline-5-sulphonic acid) complex into trioctylamine-chloroform in a sulphuric acid medium using ascorbic acid as a reductant. Many elements such as Re(VII), W(VI), U(VI), Th(IV), Cr(III), Cr(VI), V(V), Ce(IV), Ru(III), Co(II), Ni(II), Mn(II), Fe(II), Fe(III), Cd(II), Mg(II), Cu(II), Al(III), Zn(II), Pb(II), Ag(I), and As(V) are not extracted under the conditions proposed and, thus, molybdenum can be easily separated without any interference. Sulphate, chloride, nitrate, phosphate, and oxalate anions have no effect on the extraction of molybdenum. However, zirconium and palladium interfere seriously. The ratio of Mo: ferron: TOA in the extracted species is found to be 1: 1: 3 using Job’s method of continuous variations. This value has been further confirmed by the mole-ratio method. The text was submitted by the authors in English.     

Determination of low levels of uranium in solutions obtained by acid attack on phosphate rock

The uranium present in the leach liquors obtained by attack on phosphate rock with sulphuric acid can be extracted with di(2-ethylhexyl)phosphoric acid and TBP after oxidation of any iron(II), and then stripped at 65 degrees with iron(II) in 8.6M phosphoric acid. The uranium is finally determined with arsenazo III.     

Enantioselective,Potentiometric Membrane Electrodes for the Determination of L‐Pipecolic Acid in Serum

L ‐Pipecolic acid is a marker for peroxisomal disorders. Three enantioselective, potentiometric membrane electrodes were designed for the enantioanalysis of L ‐pipecolic acid. These electrodes are based on carbon paste impregnated with different maltodextrins (DE: 4.0–7.0 (I), 13.0–17.0 (II) and 16.5–19.5 (III), respectively) as chiral selectors and they can be used reliably for enantiopurity assay of L ‐pipecolic acid using a potentiometric method in the concentration ranges of 10^?8–10^?3, 10^?8–10^?5 and 10^?10–10^?6 mol/L for the maltodextrins I, II and III, respectively, based electrodes, with very low detection limits (magnitude orders of 10^?9 for I and II, respectively and 10^?12 mol/L for III). The proposed electrodes can be successfully applied for the enantioanalysis of L ‐pipecolic acid in serum samples.     

Spectrophotometric determination of palladium using 4-methyl-l ,2-cyclohexanedionedioxime

A procedure for the determination of palladium with 4-methyl-1,2-cyclohexanedionedioxime by an extraction -spectrophotometric method has been developed. Interference by coppcr(II), cobalt(Il), iron(II), or iron(III) can be eliminated by suitable masking agents. Ruthenium(III) must be absent or separated prior to the determination of palladium. The molar absorptivity of the bis(4-methyl-1,2-cyclohexanedionedioximato-N,N') palladium(II) complex has been calculated and found to be 1.51?10⁴ 1/moles-cm in chloroform at 280 mμ.     

Determination of cerium in minerals with sulphanilic acid

Cerium can be determined colorimetrically in minerals with sulphanilic acid. Cerium(III) ions are oxidized with silver(II) in 1-7% sulphuric acid. Sulphanilic acid is oxidized by cerium(IV) ions in 20% sulphuric acid. The absorbance is determined at 540 nm. In the presence of maganese or chromium, cerium can be separated by precipitation as the oxalate. Lanthanum can be used as a gathering agent if necessary.     

Synthesis and characterization of silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene and its adsorption of transition metal ions from aqueous solutions

The present study was undertaken to develop a novel adsorbent for heavy metal ions, and this paper presents the synthesis and characterization of a composite material-silica gel microspheres encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) with a core-shell structure. SG-PS-azo-SA was used to investigate the adsorption of Mn(II), Co(II), Ni(II), Fe(III), Hg(II), Zn(II), Cd(II), Cr(VI), Pd(II), Cu(II), Ag(I), and Au(III) from aqueous solutions. The results revealed that SG-PS-azo-SA has better adsorption capacity for Cu(II), Ag(I) and Au(III). Langmuir and Freundlich isotherm models were applied to analyze the experimental data, the best interpretation for the experimental data was given by the Langmuir isotherm equation with the maximum adsorption capacity for Cu(II), Ag(I), and Au(III) at 1.288 mmol g⁻¹, 1.850 mmol g⁻¹ and 1.613 mmol g^t-1, respectively. Thus, silica gel encapsulated by salicyclic acid functionalized polystyrene (SG-PS-azo-SA) is favorable and useful for the removal of Cu(II), Ag(I) and Au(III) metal ions.     

The masking effect of iron(III) on the interference from nickel and copper in the determination of tellurium by hydride generation/atomic absorption spectrometry

Iron(III) can minimize the serious interferences from copper(II) and nickel(Il) on the determination of tellurium by hydride generation/atomic absorption spectrometry. The optimal concentrations were found to be 1 g l^?1 and 2 g l^?1 Fe (III) in 4.0 mol l^?1 HCl in presence of nickel (II) and copper (II), respectively. The signals were only 25 % lower in a solution of 1.6 g 1^?1 Ni(II) than for a nickel-free solution. For copper (II), reasonable sensitivity was retained in the presence of 100 mg l^?1 Cu(II).     

Photocrosslinkable polyesters with conjugated double bonds: Reciprocity effect in laser recording

The reciprocity effect under intense illumination was studied with photocrosslinkable polyesters of p-phenylenebis(α-cyanobutadiene carboxylic acid) (I), m-phenylenebis(α-cyanobutadiene carboxylic acid) (II), and p-phenylenebis(acrylic acid) (III), with an argon ion laser as a light source. The reciprocal sensitivities of I, II, and III were 5.0, 1800, and > 10⁵ mJ/cm², respectively. II and III required sensitization to enhance their sensitivities to a level at which reciprocity effects could be measured. I obeyed the reciprocity law over a wide range of exposure times from seconds to microseconds. Both II′, a copolyester of II, and III showed a dramatic decrease of sensitivity in high-intensity/short-time exposure when sensitized by 9,10-phenanthraquinone and pyrylium salts.     

Über die Zersetzlichkeit komplexer Metallcyanide bei der Cyanidbestimmung in Abwasser

Serial studies on the behaviour of simple and complex cyanides against the attack of dilute sulphuric acid within the determination of “total cyanide” in waste water resulted in the cyanide complexes of zinc, cadmium, copper, nickel, iron(II) and iron(III) being decomposed quite rapidly by dilute sulphuric acid in the concentration range of ≦ 100 mg CN-/l. Consequently, in such cases the total amount of cyanide can be determined in the first 25 ml of the distillate.     

Chemical reduction and spectrophotometric determination of silver, copper and nickel

Silver(I), copper(II) and nickel(II) can be reduced to the metallic state by formaldehyde at pH 11, chromium(II) in 2.5M sulphuric acid, and borohydride at pH 5.5-6.0, respectively. Reoxidation of these metals with iron(III) in the presence of Ferrozine enables their determination at concentration below 1 mug/ml by measurement of the absorbance of the iron(II)-Ferrozine complex at 562 nm, with a precision better than 3%. The apparent molar absorptivities for silver, copper and nickel are 2.78 x 10(4), 5.56 x 10(4) and 5.58 x 10(4) l.mole(-1).cm(-1), respectively. The average thickness of silver films on glass surfaces can be determined in the way.     

Cacotheline as an oxidimetric reagent. Determination of Sn(II), Cu(I), Ti(III), Fe(II), V(II) and V(III)

Summary Sn(II), Ti(III), Cu(I), Fe(II), V(III) and V(II) can be titrated potentiometrically with cacotheline in 1–4M hydrochloric acid, 0.5–2M hydrochloric acid, 0.5–1.5M sulphuric acid in presence of 4 ml of 10% EDTA solution in a total volume of 50 ml, 9–10M phosphoric acid, 4–8M acetic acid and 3–8M acetic acid respectively. Cacotheline can be used for the assay of tin plate and solder. The cacotheline undergoes a 2-electron reduction reaction. A cacotheline solution (0.005M) in 0.02M hydrochloric acid is fairly stable for several months. The conditional redox potentials of cacotheline have been determined in sulphuric, phosphoric and acetic acid medium.

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Kakothelin als oxydimetriscbes Reagens. Bestimmung von Sn(II), Cu(I), Ti(III), Fe(II), V(II) und V(III)

Zusammenfassung In 1–4M Salzsäure, in 0,5–2M Salzsäure, 0,5–1,5M Schwefelsäure in Gegenwart von 4 ml 10%iger EDTA-Lösung in einem Gesamtvolumen von 50 ml, in 9–10M Phosphorsäure, in 4–8M Essigsäure bzw. in 3–8M Essigsäure kann man die genannten Kationen potentiometrisch mit Kakothelin titrieren. Dieses eignet sich auch für die Untersuchung von Lötzinn. Kakothelin erleidet dabei eine 2-Elektronen-Reduktions-Reaktion. Seine 0,005M Lösung in 0,02M Salzsäure ist einige Monate beständig. Sein Redoxpotential in Schwefelsäure, Phosphorsäure bzw. Essigsäure wurde bestimmt.

     

Mechanistic study of cerium(IV) oxidation of antimony(III) in aqueous sulphuric acid in the presence of micro amounts of manganese(II) by stopped flow technique

The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric acid medium. A minute amount of manganese(II) (10⁻⁵ mol dm⁻³) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations. The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst are Ce(SO₄)₂, [Sb(OH)(HSO₄)]⁺ and [Mn(H₂O)₄]²⁺, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed and reaction constants involved have been determined.     

The application of strongly oxidizing agents in flow injection analysis : Part 2. Manganese(III)

The application of manganese(III) as a powerful oxidizing agent in flow injction analysis is described. Manganese(III) is generated electrochemically in the flowing system at a working electrode consisting of a packed bed of gold powder. Spectrophotometric detection is used at 490 nm, where manganese(III) in sulphuric acid solution absorbs strongly. Undr the experimental conditions, the generation of manganese(III) can be accompanied by generation of manganese(IV) and permanganate; manganese(III) alone can be generated by a proper selection of the generating current and the flow rate. Results are presented for the determinatin of various organic and inorganic substances by means of manganese(III), usually at concentrations in the 10^?4—10^? mol l^?1 range. Unlike permanganate and manganese(IV), manganese(III) does not react with chloride, so that oxidizable compounds can be determined in the presence of large amounts of this species.     

Manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid medium: a kinetic and mechanistic study

The manganese(II) catalysed oxidation of glycerol by cerium(IV) in aqueous sulphuric acid has been studied spectrophotometrically at 25 °C and I = 1.60 mol dm⁻³. Stoichiometry analysis shows that one mole of glycerol reacts with two moles of cerium(IV) to give cerium(III) and glycolic aldehyde. The reaction is first order in both cerium(IV) and manganese(II), and the order with respect to glycerol concentration varies from first to zero order as the glycerol concentration increases. Increase in sulphuric acid concentration, added sulphate and bisulphate all decrease the rate. Added cerium(III) retards the rate of reaction, whereas glycolic aldehyde had no effect. The active species of oxidant and catalyst are Ce(SO₄)₂ and [Mn(H₂O)₄]²⁺. A mechanism is proposed, and the reaction constants and activation parameters have been determined.     

Hydrogen peroxide formation upon oxidation of oxalic acid in presence and absence of oxygen and of manganese(II)--III. Iron(III) and copper(II) as retarders

The formation of considerable amounts of hydrogen peroxide upon the slow addition of various oxidizing agents to oxalic acid in dilute sulphuric acid in the presence of oxygen and Mn(II) is greatly retarded in the presence of Fe(III) or Cu(II). With hydrogen peroxide as oxidizing agent and a trace of Fe(II) there is considerable decomposition of peroxide, under a nitrogen atmosphere, after a few hours at 25 degrees in light (from a tungsten lamp), and less decomposition in the dark. This decomposition is decreased by Mn(II) and also when the original mixture contains Fe(III). With oxygen as the oxidizing agent Fe(II) is about 100 times as effective an inhibitor of peroxide formation as Fe(III). With all oxidizing agents used, Cu(II) is some 6-10 times more effective as a retarder than Fe(III). The inhibition is accounted for by the reaction Fe(III) [or Cu(II)] + CO(-)(2) --> Fe(II) [or Cu(I)] + CO(2).     

2-Nitrodiphenylamine as a versatile high-potential reversible oxidation-reduction indicator

The use of 2-nitrodiphenylamine as a reversible indicator has been investigated in the titration of iron(II) with cerium(IV) sulphate, potassium dichromate and sodium vanadate in sulphuric acid media. Accurate results can be obtained with cerium(IV) sulphate in 0.5–5.0 M acid, with potassium dichromate in 5.0–7.0 M acid, and with sodium vanadate in 5.0–7.5 M acid. With cerium(IV) sulphate the titrations are preferably conducted in 2.0 M sulphuric acid or in a 1.0 M. sulphuric acid-1.0 M pechloric acid medium. Tungstic acid, acetic acid, arsenic(III) and manganese(II) do not interfere. In titrations of iron(II) with dichromate and vanadate, the colour changes at the end-point are much more vivid with 2-nitrodiphenylamine than with ferroin.