Stability Constants and Spectroscopic Properties of Thorium(IV)–Arsenazo III Complexes in Aqueous Hydrochloric Medium

The complexation characteristics of thorium–arsenazo III in the range of 1–6 mol·L^?1 hydrochloric acid media were investigated by UV–Vis absorption spectroscopy and computational analysis. The chemical equilibrium model of thorium–arsenazo III complexation was established including the species distribution of arsenazo III, the formation of thorium chloride species, and the release of protons from thorium–arsenazo III complexes. In the spectra of thorium–arsenazo III complexes, two characteristic absorption peaks were observed at 610 and 660 nm, and the latter peak showed a tendency to shift about 4 nm to higher wavelength as the acidity of the hydrochloric acid media increased from 1 to 6 mol·L^?1. Analysis of the experimental data indicates that the molar absorptivities of both 1:1 and 1:2 complexes (thorium to arsenazo III) steadily increase as the acidity of medium increases. The determined stability constants of 1:1 and 1:2 complexes at various concentrations of hydrochloric acid were extrapolated to zero ionic strength, based on the specific ion interaction theory (SIT) approach. The limiting stability constants were determined to be \( { \log }_{10} \beta_{11}^{\text{o}} \) = 8.56 ± 0.13 and \( {\log}_{10} \beta_{12}^{\text{o}} \) = 15.17 ± 0.18 with ion interaction coefficients of Δε ₁₁ = –0.57 ± 0.02 kg·mol^?1 and Δε ₁₂ = –0.60 ± 0.04 kg·mol^?1, respectively.     

Stability constants and spectroscopic properties of thorium(IV)-arsenazo III complexes in perchloric acid

The complexation of thorium with arsenazo III in perchloric acid was quantitatively investigated with ultraviolet–visible (UV–Vis) absorption spectroscopy. The UV–Vis absorption of both 1:1 and 1:2 (thorium to arsenazo III) complexes in perchloric acid were found to be highly enhanced than the previously reported absorption of the complexes in hydrochloric acid. The stability constants of thorium-arsenazo III complexes were determined via computational analysis, and the SIT (specific ion interaction theory) was employed to evaluate the dependence on ionic strength. This work contributes to a better understanding of the speciation and spectroscopic properties of thorium-arsenazo III complexes at high ionic strength.

     

Anion-exchange separation and spectrophotometric determination of thorium in geological samples

To determine thorium in geological samples it is first separated from all matrix elements by means of anion-exchange. After elution thorium is determined spectrophotometrically by using thoronol or arsenazo III. The suitability of the method for the determination of both trace and larger amounts of thorium was tested by analysing numerous geochemical standard samples with thorium contents in the range of 1-1000 ppm. In all cases very good agreement was obtained.     

Ultratrace analysis of uranium and thorium in glass

It is today a most common phenomenon that ultratrace analyses for quality control have to be carried out in industrial laboratories far from optimum conditions and in spite of the lack of best suited equipment. It was against this setting that the development of a method for the photometric determination of uranium- and thorium-traces in glasses with arsenazo III was envisaged. The method basically consists of a digestion with HF/HClO₄/H₃BO₃, an extractive preseparation of interfering Ti- and Zr-traces with TTFA/hexanol/CCl₄, an extractive separation of U- and Th-traces with TTFA/TBP/toluene and a final determination of thorium alone (in the presence of photometrically inactive U(VI)) and the sum of Th+U(IV) with arsenazo III.The concentration of uranium is calculated from the difference of the sum of both traces minus the thorium content. Uranium can be determined with nearly the same sensitivity as thorium after reduction to uranium(IV). The most suitable reducing agent for uranium(VI) to uranium(IV) is a mixture of Na₂S₂O₄/CH₂O. An optimization of the arsenazo III concentration for the determination of thorium and uranium yielded an optimal concentration of 80 mg/L arsenazo III: For the reduction of uranium concentrations of 2 g/L of Na₂S₂O₄ and 3.2 g/L CH₂O proved to be optimal. Interferences of this photometric end determination by titanium, zirconium and scandium were investigated quantitatively. The permissible excess for these elements was found to be so low that a trace-trace separation method proved to be necessary. Separation methods were checked for the separation of the matrix components of the investigated glasses from thorium and uranium. One of these methods was suitable after optimization: thorium and uranium are extracted with TTFA/TBP/toluene from a solution containing hydrochloric acid. Back-extraction is carried out with HCl/KMnO₄. For the separation of titanium- and zirconium-cotraces an extra separation method had to be developed: they are extracted with TTFA/hexanol/CCl₄ before the separation of uranium- and thorium-traces from the matrix. The glasses were digested with HF/HX. Fluoride from the hydrofluoric acid is incompletely removed by evaporation and interferes with the extraction of uranium and thorium due to complex formation. Depending on the digestion variant used 162 to 0.23 mg F^– remain in the residue of the digestion of a 5 g sample. This interference was eliminated by a digestion with HF/HClO₄/H₃BO₃ and masking of residual fluoride with AlCl₃.Abbreviations used Arsenazo III 1,8-Dihydroxynaphthalene-3,6-disulphonic acid-2,7-bis [(azo-2)-phenylarsonic acid] - Arsenazo I 1,8-Dihydroxynaphthalene-3,6-disulphonic acid-2-[(azo-2)-phenylarsonic acid] - BPAP 2- (5-Bromo-2-pyridy] azo)-5-diethylaminophenol - EDTA Ethylenediaminetetraacetic acid - HX Designation for a high boiling mineral acid - FAAS Flame atomic absorption spectrometry - FOD 1,1,1,2,3,3,-Heptafluor-7, dimethyl-4,6-octanedione - GFAAS Graphite furnace atomic absorption spectrometry - ICP-MS Inductively coupled plasma — mass spectrometry - ICP-OES Inductively coupled plasma — optical emission spectrometry - LAS Liquid absorption spectrophotometry (classical photometry) - m(Th) Mass of thorium - NAA Neutron activation analysis - pK_Diss Negative logarithm to the base 10 of the dissociation constant of a complex - TBP Tri-(n-butyl)-phosphate - TOPO Tri(n-octyl)-phosphinoxide - TTFA 1-(2-Thenoyl)-3,3,3-trifluoroacetone     

Lanthanum complexation with reagents of the arsenazo III group on the solid phase of fibrous ion exchangers

Color reactions of lanthanum with reagents of the arsenazo III group on the solid phase of fibrous materials filled with an ion exchanger are studied. Substrates and reagents of various types, sorption and complexation conditions, and effects of some concomitant components are investigated. The most pronounced analytical effect is observed upon lanthanum sorption on disks with an anion exchanger containing iminodiacetate ANKB-50 groups followed by complexation on the solid phase with arsenazo III or arsenazo M in 0.05 M HCl. The reaction with arsenazo III is characterized by the lowest detection limit (5 ng/mL), and the reaction with arsenazo M is most selective.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 4, 2005, pp. 378–383.Original Russian Text Copyright © 2005 by Savvin, Shvoeva, Dedkova.     

Spectrophotometric determination of thorium with arsenazo III in the organic phase after extraction with di-(2-ethylhexyl)orthophosphoric acid

A simple, direct colorimetric determination of thorium extracted from chloride solution with di-(2-ethylhexyl)orthophosphoric acid is described; the colour is developed in the organic phase by adding arsenazo III and then isopropanol. Two different procedures are outlined for different thorium levels; maximum absorbance occurs at 660 nm and Beer's law is obeyed within limited ranges. Molar extinction coefficients for the two methods are 4.93 · 10⁴ and 8.77 · 10⁴ respectively. With the more sensitive method, 0.696 μg Th/ml was determined with 0.0028 as standard deviation. The effects of the various parameters were studied. Among 69 foreign cations tested, serious interferences are U(VI), Se (IV), Ti(IV), Y and the rare earths. Of the common anions, only large amounts of sulpliate slightly interfered. Several ways of overcoming interferences are suggested, with particular-reference to uranium.Several extensions of the method are outlined; 2 p.p.b. Th in aqueous media can be determined by modifying the extraction step. The procedure also appears to be extremely sensitive for the light rare-earth elements.     

一组不对称变色酸双偶氮肿类试剂的合成及其与稀土等元素显色反应研究

本文设计、合成了一组新的不对称变色酸双偶氮胂类稀土显色剂。对新试剂进行了提纯鉴定,确定了组成及结构,研究了它们与稀土、钍、锆的显色反应性能。实验证明,试剂分子结构对其反应性能的影响有一定的规律性。其中o-As-DBN试剂是较优良的钍显色剂,毫克级的稀土、铀不干扰测定。     

Development of reliable analytical method for extraction and separation of thorium(IV) by Cyanex 272 in kerosene

A simple and selective spectrophotometric method has been developed for the extraction and separation of thorium(IV) from sodium salicylate media using Cyanex 272 in kerosene. Thorium(IV) was quantitatively extracted by 5 × 10⁻⁴ M Cyanex 272 in kerosene from 1 × 10⁻⁵M sodium salicylate medium. The extracted thorium(IV) was stripped out quantitatively from the organic phase with 4.0 M hydrochloric acid and determined spectrophotometrically with arsenazo(III) at 620 nm. The effect of concentrations of sodium salicylate, extractant, diluents, metal ion and strippants has been studied. Separation of thorium(IV) from other elements was achieved from binary as well as multicomponent mixtures such as uranium(VI), strontium(II), rubidium(I), cesium(I), potassium(I), Sodium(I), lithium(I), lead(II), barium(II), beryllium(II) etc. Using this method separation and determination of thorium(IV) in geological and real samples has been carried out. The method is simple, rapid and selective with good reproducibility (approximately ±2%).     

Application of ion-exchange separations to determination of trace elements in natural waters-IX: simultaneous isolation and determination of uranium and thorium

A method is described for the determination of uranium and thorium in samples of natural waters. After acidification with citric acid the water sample is filtered and sodium citrate and ascorbic acid are added. The resulting solution of pH 3 is passed through a 4-g column of Dowex 1 x 8 (citrate form) on which both uranium and thorium are adsorbed as anionic citrate complexes. Thorium is eluted with 8M hydrochloric acid and separated from co-eluted substances by anion-exchange in 8M nitric acid medium on a separate 2-g column of the same resin in the nitrate form. After complete removal of iron by washing with a mixture consisting of IBMK, acetone and 1M hydrochloric acid (1:8:1 v v ) and treatment of the resin with 6M hydrochloric acid, the uranium is eluted from the 4-g column with 1M hydrochloric acid. In the eluate thorium is determined spectrophotometrically (arsenazo III method) while fluorimetry is employed for the assay of uranium. The procedure was used for the determination of uranium and thorium in numerous water samples collected in Austria, including samples of mineral-waters. The results indicate that a simple relationship exists between the uranium and thorium contents of waters which makes it possible to calculate the approximate thorium content of a sample on the basis of its uranium concentration and vice versa.     

Analytical application of arsenazo III to the spectrophotometric determination of palladium: Preliminary investigation of the complex formation in the arsenazo III-Pd (II)--H2O system

The reaction of arsenazo III with palladium(II) was investigated. Complex species of types M₂L and ML are formed at pH 2–4; the complex M₂L shows a very sharp maximum at 630 nm while the ML species shows maximum absorption at 620 nm. The molar absorptivities of the complexes are 4.2(±0.1) · 10⁴ and 1.6(±0.2) · 10⁴ respectively. The complex ML conforms to Beer's law at 620 nm in the range 10–250 μg Pd(II)/50 ml. The sensitivity of the reaction of Pd(II) with arsenazo III is about the same as that of a new reagent, palladiazo, but the latter is more selective for Pd(II). Serious interferences might be caused by UO₂²⁺, U⁴⁺, Th⁴⁺, Cu²⁺, Ni²⁺, Co²⁺, Y³⁺ and the rare-earth elements.     

Simultaneous determination of uranium(IV) and thorium(IV) ions with Arsenazo III by partial least squares method

A multivariate calibration method, Partial Least Squares Type 1 (PLS-1), is proposed for simultaneous spectrophotometric determination of uranium and thorium ions as their complexes with arsenazo III in hydrochloric acid medium. Several data characteristics are taking into account in order to minimize the optimum number of factors required for the construction of calibration model, while using various statistical criterions of selection. Finally, the evaluated calibration model is satisfactorily applied to determination of these ions in samples that resemble sulfuric acid leach solution obtained from a uranium ore.     

Chemical analysis of manganese nodules : Part II. Determination of uranium and thorium after anion-exchange separation

A method is described for the determination of uranium and thorium in manganese nodules. After dissolution of the sample in a mixture of perchloric and hydrofluoric acids, uranium is adsorbed on the strongly basic anion-exchange resin Dowex 1 (chloride form) from 6 M hydrochloric acid. The effluent is evaporated and the residue is taken up in 7 M nitric acid—0.25 M oxalic acid; thorium is then isolated quantitatively by anion-exchange on Dowex 1 (nitrate form). Thorium is eluted with 6 M hydrochloric acid and determined spectrophotometrically by the arsenazo III method. Uranium is eluted from the resin in the chloride form with 1 M hydrochloric acid and then separated from iron, molybdenum and other co-eluted elements on a column of Dowex 1 (chloride form); the medium consists of 50% (v/v) tetrahydrofuran, 40% (v/v) methyl glycol and 10% (vv) 6 M hydrochloric acid. After removal of iron and molybdenum by washing the resin with a mixture of the same composition and with pure aqueous 1 M hydrochloric acid, the adsorbed uranium is eluted with 1 M hydrochloric acid and determined by fluorimetry. The method was used successfully for the determination of ppm-quantities of uranium and thorium in 60 samples of manganese nodules from the Pacific Ocean.     

The determination of lanthanum,cerium and thorium without separations: The determination of lanthanum and cerium in thorium

A method is proposed for the spectrophotometric determination of small quantities of lanthanum, cerium and thorium in the presence of one another without separations. Cerium is estimated from its absorption peak in the ultraviolet region, thorium with thorin, and the 3 elements together with arsenazo. The lanthanum is calculated after subtraction of the combined absorbances of the arsenazo complexes of the thorium and cerium. The procedure can be readily applied to the determination of microgram amounts of the 2 rare earths in thorium. In this case the majority of the thorium is removed from the solution by solvent extraction with TTA before the estimation of the rare earths. The interference of iron is considered and proposals made for its removal.     

Separation of Thorium(IV) from Associated Elements Using Poly-(Dibenzo-18-Crown-6) and Column Chromatography from Picric Acid Medium

A simple column chromatographic method has been developed for the separation of thorium(IV) from associated elements using poly-(dibenzo-18-crown-6). The separations are carried out from picric acid medium. The adsorption of thorium(IV) was quantitative from 0.0005–0.05M picric acid. Amongst the various eluents tested, 2.0–8.0M HCl, HBr, 1.0–6.0M HClO₄ and 5.0M acetic acid were found to be particularly efficient for the quantitative elution of thorium(IV). The capacity of poly-(dibenzo-18-crown-6) for thorium(IV) was found to be 1.29±0.01 mmol/g of crown polymer. Thorium(IV) was separated from a number of cations in binary mixtures in which most of the cations showed a very high tolerance limit. It was possible to separate thorium(IV) from a number of cations such as lanthanum(III), yttrium(III), uranium(VI), beryllium(II) and barium(II) in multicomponent mixtures. The method was extended to the determination of thorium in monazite sand. It is possible to separate and determine 5 ppm of thorium(IV) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately ±2%).     

Separation of thorium as ascorbato complex by extraction with Aliquat 336S

Thorium was quantitatively extracted with 0.1M Aliquat 336S at pH 4.5 from 0.01M ascorbic acid. It was then stripped with 2M hydrochloric acid. Thorium arsenazo III complex was determined spectrophotometrically at 655 nm. It was separated from binary and tertiary mixtures by exploiting the difference in distribution ratios of various elements from ascorbic acid media. Some separations were accomplished by selective stripping of thorium from nitric and hydrochloric acid. The method was extended for the analysis of thorium in monazite and gas mantles.     

Simultaneous Spectrophotometric Determination of Uranium and Thorium Using Arsenazo III by H‐Point Standard Addition Method and Partial Least Squares Regression

Simultaneous determination of uranium and thorium using arsenazo III as a chromogenic reagent at pH 1.70 by H‐point standard addition method (HPSAM) and partial least squares (PLS) calibration is described. Under optimum conditions, the simultaneous determinations of uranium and thorium by HPSAM were performed. The absorbencies at one pair of wavelengths, 649 and 669 nm, were monitored with the addition of standard solutions of uranium. The results of applying the HPSAM showed that uranium and thorium can be determined simultaneously with weight concentration ratios of uranium to thorium varying from 20:1 to 1:15 in the mixed sample. By multivariate calibration methods such as PLS, it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. In this study, the calibration model is based on absorption spectra in the 600–750 nm range for 25 different mixtures of uranium and thorium. Calibration matrices contained 0.10–21.00 and 0.25–18.5 μg mL^?1 of uranium and thorium, respectively. The RMSEP for uranium and thorium were 0.7400 and 0.7276, respectively. Both proposed methods (HPSAM and PLS) were also successfully applied to the determination of uranium and thorium in several synthetic and real matrix samples.     

Spectrophotometric determination of phosphate ions with the system cerium(III)Arsenazo III

A new method for the spectrophotometric determination of PO(3-)(4), based on the conversion of the complex of cerium(III) with arsenazo III (CeH(4)R(-)) into CePO(4) is proposed and used for the indirect spectrophotometric determination of phosphorus in ferro-silicon. The reaction between Ce(III) and arsenazo III has been studied spectrophotometrically and the stability constants of the complex CeH(4)R(-) have been determined: log beta(1) = 6.42 +/- 0.10 (for pH 1-3) and log beta(1) = 6.11 +/- 0.02 (for pH 5.5-7).     

A Study on the Reaction of Protein with Arsenazo III by Rayleigh Light Scattering Technique

Abstract

A new rayleigh light scattering (RLS) assay of protein was conducted in this paper. The weak RLS of arsenazo III can be enhanced greatly by the addition of proteins. Based on this, the reaction of arsenazo III and proteins was studied. A new quantitative determination method for proteins has been developed. This method is very sensitive (0.085(021.25 μg/mL for BSA), rapid (<1min), simple (one step) and free of interference from most diverse substances.     

Studies on uranium recovery from inlet stream of Effluent Treatment Plant by novel “In-House” sorbent

A fast and simple multisyringe flow injection analysis (MSFIA) method for routine determination of thorium in water samples was developed. The methodology was based on the complexation reaction of thorium with arsenazo (III) at pH 2.0. Thorium concentrations were spectrophotometrically detected at 665 nm. Under optimal conditions, Beer’s law was obeyed over the range from 0.2 to 4.5 μg mL⁻¹ thorium, a 3σ detection limit of 0.05 μg mL⁻¹, and a 10σ quantification limit of 0.2 μg mL⁻¹ were obtained. The relative standard deviations (RSD, %) at 0.5, 2.5 and 4.5 μg mL⁻¹ was 2.8, 1.5 and 0.8%, respectively (n = 10). It was found that most of the common metal ions and anions did not interfere with the thorium determination. The proposed method was successfully applied to its analysis in various water samples.     

新的不对称变色酸双偶氮衍生物的合成及其结构对稀土、钍、铋显色反应的影响

新的不对称变色酸双偶氮衍生物的合成及其结构对稀土、钍、铋显色反应的影响张华山,张军锋,黎心懿（武汉大学化学系,武汉,４３００７２）关键词变色酸双芳基偶氮衍生物,稀土,钍,铋,分光光度法变色酸双偶氮衍生物是光度法测定稀土、钍等金属的重要显色剂。其中多卤...