Determination of cholride in natural and potable water samples byturbidimetric descrete-sample automatic analysis.

The reduction of the uranyl-mellitate complex at the dropping mercury electrode has been studied in aqueous and dimethyl sulfoxide solution. In aqueous solution, besides the reduction waves of the uranyl-mellitate complex, corresponding to the reduction of U(VI) to U(V), and of U(V) to U(III), an adsorption wave and a catalytic hydrogen wave were obtained; the species formed below pH 4.0 was UO₂(H₃A)^- and above pH 4.0 was UO₂(OH)(H₃A)^2-. In dimethyl sulfoxide solution, two well-defined waves were observed; the first wave is due to reduction of a uranyl-mellitate-DMSO complex, and the second to reduction of mellitic acid. The species involved are UO₂(DMSO)₆²⁺ below pH 2.2 and UO₂(H₃A)(DMSO)₅^-1 above pH 2.2. The activation energies of the reduction process were determined.     

Polarography of uranyl-nitrilotriacetate complex

Polarographic studies of solutions of uranium(VI) and nitrilotriacetic acid were carried out in perchlorate medium at ionic strength 0.25. Reversible and diffusion-controlled reduction waves were obtained in the pH range of 1.5–4.1. Above pH 4.1, the irreversible waves became reversible in the presence of acetate buffer. Four kinds of chelate species, UO₂HX^-, UO₂X^-, UO₂(OH)X^2- and UO₂(Ac)X^2-, were identified. The U(V)-NTA complex was unstable at high pH and completely dissocitated at pH 6.30. The effects of pH and ligand concentration on the wave parameters are discussed in detail.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP)

Except for conditions of low acidity and low ratios of di(2-ethylhexyl)phosphoric acid (HDEHP) to U(VI) the data obtained for the distribution of U(VI) between sulfuric acid solutions and polyurethane foams loaded with solutions of HDEHP in nitrobenzene could be analyzed by the equation: log (4.36 D_u)=log K+1.43 log (C_d–4C_u)/(C_H)^1.4+log f_u where the polymerization number of HDEHP is about 2.8, D_u is the distribution ratio, and f_u=[UO ₂ ²⁺ ]_(aq)/[UO₂]_(aq) indicating that the extraction proceeds via the formation of a 14 UO₂:HDEHP complex. At both low acidity and HDEHP/U(VI) ratio a UO₂-HDEHP polymer is formed.     

Potassium ferrocyanide as a spectrophotometric reagent for the determination of uranium

Potassium ferrocyanide gives a colour reaction with U(VI), which is suitable for its determination. The complex absorbs in the wavelength range of 390–397 nm. The optimum pH range for colour development was 1.5–3.5. The molar absorptivity was found to be 4.65·10³ 1·mol^–1·cm^–1. Most of the anions up to 1000 g did not interfere. The method was made selective by extracting U(VI) first with DOSO from the mixture of interfering cations from 1–2M HNO₃ medium and then determining uranium in the back-extracted solution by developing the colour with ferrocyanide. 20 g/10 ml of U(VI) in the final solution could be satisfactorily determined within an RSD of ±2%.     

Sorption and separation of some elements of nuclear importance using Chelex-100

Chelex-100, in the anionic form has been studied for its ability to perform selective separation and concentration of some metal ions of nuclear importance from mineral acid solutions. The sorption behavior of Zr(IV)–Nb(V), Mo(VI), Tc(VII), Te(IV) and U(VI) from solutions of hydrochloric and sulphuric acids on Chelex-100 has been studied under static and dynamic conditions. Mo(VI) and Tc(VII) have been concentrated on the resin from hydrochloric or sulphuric acid solutions at low acidities probably, as the anions MoO ₄ ^2– and TcO ₄ ^– , respectively. Te(IV) has been isolated from hydrochloric acid solutions of normalities 6 in the form of the anionic chloro complex TeCl ₆ ^2– . Optimum conditions for elution and separation of Mo(VI), Tc(VII), Te(IV) and U(VI) were recommended.     

Kinetics and Mechanism of Catalytic Reduction of U(VI) with Hydrazine on Platinum Catalysts in Nitric Acid Media

The kinetics of U(IV) produced by hydrazine reduction of U(VI) with platinum as a catalyst in nitric acid media was studied to reveal the reaction mechanism and optimize the reaction process. Electron spin resonance (ESR) was used to determine the influence of nitric acid oxidation. The effects of nitric acid, hydrazine, U(VI) concentration, catalyst dosage and temperature on the reaction rate were also studied. In addition, the simulation of the reaction process was performed using density functional theory. The results show that the influence of oxidation on the main reaction is limited when the concentration of nitric acid is below 0.5 mol/L. The reaction kinetics equation below the concentration of 0.5 mol/L is found as: -dc(UO₂²⁺)/dt)=kc^0.5323(UO₂²⁺)c^0.2074(N₂H₅⁺)c^-0.2009(H⁺). When the temperature is 50 ℃, and the solid/liquid ratio r is 0.0667 g/mL, the reaction kinetics constant is k=0.00199 (mol/L)^0.4712/min. Between 20 ℃ and 80 ℃, the reaction rate gradually increases with the increase of temperature, and changes from chemically controlled to diffusion-controlled. The simulations of density functional theory give further insight into the influence of various factors on the reaction process, with which the reaction mechanisms are determined according to the reaction kinetics and the simulation results.     

Spectrophotometric Determination of Trace Amounts of Chromium with Citrazinic Acid

A sensitive and selective spectrophotometric method for the determination of trace amounts of chromium(VI) is described, based on diazotization and coupling reactions. Chromium(VI) oxidizes hydroxylamine in acetate buffer of pH 4.0 ± 0.5 to nitrite, which then diazotizes p-aminoacetophenone to form diazonium salt. The diazonium salt is then coupled with a new coupling agent, citrazinic acid in an alkaline medium, which gives an azo dye with an absorption maximum at 470 nm, a molar absorptivity of 2.12 × 10⁴L mol^–1cm^–1, and a Sandell's sensitivity of 0.00246 g/cm². The color is stable for 6 h and the system obeys Beer's law in the range 2–15 g chromium(VI) in a final volume of 10 mL. The detection limit of chromium(VI) is 0.04 g/mL. Chromium(III) can be determined after it is oxidized with bromine water in an alkaline medium to chromium(VI). The developed method has been successfully applied to the analysis of chromium in alloy steels, industrial effluents, and pharmaceutical preparations.     

Preparation of soluble ternary heteroazo dye complexes for the spectrophotometric determination of trace uranium(VI)

The complexing ability of typical pyridylazo, quinolylazo and thiazolylazo dyes with uranium(VI) in aqueous ethanol media are investigated in the presence and absence of aromatic carboxylic acid. Uranium(VI) forms solubilized ternary complexes with PAN, PAR, TAM, 5-Br-PADAP, 3,5-diBr-PADAP and QADAP in 48% ethanol solution containing sufficient amounts of sulfosalicylic acid and triethanolamine buffer (pH 7.8). Aromatic carboxylic acids contribute to expel the coordinated water molecules from the uranium (VI) moiety and their chelating effects have been explained by ternary complex formation. An increase in molar absorptivity and no shift in the wavelength of maximum absorbance are observed for all uranium(VI) complexes investigated. The 11 stoichiometry of uranuim(VI) and heteroazo dye in the binary complex does not change through ternary complex formation. The molar absorptivity of the uranium(VI)-3,5-diBr-PADAP-sulfosalicylic acid ternary complex at 595 nm is 8.4×10⁴l mol^–1 cm^–1 and Beer's law is valid up to 2.5gmg ml^–1 of uranium(VI). The interferences due to coexisting metal ions can be effectively masked by addition of CyDTA or Ca-CyDTA.     

A new method of uranium preseparation and concentration for neutron activation analysis

This paper introduces a new type of extractant, sym-dibenzo-16-crown-5-oxyhydroxamic acid (HL). The extraction of UO ₂ ²⁺ , Na⁺, K⁺, Sr²⁺, Ba²⁺ and Br^– were studied with HL in chloroform. The results obtained show that UO ₂ ²⁺ can be quantitatively extracted at pH above 5, whereas the extractions of K⁺, Na⁺, Ba²⁺ and Br^– are negligible in the pH range of 2–7. The dependence of the distribution ratio of U(VI) on both the concentration of the HL and pH are linear, and they have the same slope of 2. This suggests that U(VI) appears to form a 12 complex with ligand.Uranium (VI) can be selectively separated and concentrated from interfering elements such Na, K, Sr and Br by solvent extraction with HL under specific conditions. The recovery of uranium is nearly 100% and the radionuclear purity of uranium is greater than 99.99%. Therefore, it has greatly improved the sensitivity and accuracy for the detection of trace uranium from seawater by neutron activation analysis.     

Rapid and selective method for the spectrophotometric determination of tin using potassium ethylxanthate

Tin (II) forms a yellow complex with potassium ethylxanthate which can be extracted into chloroform. Tin is determined spectrophotometrically by measuring the absorbance at 360 nm. Beer's law is obeyed up to 120 g of Sn in the aqueous phase with a Sandell sensitivity of 0.013 g Sn/cm². Metal ions such as Ti(IV), Cr(VI), Mn(II), Cu(II), Zn(II), Al(III), U(VI), W(VI), Th(IV) and Zr(IV) do not interfere, but Mo(VI), Co(II) and Bi(III) do. Interference due to Fe(II, III), Ni(II) and V(V) is checked by suitable masking agents. Analysis of some synthetic and industrial samples has been carried out by the proposed method.     

Extraction of uranium (VI), plutonium (IV) and some fission products by tri-iso-amyl phosphate

The extractive properties of tri-isoamyl-phosphate (TAP), an indigenously prepared extractant, and the loading capacity of extraction solvent containing TAP for U(VI) and Pu(IV) ions in nitric solution have been investigated. The dependence of the distribution ratio on the concentration of nitric acid showed that TAP has an ability to extract these actinides, while the fission product contaminants are poorly extracted. The distribution data revealed a quantitative extraction of both U(VI) and Pu(IV) from moderate nitric acidities in the range 2–7 mol · dm^–3. Slope analysis proved predominant formation of the disolvated organic phase complex of the type UO₂(NO₃). 2TAP and Pu(NO₃)₄·2TAP with U(VI) and PU(IV), respectively. On the contrary, the extraction of fission product contaminants such as¹⁴⁴Ce,¹³⁷Cs,⁹Nb.,¹⁴⁷Pr,¹⁰⁶Ru,⁹⁵Zr was almost negligible even at very high nitric acid concentrations in the aqueous phase indicating its potential application in actinide partitioning. The recovery of TAP from the loaded actinides could be easily accomplished by using a dilute sodium carbonate solution or acidified distiled water (0.01 mol · dm^–3 HNO₃) as the strippant for U(VI) and using uranous nitrate or ferrous sulphamate as that for Pu(IV). Radiation stability of TAP was adequate for most of the process applications.     

Polarography of Uranyl Complex with Chromotropic Acid

The polarography characteristic of uranyl ion in chromotropic acid solution was investigated systematically over the pH range 2.0 to 10.0 with ligand concentrations varying from 0.010 M to 0.200 M. At pH 5.5, the one-electron reversible reduction waves were obtained. The temperature coefficient of the half-wave potential was obtained to be ?0.32 mV per degree and the mean value of i_d/h^1/2 is 0.340 ± 0.003. The electrode reaction is UO₂(HA)₂^4? + c = UO₂(HA)^2? + HA^3? Where pH 5.5, an irreversible and diffusion-controlled wave was obtained. The diffusion coefficients and kinetic parameters of complex species were determined by deducing instantaneous equations.     

IR spectroscopic investigation of the structure of polymeric uranyl di(2-ethylhexyl)phosphate molecules in C6H6 and CCl4 solutions

Using IR spectroscopy, we studied the types of coordination of POO groups in di(2-ethylthexyl)phosphate anionx X⁻ with UO ₂ ²⁺ cations in the C₆H₆ and CCl₄ solutions of the polymer molecules (UO₂X₂)_p. The polymers exhibit tridentate-bridge coordination (I), which is not typical of (MX_n)_p salts where the phosphoryl oxygen atom forms two bonds with U(VI) atoms. When a few U(VI) atoms (≳7%) interact with donar additives, all POO group I change their coordination to the usual bidentate-bridge type, , resulting in a structural transformation of the polymer. The bridging POO group are responsible for the difference in the dimerization and trimerization constants and the constants of the subsequent addition of the monomer molecules UO₂X₂ to the polymer chain (UO₂X₂)_p. It is suggested that type I coordination of X⁻ to U(VI) is due to an extended bond between the 2p²-electrons of the phosphoryl oxygen atom of the X⁻ anion and a vacant f-orbital of the U(VI) atom (p_π−f_π interaction). This unusual type of bond between uranium (VI) and tributyl phosphate (TBP) phosphoryl oxygen was found earlier for the UO₂Cl₂·2TBP complex. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturmoi Khimii, Vol. 35, No. 6, pp. 60–65, November–December, 1994. Translated by K. Shaposhnikova     

Solvent Extraction Separation of Th(IV) and U(VI) with PC-88A

Liquid-liquid extraction of Th(IV) and U(VI) has been investigated by commercial extractant PC-88A in toluene. The optimum conditions for extraction of these metals have been established by studying the various parameters like acid concentration/pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.1–1.0M HNO₃ acid and in the pH range 1.0–4.0 while U(VI) was completely extracted in the pH range 1.0–3.5 with 2.5·10^–2M and 2.·10^–2M PC-88A in toluene, respectively. The probable extracted species have been ascertained by log D-log C plot as ThR₄·4HR and UO₂R₂·2HR, respectively. The method permits separation of Th(IV) and U(VI) from associated metals with a recovery of 99.0%.     

Reaction of Plutonium(VI) with Orthosilicic Acid Si(OH)4

Reaction of Pu(VI) with Si(OH)₄ (at concentration 0.004–0.025 mol l^–1) in a 0.2 M NaClO₄ solution at pH 3–8 is studied by spectrophotometric method. In the range of pH 4.5–5.5, PuO₂(H₂O)₄OSi(OH)₃ ⁺ complex is formed, while at pH > 6, PuO₂(H₂O)₃O₂Si(OH)₂ or hydroxosilicate complex PuO₂(H₂O)₃(OH)OSi(OH)₃ is recorded. The equilibrium constants are calculated for the reactions of formation of PuO₂(H₂O)₄OSi(OH)₃ ⁺ and PuO₂(H₂O)₃O₂Si(OH)₂ and their concentration stability constants: log K ₁ = –3.91 ± 0.17 and log K ₂ –10.5; log ₁= 5.90 ± 0.17 and log ₂ 12.6. The PuO₂(H₂O)₄OSi(OH)₃ ⁺ complex is significantly less stable than analogous complex of U(VI). Calculations of the forms of Pu(VI) occurrence at the Si(OH)₄ concentration equal to 0.002 mol l^–1 showed that the maximum fraction of the PuO₂(H₂O)₄OSi(OH)₃ ⁺ complex is 10% (pH 6.5), while the fraction of PuO₂(H₂O)₃O₂Si(OH)₂ is almost 40% (pH 8).     

Extractive spectrophotometric determination of dioxouranium(VI) with the sodium salt of hexamethyleneiminecarbodithioate

The optimum conditions for the extractive spectrophotometric determination of dioxouranium(VI) with hexamethyleneiminecarbodithioate(HMICdt) have been established. Dioxouranium(VI) reacts with this ligand at pH 4.5 to form a yellowish-orange uncharged 12 metal-ligand complex which can be extracted by chloroform. The calibration graph was linear in the range of 1–20 g ml^–1 of dioxouranium(VI) at 335 nm. The molar absorptivity of the extracted species is 5.952×10³ l mol^–1 cm^–1 with Sandell's sensitivity of 0.04 g cm^–2. The average of 10 determinations of dioxouranium was 49.75 g for the samples containing 50 g of U(VI) and the variation from the mean at 95% confidence limit was 49.75±0.5955.     

Extraction and spectrophotometric determination of uranium(VI) withN-phenylcinnamohydroxamic acid

Uranium(VI) reacts withN-phenylcinnamohydroxamic acid to form an orange-yellow complex in the pH range 5.5–8.5. The orange-yellow complex, having the composition of 12 (metal:ligand), is quantitatively extractable into ethyl acetate. The spectrum of the complex exhibits a maximum absorption at 400 nm with a molar absorptivity of 6500 M^–1·cm^–1. The coloured system obeys Beer's law in the concentration range 2–40g·ml^–1 of uranium(VI). The photometric sensitivity of the colour reaction is 0.037 g·cm^–2 of uranium(VI). Most of the common ions do not interfere and the method has been found to be simple, precise, and free from the rigid control of experimental conditions. The method has been applied to the determination of uranium in synthetic matrices and potable water.     

Polarographic determination of nanomolar concentrations of molybdenum(VI)

Summary Polarographic Determination of Nanomolar Concentrations of Molybdenum (VI) A new differential pulse polarographic method for the determination of Mo(VI) is described. Mo(VI) is first chelated by 7-nitro-8-hydroxychinoline-5-sulfonic acid at pH 1. The complex ion MoO₂L₂ ^2– formed is strongly adsorbed on the surface of a dropping mercury electrode. At a potential difference of 0.95 V the complex ion is reduced to a Mo(V)-complex, which is oxidized very fast by H_aq ⁺ providing the starting complex ion for repeated redox cycles. The net process consists in the catalytic reduction of H_aq ⁺ to 1/2 H₂ in the double layer. H₂ was detected by inductively coupled plasma atomic emission spectrometry. A modified preparation method for the chelating agent and its characterization are also described. The method was used for the determination of Mo(VI) in the surface water of Lake Zürich. An average value of 0.463±0.007 ng/g (4.83±0.07 nM) was calculated from 39 single values. The errors are the confidence intervals of the corresponding means at the 99% confidence level. The standard deviation and the practical detection limit were 0.016 and 0.031 ng/g, respectively, for single determinations on the average.     

Spectrophotometric determination of trace uranium(VI) as a mixed ligand complex with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and aromatic carboxylic acid

Spectrophotometric studies on a uranium(VI) ternary complex and its analytical application are described. Uranium(VI) reacts with 5-Br-PADAP to form an unstable chelate, which precipitates on standing in 48% ethanolic aqueous solution. The colour stability of uranium(VI) complex is greatly improved by the presence of aromatic carboxylic acids. For the present purpose, o-hydroxybenzoic acid and its derivatives are best suited. The calibration graph is linear up to 2.6 g·ml^–1 of uranium(VI) at 578 nm. The role of carboxylic acid as an auxiliary ligand is discussed.     

Determination of methylviologen (Paraquat) by differential pulse polarography

Summary Determination of Methylviologen (Paraquat) by Differential Pulse Polarography The second reduction wave of methylviologen (Paraquat) has been studied at pH 2 by different polarographic techniques. The limiting current is diffusion-controlled. Evidence for dimerization of the radical formed in the first reduction step has been obtained. The n values for the reduction process have been calculated at concentration levels where the dimer and the monomer predominate. Paraquat can be determined by differential pulse polarography in the 6.0×10^–5–4.0×10^–7 M concentration range, the limit of determination being 1.7×10^–7 M. The method has been applied to paraquat determination in commercial herbicides.