Thallimetric oxidations-V Titrimetric and spectrophotometric determination of hydrogen peroxide

Titrimetric and spectrophotometric methods have been developed for the determination of hydrogen peroxide at mmole and mumole levels respectively. In these methods thallium(III) is used as the oxidant and the reduced thallium(I) is determined oxidimetrically with potassium bromate in the titrimetric method and by measuring the absorbance of thallium(III) at 260 nm in the presence of 0.1M hydrochloric acid and 1M perchloric acid in the spectrophotometric method. Photochemical redox methods for the estimation of hydrogen peroxide in the presence of a number of diverse ions are described.     

Titrimetric and Spectrophotometric Methods for the Determination of Glyoxal and Analysis of Ternary Mixtures of Its Oxidation Products

Using thallium(III) as an oxidant, we developed titrimetric and spectrophotometric methods for the estimation of glyoxal at mmole and µmole levels, respectively. In the titrimetric method, thallium(I) formed is determined oxidimetrically with potassium bromate. In the spectrophotometric method, the absorbance of thallium(III) at 260 nm in the presence of 0.1 mol/L sodium chloride and 1.0 mol/L perchloric acid is measured. A plausible mechanism for the oxidation of glyoxal is proposed. Based on the selective oxidation of the probable oxidation products of glyoxal (namely, glyoxylic acid, formic acid, and oxalic acid), a convenient titrimetric method is described for analyzing ternary mixtures of these products.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 8, 2005, pp. 806–810.Original English Text Copyright © 2005 by Siva Rao, Prasada Rao.The text was submitted by the authors in English.     

Sequential oxidimetric determination of thallium(I) and (III)

The reaction between thallium(III) and oxalic acid in sulphuric acid medium has been investigated. Spectrophotometric results show that thallium(III) can be quantitatively reduced to thallium(I) with oxalic acid in aqueous medium when heated to near boiling point. Conditions for the estimation of the excess of oxalic acid with cerium(IV) sulphate in the presence of thallium(I) and for the estimation of a mixture of thallium(I) and thallium(III) have been investigated. The method is simpler than many other redox methods reported for the determination of thallium(III) and is free from many interferences encountered in these titrations. The reagents are cheap and quite stable.     

Multicomponent determinations in flow-injection systems with square-wave voltammetric detection using the kalman filter

Electrochemical detection in flow-injection systems has become increasingly popular. Scanning electrochemical methods of detection have received less attention. The use of rapid square-wave voltammetric detection for flow injection is described. Experimental considerations for the use of square-wave voltammetric detection are discussed. Results of the application of this combination are shown for dopamine in 0.28 M sulfuric acid, and for lead(II) and thallium(I) in 0.9 M nitric acid. A linear, recursive estimator known as the Kalman filter is used to resolve overlapping responses. Empirical models consisting of the square-wave voltammetric responses of single species are used. Results are shown for mixtures of lead(II) and thallium(I) in 0.9 M nitric acid.     

Photochemical thallimetric oxidations-estimation of formic acid

A simple, rapid and convenient redox method has been developed for the estimation of formic acid. Formic acid is photochemically oxidized with thallium(III) in the presence of bromide as catalyst, and the thallium(I) formed is determined by titration with potassium bromate. The procedure can also be used for the estimation of thallium(III) with formic acid as reductant.     

Determination of thallium(III) by use of a mercury reductor

A convenient method has been developed for the determination of thallium(III) by using a mercury reductor. Thallium(III) is reduced to thallium(I) in 0.5–4N hydrochloric or sulphuric acid medium and the determination is completed by oxidative titration with potassium bromate. The method is extended to analysis of thallium(III)-thallium(I) and thallium(III)-iron(III) mixtures.     

Dichromate titration of thallium(I)

The formal redox potentials of the thallium(III)-thallium(I) couple in different acids of varying strengths are reported. The minimum concentration of hydrochloric acid required for a direct titration of thallium(I) with potassium dichromate is 5M. Thallium(I) can be titrated directly with the primary standard oxidant, potassium dichromate, at room temperature, with ferroin as indicator, in 6M hydrochloric acid. Atmospheric oxygen must be excluded.     

Thallimetric photochemical oxidation in titrimetric and spectrophotometric methods for the analysis of mixtures of oxalate and hydrogen peroxide

Thallium(III) in the presence of bromide photochemically oxidizes oxalate and hydrogen peroxide, whereas in the presence of a large excess of chloride, only oxalate is oxidized. Two procedures are based on these observations. In the titrimetric method (applied to mmol amounts of analytes) the thallium(I) formed is determined with bromate. In the spectrophotometric procedure (μmol amounts of analytes) unreduced thallium(III) is determined at 260 nm. In each case measurements are made after reaction under both conditions, so that both analytes can be determined.     

Resolution of strongly overlapped responses in square-wave voltammetry by using the Kalman filter

Various approaches have been proposed for resolving overlapped voltammograms. Such methods have become incresingly important since the advent of small computers and commercial electrochemical instrumentation capable of rapid-scan techniques. The combination of high-resolution, rapid-scan square-wave voltammetry and a linear, recursive estimator known as the Kalman filter is described. Results of the application of this combination to mixtures of thallium(I) and lead(II) in 0.9 M nitric acid are shown. Practical considerations for filter usage such as the choice of models, variances, and initial guesses are discussed, as are limits to the filter. With the Kalman filter, it was possible to quantify thallium in solutions containing as much as a 30-fold excess amount of lead, and it was possible to quantify lead in solutions containing a 60-fold excess amount of thallium. The filter is thus a useful tool for use with empirical models in multicomponent quantitation.     

Extraction separation of thallium (III) from thallium (I) with n-octylaniline

A novel method is developed for the extraction separation of thallium(III) from salicylate medium with n-octylaniline dissolved in toluene as an extractant. The optimum conditions have been determined by making a critical study of weak acid concentration, extractant concentration, period of equilibration and effect of solvent on the equilibria. The thallium (III) from the pregnant organic phase is stripped with acetate buffer solution (pH 4.7) and determined complexometrically with EDTA. The method affords the sequential separation of thallium(III) from thallium(I) and also commonly associated metal ions such as Al(III), Ga(III), In(III), Fe(III), Bi(III), Sb(III) and Pb(II). It is used for analysis of synthetic mixtures of associated metal ions and alloys. The method is highly selective, simple and reproducible. The reaction takes place at room temperature and requires 15-20 min for extraction and determination of thallium(III).     

Thallimetric oxidations-IV Estimation of malonic acid

Malonic acid is quantitatively oxidized to carbon dioxide and water when refluxed for 120 min in sulphuric acid medium (concentration 1.5M) with at least four times as much thallium(III) as that stoichiometrically required for complete oxidation. The thallium(I) formed is estimated bromatometrically in the presence of 1.5-2M hydrochloric acid, with Methyl Orange as indicator. The indicator correction is negligible. The relative mean deviation is 0.2%. Possible side-reactions and their suppression are discussed.     

Determination of phosphite,hypophosphite, tellurium and mercury

A new catalytic oxidation procedure, involving the use of a cerium(IV) sulfate reagent in perchloric acid with a mixed silver(I)—manganese(II) perchlorate catalyst, has been developed for the determination of phosphite, hypophosphite, and tellurium. By this method 15—100 mg of phosphite, 5—35 mg of hypophosphite, and 10—105 mg of tellurium may be determined with standard deviations of ±0.17, ±0.32, and ±0.21% respectively. A direct titration procedure for mercury(I) is described using a ceric perchlorate solution as titrant with the mixed catalyst system. Samples from 65–510 mg may be analyzed with a standard deviation of ±0.36%.     

Detection of hypophosphite, phosphite, and orthophosphate in natural geothermal water by ion chromatography

Current doctrine states that phosphorus is incorporated into cells in the pentavalent(V) oxidation state as orthophosphate. However, recent studies show that microorganisms contain enzymes used to metabolize reduced forms of phosphorous, including phosphite(III) and hypophosphite(I), which suggests that there is a natural source for these chemical species. This paper will discuss suppressed conductivity ion chromatography methods developed to detect hypophosphite, phosphite, and orthophosphate in a geothermal water matrix containing fluoride, chloride, bromide, nitrate, hydrogen carbonate and sulfate. All peaks were clearly resolved, and calibrations were linear with estimated 3sigma detection limits of 0.83, 0.39, and 0.35 microM for hypophosphite, phosphite, and orthophosphate, respectively.     

A Photochemical redox method for the estimation of thallium(III)

A convenient photochemical redox method for the estimation of thallium(III) by reduction with oxalic acid followed by oxidation of thallium(I) with potassium bromate has been developed. The reduction is carried out in the presence of small concentrations of chloride and bromide as catalysts.     

The development of iodide-based methods for batch and on-line determinations of phosphite in aqueous samples

Recent developments in the field of microbiology and research on the origin of life have suggested a possible significant role for reduced, inorganic forms of phosphorus (P) such as phosphite [HPO₃²⁻, P(+III)] and hypophosphite [H₂PO₂⁻, P(+I)] in the biogeochemical cycling of P. New, robust methods are required for the detection of reduced P compounds in order to confirm the importance of these species in the overall cycling of P in the environment. To this end, we have developed new batch and flow injection (FI) methods for the determination of P(+III) in aqueous solutions. The batch method is based on the reaction of P(+III) with a mixed-iodide solution containing tri-iodide (I₃⁻) and penta-iodide (I₅⁻). The oxidation of P(+III) consumes free I₃⁻ and I₅⁻ in solution. The remaining I₃⁻ and I₅⁻ subunits are then allowed to react with the amylose content in starch to form a blue complex, which has a λ_max of 580 nm. The measurement of this blue complex is directly correlated with the concentration of P(+III). The on-line FI method employs the same reaction between P(+III) and mixed-iodide producing phosphate [P(+V)] that is determined spectrophotometrically by the molybdenum blue method employing ascorbic acid at a λ_max of 710 nm. The linear range for both the batch and FI determination of P(+III) was 1.0–50 μM with detection limits of 0.70 and 0.36 μM, respectively. Interference studies for the batch method show that arsenite [As(+III)] and sulfite [S(+IV)] can also be determined by this technique; however, these interferences can be circumvented by oxidizing As(+III) and S(+IV) using KMnO₄ which is an ineffective oxidant for P(+III). Both methods were applied to P(+III) determinations in ultra-pure water and simulated creek water. Results and analytical figures of merit are reported and future work is considered.     

Solvent extraction and separation of gallium, indium and thallium with N-benzylaniline

A simple and rapid method is proposed for the separation of tervalent gallium, indium and thallium by solvent extraction with N-benzylaniline in chloroform from different concentrations of hydrochloric acid. Thallium and gallium are extracted from 1M and 7.0-7.5M hydrochloric acid respectively. Indium is finally extracted from hydriodic acid. These metals in the final extracts are determined complexometrically. Interference from some cations can easily be eliminated by reduction with sulphite, followed by selective oxidation of thallium(I) to thallium(III) with saturated bromine water, and from others by the use of thioglycollic acid as a masking agent in the extraction of gallium and indium. Most common anions cause no interference. Log-log plots of distribution coefficients vs. concentration of amine for gallium, indium and thallium indicate a 2:1 limiting mole ratio of amine to these metals.     

Some studies on thallium oxalates. VI

The effect of the thallium(I) concentration on the potentiometric titration of thallium(III) with oxalic acid in 0.1M HNO₃ or 0.05M H₂SO₄ is studied, and conditions are established for the preparation of the thallium(I) bis-oxalato diaquo thallate(III) complex. Chemical analysis of the salt corresponds to the formula T1^I(T1^III(C₂O₄)₂) · 5 H₂O. Thermal decomposition studies on the complex using TG, DTG and DTA techniques indicate the formation of thallium(I) oxalate (stable from 130° to 320°) as the intermediate, the final product being a mixture of thallium(I) oxide and thallium(III) oxide (stable from 520° to 600°). Infrared absorption spectra, X-ray diffraction patterns and microscopic observations are used to characterise the complex and the intermediate.     

Separation of bismuth from gram amounts of thallium and silver by cation-exchange chromatography in nitric acid

Traces and small amounts of bismuth can be separated from gram amounts of thallium and silver by successively eluting these elements with 0.3M and 0.6M nitric acid from a column containing 13 ml (3 g) of AG50W-X4, a cation-exchanger (100-200 mesh particle size) with low cross-linking. Bismuth is retained and can be eluted with 0.2M hydrobromic acid containing 20% v/v acetone, leaving many other trace elements absorbed. Elution of thallium is quite sharp, but silver shows a small amount of tailing (less than 1 gmg/ml silver in the eluate) when gram amounts are present, between 20 and 80 mug of silver appearing in the bismuth fraction. Relevant elution curves and results for the analysis of synthetic mixtures containing between 50 mug and 10 mg of bismuth and up to more than 1 g of thallium and silver are presented, as well as results for bismuth in a sample of thallium metal and in Merck thallium(I) carbonate. As little as 0.01 ppm of bismuth can be determined when the separation is combined with electrothermal atomic-absorption spectrometry.     

Determination of thallium(I) in solutions containing cations interfering in potentiometric ion-pair formation-based titrations

The possibility of the use of simple potentiometric coated-wire sensors in the analysis of mixtures of ions, the determination of which is based on the ion-pairing principle, was studied. Attention was especially paid on the determination of thallium(I) in the presence of alkali metal ions, mercury(II), copper(II) and silver(I). It was found that thallium(I) can selectively be titrated with sodium tetraphenylborate in diluted solutions. Interferences of ions of the alkali metals are practically negligible if their concentrations are lower than 10(-3) mol dm(-3). Interference of Cu(II) is minimized using EDTA as a masking agent, Hg(II) and Ag(I) ions are sufficiently screened by additions of sodium cyanide. In mixtures containing higher concentrations of alkali metals, thallium(I) can be oxidized to thallium(III) and selectively titrated as TlCl(-)(4) with a cationic titrant.     

Cation-exchange behaviour of the platinum group and some other rare elements in hydrobromic acid-thiourea-acetone media

Ion-exchange distribution coefficients and elution curves are presented for copper(I), silver, gold(I), palladium, platinum(II), rhodium(III), iridium(III), ruthenium(III), osmium(III), mercury(II), thallium(I), tellurium(II), lead and bismuth in mixtures of thiourea, hydrobromic acid, acetone and water, with the cation-exchange resin AGW50W-X4. The system affords excellent separations of rhodium, mercury, silver (or copper), tellurium, gold, and palladium (or platinum) from each other.