Sample preparation for the determination of radiocalcium by accelerator mass spectrometry

An accelerator mass spectrometric (AMS) technique has been developed for determining ⁴¹Ca/⁴⁰Ca ratios at terrestrial levels of 10^?16?10^?14. Calcium is extracted as calcium oxide from bone and rock samples. The calcium oxide is converted into calcium metal and subsequently into calcium hydride in a two-step reduction process. From these calcium hydride samples 5–10 μA of a negative-ion beam of CaH^?₃ is produced. A new gas-ionization detector and a high-resolution velocity detector allow discrimination against ⁴¹K and the stable isotopes of Ca, resulting in background levels of less than 6 × 10^?16. Hence it is possible (for the first time without pre-enrichment) to study the distribution of ⁴¹Ca in the terrestrial environment. The AMS method for ⁴¹Ca determination is applicable to samples of less than 1 g.     

Alpha activation of calcium and its possible use for analysis

This method is based upon the measurement of 3.95-hr⁴³Sc which is formed during α-activation from⁴⁰Ca, the most abundant (96.8%) isotope of calcium. The excitation function for the⁴⁰Ca(α, p)⁴³Sc reaction was determined and the maximum yield of⁴³Sc (about 10⁷ cpm per mg of calcium for a 1-hr irradiation at a beam current of 1 μA) was obtained at an irradiation energy of 14 MeV. The interference free sensitivity of the method at this energy was found to be 8.5·10^?12 g, for a 1-hr irradiation at a beam current of 10 μA. The elements most likely to interfere with the determination are potassium and scandium. The extent of this interference was investigated as a function of irradiation energy and methods to eliminate or subtract the activity formed from these elements are discussed. An attempt was made to determine non-destructively the calcium content of very pure silicon and aluminium and upper limits for the concentration of calcium in these samples were set at 0.27 ppb and 6.9 ppb, respectively. Magnesium, thulium oxide and yttrium oxide samples of known calcium content were also analysed.     

Rapid determination of radiostrontium in large soil samples

A new method for the determination of radiostrontium in large soil samples has been developed at the Savannah River Environmental Laboratory (Aiken, SC, USA) that allows rapid preconcentration and separation of strontium in large soil samples for the measurement of strontium isotopes by gas flow proportional counting. The need for rapid analyses in the event of a radiological dispersive device or improvised nuclear device event is well-known. In addition, the recent accident at Fukushima Nuclear Power Plant in March, 2011 reinforces the need to have rapid analyses for radionuclides in environmental samples in the event of a nuclear accident. The method employs a novel pre-concentration step that utilizes an iron hydroxide precipitation (enhanced with calcium phosphate) followed by a final calcium fluoride precipitation to remove silicates and other matrix components. The pre-concentration steps, in combination with a rapid Sr Resin separation using vacuum box technology, allow very large soil samples to be analyzed for ^89,90Sr using gas flow proportional counting with a lower method detection limit. The calcium fluoride precipitation eliminates column flow problems typically associated with large amounts of silicates in large soil samples.     

Direct spectrophotometric determination of calcium in clinical samples with carboxyazo-p-CH3

A highly sensitive and relatively interference-free spectrophotometric method for determination of calcium is described. The method is based on the reaction between calcium ions and carboxyazo-p-CH₃ in aqueous citrate medium of pH 7, to form a blue complex with maximum absorption at 716 nm. The calibration is linear up to 0.12 μg ml⁻¹ calcium with a repeatability (R.S.D.) of 1.0% at a concentration of 0.04 μg ml⁻¹ (n=5). The molar absorptivity of the complex and Sandell’s sensitivity are 3.5×10⁵ l mol⁻¹ cm⁻¹ and 0.11 ng cm⁻², its 10σ limit of quantification and the 3σ limit of detection were found to be 0.3 ng ml⁻¹ and 0.09 ng ml⁻¹ respectively. The influence of reaction variables and the effect of interfering ions are studied; no interference was observed in clinical samples. The proposed method has been applied directly to the determination of calcium in clinical samples without the need for pre-concentration, masking metal ions and digesting samples.     

Direct Spectrophotometric Determination of Calcium in Human Serum and Cerebrospinal Fluids with Amino G Acid Chlorophosphonazo

ABSTRACT

A novel spectrophotometric method based on amino G acid chlorophosphonazo (AGCPA) has been developed for measuring calcium in human serum and cerebrospinal fluids. The effects of experimental factors including pH, reagent concentrations, and interfering species on calcium determinations were investigated. In a neutral reaction media of pH 7.0, AGCPA reacts rapidly with calcium to form a stable and greenish blue complex, whose absorption maximum is at 670 nm. The molar absorptivity (?) of the complex is 7.2x10⁴ 1 mol^?1cm^?1, and the molar ratio of calcium to AGCPA in the complex is found to be 1:2. Beer's law is obeyed over the range 0.02-0.8 μg ml^?1 of calcium. No interferences were observed from the commonly coexisting species present in serum and cerebrospinal fluids. Compared to the reported and currently often used methods based on o-cresolphthalein complexone, arsenazo III and methylthymol blue, the proposed method in this work provides better analytical characteristics such as high sensitivity, good selectivity and neutral reaction media. In addition, the present method is simple and can be applied to the direct determination of calcium in human serum and cerebrospinal fluid samples with satisfactory results.     

Rapid determination of 226Ra in environmental samples

A new rapid method for the determination of ²²⁶Ra in environmental samples has been developed at the Savannah River Site Environmental Lab (Aiken, SC, USA) that can be used for emergency response or routine sample analyses. The need for rapid analyses in the event of a Radiological Dispersive Device or Improvised Nuclear Device event is well-known. In addition, the recent accident at Fukushima Nuclear Power Plant in March, 2011 reinforces the need to have rapid analyses for radionuclides in environmental samples in the event of a nuclear accident. ²²⁶Ra (T1/2?=?1,620?years) is one of the most toxic of the long-lived alpha-emitters present in the environment due to its long life and its tendency to concentrate in bones, which increases the internal radiation dose of individuals. The new method to determine ²²⁶Ra in environmental samples utilizes a rapid sodium hydroxide fusion method for solid samples, calcium carbonate precipitation to preconcentrate Ra, and rapid column separation steps to remove interferences. The column separation process uses cation exchange resin to remove large amounts of calcium, Sr Resin to remove barium and Ln Resin as a final purification step to remove ²²⁵Ac and potential interferences. The purified ²²⁶Ra sample test sources are prepared using barium sulfate microprecipitation in the presence of isopropanol for counting by alpha spectrometry. The method showed good chemical recoveries and effective removal of interferences. The determination of ²²⁶Ra in environmental samples can be performed in less than 16?h for vegetation, concrete, brick, soil, and air filter samples with excellent quality for emergency or routine analyses. The sample preparation work takes less than 6?h. ²²⁵Ra (T1/2?=?14.9?day) tracer is used and the ²²⁵Ra progeny ²¹⁷At is used to determine chemical yield via alpha spectrometry. The rapid fusion technique is a rugged sample digestion method that ensures that any refractory radium particles are effectively digested. The preconcentration and column separation steps can also be applied to aqueous samples with good results.     

Separation of radioactive strontium from natural samples by means of mixed-solvent anion exchange

A new procedure for isolation and determination of⁹⁰Sr in real natural samples is presented. It consists of bringing natural samples in a soluble form suitable for separation on an ion-exchange column, separation of calcium from strontium by means of the anion exchanger Amberlite CG-400 and 0.25M HNO₃ in methanol as eluent for calcium, and the determination of⁹⁰Sr using a low level -counter after elution with H₂O, scavenging steps and SrCO₃ precipitation. The method was tested with IAEA standards of natural samples with known contents of⁹⁰Sr, and water samples, where the concentration of⁹⁰Sr was previously determined by the standard IAEA procedure. The results obtained show that it is possible to isolate and determine low levels of⁹⁰Sr in natural samples. The procedure is favorable because of the simple separation of radioaactive strontium without using fuming nitric acid.     

Strontium-90 determination in biological and environmental samples by direct milking of its daughter product, yttrium-90

A method is presented for the determination of ⁹⁰Sr in environmental samples by direct milking of ⁹⁰Y. Pyridine-2,6-dicarboxylic acid forms an anionic complex with yttrium which is retained on an anionic resin. Most of the matrix elements are washed out of the column as neutral or uncomplexed species and yttrium is eluted by increasing the ionic force of the eluent solution. This method gives yttrium recoveries between 65% to 85% for soil, grass, milk and bone samples with very high radiochemical purity (⁹⁰Y average half-life of 66±4 hours) and a detection limit of 0.3 Bq/kg of soil. The method supports a calcium content up to 3 g per sample without any decrease in yttrium yield, allowing the measurement of milk, milk-teeth and bone samples with no concentration step in one day.     

Rapid determination of 226Ra in emergency urine samples

A new method has been developed at the Savannah River National Laboratory (SRNL) that can be used for the rapid determination of ²²⁶Ra in emergency urine samples following a radiological incident. If a radiological dispersive device event or a nuclear accident occurs, there will be an urgent need for rapid analyses of radionuclides in urine samples to ensure the safety of the public. Large numbers of urine samples will have to be analyzed very quickly. This new SRNL method was applied to 100 mL urine aliquots, however this method can be applied to smaller or larger sample aliquots as needed. The method was optimized for rapid turnaround times; urine samples may be prepared for counting in <3 h. A rapid calcium phosphate precipitation method was used to pre-concentrate ²²⁶Ra from the urine sample matrix, followed by removal of calcium by cation exchange separation. A stacked elution method using DGA Resin was used to purify the ²²⁶Ra during the cation exchange elution step. This approach combines the cation resin elution step with the simultaneous purification of ²²⁶Ra with DGA Resin, saving time. ¹³³Ba was used instead of ²²⁵Ra as tracer to allow immediate counting; however, ²²⁵Ra can still be used as an option. The rapid purification of ²²⁶Ra to remove interferences using DGA Resin was compared with a slightly longer Ln Resin approach. A final barium sulfate micro-precipitation step was used with isopropanol present to reduce solubility; producing alpha spectrometry sources with peaks typically <40 keV FWHM (full width half max). This new rapid method is fast, has very high tracer yield (>90 %), and removes interferences effectively. The sample preparation method can also be adapted to ICP-MS measurement of ²²⁶Ra, with rapid removal of isobaric interferences.     

Determination of calcium and total hardness in natural waters using a potentiometric sensor array

The determination of calcium and total hardness in natural waters is carried out with a potentiometric sensor array which consists of a series of ion-selective electrodes (ISEs) for Ca²⁺, Mg²⁺, NH₄⁺, K⁺, Na⁺, Li⁺, and H⁺. The selectivity of the calcium and magnesium ISEs is not fully achieved as other cation species may interfere with the analysis. The proposed sensor array device can overcome this drawback since it can take advantage of the cross-selectivities of cation species towards each ISE. In this approach, the multivariate data generated by the sensor array results in a richer source of analytical information which allows the quantification of calcium and total hardness in the water samples by means of chemometric methods. Results obtained are in reasonable concordance with those given by the standard method based on complexometry.     

Matrix-matched quantitative analysis of trace-elements in calcium carbonate shells by laser-ablation ICP–MS: application to the determination of daily scale profiles in scallop shell (<Emphasis Type="Italic">Pecten maximus</Emphasis>)

A micro-scale method has been developed for analysis of trace-element concentration profiles in the calcium carbonate shell of the Great Scallop (Pecten maximus). UV laser ablation at 266-nm coupled with ICP–MS detection was used to analyse daily calcite striae of shell samples to obtain high temporal resolution of trace element incorporation. Analysis of scallop shells was carefully examined to determine the quality of calcium carbonate ablation and calibration. An accurate external calibration method based on matrix matching was developed. Twelve sodium-free enriched calcium carbonate standards containing up to twenty-four elements were prepared, by co-precipitation with aqueous ammonia and NH₄HCO₃, and subsequently back-calibrated in the laboratory. These CaCO₃ standards were found to be homogenous and their use enabled sensitive quantitative analysis (detection limits of a few ng g⁻¹) over a wide range of concentrations (0.1 to 500 μg g⁻¹). Use of these CaCO₃ standards was also evaluated by analysis of three calcium-rich certified reference materials. Because calibration was consistent with the certified results, this analytical method is a sensitive tool for analysis of environmental calcium carbonate matrices. Repeated analysis of scallop shell samples collected simultaneously at the same location showed that the trace elements are homogeneously distributed along a stria. The reliability of such in-situ records of biogenic calcium carbonate (scallop shells) is apparent from the inter-individual and inter-annual reproducibility of the trace element profiles.     

Determination of low-level90Sr in environmental materials: A novel approach to the classical method

A method was developed for the separation of strontium from large amounts of calcium which does not depend on fuming nitric acid. A sample in the form of mixed carbonates or oxides is stirred into concentrated nitric acid in the proportion 17 w/v. Strontium forms insoluble nitrates while calcium remains in the solution. Two re-precipitation steps combined with an acetone wash yield a very pure strontium salt which is suitable for gravimetric determination of recovery. The method, devised originally for⁹⁰Sr assay in sea water, can also be applied to solid samples which present analytical problems due to their high calcium content.     

Rapid method for determination of 228Ra in water samples

A new rapid method for the determination of ²²⁸Ra in natural water samples has been developed at the SRNL/EBL (Savannah River National Lab/Environmental Bioassay Laboratory) that can be used for emergency response or routine samples. While gamma spectrometry can be employed with sufficient detection limits to determine ²²⁸Ra in solid samples (via ²²⁸Ac), radiochemical methods that employ gas flow proportional counting techniques typically provide lower minimal detectable activity levels for the determination of ²²⁸Ra in water samples. Most radiochemical methods for ²²⁸Ra collect and purify ²²⁸Ra and allow for ²²⁸Ac daughter ingrowth for ~36 h. In this new SRNL/EBL approach, ²²⁸Ac is collected and purified from the water sample without waiting to eliminate this delay. The sample preparation requires only about 4 h so that ²²⁸Ra assay results on water samples can be achieved in <6 h. The method uses a rapid calcium carbonate precipitation enhanced with a small amount of phosphate added to enhance chemical yields (typically >90 %), followed by rapid cation exchange removal of calcium. Lead, bismuth, uranium, thorium and protactinium isotopes are also removed by the cation exchange separation. ²²⁸Ac is eluted from the cation resin directly onto a DGA Resin cartridge attached to the bottom of the cation column to purify ²²⁸Ac. DGA Resin also removes lead and bismuth isotopes, along with Sr isotopes and ⁹⁰Y. La is used to determine ²²⁸Ac chemical yield via ICP-MS, but ¹³³Ba can also be used instead if ICP-MS assay is not available. Unlike some older methods, no lead or strontium holdback carriers or continual readjustment of sample pH is required.     

Application of laser ablation multicollector inductively coupled plasma mass spectrometry for the measurement of calcium and lead isotope ratios in packaging for discriminatory purposes

The potential of high‐precision calcium and lead isotope ratio measurements using laser ablation coupled to multicollector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS) to aid distinction between four genuine and five counterfeit pharmaceutical packaging samples and further classification of counterfeit packaging samples has been evaluated. We highlight the lack of reference materials for LA‐MC‐ICP‐MS isotope ratio measurements in solids. In this case the problem is minimised by using National Institute of Standards and Technology Standard Reference Material (NIST SRM) 915a calcium carbonate (as solid pellets) and NIST SRM610 glass disc for sample bracketing external standardisation. In addition, a new reference material, NIST SRM915b calcium carbonate, has been characterised in‐house for Ca isotope ratios and is used as a reference sample. Significant differences have been found between genuine and counterfeit samples; the method allows detection of counterfeits and aids further classification of packaging samples. Typical expanded uncertainties for measured‐corrected Ca isotope ratio values (⁴³Ca/⁴⁴Ca and ⁴²Ca/⁴⁴Ca) were found to be below 0.06% (k = 2, 95% confidence) and below 0.2% for measured‐corrected Pb isotope ratios (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb). This is the first time that Ca isotope ratios have been measured in packaging materials using LA coupled to a multicollector (MC)‐ICP‐MS instrument. The use of LA‐MC‐ICP‐MS for direct measurement of Ca and Pb isotopic variations in cardboard/ink in packaging has definitive potential to aid counterfeit detection and classification. Copyright © 2010 John Wiley & Sons, Ltd.     

Separation and determination of <Superscript>241</Superscript>Am in urine samples from radiation workers using PC88-A and alpha spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This article deals with standardization of analytical method for the determination of ²⁴¹Am isotope in urine samples using Extraction Chromatography (EC) and ²⁴³Am tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of americium along with calcium phosphate. This precipitate after treatment is further subjected to calcium oxalate co-precipitation. Separation of Am was carried out by EC column prepared by PC88-A (2-ethyl hexyl phosphonic acid 2-ethyl hexyl monoester) adsorbed on microporous resin XAD-7 (PC88A-XAD7). Am-fraction was electro-deposited and activity estimated using tracer recovery by alpha spectrometer. Ten routine urine samples of radiation workers were analyzed and consistent radiochemical recovery was obtained in the range 44–60% with a mean and standard deviation of 51 and 4.7% respectively.     

Comparison of slurry sampling and microwave-assisted digestion for calcium, magnesium, iron, copper and zinc determination in fish tissue samples by flame atomic absorption spectrometry

The development of a slurry sampling method for the determination of calcium, copper, iron, magnesium and zinc in fish tissue samples by flame atomic absorption spectrometry is described. In comparison with microwave-assisted digestion, the proposed method is simple, requires short time and eliminates total sample dissolution before analysis. Suspension medium was optimized for each analyte to obtain quantitative recoveries from fish tissue samples without matrix interferences. Nevertheless, iron recoveries higher than 46% were not found. Treatment of samples slurried in nitric acid by microwave irradiation for 15-30 s at 75-285 W permitted to achieve efficient recoveries for calcium, iron, magnesium and zinc. Further improvement in the matrix effects for iron determination was accomplished by the use of an additional step of short microwave-assisted suspension treatment. However, standard addition method was required for calcium and copper determination, being necessary hydrochloric acid as suspension medium for the last one. Although copper could not be determined in the certified reference material using microwave-assisted digestion, the accuracy of the slurry sampling method was verified for all the investigated analytes. Detection limits were 22.8 ± 8.0, 0.884 ± 0.092, 5.07 ± 0.76, 35.5 ± 0.7 and 1.17 ± 0.04 μg g⁻¹ for calcium, copper, iron, magnesium and zinc, respectively. The standard deviations obtained using slurry sampling method and microwave-assisted digestion were not significantly different, and the mean relative standard deviation of the over-all method (n = 3) of the slurry sampling method for different concentration levels was below 12%.     

Rapid determination of 237Np and Pu isotopes in water by inductively-coupled plasma mass spectrometry and alpha spectrometry

A new method that allows rapid preconcentration and separation of plutonium and neptunium in water samples was developed for the measurement of ²³⁷Np and Pu isotopes by inductively-coupled plasma mass spectrometry (ICP-MS) and alpha spectrometry. ²³⁸U can interfere with ²³⁹Pu measurement by ICP-MS as ²³⁸UH⁺ mass overlap and ²³⁷Np via peak tailing. The method provide enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then moving Pu to DGA resin for additional removal of uranium. The decontamination factor for uranium from Pu is almost 100,000 and the decontamination factor for U from Np is greater than 10,000. This method uses stacked extraction chromatography cartridges and vacuum box technology to facilitate rapid separations. Preconcentration is performed using a streamlined calcium phosphate precipitation method. Purified solutions are split between ICP-MS and alpha spectrometry so that long and short-lived Pu isotopes can be measured successfully. The method allows for simultaneous extraction of 20 samples (including QC samples) in 4?C6 h, and can also be used for emergency response. ²³⁹Pu, ²⁴²Pu and ²³⁷Np were measured by ICP-MS, while ²³⁶Pu, ²³⁸Pu, and ²³⁹Pu were measured by alpha spectrometry.     

Rapid radiochemical separation of radium from environmental samples using ion-exchanger Zeokarb-225

A rapid radiochemical method has been developed for the separation of radium in the presence of excess calcium from environmental samples such as spring waters and marine sediments. Radium is preconcentrated by co-precipitation as carbonates along with other alkaline earths. Subsequently, most of the alkaline earths are complexed with EDTA at pH 7.5 and the solution is passed through a column of Zeokarb-225 (NH ₄ ⁺ ). Radium, along with traces of calcium, is sorbed on the exchanger. Radium is desorbed with 2N HNO₃ and finally coprecipitated with 400 μg of barium as isulfate. The alphas of²²⁶Ra are counted in a silicon surface barrier detector and²²⁸Ra betas are counted in an end-window GM Counter.     

A method for estimation of Pu-isotopes in urine samples using TEVA resin and alpha spectrometry

The conventional method used for estimation of Pu-isotopes in urine samples involves anion exchange resin followed by alpha spectrometry, which takes nearly one working week for complete sample analysis. Since the results of the analysis form an important input for decision making by the plant authorities, it is always preferable to reduce overall analysis time for the estimation of Pu-isotopes in bioassay samples. This paper deals with standardization of a relatively faster method for estimation of Pu-isotopes in bioassay samples using TEVA resin and ²³⁶Pu tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of plutonium along with calcium phosphate and separation of Pu was carried out using TEVA resin. Pu-fraction was electrodeposited and activity estimated using tracer recovery by alpha spectrometer. Routine urine samples of radiation workers were analyzed and consistent radiochemical tracer recovery was obtained in the range 65–87 % with a mean and SD of 75 and 7.4 %, respectively. The standardized chromatographic technique reduces the analysis time by about 1 day as compared to conventional method for estimation of Pu-isotopes in urine samples.     

Assessment of immobilized yeast for the separation and determination of platinum in environmental samples by flow-injection chemiluminescence and electrothermal atomic absorption spectrometry

The yeast Saccharomyces cerevisiae immobilized in calcium alginate beads was used for separation and subsequent determination of Pt in environmental samples by flow-injection chemiluminescence (FI-CL) and electrothermal atomic absorption spectrometry (ETAAS). The application of a yeast column resulted in an increase in the tolerable matrix ions concentration compared to direct measurements by both detection techniques. The developed FI-CL method of Pt determination based on the catalytic effect of Pt(IV) ions on luminol oxidation in alkaline medium is characterized by a low limit of detection (0.15 ng mL^?1), and good sensitivity and precision, and can be used for analysis of Pt in water samples. Determination of Pt in more complex environmental samples can be carried out by ETAAS (LOD?=?6 ng mL^?1) after introduction of a column clean-up step with 10 mM nitric acid. The accuracy of the method was confirmed by analyzing the certified reference material of platinum ore (SARM-7), spiked grass, and road dust samples.