Chromatographische trennung von calcium und strontium durch elution mit ammoniumsulfatlösung

A method is described for the chromatographic separation of calcium and strontium adsorbed on a cation-exchange resin, by means of elution with ammonium sulphate solution. The method is suitable for Ca : Sr ratios ? 1. The separated elements can be determined directly in the eluate.     

Simultaneous ion-pair chromatography of inorganic anions and cations using on-column derivatization with chelating agents and UV detection

Six complexones have been investigated as on-column derivatizing agents for the simultaneous separation of inorganic anions and cations using ion pair chromatography. UV spectrophotometry at 210 nm has been applied for both the direct and the indirect detection of anions and anionic metal complexes. Under the experimental conditions used DCTA and DTPA have been practically applicable. Factors affecting the chromatographic behaviour of analyte ions have been studied. Chloride, nitrite, nitrate sulphate, chromate, molybdate, iron, chromium (III), copper (II), cobalt (II), nickel (II) and mercury (II) ions have been separated in 30 min with a mobile phase containing 1 mmol/1 TBA and 0.5 mmol/1 DCTA at pH 6.2 in acetonitrile-water (10:90 v/v). With DTPA as eluent and using pre-column derivatization of metal cations with DCTA eight anions and six metal cations can be separated. The detection limits are less than 0.1 mg/l for most of the investigated ions. Permanent address: Department of Analytical Chemistry, Vilnius University, Naugarduko 24, 2006 Vilnius, Lithuania     

Determination of barium and strontium in sea water

A process based on ion-exchange concentration and separation followed by flame photometry has been developed for the determination of strontium and barium at natural levels in sea water. These elements are stripped from 1-I samples of sea water by means of a cation-exchange resin in the calcium form and selectively eluted with CyDTA and EDTA respectively. Factors influencing the intensity of strontium and barium in hydrogen flames have been studied. The standard deviations of the method are 0.05 p.p.m. for strontium and 0.6 p.p.b. for barium and the accuracy of the method is more than sufficient to demonstrate clearly the variability of Sr/Cl and Ba/Cl ratios with depth and location     

人牙齿中锶的特效树脂分离及其同位素测定

采用锶特效树脂(Sr-Spec)建立了快速分离富集人牙齿中微量元素锶,并测定87Sr/86Sr的有效方法。采用HNO3-HClO4体系消解牙齿样品,以8mol/L HNO3为介质上柱,8mol/L HNO3淋洗,0.05mol/LHNO3洗脱,收集淋洗液,蒸干;采用正热电离质谱法进行87Sr/86Sr的测定。结果表明,利用Sr-Spec树脂,不仅能将锶与基质中大量钙分离,并能有效分离同位素测定中干扰元素铷。本方法可以缩短分离时间,提高分离效率,减少试剂用量,降低实验空白。采用本方法对陕南地区人牙齿牙釉质中锶进行分离,测得的87Sr/86Sr值在0.710948～0.711037之间。     

Comparative distribution coefficients and cation-exchange behaviour of the alkaline earth elements with various complexing agents

Equilibrium distribution coefficients are presented for the alkaline earth metals Be(II), Mg(II), Ca(II), Sr(II) and Ba(II) with the complexing agents acetate, formate, lactate, citrate, tartrate, alpha-hydroxyisobutyrate, malonate, malate, acetylacetonate, EDTA, EGTA and DCTA, and the AG50W-X8 cation-exchange resin. Coefficients in HCl, HNO(3), HClO(4) and NH(4)Cl are included for the sake of completeness. The merits of the various complexing agents for the separation of adjacent element pairs are discussed and experimental elution curves are presented for selected separations. Separation factors for adjacent elements are calculated at eluting agent concentrations corresponding to a distribution coefficient of 10 for the less strongly absorbed element and are presented together with the eluting agent concentrations to form a basis for comparison.     

Separation of strontium from large amounts of calcium, with application to radiostrontium analysis

The elution first of calcium and then of strontium by complex formation with cyclohexanediaminetetra-acetic acid (CyDTA) after sorption on ion-exchange columns, is shown to require careful control of pH and the concentrations of CyDTA and NH(4)(+). A procedure is described for volumetric analysis of calcium and strontium, and for use of this separation procedure before determination of (90)Sr in sea-water. Careful choice of reagents and materials is shown to be necessary for use of such a method in determination of trace amounts of radiostrontium.     

1,5-bis(dicarboxymethylaminomethyl)-2,6- dihydroxynaphthalene as a selective spectrofluorimetric reagent for calcium

1,5-Bis(dicarboxymethylaminomethyl)-2,6-dihydroxynaphthalene (BDDN) forms fluorescent complexes with aluminium, barium, beryllium, calcium, magnesium and strontium. All the complexes have 2:1 metal :ligand ratios. Barium, calcium, magnesium and strontium exhibit maximal fluorescence at pH 11.7, with excitation and emission maxima at 385 and 445 nm respectively. Aluminium and beryllium show maximal fluorescence at pH 5.8 and 5.2 respectively, the excitation and emission maxima being at 370 and 405 nm. The formation of the calcium complex provides a highly sensitive and selective determination of calcium in the range 10/2-500 ng. The fluorescence measurement of calcium should be made within 5 min of mixing the solutions because of the instability of the reagent at the given pH. Potassium cyanide may be used as a masking agent and ter- or quadrivalent cations should be removed by preliminary extraction with 8-hydroxyquinoline in chloroform at pH 6.0. In such conditions, of 33 cations studied, only magnesium (>20 ng), strontium (>70 ng) and barium (>150 ng) caused interference in the determination of 300 ng of calcium. Among 16 anions examined, only EDTA interfered seriously.     

Development of a relatively cheap and simple automated separation system for a routine separation procedure based on extraction chromatography

A robust analytical method has been developed in our laboratory for the separation of radionuclides by means of extraction chromatography using an automated separation system. The proposed method is both cheap and simple and provides the advantageous, rapid and accurate separation of the element of interest. The automated separation system enables a shorter separation time by maintaining a constant flow rate of solution and by avoiding clogging or bubbling in the chromatographic column. The present separation method was tested with two types of samples (water and urine) using UTEVA-, TRU- and Sr-specific resins for the separation of U, Th, Am, Pu and Sr. The total separation time for one radionuclide ranged from 60 to 100 min with the separation yield ranging from 68 to 98% depending on the elements separated. We used ICP-QMS, multi-low-level counter and alpha spectroscopy to measure the corresponding elements.     

Determination of total acidity and of divalent cations by ion chromatography with n-hexadecylphosphocholine as the stationary phase

An ion chromatographic (IC) method is reported for simultaneous determination of total acidity (H+), Ba2+, Ca2+, and Mg2+ in aqueous samples. A standard ODS silica column modified by coating with n-hexadecylphosphocholine was used as the separation column. Water alone was used as the eluent, with conductivity detection of the sample ions. An excess of sodium iodide was added to each sample so that both H+ and divalent cations were always eluted with iodide as the counterion. The elution order was Ba2+, Mg2+, Ca2+, and H+ with H+ being eluted much later than the divalent cations. Acetic acid and several other weak acids could also be separated because all the protons were transposed from acetic acid (HAc) to HI by the sodium iodide. Detection limits for 100 microl injection, S/N=3 were in the low micromolar range for the divalent cations and approximately 0.3 mM for H+/I-. This method was used successfully for simultaneous determination of total acidity, magnesium and calcium in HCl-type of hot-spring water.     

Separation des alcalino-terreux par l'edta sur resine echangeuse d'ions

The quantitative separation of a few mg of strontium and barium from several g of calcium is described. The alkaline earth carbonates are dissolved in 0.1 M EDTA, fixed at pH 4.8 on an ammoniacal Dowex column, and eluted, also with 0.1 M EDTA, calcium at pH 5.25, strontium at pH 6.0, barium at pH 9.0. The end of the calcium elution can be followed accurately by a sudden pH increase in the eluate(from 4.8 upto 5.25).     

New efficient calixarene amide ionophores for the selective removal of strontium ion from nuclear waste: synthesis, complexation, and extraction properties.

Three novel lower rim hexamide derivatives 5(6), 7(6), and 9(6) of p-hydroxycalix[6]arene and four octamides 5(8), 7(8)-9(8) derived from the corresponding p-hydroxycalix[8]arene were synthesized, and their potential as extractants in radioactive waste treatment was evaluated, in comparison with upper rim analogues 12(6) and 12(8) and other existing selective neutral ionophores currently used in radioactive waste treatment. Extraction of alkali and alkaline earth metal picrates from water to dichloromethane, and of the corresponding nitrates from acidic water solution simulating radioactive waste, to 2-nitrophenyl hexyl ether (NPHE), showed that the lower rim amides extract divalent cations much better than monovalent ones. The upper rim hexa-12(6) and octamide 12(8) are very inefficient ligands, hardly extracting any cation. In all cases, p-alkoxy octamides are more efficient and selective extractants than the corresponding hexamides. In the case of simulated waste solutions, the distribution coefficients for strontium removal by octamides (6.5 < D(Sr) < 30) are much higher than the corresponding value (D(Sr)) found for dicyclohexyl-18-crown-6 (DC18C6), and the same applies for the strontium/sodium selectivity, which is 6500 < D(Sr)/D(Na) < 30 000 for octamides and 47 for DC18C6. ESI-MS, UV-vis, and X-ray crystal structure studies give consistent results and indicate the formation of 2:1 (cation/ligand) strontium complexes for all octamides tested. Stability constants were determined in homogeneous methanol solution for alkali metal (log beta(11) < or = 2), calcium (4.3 < or = log beta(11) < or = 6.0; 9.4 < or = log beta(21) < or = 12.0), and strontium (5.6 < or = log beta(11) < or = 12.3) ions using a UV-vis competition method with 1-(2-pyridylazo)-2-naphthol (PAN). They confirm the high efficiency and high divalent/monovalent selectivity found in metal ion extraction experiments for the new octamide ligands. Evidence for a positive cooperative effect between the two metal ion binding sites was obtained in the case of the Ca(2+) complex of octamide 1(8).     

Preparation of alkaline earth phosphates with sol containing sodium alginate and sodium diphosphate

Magnesium hydrogen phosphate, calcium hydroxyapatite, and strontium hydroxyapatite were successfully prepared from sol consisting of sodium alginate and Na4P2O7 with Mg2+, Ca2+, and Sr2+ in the corresponding nitrates, respectively. It is revealed that the order of the addition of those substrates and the role of sodium alginate are important factors for the preparation of desired phosphate compounds. According to the previous paper on the preparation of calcium hydroxyapatite, sodium alginate was mixed with aqueous Na4P2O7, followed by the addition of the aqueous divalent cations, resulting in the poor formation of the target phosphates. However, as a revised sol-gel technique, sodium alginate was added to the mixture of Na4P2O7 and aqueous Mg2+ and Sr2+, resulting in a rather favorable formation of MgHPO4 and strontium hydroxyapatite, respectively, while the sol thus obtained was stable within a few days. However for aqueous Ca2+, calcium hydroxyapatite could not be obtained through the revised sol-gel technique. In the preparation of magnesium hydrogen phosphate, sodium alginate contributes mainly to the sol formation of the precursor. The ion exchange between Na+ in sodium alginate and aqueous Ca2+ was important for the preparation of calcium hydroxyapatite. In contrast, the reaction of sodium alginate with the mixture of Na4P2O7 and aqueous Sr2+ afforded strontium hydroxyapatite at the specific ratio of those three substrates. The structure of calcium and strontium phosphates prepared from the revised sol-gel process evidently depended on the amount of sodium alginate introduced into the mixture of Na4P2O7 and the corresponding divalent cations.     

NMR study of strontium binding by a micaceous mineral

The nature of strontium binding by soil minerals directly affects the transport and sequestration/remediation of radioactive strontium species released from leaking high-level nuclear waste storage tanks. However, the molecular-level structure of strontium binding sites has seldom been explored in phyllosilicate minerals by direct spectroscopic means and is not well-understood. In this work, we use solid-state NMR to analyze strontium directly and indirectly in a fully strontium-exchanged synthetic mica of nominal composition Na(4)Mg(6)Al(4)Si(4)O(20)F(4). Thermogravimetric analysis, X-ray diffraction analysis, and NMR evidence supports that heat treatment at 500 degrees C for 4 h fully dehydrates the mica, creating a hydrogen-free interlayer. Analysis of the strontium NMR spectrum of the heat-treated mica shows a single strontium environment with a quadrupolar coupling constant of 9.02 MHz and a quadrupolar asymmetry parameter of 1.0. These quadrupolar parameters are consistent with a highly distorted and asymmetric coordination environment that would be produced by strontium cations without water in the coordination sphere bound deep within the ditrigonal holes. Evidence for at least one additional strontium environment, where proton-strontium couplings may occur, was found via a (1)H-(87)Sr transfer of populations by double resonance NMR experiment. We conclude that the strontium cations in the proton-free interlayer are observable by (87)Sr NMR and bound through electrostatic interactions as nine coordinate inner-sphere complexes sitting in the ditrigonal holes. Partially hydrated strontium cations invisible to direct (87)Sr NMR are also present and located on the external mica surfaces, which are known to hydrate upon exposure to atmospheric moisture. These results demonstrate that modern pulsed NMR techniques and high fields can be used effectively to provide structural details of strontium binding by phyllosilicate minerals.     

FIA Potentiometric and Solvent Extraction Studies of Alkali Metal and Alkaline Earth Cation Complexation by bis(Tert-butylbenzo)-21-crown-7

Abstract

A flow injection analysis study of the potentiometric selectivity of bis[4(5)-tert-butylbenzo]-21-crown-7 (D(tBB)21C7) for cesium over the other alkali metal cations and three alkaline earth cations has been conducted. A PVC matrix membrane containing D(tBB)21C7 as an ionophore was coated on the tip of a silver wire incorporated in a flow cell. No selectivity for cesium over rubidium and only low selectivity over potassium were noted. However, very high selectivities for cesium over sodium, lithium, strontium, calcium, and magnesium were observed. Selectivity of D(tBB)21C7 in the solvent extraction of alkali metal cations was determined by the picrate extraction method. The percent extraction into deuteriochloroform decreased in the order cesium, rubidium > potassium » sodium » lithium. Thus good agreement was observed between the responses of D(tBB)21C7 towards alkali metal cations in polymeric membrane electrodes and in solvent extraction.     

Isolation of radioactive strontium from natural samples: A semi-automatic procedure

A procedure for semi-automatic isolation and determination of radioactive strontium from natural samples was developed. The method was tested by the determination of⁹⁰Sr in soil samples and the results obtained were compared to those obtained by the standard procedure. The procedure consists of leaching of strontium (and other cations as well) from soil samples with a water suspension of the cation exchanger Amberlite IR-20, the separation of strontium from other cations, e.g., potassium, calcium, sodium, barium by the anion exchangers Amberlite CG-400 or Dowex Ag 1×8 with 0.25M HNO₃ in ethanol-methanol mixture as eluent in the apparatus specially constructed for this purpose. Determination of⁹⁰Sr was done on the low-level gas-flow β-counter and by Cherenkow counting on the liquid-scintillation counter few hours after the separation. It was shown that this procedure might be successfully applied for rapid determination of⁹⁰Sr in soil samples and other natural samples in a timesaving manner.     

Determination of90Sr by thin layer radiochromatography

A simple method for the determination of⁹⁰Sr by using thin layer chromatography on silica gel or cellulose pretreated with calcium oxalate is proposed. In these conditions a complete separation between strontium and its daughter yttrium is obtained. Radioactivity of separated elements was measured by a linear multiscanner analyzer and the results were computer processed to obtain the activity of⁹⁰Sr. The method has been applied to samples of water and milk subjected to a very simple extraction procedure. Under the experimental conditions used, the detection limit is about 25 mBq of deposited radioactivity, which corresponds to about 6 Bq/l.     

Single-column method of ion chromatography for the determination of common cations and some transition metals

A single-column method for the simultaneous determination of common cations and transition metals in real samples is proposed in this paper. Eleven cations (copper, lithium, sodium, ammonium, potassium, cobalt, nickel, magnesium, calcium, strontium and zinc) were separated and analyzed by means of ion chromatography using an isocratic elution with 2.5 mM methane sulfonic acid and 0.8 mM oxalic acid as mobile phase, IonPac SCS1 (250 mm x 4 mm I.D.) as the separation column and non-suppressed conductor detection. Optimized analytical conditions were further validated in terms of accuracy, precision and total uncertainty and the results showed the reliability of the IC method. The relative standard deviations (RSDs) of the retention time and peak area were less than 0.04 and 1.30%, respectively. The coefficients of determination for cations ranged from 0.9988 to 1.000. The method developed was successfully applied to determination of cations in samples of beer and bottled mineral water. The spiked recoveries for the cations were 94-106%. The method was applied to beer and beverage without interferences.     

Effects of alkaline earth metal ion complexation on amino acid zwitterion stability: results from infrared action spectroscopy

The structures of isolated alkaline earth metal cationized amino acids are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and theory. These results indicate that arginine, glutamine, proline, serine, and valine all adopt zwitterionic structures when complexed with divalent barium. The IRMPD spectra for these ions exhibit bands assigned to carboxylate stretching modes, spectral signatures for zwitterionic amino acids, and lack bands attributable to the carbonyl stretch of a carboxylic acid functional group. Structural and spectral assignments are strengthened through comparisons with absorbance spectra calculated for low-energy structures and the IRMPD spectra of analogous ions containing monovalent alkali metals. Many bands are significantly red-shifted from the corresponding bands for amino acids complexed with monovalent metal ions, owing to increased charge transfer to divalent metal ions. The IRMPD spectra of arginine complexed with divalent strontium and barium are very similar and indicate that arginine adopts a zwitterionic form in both ions. Calculations indicate that nonzwitterionic forms of arginine are lowest in free energy in complexes with smaller alkaline earth metal cations and that zwitterionic forms are preferentially stabilized with increasing metal ion size. B3LYP and MP2 calculations indicate that zwitterionic forms of arginine are lowest in free energy for M = Ca, Sr, and Ba.     

Improvements to arapid method for separating strontium from liquid milk by treatment with a chelating resin and crown ethers

In an attempt to improve on a previously reported method¹ for rapidly isolating Sr from liquid milk, the following investigations have been carried out: (1) elution of strontium from a chelating resin with dilute nitric acid, (2) separation of strontium from calcium by extracting from this eluate into chloroform solutions of dicyclohexyl-18-crown-6 (DC18C6), (3) transfer of the strontium into aqueous solution, and (4) removal of barium from this solution by extracting into dichloromethane solutions of 21-crown-7 (21C7). Based on the findings of these studies, a separation scheme was proposed and tested by participating in an interlaboratory comparison on the analysis of⁸⁹Sr and⁹⁰Sr in skimmed milk. The separation scheme requires about 3 hours, provides strontium recoveries greater than 90%, and ensures adequate decontamination factors for the nuclides that occur in milk.     

Determination of rubidium, strontium and barium in barite by atomic-absorption spectrometry after dissolution in disodium ethylenediaminetetra-acetate

A simple and rapid method is described for determining up to 50% of barium, approximately 350 mug/g or more of strontium and approximately 1 mug/g or more of rubidium in barite samples. The method involves dissolution of the barite by refluxing with an ammoniacal disodium EDTA solution. For the determination of total strontium and rubidium, the silicate residue remaining is filtered off and decomposed with hydrofluoric and sulphuric acids to recover residual strontium and rubidium. Barium and strontium are subsequently determined by flame atomic-absorption spectrometry and rubidium is determined by graphite-furnace atomic-absorption spectrometry. Results obtained for barium and strontium in several barites by the proposed method are compared with those obtained by wavelength-dispersive and energy-dispersive X-ray fluorescence spectrometry, respectively. The method is reliable and more rapid than conventional methods.