Isobaric Isotope Research Articles

Isobaric Spike Method for Absolute Isotopic Ratio Determination by MC-ICP-MS.

Absolute isotopic ratios are required for isobaric interference corrections, spike calibrations, and isotopic analysis by external normalization methods. However, high-precision natural isotopic abundance data are lacking for many elements, particularly those with less than four isotopes or having isobaric isotopes with other elements. In this study, we developed a method for absolute isotope ratio analysis, which integrates the concept of the double-spike method with isotopic analysis of element pairs that have isobaric isotopes. Using multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS), the isotopic composition of a sample can be derived by measuring a series of mixtures of the sample and a spike element that has an isobaric isotope with the element being analyzed. We applied this method to five pairs of elements (Ca-Ti, V-Ti, Cr-Ti, Ni-Zn, and In-Sn) and obtained the absolute isotopic ratios for Ca, V, Cr, Ni, and In, as well as the relative Ca isotopic composition. By simultaneous measurement of Ti and Ca isotopes, a quantitative relationship between the instrumental mass fractionation factors and element masses was developed. After correcting for the difference in instrumental mass fractionation factors, the obtained absolute ratios agree well with the literature data and have per mil level accuracy. This method has considerable potential in measuring the absolute isotopic ratios of elements that have isobaric isotope with other elements. Such precisely determined absolute isotopic ratios and the relationship between the instrumental mass fractionation factors and elemental masses will improve isobaric interference corrections, particularly when chemical purification is imperfect or during laser ablation analysis.

Development of a proton-to-neutron converter for radioisotope production at ISAC-TRIUMF

At ISAC-TRIUMF, a 500 MeV proton beam is impinged upon “thick” targets to induce nuclear reactions to produce reaction products that are delivered as a Radioactive Ion Beam (RIB) to experiments. Uranium carbide is among the most commonly used target materials which produces a vast radionuclide inventory coming from both spallation and fission-events. This can also represent a major limitation for the successful delivery of certain RIBs to experiments since, for a given mass, many isobaric isotopes are to be filtered by the dipole mass separator. These contaminants can exceed the yield of the isotope of interest by orders of magnitude, often causing a significant reduction in the sensitivity of experiments or even making them impossible.The design of a 50 kW proton-to-neutron (p2n) converter-target is ongoing to enhance the production of neutron-rich nuclei while significantly reducing the rate of neutron-deficient contaminants. The converter is made out of a bulk tungsten block which converts proton beams into neutrons through spallation. The neutrons, in turn, induce pure fission in an upstream UCx target. The present target design and the service infra-structure needed for its operation will be discussed in this paper.

Isobaric dilution analysis as a calibration tool for long lived radionuclides in ICP-MS

A novel quantification method named isobaric dilution analysis (IBDA) is introduced for internal calibration using inductively coupled plasma mass spectrometry (ICP-MS). Unlike isotope dilution analysis (IDA), where a sample to be analysed for a target analyte element is spiked with an isotopically enriched solution of the same element, IBDA uses the fact that conventional mass analysers cannot distinguish between two isobaric isotopes of different elements. Therefore, in IBDA, the sample with the element of interest is spiked with a solution of a different element, which shares at least one isobaric isotope and shows similar chemical properties resulting in a similar response. This method offers a less expensive alternative to conventional IDA especially for long-lived radionuclides of elements for which a spiking element that fulfils the above mentioned requirements can be provided. In addition, IBDA offers the advantage of making certain metastable, sometimes monoisotopic elements accessible to internal calibration using a strategy analogous to IDA. One of the elements accessible by the new calibration strategy is technetium (Tc), which suffers from a lack of standards due to safety requirements associated with its radioactivity. In this work, the principle of IBDA is first demonstrated for a certified gadolinium standard, which was diluted with a dysprosium spike exhibiting an isobaric isotope with m/z 160. The results obtained by IBDA were compared with those obtained by a conventional IDA. The concept of IBDA was subsequently used for the determination of 99Tc in a contrast agent. Since no certified Tc standards are available, the response of 99Tc was interpolated allowing accurate determinations with an uncertainty of 1%.

Urinary protein detection by iTRAQ® associated with renal transplant complications and its modification with therapy

Abstract Background After renal transplant, surgical, infection complications, as well as graft rejection may occur; early detection through non-invasive markers is the key to change therapy and avoid biopsy. Objective The aim of the study is to determine urine protein profiles in patients undergoing renal transplant with complications and detect its variation when therapy is modified. Material and methods Urine samples were collected from patients prior the transplant and various postoperative stages. Urinary protein profiles were obtained by peptide labelling using isobaric isotopes for relative quantification (iTRAQ®). Results A total of 22 patients were included, of whom 12 developed post-transplant complication: 2 with graft rejection (1 male and 1 female) and 10 (6 males and 4 females) in the group of post-transplant infections. Using iTRAQ® 15/345 and 28/113 proteins were identified and fulfilled the acceptance criteria, in graft rejection and post-transplant infections group, respectively. Conclusions Albumin was the only protein found in both groups, the remaining proteins were different. The five proteins with higher scores in graft rejection were: alpha-1-microglobulin, 5′-nucleotidase cytosolic III, retinol-binding protein 4, membrane protein palmitoylated 4, and serine carboxypeptidase, while post-transplant infections were: mitochondrial acetyl-coenzyme A synthetase, putative adenosyl homocysteinase 2, zinc finger protein GLIS1, putative protein FAM157B, and zinc finger protein 615. It remains to elucidate the involvement of each of these in patients with renal transplantation.

Detección de proteínas urinarias por iTRAQ® asociadas a complicaciones del trasplante renal y su modificación con la terapia

BackgroundAfter renal transplant, surgical, infection complications, as well as graft rejection may occur; early detection through non-invasive markers is the key to change therapy and avoid biopsy. ObjectiveThe aime of the study is to determine urine protein profiles in patients undergoing renal transplant with complications and detect its variation when therapy is modified. Material and methodsUrine samples were collected from patients prior the transplant and various postoperative stages. Urinary protein profiles were obtained by peptide labeling using isobaric isotopes for relative quantification (iTRAQ®). ResultsA total of 22 patients were included, of whom 12 developed post-transplant complication: 2 with graft rejection (one male and one female) and 10 (6 males and 4 females) in the group of post-transplant infections. Using iTRAQ® 15/345 and 28/113 proteins were identified and fulfilled the acceptance criteria, in graft rejection and post-transplant infections group, respectively. ConclusionsAlbumin was the only protein found in both groups, the remaining proteins were different. The 5 proteins with higher scores in graft rejection were: alpha-1-microglobulin, 5’-nucleotidase cytosolic III, retinol-binding protein 4, membrane protein palmitoylated 4, and serine carboxypeptidase, while post-transplant infections were: mitochondrial acetyl-coenzyme A synthetase, putative adenosyl homocysteinase 2, zinc finger protein GLIS1, putative protein FAM157B, and zinc finger protein 615. It remains to elucidate the involvement of each of these in patients with renal transplantation.

Application of mass spectrometric isotope dilution methodology for 90Sr age-dating with measurements by thermal-ionization and inductively coupled-plasma mass spectrometry

Application of an isotope-dilution method for determining 90Zr and 90Sr in a 90Sr source material spiked with 86Sr and 92Zr is described. A miniature gas pressurized extraction chromatography (GPEC) system with a column containing Eichrom Sr Resin™ was used for separating the elements so isobaric isotopes could be measured by mass spectrometry. Zirconium was rinsed through the column with 3 M HNO3/trace HF and strontium was eluted with 1% acetic acid. Two mass spectrometric techniques, inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS), were used for measuring isotope ratios. Data were obtained with 90Sr from a blood-irradiator source. Results from the TIMS measurements gave a decay time of 45.16 ± 0.26 years, and those from the ICP-MS gave 45.24 ± 0.20 years (uncertainties are expanded uncertainty, k = 2). Quadrupole ICP-MS is preferable to TIMS in this application if the ICP-MS data are suitably corrected for non-linearity and mass discrimination.

Multiple linear regression and on-line ion exchange chromatography for alternative Rb–Sr and Nd–Sm MC-ICP-MS isotopic measurements

A mathematical procedure of multiple linear regression in combination with on-line liquid chromatography was applied for the measurement of Sr and Nd isotope ratios by multicollector ICP-MS in the presence of isobaric isotopes. The separation of Rb and Sr and the separation of Nd and Sm were accomplished by ion exchange chromatography with large volume injection. This mode of injection allowed wide flat-topped chromatographic peaks to be obtained while maintaining chromatographic resolution and avoiding sample dilution. The application of the multiple linear regression procedure to the raw chromatographic data allowed the determination of the isotope ratios of Sr or Nd without interferences from isobaric isotopes. For Sr measurements, the raw 87Sr/86Sr isotope ratio precision (0.006 to 0.010%) was similar to that of continuous sample introduction (ca. 0.003%) at the same concentration level (50 ng g−1). The mathematical procedure was first evaluated for the cation exchange separation of Rb and Sr. Strontium isotope ratios, obtained using NIST SRM 987, were in agreement with the certified values (bias ca. 0.01%). For the case of Nd and Sm, their chromatographic separation was accomplished by anion exchange using EDTA as mobile phase. Neodymium eluted at 12.8 minutes while samarium eluted at 17.5 minutes, showing flat-topped chromatographic peaks and maintaining baseline neodymium–samarium separation. Precise neodymium and samarium isotope ratios suitable for Nd–Sm dating could be measured by MC-ICP-MS using the proposed multiple linear regression procedure using only one cup configuration.