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PubMed2005

On-line systems for continuous water and gas isotope ratio measurements.

New continuous on-line techniques for water and air extracted from ice cores are developed. Water isotope ratio determination on any of the water phases (water vapour, water, ice) is of great relevance in different research fields, such as climate and paleoclimate studies, geological surveys, and hydrological studies. The conventional techniques for water isotopes are available in different layouts but all of them are rather time-consuming. Here we report new fast on-line techniques that process water as well as ice samples. The analysis time is only approximately 5 min per sample which includes equilibration and processing. Measurement precision and accuracy are better than 0.1 per thousand and 1 per thousand for delta18O and deltaD, respectively, comparable to conventional techniques. The new on-line techniques are able to analyze a wide range of aqueous samples. This allows, for the first time, to make continuous isotope measurements on ice cores. Similarly, continuous and fast analysis of aqueous samples can be of great value for hydrological, geological and perhaps medical applications.Furthermore, a new technique for the on-line analysis of air isotopes extracted from ice cores is developed. This technique allows rapid analyses with high resolution of the main air components nitrogen, oxygen, and argon. Measurement precision is comparable to precisions obtained by conventional techniques. It is now possible to measure delta15N and delta18O(atm) over entire ice cores helping to synchronize chronologies, to assess gas age-ice age differences, and to calibrate the paleothermometry for rapid temperature changes. This new on-line air extraction and analyzing technique complements the water methods in an ideal way as it separates the air from the melt-water of an ice sample. The remaining water waste flux can directly be analyzed by the water methods.

Climate↗
PubMed1990

Secondary 18O isotope effects as a tool for studying reactions of phosphate mono-, di-, and triesters.

Secondary 18O isotope effects have been developed as a tool for determining transition state structures in enzymatic and nonenzymatic phosphoryl transfer reactions. 18O substitution in the nonbridge oxygens of a phosphoryl group makes the reaction go faster when the bond order is higher to these oxygens in the transition state than in the reactant, whereas the reaction goes slower if the bond order is less. The isotope effects are measured by the remote label method, using an isotope ratio mass spectrometer for analysis. The bond order to p-nitrophenolate ion when it is the leaving group is indicated by the secondary 15N isotope effect in the nitro group, with a value of 1.0028 representing nearly complete bond cleavage. It appears that the transition states for phosphoryl transfer have no more than one negative charge on the nonbridge oxygens, so that reactions of monoesters are dissociative, reactions of triesters are associative, and reactions of diesters are SN2 with half bond order to entering and leaving groups.

Hydrolysis↗
PubMed2006

Temporal and intrapopulation variation in prey choice of wintering geese determined by stable isotope analysis.

1. Individual variability in prey preferences can have marked effects on many demographic parameters from individual survival and fecundity to the vital rates of entire populations. A population level response is ultimately determined by individual prey choices; however, the effect of individual dietary choice is often overlooked. 2. We determined prey choice by individual consumers, light-bellied Brent geese Branta bernicla, during the overwintering period. Two hundred and eighty-one individuals were sampled at distinct temporal points over two winters. Stable isotopic ratios of carbon and nitrogen for blood cells and blood plasma, from each sampled individual were measured. Isotopic ratios for potential prey items were also measured. 3. Delta15N and delta13C for blood samples were both significantly different between sample months. Generally we found a decrease in both isotopic ratios during the course of the winter. All potential prey items were also isotopically distinct. Multisource mixing models (isosource) were used to determine the range of possible contribution to the diet of individuals. 4. During early winter, diet consisted almost exclusively of sea grass Zostera spp. The level of Zostera spp. in the diet dropped until mid-winter, and was supplemented by the utilization of green algae Ulva lactuca, and Enteromorpha spp., and terrestrial grasses. Terrestrial grass comprised an increasing proportion of the diet in late winter, representing virtually the exclusive food source by April. 5. By examining intrapopulation variability in resource utilization we highlight a number of ecologically important factors not addressed by previous population level studies.

Animals↗
PubMedDate not supplied

[Applications of stable isotopes in biomedical sciences].

The employment of stable isotopes technology allows to perform a wide range of studies in vivo avoiding the utilisation of radioactive isotopes. As stable isotopes naturally occur in nature, the technique detects the enrichment in breath air of the tracer administered. Stable isotopes technology is increasingly being used in biomedical investigation due to the security of its use and the development and availability of new substrates. Breath tests such 13C-urea in the detection of Helicobacter pylori and 13C-octanoic acid for gastric emptying are the most important clinical applications.

Amino Acids↗
PubMed2003

High isotope counts and sentinel node positivity in patients with melanoma.

BACKGROUND: Radioisotope mapping is an essential technical component of sentinel lymph node (SLN) biopsy, and most authors define success by an arbitrary threshold SLN-background ratio. HYPOTHESIS: Few studies have examined the degree to which the relative level of SLN counts correlates with the presence of metastasis. Having removed the SLN with the highest counts, there are no data suggesting how far the surgeon should persist in removing additional SLNs that contain much lower levels of isotope. METHODS: We performed 134 SLN biopsy procedures in 132 patients with melanoma. Successful isotope localization was defined using an SLN/"hottest" SLN ratio; we defined an SLN as any node containing counts at least 10% of that of the hottest SLN. RESULTS: Of 83 patients with more than 1 SLN site identified, 21 (25%) had SLNs that contained metastasis. In 17 (81%) of these cases, the SLN with the highest countcontained tumor, but in 4 (19%) it was benign. Among these 4 patients, the counts of the hottest benign SLNs exceeded those of SLNs positive for metastasis on histological examination by a ratio of at least 10:1, and the counts of the positive SLNs were less than 4:1 of those of the background counts or the presence of blue dye failed to identify the positive SLN. No optimum ratio of SLN/SLN or SLN/background counts identified the positive SLN in all cases. CONCLUSIONS: Although the SLN with the highest counts contained metastasis in 81% of patients with malignant melanoma and multiple SLNs, neither a relatively high isotope count nor the presence of blue dye consistently predicted SLN positivity. For maximum accuracy, SLN biopsy requires the removal of all nodes containing isotope regardless of the relative magnitude of counts and the concurrent use of blue dye to salvage those procedures in which isotope mapping fails.

Adult↗
PubMed1999

Experimental calibration and field investigation of the oxygen isotopic fractionation between biogenic aragonite and water.

Marine molluscs have long been recognised as potential records of palaeoclimate change using the patterns and differences in the stable isotopic composition of the carbonate shells. The aim of this study is to improve the robustness of this approach for aragonitic molluscs by completing the first experimental calibration of the fractionation between water and biogenic aragonite. Fractionation factors were calibrated by growing specimens of the freshwater mollusc Lymnaea peregra under controlled conditions of water temperature and isotopic composition. Fifteen populations of L. peregra were maintained at constant temperature and isotopic conditions for five months (at five different temperatures and using three different water compositions). Water samples and temperature measurements were taken regularly throughout the experiment. The temperature dependence of the fractionation factor, between 8 and 24 degrees C, is given by: 1000 ln alpha=16.74x(1000T(-1))-26.39 (T in Kelvin) and the relationship between temperature (T), delta(18)O(carb) and delta(18)O(wat) is given by: T=21.36-4.83xdelta(+ degrees )O(carb)-delta(+ degrees )O(wat) (T is in degrees C, delta(18)O(carb) is with respect to Vienna Pee Dee Belemnite (PDB), the International Atomic Energy Agency (IAEA) replacement standard for PDB, and delta(18)O(wat) is with respect to Vienna standard mean ocean water (VSMOW)) The outcome of the controlled experiment is compared with previous studies on synthetic, and biogenic, calcite and aragonite from field and laboratory investigations. These comparisons suggest that although a vital offset exists between the fractionation of isotopes in synthetic and biogenic aragonite for molluscs in general, there is no vital effect that is specific either to freshwater, or to individual, genera. Therefore, the calibrated relationship may be used for any freshwater or marine mollusc to derive palaeotemperatures providing the isotopic composition of the environmental water can be reliably constrained. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2000

Error-systematics of determining simultaneously the (6 )Li /(7)Li and the (10)B/(11)B abundance ratios as Li(2)BO(2)(+): considerations for analyte elements of varying isotopic abundance patterns.

In the Li(2)BO(2)(+) ion beam method of isotopic analysis of elements, the (two) analyte isotopic abundance ratios (E( i)'s) are determined by solving a set of (two) simultaneous equations: f( i)(E( i)'s) = R( i) +/- delta( i), (i = 1, 2) where the R( i)'s are the measured isotopic molecular abundance ratios. We have shown recently that, in the process of solution of these equations, the experimental errors (delta( i)'s) are transformed into the actual errors of analysis, delta(E)'s, through some multiplication factors (MFs). For a given isotopic abundance distribution (IAD) of the Li(2)BO(2)(+) ions, the MFs are shown to depend on the combination of two molecular pairs (CTMPS) used as the monitor pairs for measurements, thereby indicating the requirement of careful selection of monitor pairs for avoiding large (propagated) errors in analysis. In this work, we study how the requirements for a correct analysis vary with the IADs of the elements to be analyzed. The results not only lay great emphasis on the need for proper selection, but also show that no CTMPS can be identified as the universal monitor pairs irrespective of molecular IAD. These observations are, moreover, independent of the actual isotopic abundances of the monitor ions and/or the achievable measurement accuracy (delta( i)). It is noted further that, depending on the IADs of the analyte elements and hence the specific IAD of the Li(2)BO(2)(+) ions, it may also happen that none of the different possible CTMPS really fits the criteria as the recommended monitor pairs, and then one has to ensure that the measurements are not only accurate but as perfect as possible (delta( i)'s --> 0) so as to achieve a reasonable accuracy in analysis. These findings are explained in terms of variations of MFs as a function of molecular IAD, and elaborated using experimental data. A comparative discussion on the determination of both (6)Li/(7)Li and (10)B/(11)B abundance ratios together, and that of either of them, as Li(2)BO(2)(+), is also presented with a view to highlighting different possible aspects of the involvement of computation steps in analysis. The important implication of the present investigation is that it sets guidelines for the general problem of accurately analyzing unknown samples, irrespective of their sources of origin. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗
PubMed1985

Measurement of isotope ratios in organic compounds at picomole quantities by capillary gas chromatography/quadrupole electron impact mass spectrometry.

Measurements of isotope ratios in organic compounds at nanomolar concentrations in biological fluids require sensitive and selective gas chromatographic/mass spectrometric methods. The efficiency of sample preparation procedures must be high and gas chromatographic conditions must assure high resolution chromatography producing narrow, intense peaks. Mass spectrometric conditions must create suitable mass fragments, preferably in the high mass range. Detection, controlled by selected ion monitoring (SIM), requires the use of small mass intervals and adequate acquisition times. However, the choice of optimal conditions is limited by the need to acquire multiple data points for the eluting compound. The effects of these variables on the precision of isotope ratio measurements have been investigated to develop an optimal method for isotope ratio measurements in serum bile acids at low concentrations (0.05-8 micromol l-1). With a 25 m X 0.32 mm fused silica capillary OV-1701 column and cold on-column injection, peak widths of 10 s were obtained. Quadrupole mass spectrometry in the electron impact ionization mode (70 eV) and selected ion monitoring (SIM)(mass interval 1/16 u, acquisition time 100 ms) allowed precise (cv less than 1.5%) isotope ratio measurements for chenodeoxycholic, cholic and deoxycholic acid in a single run at quantities as low as 5 pmol injected on the column. SIM switching during the run permitted isotope ratio measurements (cv less than 2.2%) for an additional six bile acids, normally detected in the serum of healthy subjects.

Bile Acids and Salts↗
PubMed1994

Development of a new method for the determination of thyroxine in serum based on isotope dilution gas chromatography mass spectrometry.

A new gas chromatographic/mass spectrometric method in combination with isotope dilution for the determination of thyroxine in serum is described. Special attention was paid to the methylation step of thyroxine, which was investigated using methanolic HCl, dimethylformamide/dimethylacetal and diazomethane, the latter giving the best results in terms of reproducible isotope ratios. For internal standardization, (13C6)-thyroxine was dissolved in fraction V human albumin solution (70 g l-1). The internal standard-in-albumin solution was mixed with known amounts of thyroxine standard, dissolved in 0.05 M Na2HPO4 buffer at pH 11.6, to give isotope ratios of 0.75, 1.00 and 1.25. The same internal standard solution was also used for isotope dilution of the unknown serum samples. The volume of serum was adapted to give a 1:1 isotope ratio. Sample pretreatment consisted of protein precipitation and a two-step liquid/liquid extraction procedure. After methylation of unlabelled and labelled thyroxine with diazomethane and perfluoroacylation with pentafluoropropionic anhydride and heptafluorobutyric anhydride, respectively, mass spectrometric monitoring was done at m/z 951/957 and 1001/1007. Quantitative determination of thyroxine in five serum samples in duplicate, during three consecutive days, showed a mean overall imprecision of 1.0% and a deviation of +0.4% from the target value as determined by a definitive method.

Albumins↗
PubMed2004

Analysis of the 13C NMR spectra of molecules, chiral by isotopic substitution, dissolved in a chiral oriented environment: towards the absolute assignment of the pro-R/pro-S character of enantiotopic ligands in prochiral molecules.

We examined and discuss the proton- and deuterium-decoupled carbon-13 1D spectrum of a molecule, chiral by virtue of the isotopic substitution, dissolved in a chiral oriented medium which simultaneously exhibits chiral discrimination, enantiomeric enrichment and isotope effect. Using the 1-deutero-(2',3',4',5',6'-pentadeuterophenyl)phenylmethanol orientationally ordered in a chiral nematic liquid crystal as illustrative example, we point out three important features. First, we demonstrate that the absolute assignment of the pro-R/pro-S character may be derived from the absolute configuration of the isotopically chiral analogue. Second, we report evidence that isotopic effect on (13)C chemical shift anisotropy is negligible in a weakly orienting solvent. Third, we definitely establish that the molecular orientation of prochiral C(s) symmetry molecules and their parent compounds that are chiral by virtue of the isotopic substitution is the same.

Journal Article↗
PubMed1988

The use of biotinylated DNA probes in parentage testing: non-isotopic labeling and non-toxic extraction.

With a few exceptions DNA probing techniques require the use of radioisotopes and toxic DNA extraction techniques which render the method expensive, potentially hazardous and time-consuming. Most isotopic labeling techniques use the isotope 32P and require 3-10 days to visualize bands after hybridization. An alternative approach is based on the use of non-isotopic detection methods. The available non-isotopic techniques were assessed and their practicality tested. All probes analyzed were tested on samples extracted with a non-toxic extraction procedure using 6 M NaCl as the substitute for phenol and isochloroform. By manipulating probe sizes, blocking agents, selection of membrane and detection system, it is feasible to use non-isotopic labeling and detection in routine parentage testing. Reproducible results were obtained with labeling a variety of DNA probes of various sizes, plasmid and inserts. With an absence of waste disposal costs, probes that are stable for over two years and a staining procedure which takes 3-5 h versus days the technique is well suited for a normal laboratory setting. The next key to the acceptability of DNA testing will be the commercial availability of DNA probes for widespread use.

Biotin↗
PubMed2004

Simultaneous determination of mono-, di- and tributyltin in environmental samples using isotope dilution gas chromatography mass spectrometry.

The development of a rapid, precise and accurate speciation method for the simultaneous determination of mono-, di- and tributyltin in environmental samples is described. The method is based on using isotope dilution gas chromatography/mass spectrometry (GC/MS) with electron ionization, a widely used technique in routine testing laboratories. A mixed spike containing (119)Sn-enriched monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) was used for the isotope dilution of the samples. Five molecular ions were monitored for each analyte, corresponding to the (116)Sn, (117)Sn, (118)Sn, (119)Sn and (120)Sn isotopes. The detection at masses corresponding to (116)Sn and (117)Sn were used to correct for m + 1 and m + 2 contributions of (13)C from the organic groups attached to the tin atom on the (118)Sn, (119)Sn and (120)Sn masses with simple mathematical equations and the concentrations of the butyltin compounds were calculated based on the corrected (118)Sn/(119)Sn and (120)Sn/(119)Sn isotope ratios. The (119)Sn-enriched multispecies spike was applied with satisfactory results to the simultaneous determination of MBT, DBT and TBT in three certified reference materials: two sediments, PACS-2 and BCR 646, and the mussel tissue CRM 477. The method was compared with a previously published GC/inductively coupled plasma MS isotope dilution procedure, developed in our laboratory, by injecting the same samples into both instruments. Comparable analytical results in terms of precision and accuracy are demonstrated for both atomic and molecular mass spectrometric detectors. Thus, reliable quantitative organotin speciation analysis can be achieved using the more widespread and inexpensive GC/MS instrument.

Animals↗
PubMed2006

Isotope dilution SPME GC/MS for the determination of methylmercury in tuna fish samples.

The development of a rapid, precise and accurate analytical method for the determination of methylmercury in tuna fish samples is described. The method is based on the use of isotope dilution GC/MS with electron impact ionization, a widespread technique in routine testing laboratories. A certified spike containing (202)Hg-enriched methylmercury was used for the isotope dilution of the samples. After extraction of the methylmercury from the sample, methylmercury was propylated using sodium tetrapropyl borate in SPME vials and the analytes were sampled from the headspace for 15 min. For isotope measurements, the molecular ion (MePrHg(+)) was used in the SIM mode. Five molecular ions were monitored, corresponding to the (198)Hg, (199)Hg, (200)Hg, (201)Hg and (202)Hg isotopes. The detection at masses corresponding to (198)Hg was used to correct for m + 1 contributions of (13)C from the organic groups attached to the mercury atom on the (199)Hg, (200)Hg, (201)Hg and (202)Hg masses with simple mathematical equations, and the concentration of methylmercury was calculated on the basis of the corrected (200)Hg/(202)Hg isotope ratio. The (202)Hg-enriched methylmercury spike was applied, with satisfactory results, to the determination of methylmercury in the certified reference material BCR 464. The method was successfully applied to the determination of methylmercury in tuna fish samples, and the obtained results were included in the CCQM-P39 interlaboratory exercise, organized by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) with excellent agreement between our results and the average obtained by the other participants.

Algorithms↗
PubMed2006

Differentially isotope-coded N-terminal protein sulphonation: combining protein identification and quantification.

Most proteomic labelling technologies intend to improve protein quantification and/or facilitate (de novo) peptide sequencing. We present here a novel stable-isotope labelling method to simultaneously identify and quantify protein components in complex mixtures by specifically derivatizing the N-terminus of proteins with 4-sulphophenyl isothiocyanate (SPITC). Our approach combines protein identification with quantification through differential isotope-coded labelling at the protein N-terminus prior to digestion. The isotope spacing of 6 Da (unlabelled vs. six-fold 13C-labelled tag) between derivatized peptide pairs enables the detection on different MS platforms (MALDI and ESI). Optimisation of the reaction conditions using SPITC was performed on three model proteins. Improved detection of the N-terminally derivatized peptide compared to the native analogue was observed in negative-ion MALDI-MS. Simpler fragmentation patterns compared to native peptides facilitated protein identification. The 13C-labelled SPITC resulted in convenient peptide pair spacing without isotopic overlap and hence facilitated relative quantification by MALDI-TOF/TOF and LC-ESI-MS/MS. The combination of facilitated identification and quantification achieved by differentially isotope-coded N-terminal protein tagging with light/heavy SPITC represents, to our knowledge, a new approach to quantitative proteomics.

Animals↗
PubMed2003

The potential use of continuous-flow isotope-ratio mass spectrometry as a tool in forensic soil analysis: a preliminary report.

The use of continuous-flow isotope-ratio mass spectrometry (CF-IRMS) as a tool in soil analysis has been assessed as part of a larger study using a number of geological techniques applied in a forensic context. Carbon and nitrogen isotopic ratios, delta13C and delta15N, have been analysed to investigate situations which have arisen from crime casework. Three questions have been addressed: the role of spatial variation found over the short-scale (less than 20 m), temporal variation over a period of almost 2 years, and the variation found between source soils and soil transferred to footwear soles during a simple one-stage transfer process. Results are presented for the three experiments. The use of carbon and nitrogen isotopes has been shown to be useful in discriminating between soil types and sample locations, even when sampling occurs at a different time (as might be the case with a crime scene). In cases of primary transfer (from a source soil by a one-stage transfer to another surface, in this case, shoes and boots), the combination of carbon and nitrogen isotope ratios is a valuable tool in discriminating between sites and in showing the relationship of the transferred samples to the relevant source soils. Used in combination with other analytical techniques, isotopic analysis may prove to be a useful tool in a forensic context.

Carbon↗
PubMed2006

Site-specific carbon isotope analysis of aromatic carboxylic acids by elemental analysis/pyrolysis/isotope ratio mass spectrometry.

Site-specific carbon isotope composition of organic compounds can provide useful information on their origin and history in natural environments. Site-specific isotope analyses of small amounts of organic compounds (sub-nanomolar level), such as short-chain carboxylic acids and amino acid analogues, have been performed using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/pyrolysis/IRMS). These analyses were previously limited to volatile compounds. In this study, site-specific carbon isotope analysis has been developed for non-volatile aromatic carboxylic acids at sub-micromolar level by decarboxylation using a continuous flow elemental analysis (EA)/pyrolysis/IRMS technique. Benzoic acid, 2-naphthylacetic acid and 1-pyrenecarboxylic acid were pyrolyzed at 500-1000 degrees C by EA/pyrolysis/IRMS to produce CO2 for delta13C measurement of the carboxyl group. These three aromatic acids were most efficiently pyrolyzed at 750 degrees C. Conventional sealed-tube pyrolysis was also conducted for comparison. The delta13C values of CO2 generated by the continuous flow technique were within 1.0 per thousand of those performed by the conventional technique, indicating that the new continuous flow technique can accurately analyze the carbon isotopic composition of the carboxyl group in aromatic carboxylic acids. The new continuous flow technique is simple, rapid and uses small sample sizes, so this technique will be useful for characterizing the isotopic signature of carboxyl groups in organic compounds.

Journal Article↗
PubMed1994

Comparison of sensitivities of cells to X-ray therapy, chemotherapy, and isotope therapy using a tumor spheroid model.

Numerous treatment modalities have been used in treating microscopic carcinoma confined to the peritoneal cavity. However, there is little information at the cellular level regarding which modality is most effective in eradicating small nests of tumor cells. In order to determine whether chemotherapy, X rays, or isotope therapy is most effective, we have compared in a three-dimensional spheroid model the survival of cells after treatment with cis-platinum, X ray, or the investigational high-energy isotope 212-bismuth (Bi-212). In this study, V-79 cells were grown to 100-microns diameter spheroids. In killing spheroids, high-energy isotopes were at least six times more effective than X rays at fractionated doses of up to 1300 cGy. High-energy isotopes appear also to be as efficient as cis-platinum. Regardless of exposure time to treatment, Bi-212 was more toxic to spheroids than the other treatment modalities. From this study we conclude that high-energy isotope therapy biologically is very effective in eradicating microscopic nests of cells.

Animals↗
PubMed2001

The Rotational Spectra, Isotopically Independent Parameters, and Interatomic Potentials for the X(1)(2)Pi(3/2) and X(2)(2)Pi(1/2) States of BrO.

Observations of the rotational spectrum of BrO have been extended to include vibrational levels up to v = 8 in the X(1)(2)Pi(3/2) and v = 7 in the X(2)(2)Pi(1/2) states. The rotational spectra of isotopically enriched Br(18)O, X(1), v = 0, 1 and X(2), v = 0 have been observed as well. The spectra of all four isotopic species have been fit to a Hamiltonian in which the parameters have fixed isotopic ratios. An extensive set of isotopically independent parameters has been determined. Interatomic potentials have been derived for both the X(1) and X(2) states. The hyperfine constants and their vibrational dependencies have been determined more precisely and several of them have been determined for the first time. These are interpreted in terms of the electronic structure of the molecule. The isotope relations among the constants have provided a means of decorrelating the electron spin-rotation constant gamma from the fine-structure centrifugal distortion constant, A(D), and have allowed the first determination of an effective value for gamma. Copyright 2001 Academic Press.

Journal Article↗