Voltammetric Analysis of Iodide and Diffusion Coefficients Between 25 and 85°C

The oxidation wave of iodide in 0.075 mol-L^–1 H₂SO₄ was analyzed at 25, 40, 55, 70, and 85°C. The reversibility of the I₂/I^– system was checked using logarithmic transforms, half-wave potentials, and by studying I ^–1 = f(^–1/2). The limiting currents obtained enabled us to determine the diffusion coefficient of I^– using Newman's equation. These experimental results were compared with Nernst's limiting values. The Stokes–Einstein equation is not verified. Hydration numbers for I^– at different temperatures were established. An empirical equation is proposed to predict the evolution of diffusion coefficients in a sulfuric acid medium with temperature.     

Ion chromatographic determination of iodide in urine and serum using a tubular ion-selective electrode based on a homogeneous crystalline membrane

The use of a laboratory-made iodide ion-selective electrode with tubular configuration and based on a crystalline membrane (AgI/Ag₂S) as the detector for ion chromatographic determination of iodide in urine and serum is described. A CIS reversed-phase column was coated withN-cetylpyridinium chloride to prepare a low-exchange-capacity analytical column and with hexadecyltrimethylammonium bromide to prepare a concentrator pre-column. A 2.0 ml min^–1 flow rate of deionized water and 0.1 mol 1^–1 KNO₃ solution was used for the pre-concentration and for the chromatographic separation, respectively. For optimum performance of the detector a background level of iodide was added into the column effluent. A linear relationship (r = 0.9997) between tubular electrode potential (as peak height) and iodide concentration in the range 5–400 g 1^–1 and a detection limit of 1.47 g 1^–1 were obtained. The method shows good reproducibility for both peak height (2.2% RSD) and retention time (1.3% RSD). Recoveries on its application to the samples were 93.0–100.9% for urine and 91.4–106.0% for serum.     

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.     

Speciation studies by capillary electrophoresis – simultaneous determination of iodide and iodate in seawater

A capillary electrophoresis (CE) method was developed for the simple and highly-sensitive determination of iodine species in seawater. The proposed method is based on the on-capillary preconcentration of iodide and iodate using the principle of transient isotachophoresis (tITP) stacking, and direct UV detection of the separated species at 226 and 210 nm, respectively. The preconcentration procedure takes advantage of the electrokinetic introduction of the terminating ion [2-(N-morpholino)ethanesulfonate (MES)] into the capillary, that enables a longer tITP state. The appropriate conditions for the tITP step were optimized by varying the MES and sample injection time and the concentration of cetyltrimethylammonium chloride (CTAC). The latter component of the separation electrolyte (SE) was shown to strongly affect the migration and therefore the enrichment of iodide due to specific ion-association. The optimized separations were performed in 12.5 mM CTAC, 0.5 M NaCl (pH 2.4). Valid calibration is demonstrated in the range 3–60 g L^–1 iodide (R=0.9992) and 40–800 g L^–1 iodate (R=0.9994). The detection limits achieved were 0.23 g L^–1 (2 nM) for iodide and 10 g L^–1 (57 nM) for iodate. Such sensitivity and linearity thresholds allowed the reported tITP-CE system to be applied to direct speciation analysis of surface and seabed seawater. The comparison of CE results with those of an ion-chromatography (IC) technique proved that the method has acceptable accuracy.     

Spectrophotometric determination of microamounts of yttrium with 1-amino-4-hydroxyanthraquinone

Summary 1-amino-4-hydroxyanthraquinone (AMHA) is proposed as a spectrophotometric reagent for the determination of yttrium. The solution equilibria ofAMHA complexes with Y(III) have been studied spectrophotometrically in 50% (v/v) ethanol at 25°C and an ionic strength ofI=0.1 mol·dm^–3 (NaClO₄). The complexation reactions were investigated and characterized using graphical logarithmic analysis of the absorbance graphs. The composition, molar absorptivities, and stability constants of the chelates ofAMHA with Y(III) have been determined spectrophotometrically. A simple, rapid, selective, and sensitive method for the spectrophotometric determination of microamounts of Y(III) is developed based on the formation of the violet YLH⁺ complex with _max=580nm atpH 6.2(=0.98×10⁴l·mol^–1·cm^–1). Interferences and their elimination have been studied. Many foreign ions are tolerated in considerable amounts; 45–60 fold amounts of rare earths do not interfere with the determination of yttrium. In the determination of yttrium in synthetic polymetallic samples the relative error and relative standard deviation of the method were found to be better than 1 and 0.5%, respectively.

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Spektrophotometrische Bestimmung von Mikromengen Yttrium mit 1-Amino-4-hydroxyanthrachinon

Zusammenfassung 1-Amino-4-hydroxyanthrachinon (AMHA) wird als spektrophotometrisches Reagens zur Bestimmung von Yttrium vorgeschlagen. Die Gleichgewichte von Komplexen ausAMHA und Y(III) in Lösung wurden in 50% (v/v) Ethanol bei 25°C und einer lonenstärke vonI=0.1M (NaClO₄) untersucht. Die Komplexierungsreaktionen wurden durch graphische logarithmische Analyse der Extinktionskurven charakterisiert. Die Zusammensetzungen, die molaren Extinktionen und die Stabilitätskonstanten der Chelate vonAMHA mit Y(III) wurden spektrophotometrisch bestimmt. Eine einfache, schnelle, selektive und empfindliche Methode zur spektrophotometrischen Bestimmung von Mikromengen Y(III) wurde entwickelt. Sie basiert auf der Bildung des violetten YLH⁺-Komplexes mit _max=580 nm beipH 6.2 (=0.98×10⁴l·mol^–1·cm^–1). Störungen und ihre Beseitigung werden ebenfalls diskutiert. Viele Fremdionen werden in beträchtlichen Mengen toleriert; 45–60 facher Überschuß an Seltenen Erden stört die Bestimmung von Yttrium nicht. Der relative Fehler und die relative Standardabweichung der Methode bei der Bestimmung von Yttrium in synthetischen polymetallischen Proben waren besser als 1 bzw 0.5%.

     

Determination of traces of bismuth by quenching of solid-substrate room-temperature phosphorescence from morin-labeled silicon dioxide nano-particles

Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO₂) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO₂ solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (I_p) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot^–1 (sample volume 0.40 L spot^–1, corresponding to the concentration range 0.40–36.0 fg mL^–1). The regression equation of the working curve is I_p=14.86+5.279×[Bi³⁺] (ag spot^–1) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot^–1 (corresponding to a concentration of 6.5×10^–17 g mL^–1).This sensitive, reproducible and accurate method has been used for successful analysis of real samples.     

Determination of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts by electrothermal atomic absorption spectrometry after preconcentration by column solid phase extraction

Methods are described for the determination of trace and ultra trace amounts of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts. Separation and preconcentration of trace metals is achieved by a column solid phase extraction procedure using silica gel modified with derivatives of dithiocarbamates — Na-DDTC (sodium diethyldithio-carbamate and HMDTC (ammonium hexamethylene-dithiocarbamate) as column packing material. The influence of the sorbent preparation procedure on the degree of sorption of the trace analytes is examined for different pH values of the sample solution. Isobutylmethyl ketone (IBMK) is proposed as an effective eluent for quantitative elution of retained metal ions. Optimal instrumental parameters for ETAAS determination of preconcentrated elements in organic eluate are presented. Practical application of sorbents in analysis of natural waters and alkali and alkaline earth salts is demonstrated. Proposed preconcentration procedure combined with ETAAS determination of trace analytes allows the determination of 0.04 g l^–1 Cd, 0.1 g l^–1 Cr, Cu, and Mn and 0.3 g l^–1 Co, Fe, Ni and Pb in natural waters and 1.10^–7% Cd, 3.10^–7% Cr and Mn, 7.10^–7% Co, Ni and Pb and 2.10^–6% Cu and Fe in alkali and alkaline earth salts.     

Determination of trace scandium by ion-exchanger phase spectrophotometry withp-nitrochlorophosphonazo

Ion-exchanger phase Spectrophotometry withp-nitrochlorophosphonazo (CPApN) has been developed for the determination of scandium. The linear range is 1–8 g of scandium in 50 ml of solution, using 0.8 g of resin, with an apparent molar absorptivity of 2.76 × 10⁵ 1 mol^–1 cm^–1. Aluminum and rare earth elements in reasonable amounts do not interfere. The method has been applied successfully to the determination of scandium in alloys, with relative standard deviations of 2–4%.     

Rapid Determination of Mercury in Water by Stripping Voltammetry at a Gold-Modified Carbon Electrode

A procedure was developed for determining mercury in natural water by stripping voltammetry on a gold-modified carbon electrode. The concentration dependence of the anodic stripping current of mercury is linear in the range 0.02–5 g/L Hg(II). The interference of Fe(III), Cu(II), Cl^–, Br^–, I^–, and F^– ions with the determination of mercury was studied. Ozonation was used for rapid sample preparation. The detection limit for mercury was 0.02 g/L at an electrolysis time of 5 min.     

Ab initio MP2 calculations of the products of acetylene addition to HgCl2

Gas-phase reaction of acetylene with HgCl₂ resulting in -chlorovinylmercury derivatives and their interaction with Cl^– and I^– anions and KI molecule was studied by the ab initio MP2 method with the Dunning—Hay double zeta basis set and LanL pseudopotential for Hg, K, and I atoms. The reaction was shown to proceed via a -complex of acetylene and HgCl₂ (the calculated enthalpy of formation is –6.5 kcal mol^–1). According to calculations, the activation energy of formation of cis--chlorovinylmercury chloride from acetylene and HgCl₂ is 31 kcal mol^–1. Chloride and iodide anions and KI molecule are readily added to both cis- and trans-isomer of -chlorovinylmercury chloride to give stable species.     

Kinetic Determination of Iodide by the Oxidation Reaction of o-Phenylenediamine with Chloramine B

A kinetic method was developed for the determination of iodide ions. The method is based on the catalytic effect of iodide ions on the oxidation reaction of o-phenylenediamine with Chloramine B in an acidic solution and has a detection limit of 1 × 10^–4 g/mL. It was demonstrated that the method could be used for the determination of iodides in natural waters.     

Determination of the nature of the diperiodatocuprate(III) species in aqueous alkaline medium through a kinetic and mechanistic study on the oxidation of iodide ion

The nature of the diperiodatocuprate(III) (DPC) species present in aqueous alkaline medium has been investigated by a kinetic and mechanistic study on the oxidation of iodide by DPC. The reaction kinetics were studied over the 1.0 × 10^–3–0.1 mol dm^–3 alkali range. The reaction order with respect to DPC, as well as iodide, was found to be unity when [DPC] [I^–]. In the 1.0 × 10^–3–1.0 × 10^–2 mol dm^–3 alkali region, the rate decreased with increase in the alkali concentration and a plot of the pseudo-first order rate constant, k versus 1/[OH^–] was linear. Above 5.0 × 10^–2 mol dm^–3, a plot of k versus [OH^–] was also linear with a non-zero intercept. An increase in ionic strength of the reaction mixtures showed no effect on k at low alkali concentrations, whereas at high concentrations an increase in ionic strength leads to an increase in k. A plot of 1/k versus [periodate] was linear with an intercept in both alkali ranges. Iodine was found to accelerate the reaction at the three different alkali concentrations employed. The observed results indicated the following equilibria for DPC.[Cu(H₂IO₆)₂]^3- [Cu(H₂IO₆)]^- + H₂IO₆ ^3- [Cu(H₂IO₆)] + OH^- [Cu(HIO₆)]^- + H₂OA suitable mechanism has been proposed on the basis of these equilibria to account for the kinetic results.     

Microdetermination of bromate ions with antipyrine

Summary A spectrophotometric method for the micro-determination of bromate ions has been described. A red colored complex is obtained when 3 ml of 5% antipyrine, 3 ml of 60% perchloric acid and 1 ml of 0.1M sodium nitrite solution are added in a solution containing bromate ions. The maximum absorbance occurs at 525 nm. Beer's law is obeyed for solutions containing 25.0–140.0/ml of bromate ions. Sensitivity has been found to be 0.029g BrO₃ ^–/cm² for logI ₀/I=0.04 with a molar absorptivity of 2·10³ moles^–1, cm^–1. liter. As(III), Ce(IV), Fe(III), CrO₄ ^2–, Cr₂O₇ ^2–, and Cl^– interfere in the determination.

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Zusammenfassung Eine spektrophotometrische Methode zur Mikrobestimmung von Bromationen wurde beschrieben. Nach dem Zusatz von 3 ml 5%iger Antipyrinlösung, 3 ml 60% iger Perchlorsäure und lml 0,1 ·m Natriumnitrit zu einer bromathaltigen Lösung erhält man eine rot gefärbte Komplexverbindung. Deren Absorptionsmaximum liegt bei 525 nm. Lösungen mit 25,0 bis 140,0g Bromat/ml entsprechen dem Beerschen Gesetz. Die Empfindlichkeit der Reaktion beträgt 0,029g BrO₃ ^–/cm₂ für logI ₀/I=0,04 mit einer molaren Absorption von 2 · 10³ m^–1 · cm^–1 · 1. As(III), Ce(IV), Fe(III), CrO₄ ^2–, Cr²O₇ ^2– und Cl^– stören die Bestimmung.

     

Quantitative chemical analysis on paper. I

Summary A method has been proposed for the determination of small quantities of Cl^–, SCN^– and I^– in mixtures. The method is based on the use of filter paper evenly impregnated with Ag₂CrO₄. The method permits the determination of 5 to 50g of Cl^–; 15 to 100g of I^– and 10 to 150g of SCN^– with an accuracy of 1.5%.The method may also be used for determination of SCN^– alone.

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Zusammenfassung Ein Verfahren für die Bestimmung kleiner Mengen Chlorid, Rhodanid und Jodid in deren Gemischen wird vorgeschlagen. Es beruht auf der Verwendung eines mit Silberchromat gleichmäßig imprägnierten Filtrierpapierstreifens und ermöglicht die Bestimmung von 5 bis 50g Chlorid,15 bis 100g Jodid und 10 bis 150g Rhodanid mit einer Genauigkeit von 1,5%. Das Verfahren kann auch für die Bestimmung von Rhodanid allein verwendet werden.

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Résumé On a proposé une méthode pour le dosage de petites quantités de Cl^–, SCN^–, et I^– en mélanges. La méthode est fondée sur l'emploi d'un papierfiltre uniformément imprégné d'Ag₂CrO₄. Elle permet le dosage de 5 à 50g de Cl^–, 15 à 100g d'I^– et de 10 à 150g de SON^–, à la précision de 1,5%. On peut aussi utiliser la méthode pour le dosage de SCN^– seul.

     

Thermodynamics of the dissociation of ammonium ion in seawater from 5 to 40°C

The dissociation constant of NH ₄ ⁺ and the associated thermodynamic functions H° and S° in synthetic seawaters of salinity 20.31, 35.00, and 44.55 have been determined by emf measurements of cells without liquid junction over the temperature range 5 to 40°C. Cells with hydrogen electrodes and silver-silver chloride electrodes, whose standard potentials in seawater media were determined in an earlier investigation, were used. At a given temperaturet (in °C), pK _a varies linearly with the formal ionic strengthI _f (uncorrected for ion pairing) according to pK _a=pK _a ^w +(0.1552–0.0003142t)I _f where pK _a ^w is the pK in pure water. The medium effect of seawater on H° amounts to less than 200 cal-mole^–1 for a change inI _f from 0 to 0.72 mole-kg^–1, and S° is less than 1 cal-°K^–1-mole^–1 in all of the media studied, as it is in water. The observed salt effect on pK _a is in close agreement with values predicted from theories of ion-ion interactions.     

Extraction-spectrophotometric determination of iron with 2-(2′-benzothiazolylazo)-4,6-dimethylphenol

An extraction-spectrophotometric method for the determination of trace amounts of iron based on its extraction into chloroform with 2-(2-benzothiazolylazo)-4,6-dimethylphenol (BTADMP) from a pH 6.5 medium has been developed. The extracted 12 FeBTADMP complex species allow the determination of 4–30gmg of iron (=3.92×10⁴1·mol^–1·cm^–1 at 790 nm). The method is highly selective and has been applied to the determination of iron in polymineral-polyvitamin pharmaceutical products.     

Kinetics of the oxidation of iodide by copper(III)-imine-oxime complexes

Summary The copper(III)-imine-oxime complexes [Cu^III(Enio)]⁺ and [Cu^III(Pre)]⁺ {EnioH₂ =N,N-ethylene bis(isonitrosoacetylacetoneimine) and PreH₂ = N,N-propylene bis (isonitrosoacetylacetoneimine)} react very rapidly with iodide. The rate law under fixed conditions for the reaction is given by the equation: –d[Cu^III]/dt = (2k₂[I^–] + 2k₃[I^–]²)[Cu^III] The [Cu^III(Enio)]⁺ reaction was pH-independent whereas the [Cu (Pre)]⁺ reaction rate increased with increasing pH. Both the k₂ and the k₃ pathways are believed to involve one-electron transfer. An inner-sphere mechanism may operate in the pathway, first-order in [I^–].     

Spectrophotometric and derivative spectrophotometric determination of copper (II) with dithizone in aqueous phase

A Spectrophotometric and derivative Spectrophotometric study of Cu-dithizonate complex in aqueous phase in the presence of Triton X-100, a neutral surfactant, is reported. The system obeys Beer's law between 1.0 × 10^–6–9.0 × 10^–6 mol/l of Cu²⁺; detection limit is 12 ng/ml. The molar absorption coefficient, specific absorptivity and Sandell's sensitivity of the complex are 3.06 × 10⁴ 1 mol^–1 cm^–1, 0.4825 ml g^–1 cm^–1 and 2.1 × 10^–3 g cm^–2, respectively. The conditional stability constant of the 1 2 complex, calculated considering simultaneously existing equilibria, has been found to be 1.73 × 10¹¹ I² mol² (I = 0.07, pH 1.4, temperature = 10 °C). Absorption studies in the derivative mode have been carried out to determine the absorption maximum of the complex and to overcome interference due to the presence of certain metal ions. The method has been validated by determination of copper in beers, wines, human hair, goat liver and fly ash samples.