Accurate Determination of Lithium Isotopic Compositions in Geological Samples by Multi-collector Inductively Coupled Plasma-Mass Spectrometry

Accurate determination of lithium (Li)isotopic composition in natural geological samples is the basis for Li isotope geochemical studies. In this study, a method contained preparation of geological materials (water and rock) and accurate determination of Li isotopic composition was set up. The separation of Li from water and rock samples was implemented by a single column containing 1.5 mL of Bio-Rad AG 50W-X12 (200–400 mesh) resin, with 0.40 M HCl and 1.0 M HCl as eluents. Only 8.5 and 14 mL of eluents were used to separate Li from water and rock samples with this method, respectively. Blank signal of the operation procedure was (2.4 ± 0.1) mV, which was almost same as the 2.3 mV of the 2% HNO₃ signal used in this study. Experimental results showed that Li isotopic fractionation during leaching process was significant and deviation of δ⁷Li values in these samples with incompletely recovered Li reached up to 50‰. Lithium isotopic ratios were determined by multi-collector ICP-MS (Nu Plasma II) using the sample standard bracketing (SSB) method. L-SVEC standard with similar Li concentration to samples (about 80 ng mL^?1) was used in this study. The external precision (2σ) of this technique, determined by repeated measurement of pure Li standard solutions and seawater was < ±0.8‰. The measured δ⁷Li values of seawater and rock standards AGV-2, BCR-2 and GSP-2 were +31.4‰ ± 0.7‰ (n = 18), +7.23‰ ± 0.16‰ (n = 4), +3.7‰ ± 0.7‰ (n = 8) and ?0.10‰ ± 0.18‰ (n = 4), respectively, similar to previously published values. This method could be used to accurately determine Li isotopic composition of various types of geological samples such as waters and rocks. The advantage of this method was that the amount of resin and reagent was reduced to 50% or less of the previous studies, thereby significantly improving the work efficiency and reducing the operation procedure blank.     

Preparation and characterisation of synthetic mixtures of lithium isotopes

Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li₂CO₃ compounds. The starting materials, 99.9981% enriched ⁶Li, and 99.9937% enriched ⁷Li, were purified by ion exchange, and the purified materials converted from LiOH to Li₂CO₃ by reaction with CO₂. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li₂CO₃ carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g^–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(⁶Li)/n(⁷Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10^–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.     

Atomicm absorption spectrometric determination of the isotopic composition of lithium by an ultimate absorbance-ratio technique

The conventional absorbance-ratio technique for determining the isotopic composition of lithium by atomic absorption spectrometry is improved by the use of “ultimate absorbance ratios” of sample solutions. These ratios are obtained by extrapolating the linear portion of lithium content/absorbance-ratio plots to the intercept at 0 mol m^?3 lithium. These graphs are obtained measuring the absorbances of solutions of known ⁶Li abundance and of various lithium contents with natural and ⁶Li-enriched lithium hollow-cathode lamps. Linear calibration is attained over the range 0.0–99.3% ⁶Li, and the lithium isotopic abundance can be determined with an absolute error of ±0.7% ⁶Li for > 0.01 mol m^?3 lithium solutions. The method requires neither prior measurement of the total lithium content in sample solutions nor adjustment of the content to match that in the standard solutions.     

Determination of lithium and its isotopic composition by activation analysis and measurement of8Li and17N

The non-destructive determination of lithium was performed by using a Cerenkov counter for the detection of the 13 MeV (max) β-particles from the 0.84 sec⁸Li produced by the reaction⁷Li(n,γ)⁸Li. Under optimal conditions for a favorable signal-to-noise ratio, a count rate of about 35 cps/μg lithium at the beginning of the measurement was obtained, with a background of 4.5 cps and a working range of 3–400 μg lithium. The interference of other elements was studied. Several lithium-containing minerals and a sample of Dead Sea water were analyzed. The isotopic composition of lithium in aqueous solutions was determined by the simultaneous measurement of the neutrons produced by the reactions⁶Li(n,α)t and¹⁸O(t,α)¹⁷N, and the β-particles emitted by⁸Li.     

Spektrofotometrische bestimmung von calciumspuren nach ihrer abtrennung aus konzentrierten Lithiumchlorid-Lösungen mittels kationenaustausch

Calcium was separated from 1–2 M solutions of lithium chloride by means of Wofatit CP cation exchanger. Calcium was quantitatively separated from lithium by elution with 1 M ammonium chloride. Calcium, was eluted with hydrochloric acid and, eventually, measured spectrophotometrically at 567 mμ after addition of buffer and cresolphthalexone. The sensitivity was found to be 0.002 μg Ca/cm2 and Beer's law was obeved up to 15 μg Ca. With l g of lithium, the limit of determination was 10^-4% Ca.     

Structural mechanism of selective binding of lithium on a solid matrix of Al(OH)3 from aqueous solutions

The structure of intercalation complexes of aluminum hydroxide with lithium salts is investigated by X-ray diffractometry and by²¹Al,⁷Li, and¹H NMR. The lithium ions occupy vacant positions in the octahedral voids of aluminum hydroxide, and all atoms of gibbsite change localization. Parameters of the²⁷Al and⁷Li quadrupole and¹H dipole-dipole interaction tensors in anhydrous and aqueous intercalates of gibbsite with lithium salts are determined. A mechanism is suggested for the interaction of gibbsite with aqueous solutions of lithium salts. Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch, Russian Academy of Sciences (Novosibirsk). Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences (Novosibirsk). Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 448–452, May–June, 1998. This work was supported by RFFR grant No. 96-03-33069.     

Isotopic analysis of lithium by prompt alpha measurement during deuteron irradiation

Charged particle spectrometry was used to determine the isotopic concentration of lithium in lithium fluoride targets irradiated with a deuteron beam of 4.0 MeV. Alpha particles emitted by the⁶Li(d, α)⁴He and⁷Li(d, α)⁵He reactions were used as a measure of⁶Li and⁷Li, respectively. From the⁶Li/⁷Li α-count ratio the isotopic concentration of⁶Li was determined for isotopic concentrations over the range 7.42 (natural) to about 30 atom%⁶Li, with a relative standard deviation of±4.1%. Alpha particles from the¹⁹F(d, α)¹⁷O reaction could also be measured as an internal standard, extending the measurements from natural to 100 atom%⁶Li and giving a relative standard deviation of ±1.9%. The effect of target thickness on the accuracy of the determinations was investigated.     

CBNM - determination of Li in BCR reference materials RM 303 and RM 304 lyophilized serum by isotope dilution mass spectrometry (IDMS)

Summary Lithium was determined in two BCR Candidate Reference Materials 303 and 304 by Isotope Dilution Mass Spectrometry using the state-of-the-art performance of isotope-specific methods gained during previous certifications of ⁶LiF reference targets used for the determination of the neutron lifetime [1]. After reconstitution of the serum, four aliquots of each of the two candidate materials from four different bottles were spiked with a previously characterized enriched ⁶Li spike [2] which is now available as CBNM IRM-615 and has a certified ⁶Li/⁷ Li ratio of 21.78±0.12 and a certified lithium concentration of 4.001±0.028 mol/g solution. The serum aliquots were digested in an HNO₃/H₂O₂ mixture and after evaporation of the acid, the lithium was separated on a cation exchange column, eluted with 0.3 mol/L HCl and used as LiCl for mass spectrometric measurement on an NBS type thermal ionization mass spectrometer. Similarly an unknown sample BCR X, provided by BCR to check the performance of the certifying laboratories, was analyzed. In addition the chemical preparation method was controlled by assaying NBS (NIST) SRM 909. The chemical blank was determined by IDMS using ⁶Li enriched CBNM IRM-615. The measurements were corrected for isotopic fractionation using the Isotopic Reference Material CBNM IRM-016 chemically prepared in the same way as the samples. The CRM samples as well as the BCR X sample and the NBS SRM 909 were also analyzed for isotopic composition to verify whether they had indeed natural isotopic composition. The final results have an overall uncertainty of 1.2 and 1.5%, respectively. This overall uncertainty (on a 2s basis or an estimate thereof) takes into account all uncertainty contributions of statistical as well as of systematic nature (uncertainties on used reference materials, density and blank determinations). The final results compare favorably with the values proposed by BCR for certification, but have a smaller (better) uncertainty: CRM 303: (0.517 4±0.005 7) mmol/L, CRM 304: (0.987±0.014) mmol/L     

Green and efficient extraction strategy to lithium isotope separation with double ionic liquids as the medium and ionic associated agent

The paper reported a green and efficient extraction strategy to lithium isotope separation. A 4-methyl-10-hydroxybenzoquinoline (ROH), hydrophobic ionic liquid—1,3-di(isooctyl)imidazolium hexafluorophosphate ([D(i-C₈)IM][PF₆]), and hydrophilic ionic liquid—1-butyl-3-methylimidazolium chloride (ILCl) were used as the chelating agent, extraction medium and ionic associated agent. Lithium ion (Li⁺) first reacted with ROH in strong alkali solution to produce a lithium complex anion. It then associated with IL⁺ to form the Li(RO)₂IL complex, which was rapidly extracted into the organic phase. Factors for effect on the lithium isotope separation were examined. To obtain high extraction efficiency, a saturated ROH in the [D(i-C₈)IM][PF₆] (0.3 mol l^?1), mixed aqueous solution containing 0.3 mol l^?1 lithium chloride, 1.6 mol l^?1 sodium hydroxide and 0.8 mol l^?1 ILCl and 3:1 were selected as the organic phase, aqueous phase and phase ratio (o/a). Under optimized conditions, the single-stage extraction efficiency was found to be 52 %. The saturated lithium concentration in the organic phase was up to 0.15 mol l^?1. The free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) of the extraction process were ?0.097 J mol^?1, ?14.70 J mol K^?1 and ?48.17 J mol^?1 K^?1, indicating a exothermic process. The partition coefficients of lithium will enhance with decrease of the temperature. Thus, a 25 °C of operating temperature was employed for total lithium isotope separation process. Lithium in Li(RO)₂IL was stripped by the sodium chloride of 5 mol l^?1 with a phase ratio (o/a) of 4. The lithium isotope exchange reaction in the interface between organic phase and aqueous phase reached the equilibrium within 1 min. The single-stage isotope separation factor of ⁷Li–⁶Li was up to 1.023 ± 0.002, indicating that ⁷Li was concentrated in organic phase and ⁶Li was concentrated in aqueous phase. All chemical reagents used can be well recycled. The extraction strategy offers green nature, low product cost, high efficiency and good application prospect to lithium isotope separation.     

The neutron activation determination of lithium in the presence of alkali metals and magnesium

A neutron activation method for lithium in the presence of alkali metals or magnesium has been developed, utilizing the ⁶Li(n,α)³H and ¹⁶O(t,n)¹⁸F nuclear reactions. After a short thermal neutron irradiation with a. lithium standard, 112-min fluorine-18 is separated by a lead chlorofluoridc precipitation. The annihilation photons from the separated fluorine-18 are counted using 2 sodium iodide detectors, a fast-slow coincidence system and a multichannel analyzer. Precision in a synthetic l% lithium-in-sodium matrix was found to be ± 2.0% standard deviation, whereas the accuracy of the method is estimated to be ± 3% or better. The ultimate sensitivity in pure solution is estimated to be about 0.2 p.p.b. and in a sodium matrix about 0.5 p.p.m. The only interferences are several positron emitters, easily discriminated from by chemical separation, decay or by means of other nuclear parameters. Three hours are required for a duplicate determination, following initial sample preparation and dilution. To use the method, the lithium isotopic abundance must be known or determined by mass spectrometry because of the prevalence of depleted litliium in metal and salts.     

Differential pulse polarographic determination of traces of iron in solar-grade silicon

Iron is determined, after volatilization of the matrix as hexafluorosilicic acid, by means of the polarographic iron(III) wave in a 0.1 M triethanolamine—0.1 M potassium bromate—0.5 M sodium hydroxide medium. Differential pulse polarography provides a detection limit of about 0.15 μg g^-1 with a precision of 1–2% and linear calibration graphs up to 0.5 μg Fe(III) ml^-1.     

Isotopic analysis of7LiOH samples by SSMS

A methodology for the isotopic determination of lithium in enriched⁷LiOH.2H₂O samples by SSMS is described. The photoplate emulsion calibration curve was not used. The accuracy of the results was checked against the analysis of LiOH.2H₂O with natural isotopic composition, and it was found that the result obtained was accurate within 5% with respect to the published natural value. The accuracy was improved using an enriched in⁷Li reference sample. The technique was applied to the analysis of batches of⁷LiOH.2H₂O to be used in a nuclear power reactor to control the pH in the water cooling system.SSMS: Spark Source Mass Spectrometry.     

Trace fluoride determination with specific ion electrode

A method is described for determining 10^-5–10^-4M fluoride in a variety of solutions potentiometrically with a fluoridc-specific electrode, by a standard addition method. Any change of ionic strength or the nature of the solution that might alter activity coefficients or junction potentials is minimized. The relationship between potential and fluoride concentration thus follows the Nernst equation, and the unknown concentration can be calculated. Experimental data are given for solutions of sodium choride, sodium nitrate, acidified sodium silicate and sodium hydroxide, lithium chloride, and phosphoric acid. Metal ions (e.g., Al³⁺, UO₂²⁺, Fe³⁺, Th⁴⁺) that interfere by forming complexes with fluoride can be precomplexed with phosphoric acid. The relative error is estimated at 10%, and the relative standard deviation is less than 5% over the concentration range 10^-5–10^-4M fluoride.     

The elemental and isotopic determination of lithium by the coincidence measurement of complementary particles

The coincident measurement of both nuclear products at their complementary angles was used to determine⁶Li by the reactions⁶Li(d, α)⁴He and⁶Li(p, α)³He, and⁷Li by the reaction⁷Li(p, α)⁴He. Elemental lithium was determined in natural samples or samples of known isotopic composition. Isotopic analyses could be carried out over the entire range from 0 to 100 atom% with a relative standard deviation of about 4%. The CMCP technique is highly specific and effectively eliminates interference and background.     

Chemiluminescence for the determination of traces of cobalt(II) by continuous flow and flow injection methods

Flow injection analysis, with chemiluminescence detection, is used to determine traces of cobalt(II) by means of the gallic acid—hydrogen peroxide—sodium hydroxide system containing a small amount of methanol to increase the sensitivity. This permits the determination of cobalt(II) more selectively than any other chemiluminescent system with a detection limit of 0.04 μg l^-1 (continuous sample flow) or 0.04 ng (10-μl sample injection). The linear range is 3 orders of magnitude, the sampling rate is 20 h^-1, and the relative standard deviation is 5.9% for 0.06 ng Co(II) (n = 10). Silver(I), the strongest enhancer after cobalt(II), provides a signal 1.3% of that for Co(II). A few precipitants and complexing agents suppress the signal.     

Neutron activation analysis of6Li isotopic abundance using a low background liquid scintillation counter

A neutron activation method based on the measurement of tritium radioactivity produced by⁶Li (n,)³H reaction was applied to determine the isotopic abundance of⁶Li in aqueous solution with known lithium concentration. Tritium radioactivity was measured with a low background liquid scintillation counter over a period of 2000 min. The present method demonstrated a good linearity between the isotopic abundance of⁶Li and tritium radioactivity produced per unit amount of lithium in a wide range of lithium concentration. A comparison of the present data with those from mass spectrometry showed agreement, though our method was 10 times less sensitive, than mass spectrometry. The present new approach should thus prove quite useful for determining the isotopic abundance of⁶Li.     

Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 μg l^?1 of tin in the MIBK solution or 0.2–0.3 μg g^?1 in the rock. The concentration range is linear between 2.5 and 500 μg l^?1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 μg l^?1 level and < 7% at the 10–30 μg l^?1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 μg g^?1 or less.     

Carbon isotopic composition effects on interatomic interactions and the properties of diamond

The interatomic interaction potential parameters were determined for ¹²C and ¹³C in diamond. The results were used to obtain the isotopic dependences of such diamond properties as the Debye temperature, molar heat capacity, thermal expansion coefficient, energies of vacancy formation and self-diffusion, surface energy, and longitudinal velocity of sound. The isotopic dependence of isochoric heat capacity disappeared as the temperature increased. Sign inversion was observed for the isotopic dependence of the thermal expansion coefficient at a certain temperature: its growth changed into a drop. This approach was also used to estimate changes in the interatomic interaction potential and crystal bulk compression modulus of lithium in going from ⁷Li to ⁶Li. The isotopic dependences of phase transition parameters and the whole p-T phase diagram of a simple substance were predicted.     

Transport Properties of Solid Electrolytes: Effect of the Isotope Composition of Lithium Charge Carriers

The isotope composition of lithium charge carriers is experimentally found to severely affect transport in solid electrolytes -Li₃BO₃, Li₃N, Li₃AlN₂, Li₅SiN₃, Li₆MoN₄, Li₆WN₄, and LiCl. The lithium cation conduction of these decreases with increasing content of ⁶Li or ⁷Li and reaches a minimum at [⁶Li] = [⁷Li]. The activation energy for conduction increases, reaches a maximum in the same compositions, and then diminishes. Rates of spin–lattice relaxation of ⁷Li nuclei in electrolytes are studied by an NMR method at 15–35 MHz. The calculated activation energy for short-range motion (to one interatom distance) of lithium charge carriers in crystal lattices of electrolytes is lower than that for ionic conduction by 2–3 times, which is attributed to two types of correlation (electrostatic, isotopic) of charge carriers.     

The application of resonance monochromators to the determination of lithium in blood serum by atomic absorption spectrophotometry

Lithium in blood serum can be determined rapidly and with sufficient accuracy by atomic absorption measurement of solutions of blood serum diluted with water, using either a conventional atomic absorption spectrophotometer or one with a resonance monochromator. Calibrating solutions contain sodium and potassium at approximately the concentrations present in the serum solutions as these metals cause a slight enhancement of lithium absorption in the air/coal gas flame. Results are reproducible to within ±0.2 μg Li/ml in the serum and the limits of sensitivity attainable for samples diluted 1:10 are 0.3μg Li/ml in the serum with the conventional instrument and 0.6 μg Li/ml in the serum with the resonance monochromator.