Chemical Separation Scheme Research Articles

High-precision Sm isotope analysis by thermal ionisation mass spectrometry for large meteorite samples (>1 g).

This study presents a new procedure for high-precision Sm isotope analysis by thermal ionisation mass spectrometry (TIMS) for geological samples. A four-step chemical separation scheme results in sharp separation of Sm and Nd from the same sample aliquot. The first step utilises anion exchange resin to remove Fe from the sample solution. Two different liquid-liquid extraction resins are then used to isolate rare-earth elements (TRU-Spec) and purify Sm from Nd (DGA). Fractionation occurs on the DGA resin due to the nuclear field shift effect, but this is negligible if yields greater than 70% are achieved. Different analytical setups were tested to ascertain their ionisation efficiencies on TIMS. The effect of activators composed of Pt and Ta was tested on single Re filaments but the conventional double Re filament assembly provided efficient ionisation and more stable ion beams. The determination of nucleosynthetic isotope variations requires high precision for all Sm isotope ratios. We aimed to improve the precision on the scarce 144Sm isotope (3% of all Sm). Static, multistatic and dynamic methods were tested. Isotope ratios were normalised to both 147Sm/152Sm and 152Sm/148Sm for comparison. The dynamic methods failed to provide better precision on ratios involving 144Sm, whereas the multistatic method yielded improved precisions between 13 and 22 ppm (twice the standard deviation, 2 SD) on the 144Sm/152Sm ratio. Synthetic standards have variable Sm isotope compositions, thus requiring systematic and precise characterisation against terrestrial samples. Analyses conducted using this new procedure yielded high-precision values which were consistent with literature data for an array of terrestrial rock standards and the meteorite Allende.

Fusion and chemical separation of Am, Pu and Sr from barite-concrete

The goal of this study was to omit the hazardous hydrofluoric acid for silica removal before fusion of barite-concrete. Furthermore, the goal was to establish a chemical separation technique to simultaneously determine the activity concentrations of 241Am, 238Pu, 239+240Pu and 90Sr of one sub-sample. After the fusion process, using Li-metaborate/Li-tetraborate, the colloidal silica could be successfully flocculated using polyethylene glycol (PEG-2000). A chemical separation scheme using the resins DGA—BIO-RAD AG 1-X2/UTEVA—DGA and TEVA for the actinides and DGA and Sr resin for Sr was successfully established, underlined by the quantitative 243Am, 242Pu and 85Sr average tracer recoveries of at least 60%, and in best cases up to 86%.

Design of Multiperiod C–H–O Symbiosis Networks

Recently, the problem of designing a carbon, hydrogen, and oxygen symbiosis network (CHOSYN) has been introduced to enable the systematic integration of multiple plants and to determine chemical conversion, separation, and allocation schemes through a multiscale atomic targeting approach. The previous contributions in designing CHOSYNs assumed a single mode of operation for all participating plants. Since some plants may have seasonable variabilities, multiple modes of operation may be necessary. Each mode of operation is characterized by different flow rates and compositions of the integrated streams. The objective of this work is to develop a multiperiod approach to design a CHOSYN by considering multiple modes of operation throughout the year. A multiscale targeting approach is proposed to determine the optimal type and size of the common infrastructure for all participating plants under different modes of operation. A case study involving five industrial plants and two modes of operation is presented ...

Rare-earth element fractionation in uranium ore and its U(VI) alteration minerals

A cation exchange chromatography method employing sulfonated polysterene cation resin (DOWEX AG50-X8) was developed in order to separate rare-earth elements (REEs) from uranium-rich materials. The chemical separation scheme is designed to reduce matrix effects and consequently yield enhanced ionization efficiencies for concentration determinations of REEs without significant fractionation using solution mode-inductively coupled plasma mass spectrometry (ICP-MS) analysis. The method was applied to determine REE abundances in four uraninite (ideally UO2) samples and their associated U(VI) alteration minerals. In three of the samples analyzed, the concentration of REEs for primary uraninite are higher than those for their corresponding secondary uranium alteration phases. The results for U(VI) alteration minerals of two samples indicate enrichment of the light REEs (LREEs) over the heavy REEs (HREEs). This differential mobilization is attributed to differences in the mineralogical composition of the U(VI) alteration. There is a lack of fractionation of the LREEs in the uraninite alteration rind that is composed of U(VI) minerals containing Ca2+ as the interlayer cation (uranophane and bequerelite); contrarily, U(VI) alteration minerals containing K+ and Pb2+ as interlayer cations (fourmarierite, dumontite) indicate fractionation (enrichment) of the LREEs. Our results have implications for nuclear forensic analyses since a comparison is reported between the REE abundances for the CUP-2 (processed uranium ore) certified reference material and previously determined values for uranium ore concentrate (UOC) produced from the same U deposit (Blind River/Elliott Lake, Canada). UOCs represent the most common form of interdicted nuclear material and consequently is material frequently targeted for forensic analysis. The comparison reveals similar chondrite normalized REE signatures but variable absolute abundances. Based on the results reported here, the latter may be attributed to the differing REE abundances between primary ore and associated alteration phases, and/or is related to varying fabrication processes adopted during production of UOC.

Triple-Quadrupole Inductively Coupled Plasma-Mass Spectrometry with a High-Efficiency Sample Introduction System for Ultratrace Determination of (135)Cs and (137)Cs in Environmental Samples at Femtogram Levels.

High yield fission products, (135)Cs and (137)Cs, have entered the environment as a result of anthropogenic nuclear activities. Analytical methods for ultratrace measurement of (135)Cs and (137)Cs are required for environmental geochemical and nuclear forensics studies. Here we report a highly sensitive method combining a desolvation sample introduction system (APEX-Q) with triple-quadrupole inductively coupled plasma mass spectrometry (AEPX-ICPMS/MS) for the determination of (135)Cs and (135)Cs/(137)Cs isotope ratio at femtogram levels. Using this system, we introduced only selected ions into the collision/reaction cell to react with N2O, significantly reducing the isobaric interferences ((135)Ba(+) and (137)Ba(+)) and polyatomic interferences ((95,97)Mo(40)Ar(+), (119)Sn(16)O(+), and (121)Sb(16)O(+)). Compared to the instrument setup of ICPMS/MS, the APEX-ICPMS/MS enables a 10-fold sensitivity increase. In addition, an effective chemical separation scheme consisting of ammonium molybdophosphate (AMP) Cs-selective adsorption and two-stage ion-exchange chromatographic separation was developed to remove major matrix and interfering elements from environmental samples (10-40 g). This separation method showed high decontamination factors (10(4)-10(7)) for major matrix elements (Al, Ca, K, Mg, Na, and Si) and interfering elements (Ba, Mo, Sb, and Sn). The high sensitivity of APEX-ICPMS/MS and the effective removal sample matrix allowed reliable analysis of (135)Cs and (137)Cs with extremely low detection limits (0.002 pg mL(-1), corresponding to 0.006 Bq mL(-1) (137)Cs). The accuracy and applicability of the APEX-ICPMS/MS method was validated by analysis of seven standard reference materials (soils, sediment, and plants). For the first time, ultratrace determination of (135)Cs and (135)Cs/(137)Cs isotope ratio at global fallout source environmental samples was achieved with the ICPMS technique.

Integrated separation scheme for measuring a suite of fission and activation products from a fresh mixed fission and activation product sample

Mixed fission and activation materials resulting from various nuclear processes and events contain a wide range of isotopes for analysis spanning almost the entire periodic table. This work describes the production of a complex synthetic sample containing fission products, activation products, and irradiated soil, and determines the percent chemical recovery of select isotopes through the integrated chemical separation scheme. Based on the results of this experiment, a complex synthetic sample can be prepared with low atom/fission ratios and isotopes of interest accurately and precisely measured following an integrated chemical separation method.

Determination of precise ¹³⁵Cs/¹³⁷Cs ratio in environmental samples using sector field inductively coupled plasma mass spectrometry.

Recent advances in sector field inductively coupled plasma mass spectrometry (ICP-SFMS) have led to significant sensitivity enhancements that expand the range of radionuclides measurable by ICP-MS. The increasing capability and performance of modern ICP-MS now allows analysis of medium-lived radionuclides previously undertaken using radiometric methods. A new generation ICP-SFMS was configured to achieve sensitivities up to 80,000 counts per second for a 1 ng/L (133)Cs solution, providing a detection limit of 1 pg/L. To extend this approach to environmental samples it has been necessary to develop an effective chemical separation scheme using ultrapure reagents. A procedure incorporating digestion, chemical separation and quantification by ICP-SFMS is presented for detection of the significant fission product radionuclides of cesium ((135)Cs and (137)Cs) at concentrations found in environmental and low level nuclear waste samples. This in turn enables measurement of the (135)Cs/(137)Cs ratio, which varies with the source of nuclear contamination, and can therefore provide a powerful dating and forensic tool compared to radiometric detection of (137)Cs alone. A detection limit in sediment samples of 0.05 ng/kg has been achieved for (135)Cs and (137)Cs, corresponding to 2.0 × 10(-3) and 160 mBq/kg, respectively. The critical issue is ensuring removal of barium to eliminate isobaric interferences arising from (135)Ba and (137)Ba. The ability to reliably measure (135)Cs/(137)Cs using a high specification laboratory ICP-SFMS now enables characterization of waste materials destined for nuclear waste repositories as well as extending options in environmental geochemical and nuclear forensics studies.

Analysis of Th, U, Pu, and Am in radioactive metal waste using extraction chromatography

In order to analyze actinide elements in radioactive metal waste, the dissolution and chemical separation conditions were optimized. The surfaces of a type 304 stainless steel plate and of pipe waste sampled from the prototype advanced thermal reactor (Fugen) were dissolved in mixed acid solution (HNO3:HCl:H2O = 1:1:4). The resulting solution was evaporated to dryness and dissolved with 2 mol/dm3 of HNO3 to prepare sample solutions. In order to analyze trivalent actinide elements in the sample solution containing a large amount of Fe(III) (>0.1 g) using TRU resin, the effect of Fe(III) concentration on the recovery of Am(III) and reduction effect of Fe(III) to Fe(II) with ascorbic acid were studied. On the basis of results of this study, chemical separation scheme was constructed and Pu and Am in the sample solutions were separated. Thorium and U in the sample solutions were separated with UTEVA resin. High recoveries for all experimented elements were obtained from the analysis of spiked sample solutions, the effectiveness of the method was confirmed.

Methodology for determination of 89Sr and 90Sr in radiological emergency: II. Method development and evaluation

In this work a method for the determination of both 89Sr and 90Sr is presented. The method can potentially be used in radiological emergency and deliver results shortly after an incident. The method development was based on theoretical calculations of potential interferences from other fission products and how these could be discriminated when applying different chemical separation schemes. Validation was done on reactor coolant water containing short-lived fission products, and on a reference material. The results indicate that correct results of 89Sr and 90Sr can be obtained 4 and 9 days, respectively, after an incident.

Modeling of gamma-ray spectra to direct efficient chemical separations

A project has been undertaken at Pacific Northwest National Laboratory (PNNL) to tailor a series of efficient chemical separations to allow the rapid quantification of gamma-ray emitting isotopes in mixed fission product (MFP) samples. In support of that goal, modeling of singles and coincident gamma-ray spectra that would result from various chemical separation strategies has been performed. These simulated spectra have identified likely instances of spectral interference and have provided an estimate of the time window available for the detection of radionuclides following various chemical separation schemes. A description of results to date is presented here, demonstrating the utility of this approach for improved processing and analysis of fission product samples.

Separation of group five elements by reversed-phase chromatography

A chemical separation method based on reversed-phase chromatography has been developed to separate the group five elements from the reaction products produced in the bombardment of 243Am with 48Ca ions. Decontamination factors on the order of 106 were achieved for group-three elements such as americium, and 107 or more for selected reaction products as measured by gamma-ray spectrometry pre-and post-chemistry. Details of the chemical separation scheme are discussed and compared to previously reported results.

Measurement of 63Ni produced in Cu samples by the Hiroshima atomic bomb

The 63Ni in copper samples exposed by the Hiroshima atomic bomb was clearly measured for the first time by liquid scientillation method For the measurement, the chemical separation scheme previously developed was improved The obtained result was agreed with that estimated by the new dosimetry system for atomic bomb survivor studies, DS02.

Demonstration of Enantiomer Specificity of Proteins and Drugs

In addition to the traditional use of molecular models of tetrahedral asymmetric centers, the concept of chirality and its importance to protein–drug interactions is demonstrated in a guided classroom activity. A watchglass with three different colored Post-it Notes is set on a desktop or table surface to simulate a molecular binding site of a protein. As students build models of symmetric and asymmetric centers, the models are tested for binding to the watchglass "binding site". By relating the chiral or achiral models to various common or familiar drugs, students can easily understand the importance of chirality in protein–drug interactions. This approach can be easily adapted to the knowledge base of the student and can include concepts of prochirality, nomenclature, properties, and chemical separation schemes of enantiomers.See the Discussion on this Tested Demonstation.

142Nd evidence for early Earth differentiation

We measured 142Nd/ 144Nd in metabasalts and metagabbros from the western and southern parts of the Isua Supracrustal Belt, West Greenland. The samples were selected based on field and thin section criteria so as to minimize metamorphic effects on the isotope systematics. We developed a new multi-stage chemical separation scheme and a new isotope measurement technique using multiple-collector inductively coupled plasma mass spectrometry and, upon replication of measurements, achieved a precision better than 20 ppm. Out of eight samples, three show a positive 142Nd anomaly of 30 ppm consistent with a previous measurement by Harper and Jacobsen [Nature 360 (1992) 728–732]. These samples also define a 147Sm– 143Nd isochron age that agrees with the commonly accepted U–Pb zircon age of 3.78 Ga for Isua, while the non-anomalous samples show substantial dispersion. The latter lack of coherence is interpreted as indicating either isotopic heterogeneities in the Isua upper mantle or redistribution of Nd by fluids during late Archean metamorphic events. Scatter among the non-anomalous samples is also observed for the Lu–Hf isotope systematics and confirms the severity of metamorphic remobilization. If the 147Sm– 143Nd and 146Sm– 142Nd systems are explained by a two-stage model, it is required that the upper mantle went through a major differentiation event within a few tens of millions of years after planetary accretion. If early Archean convection decoupled the two Nd isotope systems, this necessitates that the episode of differentiation took place within no more than 150 Myr of planetary accretion. One interpretation of the high-Sm/Nd reservoir is that it represents the remnants of a stagnant lithospheric lid overlying a magma ocean. Because the lid is shattered by impacts, it is unable to sink. Alternative explanations, such as an ultra-deep magma ocean at the core–mantle boundary or massive subduction of early crust, call for the early burial of enriched material and the ubiquitous presence of a 142Nd anomaly in the early Archean mantle.

A New Digestion and Chemical Separation Technique for Rapid and Highly Reproducible Determination of Lu/Hf and Hf Isotope Ratios in Geological Materials by MC‐ICP‐MS

A new digestion procedure and chemical separation technique has been developed for measurement of Lu/Hf and Hf isotope ratios that does not require high‐pressure bombs or use of HF or HClO4 acids. Samples are digested in dilute HCl or HNO3 after flux‐fusion at 110 0 °C in the presence of lithium metaborate. High field strength elements (HFSE) and rare earth elements (REE) are separated from this solution by co‐precipitation with iron hydroxide. The dissolved precipitate (in 2 mol l−1 HCl) is loaded directly onto a standard cation exchange column which separates remaining sample matrix from the heavy REE (Lu+Yb), and the middle‐light REE and HFSE (Hf). The middle‐light REE and individual HFSE are then separated (10.5, 9 and 6 mol l−1 HCl) using a miniaturized column containing TEVA spec resin which provides a REE‐, Ti‐ and Zr‐free Hf cut. This chemical separation scheme can also be readily adapted for isotopic analysis of the Sm‐Nd system and/or the other HFSE (Ti, Zr). Total procedural blanks for this technique are < 10 0 pg and < 2 pg for Hf and Lu, respectively, even when digesting large (0.5 g) samples.We present data from replicate digestions of international rock reference materials which demonstrate this technique routinely reproduces Lu/Hf ratios to < 0.2% (2s) and 176 Hf/177 Hf isotope ratios to < 30 ppm (2s). Moreover, the technique is matrix‐independent and has been successfully applied to analysis of diverse materials including basalts, meteorites, komatiites, kimberlites and carbonatites. The relative simplicity of this technique, coupled with the ease of digestion (and sample‐spike equilibration) of large difficult‐to‐dissolve samples, and the speed (2 days) with which samples can be digested and processed through the chemical separation scheme makes it an attractive new method for preparing samples for Lu‐Hf isotopic investigation.

The complexation of `dissolved' Cu, Zn, Cd and Pb by soluble and colloidal organic matter in Narragansett Bay, RI

It is widely accepted that the speciation of most bioactive metals in seawater is regulated by natural organic ligands, but the nature of these molecules has remained a mystery. We used a combination of physical and chemical separation schemes to better characterize organic molecules complexing Cu, Zn, Cd, and Pb in Narragansett Bay, RI. Conventionally filtered ( 1 kDa), with the bulk of it found in the 1–8 kDa colloidal size range. Of the three Cu-binding ligand classes measured, the strongest class occurred mainly in the soluble fraction while the weaker Cu-binding ligand classes were predominantly colloidal (>1 kDa). Approximately 40% of chelated Pb was colloidal but, in contrast to Cu, the bulk of these ligands resided in the larger colloidal size range (8 kDa–0.2 μm). Thus, a continuum of metal complexing ligand size exists, spanning from truly soluble to colloidal, the nature of which differs for individual bioactive metals. These findings support the hypothesis that metal complexation in seawater is dominated by distinct, metal-specific ligand molecules. A central question that now emerges is whether these ligand molecules function predominantly to buffer metal ion activities in seawater, thereby decreasing metal sorption to particulates, or to facilitate metal removal by sweeping organically bound metals into particulate phases via colloid aggregation.

An Alternative Method for the Determination of Excess 210Pb in Sediments

Nowadays, there are several multidetector low-level proportional counters on the market, which are able to measure up to 16 samples simultaneously. Such counters are particularly useful for 210Pb dating, when a core is split into many samples to be analysed. In order to preserve this advantage, a simple radiochemical method should be applied for atmospheric, or excess, 210Pb prior to its determination by beta counting. Starting from a 0.5 M HBr leaching step, a simple chemical separation scheme based on anionic ion exchange was developed. In this method, the lead present in the eluate is precipitated as lead chromate and the 210Pb is determined through the beta counting of 210Bi. The application is discussed of the above chemical separation procedure to marine sediment reference samples, IAEA 368 and IAEA 135, as well as to sediment cores from different environments. Using 5 g of dry sediment sample and 24,000 s counting time, a detection limit of 3 mBq.g-1 can be achieved.

Searching for Cluster Decay of 232Th: A Chemical Separation Scheme for Sodium-24 from Thorium

Searching for Cluster Decay of ²³²Th: A Chemical Separation Scheme for Sodium-24 from Thorium

Measurement of stable isotopes of bromine in biological fluids with inductively coupled plasma mass spectrometry.

A method is reported for the accurate measurement of the two stable isotopes of bromine in biological fluids of interest in human metabolic studies. The method is based on inductively coupled plasma mass spectrometry (ICP-MS).It is shown that the background ion beam intensities at m/z= 79 and 81 are typically in the range 70–335 and 600–7200 ions s–1, respectively, when de-ionised water is aspirated into the plasma. The corresponding range for 1.0 µg ml–1 of natural Br is 9700–18 500 ions s–1 at m/z= 79. The detection limit (3[graphic omitted]) for Br is in the range 2–5 ng ml–1. A method is given for automatic correction of the argon contribution at m/z= 81.Data are presented which show that the isotope ratio 81Br/79Br can be measured routinely with a precision (relative standard deviation) of 1% or better. The measured ratio is independent of the Br concentration in the range 3–20 µg ml–1. Linear regression equations are obtained for stable isotope calibration graphs over the range 0.997–5.322 (MIR81/79). However, the slopes of these plots deviate considerably from the expected value of one.Two chemical separation schemes are described, Scheme I, based on cation exchange and Scheme II, based on distillation from acidified solutions. The former is applicable to plasma (and possibly saliva) samples whereas the latter is successful for urine. The presence of large amounts of sulphate produces significant enhancement of the ion intensity at m/z= 81 (due to 32S16O31H+). Distillation permits the required separation of Br from sulphate, whereas precipitation with Ba(NO3)2 does not appear to be satisfactory.Application of the method of standard additions and stable isotope dilution analysis to samples of urine from several subjects indicates that this method permits quantitative analysis of bromine to be carried out with a precision (and accuracy) of about 2%.

Separation and recovery of various sulphur species in sedimentary rocks for stable sulphur isotopic determination

Existing methods to extract particular forms of sulphur in rocks and sediments are reviewed and evaluated for application in a chemical scheme to recover sulphur as either Ag 2S or BaSO 4 precipitates for isotopic analysis. The S species distinguished include “acid-soluble” sulphides and sulphates, elemental S, pyrite, barite and various categories of organically bound S. There is no evidence of cross-contamination or isotopic fractionation during the separation as applied to mixtures synthesized from internal control samples; the precision obtained on repetitive extractions is equivalent to that of the measurement technique itself, typically, ±0.2‰ in the δ 34S-value. The chemical separation scheme is demonstrated by application to sections of peat collected from the Howards Pass XY Deposit in the Yukon Territory, Canada.