Separation and direct UV detection of lanthanides complexed with cupferron by capillary electrophoresis

Separation and detection of lanthanides by capillary zone electrophoresis in the presence of cupferron (N-nitroso-N-phenylhydroxylamine) as UV absorbing complexing agent were investigated. The resolution of partially complexed positively charged cupferron complexes is improved by using a buffer ligand competing with cupferron for metal ions. When hydroxyisobutyric acid (HIBA) is used as buffer and competing ligand, it provides complete separation of all 14 lanthanides with good peak shapes. An on-column separation of 14 lanthanides was achieved in only 7 min using 0.1 mmol/l cupferron, 15 mmol/1 HIBA at pH 4.9. The separation efficiencies for the optimum separation condition are between 77,000 and 208,000 theoretical plates. Determination of lanthanide complexes was performed by direct UV detection at 210 nm. Detection limits (signal-to-noise ratio=3) are ca. 0.24-0.47 microg/ml for lanthanides. Under optimum conditions, the complete separation of thorium and uranium from mixed lanthanides was achieved.     

Separation and direct UV detection of lanthanides complexed with pyridine-2-carboxylic acid by capillary electrophoresis

Separation and detection of lanthanides by capillary zone electrophoresis in the presence of pyridine-2-carboxylic acid (picolinic acid) as UV-absorbing complexing agent were investigated. The resolution of partially complexed positively charged complexes is improved by using two buffer ligands competing with picolinic acid for metal ions. When hydroxyisobutyric acid (HIBA) and formic acid are used together as competing ligands, this provides complete separation of all 14 lanthanides with good peak shapes. An on-column separation of 14 lanthanides was achieved in only 9 min using 0.8 mmol/l picolinic acid, 10 mmol/l HIBA and 25 mmol/l formic acid at pH 4.7. Determination of lanthanide complexes was performed by direct detection at 210 nm. Detection limits (signal-to-noise ratio=3) are ca. 0.53-0.96 microg/ml.     

Separation and direct UV detection of complexed lanthanides,thorium and uranyl ions with 2-thenoyltrifluoroacetone by using capillary zone electrophoresis

Separation and detection of lanthanides, thorium and uranyl ions by capillary zone electrophoresis in the presence of 2-thenoyltrifluoroacetone (HTTA) as UV-absorbing complexing agent were investigated. The separation of positively charged complexes is partially improved by using a competing ligand in buffer with HTTA for metal ions. When 2-hydroxyisobutyric acid (HIBA) is used as competing ligand, complete separation of thorium, uranyl and lanthanides ions were observed. Some separation parameters such as pH value, the concentration of carrier electrolyte, applied voltage, the concentration of ligand in buffer and the temperature were also optimized. Under the selected conditions, the complete separation of thorium and uranyl from each other and from lanthanides was accomplished in only 12 min using 1 mmol/L HTTA, 50 mmol/L HIBA, 5 mmol/L NaNO₃, 5 % methanol with a pH 5.2 at a capillary temperature of 25 °C. Direct photometric detection at 210 nm using a voltage of 25 kV and an electrokinetic injection (100 mm for 6 s) were used.     

Applications of pressurized cation exchange chromatography for fission yield determination

In order to determine the fission yields of lanthanides precisely, lanthanides with carriers of 1–2 mg per element are separated from each other by means of pressurized cation exchange chromatography-HIBA concentration gradient elution: The effects of initial loading technique, concentration gradient, flow rate, and temperature on separation were investigated in detail. Under the optimum conditions adopted according to the results given in this work, all the lanthanides can be completely separated within about 90 minutes with a recovery of more than 95% and purity higher than 99%.     

Chiral CE of aromatic amino acids by ligand-exchange with zinc(II)-L-lysine complex

A novel method of chiral ligand-exchange CE was developed with either L- or D-lysine (Lys) as a chiral ligand and zinc(II) as a central ion. This type of chiral complexes was explored for the first time to efficiently separate either individual pairs of or mixed aromatic amino acid enantiomers. Using a running buffer of 5 mM ammonium acetate, 100 mM boric acid, 3 mM ZnSO(4) x 7H(2)O and 6 mM L-Lys at pH 7.6, unlabeled D,L-tryptophan, D,L-phenylalanine, and D,L-tyrosine were well separated, giving a chiral resolution of up to 7.09. The best separation was obtained at a Lys-to-zinc ratio of 2:1, zinc concentration of 2-4 mM and running buffer pH 7.6. The buffer pH was determined to have a strong influence on resolution, while buffer composition and concentration impacted on both the resolution and peak shape. Boric acid with some ammonium acetate was an adoptable buffer system, and some additives like ethylene diamine tetraacetic acid capable of destroying the complex should be avoided. Fine-tuning of the chiral resolution and elution order was achieved by regulating the ratio of L-Lys to D-Lys; i.e. the resolution increased from zero to its highest value as the ratio ascended from 1:0 to 1:infinitive, and L-isomers eluted before or after D-isomers in excessive D- or L-Lys, respectively.     

Significant impact of lanthanide contraction on the structure of the phenanthroline complexes

The structure of La, Nd, Eu and Lu complexes with N,N,N',N'-tetrabutyl-1,10-phenanthroline-2,9-dicarbox- amide ligand was examined using X-ray diffraction analysis. Due to the effect of lanthanide contraction, lutetium forms unique type of complex having the coordination number 9 in contrast to other 10-coordinated lanthanides.     

Extraction separation of rare-earth ions via competitive ligand complexations between aqueous and ionic-liquid phases

The extraction separation of rare earth elements is one of the most challenging separation processes in hydrometallurgy and advanced nuclear fuel cycles. The TALSPEAK process (trivalent actinide lanthanide separations by phosphorus-reagent extraction from aqueous komplexes) is a prime example of these separation processes. The objective of this paper is to explore the use of ionic liquids (ILs) for the TALSPEAK-like process, to further enhance its extraction efficiencies for lanthanides, and to investigate the potential of using this modified TALSPEAK process for separation of lanthanides among themselves. Eight imidazolium ILs ([C(n)mim][NTf(2)] and [C(n)mim][BETI], n = 4,6,8,10) and one pyrrolidinium IL ([C(4)mPy][NTf(2)]) were investigated as diluents using di(2-ethylhexyl)phosphoric acid (HDEHP) as an extractant for the separation of lanthanide ions from aqueous solutions of 50 mM glycolic acid or citric acid and 5 mM diethylenetriamine pentaacetic acid (DTPA). The extraction efficiencies were studied in comparison with diisopropylbenzene (DIPB), an organic solvent used as a diluent for the conventional TALSPEAK extraction system. Excellent extraction efficiencies and selectivities were found for a number of lanthanide ions using HDEHP as an extractant in these ILs. The effects of different alkyl chain lengths in the cations of ILs and of different anions on extraction efficiencies and selectivities of lanthanide ions are also presented in this paper.     

Complexation of Cerium Group Lanthanides with L-Malic Acid under an Excess of Metal Ions

Complexation of cerium group lanthanide ions (Ce, Pr, Nd, Sm) with L-malic acid in aqueous solutions was studied by pH-metric titration at a malic acid : lanthanide concentration ratio of 1 : 2, in the pH range of 3.0 to 9.0, and at ionic strength of 0.1 mol/l (KCl). The composition and the stability constants of L-malate complexes and hydroxo complexes of lanthanides were determined.     

Separation and determination of metal cations in milk and dairy products by CE

To prevent casein adsorption and improve between-run repeatability, a CE procedure is developed for cation analysis in milk using a modified imidazole/alpha-hydroxyisobutyric acid (HIBA) BGE system to operate at pH 6 to match the pH of milk and elevate imidazole concentration to enhance its buffer action. The procedure is shown to produce a fast, economic and efficient method for cation separation in milk with only simple dilution. Upon direct hydrodynamic injection of diluted milk sample at 8 cm for 30 s in an uncoated column with a BGE consisting of 10 mM imidazole, 10 mM HIBA and 10% methanol at pH 6.0 under +18 kV, baseline separation was achieved for K(+), Na(+), Ca(2+), Mg(2+), Mn(2+), Cd(2+), Co(2+), Ni(2+)and Zn(2+). Agreeable results at 95% confidence level were obtained using CE and inductively coupled plasma-atomic emission spectrometry (ICP-AES) for milk samples after protein removal. Baseline-resolved peaks for essential minerals were obtained for fresh and non-refrigerated reconstituted milks. Long-term stability was demonstrated by repeated determinations without rinsing and improvement in repeatability was shown by rinsing with 60 mM SDS in BGE. Information on metal speciation useful for nutritional assessment was obtained from CE to complement the ICP methods.     

Separation and quantification of lanthanides in synthetic standards by capillary electrophoresis: a new experimental evidence of the systematic "odd-even" pattern observed in sensitivities and detection limits

The systematic zigzag pattern of sensitivities and detection limits (LODs) of lanthanides, previously observed in mass spectrometric and chromatographic measurements, was once more investigated through the indirect photometric detection with capillary electrophoresis. Well-designed chemometric experiments were performed for the electrophoretic separation and detection of lanthanides using standards with similar concentrations. A fused silica capillary 355 mm x 75 microm was used. Complete separation for all 14 lanthanides was achieved in approximately 3 min at a capillary temperature of 15 degrees C. Indirect photometric detection at 214 nm using a voltage of +25 kV and a hydrostatic injection (100 mm for 20 s) were used. The background electrolyte used consisted of an optimum mixture of 0.004 M HIBA (as complexing agent) and 0.010 M UVCat-1 (as a UV-absorbing co-ion) with a pH 4.4. A good reproducibility in migration times (<2.7% RSD), peak areas (<3.8% RSD) and peak heights (2.7% RSD) were systematically obtained. Calibration curves based on both peak areas and peak heights (from seven replicates) were prepared using weighted least-squares regressions, which were employed for the correct estimation of individual sensitivities and LODs. For a better estimation of LODs, the lowest concentration standard was injected 30 times. A new experimental evidence of the systematic "odd-even" pattern was again observed in the lanthanide sensitivities (and therefore in LODs). The calculated sensitivities were greater for lanthanides with an odd-atomic number than for their corresponding neighboring element with an even-atomic number (i.e., (57)La-(58)Ce, (59)Pr-(60)Nd; (63)Eu-(64)Gd, etc.). Concerning the LODs, a systematic zigzag pattern was observed where the odd atomic number elements have lower LODs than the even atomic number neighbor elements (i.e., (57)La-(58)Ce; (59)Pr-(60)Nd; (63)Eu-(64)Gd, etc.). The possible origin of this "odd-even" effect is briefly discussed. Accuracy errors were less than 5% for lanthanide concentrations of three synthetic standard solutions, which were considered as "unknown" samples.     

Use of tetracycline as complexing agent in radiochemical separations

The use of the antibiotic agent tetracycline for analytical purposes in solvent extraction procedures is presented. Individual extraction curves for the lanthanides, zinc, scandium, uranium, thorium, neptunium and protactinium were obtained. Separation of those elements one from another, and of uranium from selenium, bromine, antimony, barium, tantalum and tungsten was carried out. In all cases benzyl alcohol was the diluent used to dissolve tetracycline hydrochloride. Sodium chloride was used as supporting electrolyte for the lanthanide separations and sodium perchlorate for the other elements mentioned. Stability or formation constants for the lanthanide complexes as well as for thorium complex with tetracycline were determined by using the methods of average number of ligands, the limiting value (for thorium), the two parameters and the weighted least squares. For the lanthanides, the stability constants of the complexes Ln(TC)₃ go from 9.35±0.22 for lanthanum up to 10.84±0.11 for lutetium. For the Th(TC)₄ complex the formation constant is equal to 24.6±0.3. Radioisotopes of the respective elements were used for the determinations. When more than one radioelement was present in an experiment, a multichannel analyser coupled to Ge(Li) or NaI(Tl) detectors was used for counting the activities. When only one radioisotope was used, counting of the radioisotopes was made with a single-channel analyser (integral mode counting) coupled to a NaI(Tl) detector. Uranium was determined by activation analysis (epithermal neutrons). Radioisotopes of the elements were obtained by irradiation in the IPEN swimming-pool reactor. The natural radioisotope^{2 3 4}Th was used as label in the thorium experiments. In some separation procedures such as in the case of the pair uranium-neptunium, and of the pair scandium-zinc, the separation was obtained by properly adjusting the pH value of the aqueous phases, before the extraction operation. In other cases, addition of masking agents to the extraction system was required in order to perform the separation between the elements under study. In this way ethylenediaminetetraacetic acid (EDTA) was used as masking agent for scandium and the lanthanides in order to allow separation of uranium from those elements. Diethylenetriaminepentaacetic acid (DTPA) was used as masking agent for thorium in order to extract uranium into the organic phase. Separations of protactinium from thorium, and of uranium from protactinium and thorium, were accomplished by using sodium fluoride as masking agent for protactinium and DPTA as masking agent for thorium and protactinium at the same time. In the case of the separation of the lanthanides one from another it is necessary to resort to a multi-stage extraction procedure since the stability constants for those elements are too close.     

Lanthanide Structures, Coordination, and Extraction Investigations of a 1,3-Bis(diethyl amide)-Substituted Calix[4]arene Ligand

The synthesis and structure determinations of lanthanum, samarium, ytterbium, and lutetium complexes of 5,11,17,23-tetra-tert-butyl-25,27-bis((diethylcarbamoyl)methoxy)-26,28-dihydroxycalix[4]arene (L) are described. The four structures display similar characteristics with the trivalent lanthanide cation being encapsulated in an eight-coordinate oxygen environment, consisting of six oxygens from the calixarene, a water molecule, and unidentate picrate for lanthanum [La(L-2H)(picrate)(H(2)O)]; and bidentate chelating picrate for the other lanthanides [Ln(L-2H)(picrate)]Ln = Sm, Yb, Lu. Under optimised experimental conditions solvent extraction investigations showed the calix[4]arene ligand L exhibited generally very high percentage extractabilities of lanthanide cations into dichloromethane, presumably on account of the ligand's unique lower rim oxygen containing coordination sphere and its lipophilic exterior.     

Determination of lanthanides in synthetic standards by reversed-phase high-performance liquid chromatography with the aid of a weighted least-squares regression model estimation of method sensitivities and detection limits

A reversed-phase liquid chromatography method was used for determining lanthanides in synthetic standards. The separation of lanthanide group was achieved in less than 15 min using a linear gradient program of alpha-hydroxyisobutyricacid eluent from 0.05 to 0.5 M (pH 3.8) with a UV-Vis detection system at 658 nm. A post-column reagent of Arsenazo III was employed for improving the sensitivity and selectivity of the method as well as for lowering the limits of detection (LODs). Linear calibration curves for all lanthanides were constructed using an ordinary least-squares (OLS) regression as well as a weighted least-squares (WLS) regression model for taking into account the heteroscedastic errors. The WLS model was successfully used for a better estimation of the sensitivities and the LODs of the RP-HPLC method than the conventional OLS model. The lanthanide sensitivity obtained from the slope of each calibration curve seems to be better for a lanthanide with an odd-atomic number compared to its neighboring element with an even-atomic number, as if nature is helping us to quantify the concentrations of the less abundant lanthanides. This observation was also confirmed when the LODs computed for all lanthanides were examined. The LODs observed for all lanthanides depicted a clear systematic "zigzag" pattern. This is actually the first time that the lanthanide detection limits determined by a HPLC method are shown to mimic the zigzag patterns for the concentration data in geological and cosmological materials. Such a "zigzag" pattern should be used as a standard criterion for evaluating the quality of detection limit data.     

Comparative evaluation of three alpha-hydroxycarboxylic acids for the separation of lanthanides by dynamically modified reversed-phase high-performance liquid chromatography

The resolution for the three homologues of alpha-hydroxycarboxylic acids viz. lactic acid, alpha-hydroxyisobutyric acid (alpha-HIBA) and alpha-hydroxy-alpha-methylbutyric acid (alpha-H-alpha-MBA), was compared for the individual separation of 14 lanthanide elements under identical experimental conditions. Alpha-HIBA was found to be the best for separation of heavier lanthanides (Tb to Lu) while alpha-H-alpha-MBA led to a better separation for lighter lanthanides (La to Eu). All the 14 lanthanides were separated by gradient HPLC employing both alpha-HIBA and alpha-H-alpha-MBA so that there was reasonable resolution among all the peaks and the separation was completed in a short time.     

Mechanism for Solvent Extraction of Lanthanides from Chloride Media by Basic Extractants

The solvent extraction of lanthanides from chloride media to an organic phase containing an anion exchanger in the chloride form is known to show low extraction percentages and small separation factors. The coordination chemistry of the lanthanides in combination with this kind of extractant is poorly understood. Previous work has mainly used solvent extraction based techniques (slope analysis, fittings of the extraction curves) to derive the extraction mechanism of lanthanides from chloride media. In this paper, EXAFS spectra, luminescence lifetimes, excitation and emission spectra, and organic phase loadings of lanthanides in dry, water-saturated and diluted Aliquat 336 chloride or Cyphos IL 101 have been measured. The data show the formation of the hydrated lanthanide ion [Ln(H₂O)_8–9]³⁺ in undiluted and diluted Aliquat 336 and the complex [LnCl₆]^3? in dry Aliquat 336. The presence of the same species [Ln(H₂O)_8–9]³⁺ in the aqueous and in the organic phase explains the small separation factors and the poor selectivities for the separation of mixtures of lanthanides. Changes in separation factors with increasing chloride concentrations can be explained by changes in stability of the lanthanide chloro complexes in the aqueous phase, in combination with the extraction of the hydrated lanthanide ion to the organic phase. Finally, it is shown that the organic phase can be loaded with 107 g·L^?1 of Nd(III) under the optimal conditions.     

Principal component analysis and cluster analysis for the characterisation of marbles by capillary electrophoresis

Chemical characterisation has been carried out on 25 quarry marbles collected from Marmara, Aegean and Thrace regions of Turkey. Ten elements were determined by capillary electrophoresis (CE). Principal component analysis and cluster analysis techniques were utilised to define grouping of different marble samples. These techniques showed that the analysed marbles were differentiable mainly by provenance. Experimental conditions such as pH, applied voltage and concentration of α-hydroxyisobutyric acid (HIBA) were optimised to achieve the best separation of metal ions using central composite design. The optimum pH 3.7, applied voltage 15 kV and concentration of HIBA 10 mM were found to provide the best separation for all metal ions investigated.     

Capillary electrophoresis coupled with in‐column fiber‐optic laser‐induced fluorescence detection for the rapid separation of neodymium

In this study, in‐column fiber‐optic (ICFO) laser‐induced fluorescence (LIF) detection technique is coupled with capillary electrophoresis (CE) for the rapid separation of neodymium for the first time. The effects of buffer concentration, buffer pH, and separation voltage on the CE behaviors, including electrophoretic efficiency and detection sensitivity, are investigated in detail. Under the optimal condition determined in this study (15 mM borate buffer, pH 10.50, separation voltage 24 kV), neodymium could be separated effectively from the neighboring lanthanides (praseodymium and samarium) within several minutes, and the limit of detection for neodymium is estimated to be at the ppt level. The ICFO‐LIF‐CE system assembled in this study exhibits unique performance characteristics such as low cost and flexibility. Meanwhile, the separation efficiency and detection sensitivity of the assembled CE system are comparable to or somewhat better than those obtained in the previous traditional CE systems, indicating the potential of the assembled CE system for practical applications in the fields of spent nuclear fuel analysis, nuclear waste disposal/treatment, and nuclear forensics.     

Multiple bicyclic diamide-lutetium complexes in solution: chemometric analysis of deep-UV Raman spectroscopic data

The investigation of complex formation between a bicyclic diamide, a novel chelating agent for lanthanides and actinides, and lutetium in an acetonitrile solution is reported. A free ligand and its lutetium complexes showed weak, noncharacteristic near-UV absorption and no fluorescence, which limited the application of absorption and fluorescence spectroscopies for studying this system. Deep-UV Raman spectroscopy combined with chemometric analysis was shown to be a powerful tool for quantitative characterization of multiple equilibria between lutetium and a bicyclic diamide. Several chemometric methods were utilized for a comparative analysis of Raman spectroscopic data. It was found that a recently developed stepwise maximum angle calculation algorithm followed by alternative least squares (ALS) was more efficient than the commonly used combination of evolving factor analysis and ALS methods, especially when little or no information about the system composition and the spectra of individual components was available. A free ligand and 1:1, 1:2, and 1:3 metal-ligand complexes were distinguished in a bicyclic diamide-lutetium solution. The composition evolution of the solution during the course of titration with lutetium was described, and the stepwise stability constants of complex formation, K(1):K(2) = 0.80 +/- 0.15 (K(1,2) > 10(8) M(-1)) and K(3) = (5.5 +/- 1) x 10(3) M(-1), were estimated.     

Recent developments in the manufacture of 173lutetium targets

To better model nuclear processes there is an interest in measuring neutron capture cross sections of lanthanide radioisotopes. A natural hafnium target was irradiated with 100 meV protons at the Los Alamos Isotope Production Facility at the Los Alamos Neutron Science Center (LANSCE) to produce neutron poor lutetium radioisotopes. After irradiation, the target was allowed to cool to allow shorter lived lutetium isotopes to decay. This left predominately ¹⁷³Lu with small amounts of ¹⁷⁴Lu. The hafnium target was then chemically processed to isolate the lanthanide fraction through ion exchange techniques. Recent efforts have focused on the separation of lanthanide species to produce an elementally pure lutetium product, the manufacture of small high density lutetium targets, and neutron capture cross section measurements.     

Microemulsion electrokinetic chromatography of corticosteroids. Effect of surfactants and cyclodextrins on the separation selectivity

The separation of neutral hydrophobic corticosteroids (cortisone, cortisone acetate, hydrocortisone, hydrocortisone acetate, prednisolone and prednisolone acetate) by microemulsion electrokinetic chromatography (MEEKC) was studied. In the preparation of microemulsion, heptane was the solvent, n-butanol the co-surfactant and, as anionic surfactants, sodium dodecyl sulfate (SDS) or taurodeoxycholic acid sodium salt (STDC) were employed. Using an acidic running buffer, (phosphate pH 2.5) a strong suppression of the electroosmotic flow (EOF) was observed; this resulted in a fast anodic migration of the analytes partitioned into the negatively charged microemulsion droplets. Under these conditions, STDC showed better separation of corticosteroids than the conventional SDS; however, the use of a single anionic surfactant did not provide the required selectivity. The addition of the neutral surfactant polyoxyethylene glycol octadecyl ether (Brij 76) significantly altered the migration of each analytes allowing a better tuning of separation; however, in order to obtain adequate resolution between couples of adjacent critical peaks, the addition of neutral cyclodextrins (CDs) was found to be essential. This apparently complex system (CD-MEEKC), was optimized by studying the effect of the most important parameters affecting separation: STDC concentration, Brij 76 concentration, nature and concentration of cyclodextrins. Following a rational step-by-step approach, the optimised conditions providing the complete separation of the analytes were found to be: 4.0% STDC, 2.5% Brij 76, 6.6% n-butanol, 1.36% heptane and 85.54% of a solution 5 mM beta-CD in 50 mM phosphate buffer (pH 2.5). The optimized system was preliminary applied to the detection of corticosteroids related substances at impurity level and it could be considered a useful orthogonal alternative to HPLC methods.