Determination of uranium in technological waters by ion-pair liquid chromatography

U(VI) can be efficiently determined in the range 0.3-1OmM after its separation from Th(IV), Zr(IV), Al(III), Fe(III), lanthanides and other ions by ion-pair liquid chromatography on a 3 x 150 mm glass column packed with Separon SGX C18 modified with sorbed ammonium dodecyl sulphate. Traces of uranium can be preconcentrated directly on the analytical column from acidified water solutions and separated from Th, Zr, Al, Fe, lanthanides and other elements, with an enrichment factor of $ 100 and recovery of 98 +/- 8%, by isocratic or pH or concentration gradient elution with ammonium 2-hydroxy-2-methylpropionate or ammonium citrate solution. Post-column derivatization with 25muM Arsenazo III in 0.1M formate buffer at pH 2.7 is used for detection and quantification.     

Modeling the retention mechanism for high‐performance liquid chromatography with a chiral ligand mobile phase and enantioseparation of mandelic acid derivatives

The chromatographic retention mechanism describing relationship between retention factor and concentration of Cu²⁺(l ‐phenylalanine)₂ using chiral ligand mobile phase was investigated and eight mandelic acid derivatives were enantioseparated by chiral ligand exchange chromatography. The relationship between retention factor and concentration of the Cu²⁺(l ‐phenylalanine)₂ complex was proven to be in conformity with chromatographic retention mechanism in which chiral discrimination occurred both in mobile and stationary phase. Different copper(II) salts, chiral ligands, organic modifier, pH of aqueous phase, and conventional temperature on retention behavior were optimized. Eight racemates were successfully enantioseparated on a common reversed‐phase column with an optimized mobile phase composed of 6 mmol/L of l ‐phenylalanine or N,N‐dimethyl‐l ‐phenylalanine and 3 mmol/Lof copper(II) acetate or copper(II) sulfate aqueous solution and methanol.     

Determination of potassium in sea-water by capillary isotachophoresis

Summary A new analytical procedure for the determination of potassium in sea-water was developed using capillary isotachophoresis and ion-exchange. After the sea-water sample was passed through the column packed with an ammonium form cation-exchange resin, sodium ion was removed with 2×10^–2 mol/l ammonium chloride solution and then potassium ion was eluted with 3×10^–1 mol/l ammonium chloride solution. Simultaneous determination of potassium and sodium ions was performed with a newly developed electrolyte system; the leading electrolyte was 5 mmol/l cesium hydroxide containing 2 mmol/l 18-crown-6, 0.01% hydroxypropyl methylcellulose (HPMC) and 70% methanol; the terminating electrolyte was 5 mmol/l tetrabutylammonium bromide containing 0.01% HPMC and 70% methanol. A large amount of ammonium in the eluate did not interfere with the isotachophoretic measurement of potassium and sodium ions. A linear working curve was obtained for artificial sea-water samples containing up to 700 mg/l potassium ion. The proposed method was applied to the determination of potassium in surface and bottom sea-water samples.

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Kaliumbestimmung in Meereswasser durch Capillar-Isotachophorese

     

Highly Selective Recovery of Lanthanides by Using a Layered Vanadate with Acid and Radiation Resistance

It is of vital importance to capture lanthanides (nuclear fission products) from waste solutions for radionuclide remediation owing to their hazards. The effective separation of lanthanides are achieved by an acid/base‐stable and radiation‐resistant vanadate, namely, [Me₂NH₂]V₃O₇ ( 1 ). It exhibits high adsorption capacities for lanthanides (q_m^Eu=161.4 mg g^?1; q_m^Sm=139.2 mg g^?1). And high adsorption capacities are maintained over a pH range of 2.0–6.9 (q_m^Eu=75.1 mg g^?1 at low pH of 2.5). It displays high selectivity for Eu³⁺ (simulant of An³⁺) against a large excess of interfering ions. It can efficiently separate Eu³⁺ and Cs⁺ (or Sr²⁺) with the highest separation factor SF_Eu/Cs of 156 (SF_Eu/Sr of 134) to date. The adsorption mechanism is revealed by calculations and XPS, EXAFS, Raman, and elemental analyses. These merits combined with facile synthesis and convenient elution makes the title vanadate a promising lanthanide scavenger for environmental remediation.     

Colloidal magnesium aluminum hydroxide and heterocoagulation with a clay mineral. I. Properties of colloidal magnesium aluminum hydroxide

Magnesium aluminum hydroxide, the most important member of layered double hydroxides, was peptized by intense washing. The particle diameter, 70–130 nm, depended on the temperature of aging the parent material. The electrophoretic mobility of the particles decreased with increasing pH, from 3.7 × 10⁻⁸ m²/Vs at pH 5 to 0.5 × 10⁻⁸ m²/Vs at pH 12.3. An isoelectric point at pH∼7 was reached with the addition of 87 mmol/l NaSCN, 3 mmol/l Na₂SO₄ and Na₂CO₃, and 0.7 mmol/l Na₂HPO₄. The critical coagulation concentration for the 2% (w/w) dispersion was 88 mmol/l NaCl, 1.8 mmol/l Na₂CO₃, 1.4 mmol/l Na₂SO₄, and 1.2 mmol/l Na₂HPO₄ at pH∼7. The 2% dispersion at pH∼7 showed an almost Newtonian flow behavior. Yield values were developed after salt addition. The 2% dispersion reached a yield value of 2 Pa at 100 mmol/l NaCl, 3 Pa at 100 mmol/l Na₂SO₄, and 5 Pa at 100 mmol/l Na₂CO₃. Sodium phosphate in comparison with the other salts showed a liquefying effect. The yield value increased to 3 Pa at 1–10 mmol/l Na₂HPO₄ and decreased to 0.5 Pa at 100 mmol/l Na₂HPO₄. Received: 28 February 2001 Accepted: 8 March 2001     

Influence of the Lanthanide Ion and Solution Conditions on Formation of Lanthanide Wells–Dawson Polyoxotungstates

Lanthanide complexes of polyoxometalates, including the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, have been pioneered by Michael T. Pope, to whom this paper is dedicated. Examination of the solid-state and solution behavior of lanthanide complexes of the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand are reported here to identify trends that will facilitate rational synthesis of hybrid organic lanthanide polyoxometalate complexes. Therefore, combining our data with that obtained by Pope and others a number of trends come into view. It is clear that there are two structural types for the 1:1 or 2:2 [Ln(H₂O)_X(α₂-P₂W₁₇O₆₁)]₂ ¹⁴⁻ species. The early lanthanides show a “cap to cap” structure that allows the Ln ion to be 9 coordinate and accommodates the longer bond lengths. The mid-late lanthanides show a “cap to belt” structure that allows the lanthanides to be 8 coordinate; this structural type is appropriate for the shorter bond lengths of the later lanthanides. The 1:1⇌1:2 equilibrium, that was observed by Pope for the Ce(III) analog is prevalent for the early- mid lanthanides. This equilibrium is slightly dependent on pH; however, cations have a major influence on this equilibrium. Larger, poorly hydrated cations appear to favor the 1:2 species for the early to mid lanthanides. Cations do not appear to influence the equilibrium for the later lanthanides; for all counterions, the 1:1 species was stable with no trace of the 1:2 species. Stability constants, K1 and K2, for the early to mid lanthanides were measured in this study by a competitive method and compared well with other published stability constant determinations. We suggest that the stability constants are not only dependent on the strength of interaction of the Ln with the α₂-P₂W₁₇O₆₁ ¹⁰⁻ ligand, but are also significantly influenced by the medium. The medium may bias the equilibria of the early-mid lanthanides and later lanthanides. The log K₁/log K₂ ratios are very close, suggesting that it is difficult to separate the 1:1 and 1:2 Ln: α₂-P₂W₁₇O₆₁ ¹⁰⁻ species.Electronic Supplementary Material Supplementary material for this article is available at and is accessible for authorized users.This paper is dedicated to Professor Michael T. Pope in honor of his substantial and sustained contributions to polyoxometalate chemistry and his inspiration to scientists working in the field.     

Effect of EDTA on copper-induced inhibition of rat myometrial ecto-ATPase activity

Abstact  The aim of this study was to examine in vitro chelator’s ability to prevent copper-induced inhibition of rat myometrial ecto-ATPase activity. The effects of increasing CuSO₄ concentrations, in the absence and presence of 1 mmol/l EDTA, showed sigmoidal and complete inhibition relative to the control enzyme activity. IC₅₀ values, 1.15 × 10⁻⁴ and 1.71 × 10⁻³ mol/l in the absence and presence of EDTA, respectively, were determined by Hill analysis from experimental curves. According to the results presented in this work, 1 mmol/l EDTA increased by one order of magnitude CuSO₄ concentration for half-maximal inhibition (IC₅₀), by decreasing Cu²⁺ concentrations, available to form inactive CuATP²⁻ complex. The article is published in the original.     

Liquid—liquid distribution of ion associates of tetraiodopalladate(II) with quaternary ammonium counter ions

The distribution behaviour of ion association of Pdl^2?₄ with ten quaternary ammonium cations between chloroform and an aqueous phase was examined and extraction constants (log K_ex) were determined. Linear relationships between log K_ex and the number of methylene groups in the quaternary ammonium ions were observed. Quantitative extraction of palladium was achieved with Zeph⁺ or TBA⁺; the molar absorptivity was 2.5 × 10⁴ l mol^?1 cm^?1 at 344 nm. The effect of other ions on the spectrophotometric determination of palladium, based on their extraction, is reported.     

Extraction chromatographic separation of iron from complex liquid samples and the determination of <Superscript>55</Superscript>Fe

Summary Iron separation is described from liquid samples with a high concentration of ions that enables simple determination of ⁵⁵Fe. One of the described methods consists of iron precipitation from a large volume seawater by sodium hydroxide and/or ammonium carbonate and separation from other elements (Ca, Sr, Cu, Mg, etc.) on a TRU column with 4M HCl or 8M HNO₃. In the other procedure iron is separated directly from a mixture of seawater samples and HCl on a TRU column. In both methods, the iron recovery is almost 100%. After separation, ⁵⁵Fe is determined by counting with a liquid scintillation counter. The binding of Fe and Zn on TEVA, U/TEVA and TRU resins from seawater solutions of HCl and HNO₃depends on the type of the resin, concentration of acid and other ions. Iron and zinc can be separated from seawater on a U/TEVA column with 2M HCl.     

Sequential separation of actinides and lanthanides by extraction chromatography using a CMPO-TBP/XAD7 column

CMPO/TBP sorbed on Amberlite XAD7 resin was used for the separation of actinides and lanthanides from nitric acid solutions by extraction chromatography. The distribution ratios of actinides and lanthanide fission products (Ce, Eu) as a function of acid concentration and some complexing agents were determined. In strong HNO₃ medium (>1 mol/l) the tri-, tetra- and hexavalent actinides as well as the lanthanides have shown great affinity for the CMPO/TBP/XAD7 sorbent. The same behavior was found in HCl medium except for trivalent actinides and lanthanides which show lower distribution values in the same acid range. The effect of some complexing agents as DTPA and ammonium oxalate were also investigated. In DTPA only hexavalent actinides showed higher distribution value. On the basis of these differences, an alternative procedure for actinide-lanthanide separation and actinides from each other is proposed.     

(Diisopropylamido) bis (methylcyclopentadienyl) lanthanides as single-component initiators for polymerization of methyl methacrylate

It was first found that (diisopropylamido)bis(methylcyclopentadienyl)lanthanides (MeC₅H₄)₂LnN(i-Pr)₂(THF) (Ln = Yb ( 1 ), Er ( 2 ), Y ( 3 )) exhibit extremely high catalytic activity in the polymerization of methyl methacrylate. The reactions can be carried out over a quite broad range of polymerization temperatures from -78 to 40°C. The catalytic activity of the complexes increases with an increase of ionic radii of the metal elements, i.e. Y > Er > Yb. The results of GPC (gel permeation chromatography) indicate that the number-average molecular weights (M_n) of polymers obtained exceed 100 × 10³ and the molecular weight distribution (M_w/M_n) becomes broad with the increase of temperature. Furthermore highly syndiotactic PMMA (87.7%) can be obtained by lowering the reaction temperature to −78°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1593–1597, 1998     

Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Catalytically active MnO_x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO_x catalysts form without supports in situ under photocatalytic conditions. Our most active ⁴MnO_x catalyst (～0.84 mmol O₂ mol Mn^?1 s^?1) forms from a Mn₄O₄ bearing a metal–organic framework. ⁴MnO_x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m²g^?1) and small regions of crystallinity and layer flexibility. In contrast, the ^SMnO_x formed from Mn²⁺ salt gives an amorphous species of lower surface area (80 m²g^?1) and lower activity (～0.15 mmol O₂ mol Mn^?1 s^?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p_3/2 core levels detects enriched Mn³⁺ and Mn²⁺ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.     

First Homoleptic Rare Earth Carbazolates: Synthesis,Crystal Structures,Spectroscopic and Thermal Investigations of Divalent 1[Ln(NC12H8)2] with Ln = Europium and Ytterbium

The compounds [Ln(NC₁₂H₈)₂], Ln = Eu and Yb, were obtained in solvent free reactions of the rare earth elements europium and ytterbium with the amine carbazole. Single crystals of both compounds were grown from the melt syntheses, no recrystallization from solvents was necessary. The new compounds are the first examples of homoleptic carbazolates of the rare earth elements furthermore exhibiting divalent lanthanides. In absence of any solvent, carbazole as the sole coordination partner shows η⁶‐π‐coordination in addition to the μ₁‐ and μ₂‐coordination of the nitrogen atoms. This results in a one‐dimensional chain structure of dimers with a formal C.N. of 6 for the rare earth elements and thus being low for divalent lanthanides. The products were investigated by X‐ray single crystal and powder diffraction, Mid IR, Far IR and Raman spectroscopy, and with DTA/TG regarding their thermal behaviour. Both compounds [Ln(NC₁₂H₈)₂], Ln = Eu (1) and Yb (2) , crystallize isotypic in the triclinic space group P1.     

Noncovalent Tagging Proteins with Paramagnetic Lanthanide Complexes for Protein Study

The site‐specific labeling of proteins with paramagnetic lanthanides offers unique opportunities for NMR spectroscopic analysis in structural biology. Herein, we report an interesting way of obtaining paramagnetic structural restraints by employing noncovalent interaction between a lanthanide metal complex, [Ln(L)₃]^n? (L=derivative of dipicolinic acid, DPA), and a protein. These complexes formed by lanthanides and DPA derivatives, which have different substitution patterns on the DPA derivatives, produce diverse thermodynamic and paramagnetic properties when interacting with proteins. The binding affinity of [Ln(L)₃]^n? with proteins, as well as the determined paramagnetic tensor, are tunable by changing the substituents on the ligands. These noncovalent interactions between [Ln(L)₃]^n? and proteins offer great opportunities in the tagging of proteins with paramagnetic lanthanides. We expect that this method will be useful for obtaining multiple angles and distance restraints of proteins in structural biology.     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Structural study of lanthanides(III) in aqueous nitrate and chloride solutions by EXAFS

Structural studies of lanthanide ions (Nd³⁺≈Lu³⁺: about 1 mol/l) in the aqueous chloride (HCl: 0≈6 mol/l) and nitrate (HNO₃: 0?13 mol/l) solutions were carried out by extended X-ray absorption fine structure (EXAFS). The radial structural functions appeared to be mainly characterized by hydration in both chloride and nitrate systems and coordination of nitrate ion in nitrate systems. These results indicated that nitrate ion forms inner-sphere complex with lanthanide but chloride ion hardly forms one. The quantitative analyses of EXAFS data have revealed that the total coordination numbers of lanthanide ranged from about 9 for light lanthanides to about 8 for heavy lanthanides in all the samples. The bond distances of Ln?O were from about 2.3 to 2.5 Å for Ln?OH₂ and from about 2.4 to 2.6 Å for Ln?O₂NO. Nitrate ion locates at 0.1 Å longer position than water, it suggested that nitrate ion ligates more weakly than water.     

The quantitative separation of calcium from magnesium,aluminium and other elements by cation-exchange chromatography in ethanol-hydrochloric acid

Magnesium can be separated from calcium by elution with 3.0 M hydrochloric acid containing 60% ethanol from a column of AG₅₀W-X8 cation-exchange resin. Calcium is retained and can be eluted with 3.0 M hydrochloric acid or 2.0 M nitric acid. The separation factor of (α_Mg^ca=5.6 is considerably higher than that in aqueous hydrochloric acid and comparable to those obtained with organic complexing reagents. Separations are sharp and quantitative; up to 10 mmol of magnesium can be separated from 0.01 mmol of calcium and vice versa on a 60-ml column. Al, Fe(III), Mn, Ni(II), Co(II), Zn, Cd, Cu(II), Pb(II), U(VI), Be, Ga, Ti(IV) in the presence of H₂O₂ and many other elements accompany magnesium and can be separated from calcium quantitatively. Sr, Ba, Zr, Hf, Th, Sc, La and the rare earths are retained together with Ca, but can be separated by other methods.     

Electrochemical characteristics of H2O2 microarray electrodes as base elements of biosensors

Summary The electrochemical characteristics were examined of band- and square-type MAEs (microarray electrodes) with 10, 20 and 30 m band width and side length prepared by using standard planar processing in K₃Fe(CN)₆ solution. Among them, S1–5 square-type MAE with 10 m side length and 9.0×10^–3 mm² in the total area exhibits the largest current density and the shortest response time. The H₂O₂ calibration curve obtained at the S1–5 shows linearity from 0.1 to 5.0 mmol/l, a mean slope of 550 nA/mmol/l with a CV (variation coefficient) of 16.1%. A glucose sensor based on the S1–5 was prepared and its sensitivity was 21 nA/mmol/l, ten-fold greater than that of a single ME (microelectrode) reported lately.     

Determination of Rare Earth Elements in Garnet Minerals,Geological Materials by Inductively Coupled Plasma–Atomic Emission Spectral and Mass Spectral Analysis

Abstract

The performance of inductively coupled plasma–atomic emission spectrometry (ICP‐AES) for the determination of 14 lanthanides and Yttrium was evaluated by comparison with inductively coupled plasma–mass spectral (ICP‐MS) analysis. The geochemical reference samples (GRS), DNC‐1(diabase), AGV‐1(andesite), Sy‐2(syenite), MRG‐1(gabbro), AN‐G(anorthosite), AC‐E(granite), and MAG‐1(marine mud) were chosen as test materials and analyzed for checking the precision and reproducibility of the methods. The mineral garnet is separated from the black sands of the southwest coast of India, and the combined cation exchange–ICP method of AES analysis and MS analysis were carried out for the determination of rare earth elements. Both techniques are within the requirements needed for garnet minerals. The determination of rare‐earth elements in these minerals, which contain other elements as major contribution and trace distribution of rare‐earth elements, shows that ICP applied under the proper working condition lives up to the expectations. Major element analysis gives the formula of garnet of Manavalakurichi (MK) as (FeCaMg)_2.79Al_2.07Si_3.05O₁₂ approximated to Fe₃Al₂Si₃O₁₂, hence of almandine-type garnet. The enrichment of heavy lanthanides compared to the light lanthanides indicates that these lanthanides occupy the coordinaton site of Fe²⁺ by replacement. Both techniques are excellent in determining the very low concentration of lanthanides in geological materials, specifically garnet.     

Factors influencing the stability of H-bonds between guanidinium ions and counter ions or neutral ligands

Guanidinium ions can form H-bonds either with counter ions with proton acceptor sites or with neutral ligands. In solvents as nitrobenzene their formation constants K _h depend a priori on the pK _a of the guanidinium ion in water. Nevertheless the sequence of these constants is perturbed by two other factors: the number of equivalent N–H sites and the steric hindrance of the substituents of the guanidinium ion. In this work the stability constants K _h of guanidinium and methyl or phenyl substituted guanidinium ions with counter ions and neutral ligands were determined from the conductimetric data in nitrobenzene at 25°C. The constants are first divided by the number of available proton donor sites yielding K _h ^/* . Considering only the cases where steric hindrance is not important, correlations are established between log K _h ^/* and the pK _a of the guanidinium ion in water, also corrected for the number of available sites. The effect of steric hindrance in the other systems can be estimated from the comparison of the actual value of K _h ^/* with that of K _h ^/** predicted by the correlations. To a rough approximation, the effect of the steric hindrance can be described by factors _i characterizing the guanidinium ion and _j characterizing the partner as expressed by the relation log₁₀K _h ^** /K _h ^* = _ij.