Precise Isotope Research Articles

Multielemental trace analysis of biological materials using double focusing inductively coupled plasma mass spectrometry detection

The analytical potential of double focusing-inductively coupled plasma-mass spectrometry (DF-ICP-MS) for total elemental analysis in clinical samples (serum, blood, urine and other biological fluids), tissues and food products is illustrated by reviewing typical applications recently published. Also, the use of DF-ICP-MS as specific detector for trace element speciation in biological samples is discussed. After adequate separation of interferences in the chromatographic column, low resolution measurements ( R = 300) can be used to provide enhanced sensitivities of more than 100 times compared with quadrupole-inductively coupled plasma-mass spectrometry (Q-ICP-MS). This capability is extremely valuable in speciation studies. Also, the use of DF-ICP-MS at low resolution could provide very precise isotope ratio measurements for isotope dilution analysis due to the ‘flat topped’ peaks obtained at this resolution. Unfortunately, the literature on these last two issues is rather scarce so far, in spite of their extremely high analytical possibilities for biological research. Moreover, the bright future of DF-ICP-MS as a most powerful multielemental detector for trace element applications in biological systems will be highlighted. Apart from applications detailed above other important application fields can be envisaged. In particular, we will speculate on its possible use to confirm/establish ‘reference values’ of trace element content in ‘normal’ populations and so to help to diagnose health and disease status, related with trace element total content or their speciation in clinical specimens.

Precise isotope ratio measurements for uranium, thorium and plutonium by quadrupole-based inductively coupled plasma mass spectrometry

Precise long-term measurements of uranium and thorium isotope ratios was carried out in 1 μg/L solutions using a quadrupole inductively coupled plasma mass spectrometer (ICP-QMS). The isotopic ratios of uranium (235U/ 238U = 1, 0.02 and 0.00725) were determined using a cross-flow nebulizer (CFN, at solution uptake rate of 1 mL/min) and a low-flow microconcentric nebulizer (MCN, at solution uptake rate of 0.2 mL/min) over 20 h. For 1 μg/L uranium solution (235U/238U = 1) relative external standard deviations (RESDs) of 0.05% and 0.044% using CFN and MCN, respectively, can be achieved. Additional short term isotope ratio measurements using a direct injection high-efficiency nebulizer (DIHEN) of 1 μg/L uranium solution (235U/238U = 1) at a solution uptake rate of 0.1 mL/min yielded an RSD of 0.06–0.08%. The sensitivity of solution introduction by DIHEN for uranium, thorium and plutonium (145 MHz/ppm, 150 MHz/ppm and 177 MHz/ppm, respectively) increased significantly compared to CFN and MCN and the solution uptake rate can be reduced to 1 μL/ min in DIHEN-ICP-MS. Isotope ratio measurements at an ultralow concentration level (e.g. determination of 240Pu/ 239Pu isotope ratio in a 10 ng/L Pu waste solution) were carried out for the characterization of radioactive waste and environmental samples.

Ultratrace and Isotope Analysis of Long-Lived Radionuclides by Inductively Coupled Plasma Quadrupole Mass Spectrometry Using a Direct Injection High Efficiency Nebulizer

The direct injection high efficiency nebulizer (DIHEN) was explored for the ultrasensitive determination of long-lived radionuclides ((226)Ra, (230)Th, (237)Np, (238)U, (239)Pu, and (241)Am) and for precise isotope analysis by inductively coupled plasma mass spectrometry (ICPMS). The DIHEN was used at low solution uptake rates (1-100 μL/min) without a spray chamber. Optimal sensitivity (e.g., (238)U, 230 MHz/ppm; (230)Th, 190 MHz/ppm; and (239)Pu, 184 MHz/ppm) was achieved at low nebulizer gas flow rates (0.16 L/min), high rf power (1450 W), and low solution uptake rates (100 μL/min). The optimum parameters varied slightly for the two DIHENs tested. The detection limits of long-lived radionuclides in aqueous solutions varied from 0.012 to 0.11 ng/L. The sensitivity of the DIHEN was improved by a factor of 3 to 5 compared with that of a microconcentric nebulizer (MicroMist used with a minicyclonic spray chamber at a solution uptake rate of 85 μL/min) and a factor of 1.5 to 4 compared with that of a conventional nebulizer (cross-flow used with a Scott type spray chamber at a solution uptake rate of 1 mL/min). The precision of the DIHEN ranged from 0.5 to 1.7% RSD (N = 3) for all measurements at the 10 ng/L concentration level (∼3 pg sample size). The sensitivity decreased to 10 MHz/ppm at a solution uptake rate of 1 μL/min. The precision was about 5% RSD at a sample size of 30 fg for each long-lived radionuclide by the DIHEN-ICPMS method. The oxide to atom ratios were less than 0.05 (except ThO(+)/Th(+) ) and decreased under the optimum conditions in the following sequence: ThO(+)/Th(+) > UO(+)/U(+) > NpO(+)/Np(+) > PuO(+)/Pu(+) > AmO(+)/Am(+) > RaO(+)/Ra(+). Atomic and oxide ions were used as analyte ions for ultratrace and isotope analyses of long-lived radionuclides in environmental and radioactive waste samples. The analytical methods developed were applied to the determination of long-lived radionuclides and isotope ratio measurements in different radioactive waste and environmental samples using the DIHEN in combination with quadrupole ICPMS. For instance, the (240)Pu/(239)Pu isotope ratio was measured in a radioactive waste sample at a plutonium concentration of 12 ng/L. This demonstrates a main advantage of DIHEN-ICPMS compared with α-spectrometry, which cannot be used to selectively determine (239)Pu and (240)Pu because of similar α energies (5.244 and 5.255 MeV, respectively).

Boron isotope ratio measurements with a double-focusing magnetic sector ICP mass spectrometer for tracing anthropogenic input into surface and ground water

Double-focusing magnetic sector inductively coupled plasma mass spectrometry (ICP-MS) is used for precise boron isotope ratio measurements in surface and ground water. The precision is in the range of 1–2‰. Boron in detergents has a characteristic isotope ratio that can be used to identify the boron source. Anthropogenic input of boron into surface and ground water has been successfully identified by analysing the boron isotope ratios in an area north of the Harz Mountains in Germany. The method was validated by comparing the results of the boron isotope ratio measurements with the lithium concentration. Lithium is anthropogenically released in the study area and is used as a second independent tracer. The conclusions from the boron isotope ratio measurements agree exactly with those from analysis of Li concentrations in the study area.

Precise sulfur isotope ratio measurements in trace concentration of sulfur by inductively coupled plasma double focusing sector field mass spectrometry

T. Prohaska, C. Latkoczy and G. Stingeder, J. Anal. At. Spectrom., 1999, 14, 1501 DOI: 10.1039/A901973A

Application of double-focusing sector field ICP mass spectrometry with shielded torch using different nebulizers for ultratrace and precise isotope analysis of long-lived radionuclides

The capability of double-focusing sector field ICP-MS with a plasma-shielded torch using different nebulizers (a Meinhard nebulizer with a Scott-type spray chamber with a solution uptake rate of 1 ml min –1 ; a MicroMist microconcentric nebulizer used with a minicyclonic spray chamber with a solution uptake rate of 0.085 ml min –1 ; an ultrasonic nebulizer with a solution uptake rate of 2 ml min –1 ; and a direct injection high-efficiency nebulizer with a solution uptake rate of 0.085 ml min –1 ) for the introduction of radioactive sample solutions into the ICP was investigated. The total amount of analyte for each long-lived radionuclide ( 226 Ra, 230 Th, 237 Np, 238 U, 239 Pu and 241 Am; concentration of each was 1 ng l –1 in the aqueous solution) using different nebulizers was 5 pg for the Meinhard nebulizer, 0.4 pg for the MicroMist microconcentric nebulizer and 10 pg for the ultrasonic nebulizer. The application of the shielded torch yielded an increase in sensitivity for all these nebulizers of up to a factor of 5 compared with the original configuration without a shielded torch. Sensitivities of about 2000 MHz ppm –1 were measured for the radionuclides investigated (except for 226 Ra) using the MicroMist microconcentric nebulizer with a shielded torch. The detection limits were in the sub-pg l –1 range and the precision ranged from 1 to 2% RSD (n=5) for the 1 ng l –1 concentration level (0.4 pg sample size). A further increase in sensitivity for long-lived radionuclides of nearly one order of magnitude in comparison with the MicroMist microconcentric nebulizer was observed using ultrasonic nebulization, but the amount of analyte required was significantly higher (by a factor of 25). In contrast, the direct injection high-efficiency nebulizer (DIHEN) in double-focusing sector field ICP-MS (DF-ICP-MS) with a shielded torch resulted in a decrease in sensitivity in comparison with the unshielded torch because of a higher water load due to the direct injection of aqueous solution into the plasma. At low solution uptake rates (down to several µl min –1 ), the uranium solutions were analyzed by DIHEN-ICP-MS using a double-focusing sector field instrument with higher sensitivity than quadrupole-based ICP-MS. Flow injection was used for sample introduction to measure small sample volumes of radioactive waste solutions (20 µl). The determination of 237 Np at a concentration of 10 ng l –1 by flow injection DF-ICP-MS was possible with a precision of 2.0% (RSD, n=5). In order to avoid mass spectral interferences and matrix effects long-lived radionuclides (e.g., of U, Th and 99 Tc) were separated from the radioactive waste matrix by liquid-liquid extraction or ion exchange. The methods developed for the precise determination of the concentration and isotopic ratios of long-lived radionuclides were applied to aqueous standard solutions and radioactive wastes by double-focusing sector field ICP-MS. The precision of Pu isotopic analysis by double-focusing ICP-MS with a shielded torch was 0.2, 2 and 14% for 1000, 100 and 10 pg l –1 (amount of analyte: 500, 50 and 5 fg), respectively.

Precise Determination of Cadmium, Indium and Tellurium Using Multiple Collector ICP‐MS

New sample preparation and ion‐exchange separation methods as well as instrumental measurement protocols were established for the determination of trace‐level Cd, In, and Te concentrations in geological materials by isotope‐dilution mass spectrometry. High precision isotope ratio measurements were performed with a multiple collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS). The mass biases incurred for In and Te were corrected by adding and monitoring Pd and Sb standard solutions, respectively. Mass fractionation of Cd was corrected by using the mass fractionation factor calculated from the measurement of a standard solution. The measurement precision was better than 1 % for Cd, In and Te. Detection limits were < 1 ng g‐1 for Cd, < 0.02 ng g‐1 for In and Te. Using these new analytical techniques, the concentrations of Cd, In and Te were determined in six international geological reference materials. Concentrations could be reproduced within 3% for Cd, 4% for In and 10% for Te. Sample heterogeneity and volatility problems might have been the reason for the relatively large differences between Te replicates. Our results displayed excellent reproducibility compared with those of other techniques and agree well with data from previously published recommended values.

SEPARATION OF SAMARIUM ISOTOPES BY A CROWN ETHER

ABSTRACT Samarium isotopes were fractionated in a liquid-liquid extraction system using dicychlohexano-18-crown-6. High precision isotope ratio measurements with a multicollector mass spectrometer made it possible to evaluate the contributions of the nuclear size and shape and the nuclear spin to the chemical isotope separation effect. The maximum value of the unit mass enrichment factor (ϵu was observed to be 0.00161 ± 0.00002. The odd/even enrichment factor of 147Sm was ϵO/E = −0.00101 ± 0.00062 and that of 149Sm was ϵO/E = −0.00049 ± 0.00050. Enrichment factors were affected by nuclear mass, nuclear volume and nuclear spin in addition to vibrational motion of molecule. The nuclear volume effect was 1.94 times as large as the nuclear mass effect. The odd/even atomic mass effect was explained with 6s2-6s6p transition in optical isotope shift of Sm I. The correction due to the nuclear spin of 147Sm was ϵspin; = −0.0016 and that of 149Sm was ϵspin; = −0.0014.

Static multicollection of Cs 2BO 2+ ions for precise boron isotope analysis with positive thermal ionization mass spectrometry

Static multicollection of Cs 2BO 2 + ions ( m z = 308 and 309 ) for precise boron isotope analysis has been established by employing a newly developed double collector package in the modified Finnigan-MAT 261 thermal ionization mass spectrometer (TIMS). This method reduces the data acquisition time to 5 min which is approximately one order of magnitude shorter than conventional peak jumping method, and it is easier to measure small sample size as low as 0.1 μg of boron. The analytical precision for individual runs and reproducibility of measured 11 B 10 B ratios of NBS 951 boric acid with static multicollection, respectively, are ±0.007−0.025% (2 σ mean) and ±0.012% (2 σ mean), for 1 μg of B, and ±0.015−0.032% (2 σ mean) and ±0.023% (2 σ mean), for 0.1 μg of B. This analytical precision and reproducibility are essentially identical to those previous works with peak jumping method measuring sample amounts more than 1 μg of B.

High-yield lithium separation and the precise isotopic analysis for natural rock and aqueous samples

A high-yield lithium separation technique for rock and aqueous samples has been established together with precise Li isotope analysis by thermal ionization mass spectrometry. Four separate stages of ion-exchange chromatography were carried out using organic ion-exchange resin. An ethanol-HCl solution was used for complete separation of Li from Na at the third column state. Total reagent volume for the entire chemical process was reduced to 42 ml and 33.3 ml for rock samples and seawater, respectively. The recovery yield and total procedural blank are 99.2–99.3% and 11 pg, respectively. Li 3PO 4 was used as an ion-source material in the mass spectrometric analysis. The in-run precision and reproducibility of measured 7Li/ 6Li ratios were ±0.04–0.07‰ (2 σ mean) and 0.37‰ (relative standard deviation; RSD) for rock and ±0.05-0.08‰ (2 σ mean) and 0.35‰ (RSD) for seawater. In this method, Rb, Sr, Sm, Nd, La and Ce can be collected after Li elution in the first column chromatography, then separated by the following specific procedures for these elements. Therefore, this method makes possible multi-isotope analysis for Li-poor and restricted small amounts of samples such as meteorites and mantle materials, extending to Li isotope geochemistry and cosmochemistry.

Applications of Multiple Collector-ICPMS to Cosmochemistry, Geochemistry, and Paleoceanography

Multiple collector-inductively coupled plasma mass spectrometry (MC-ICPMS) is a new technique for the measurement of isotopic compositions at high precision, and is of great relevance to planetary, earth, ocean, and environmental sciences. The method combines the outstanding ionization efficiency of the ICP source with the superior peak shapes achievable from the ion optical focal plane of a large dispersion magnetic sector mass spectrometer, utilizing simultaneous multiple collection to achieve the most precise isotopic measurements yet made for many elements—particularly those with high first ionization potential. The addition of a laser facilitates studies for which spatial resolution is required. This method is still in its infancy, yet diverse applications have already led to a number of important scientific developments. Here we review some of these accomplishments and the potential for further work. The Lu-Hf isotopic system, for many years considered analytically challenging, is now relatively straightforward and offers great promise in fields as diverse as garnet geochronology, hydrothermal fluxes to the oceans, and crustal evolution. The age of the Earth’s core, the Moon, and Mars have been measured using a new short-lived chronometer 182Hf- 182W. Other such new chronometers will follow. High precision isotope dilution measurements of the Earth’s inventory of many poorly understood elements such as In, Cd, Te, and the platinum group elements are providing tests for models for the accretion of the inner solar system. The small natural isotopic variations in elements such as Cu and Zn, produced by mass dependent fractionation, are now measurable at high precision with this method, and entirely new fields of stable isotope geochemistry can be developed. Similarly, measurements of small nucleosynthetic isotopic anomalies should be made easier for some elements. Measurements of U and Th isotopic compositions at very high sensitivity and reproducibility are now possible, allowing the development of higher resolution Quaternary geochronology. Finally, using laser ablation, the first precise in situ Sr, Hf, W, and Pb isotopic measurements have been made in natural materials, opening up a range of microanalytical isotopic studies in petrology and marine geochemistry. MC-ICPMS offers exciting times ahead in areas well beyond the bounds of geochemistry. Indeed, MC-ICPMS is likely to become the method of choice for many isotopic measurements because it is a more user friendly and efficient method for the acquisition of high precision data. It is also much more versatile, permitting elements to be measured that were previously considered intractable, and allowing the acquisition of data in situ, all with a single mass spectrometer. The limiting factor on the sensitivity is the transmission which is ≤2% for all instruments thus far designed. If it is found possible to improve the transmission still further, thermal ionization mass spectrometry, the technique that has, thus far, provided the high precision measurements necessary for most of the vast field of radiogenic isotope geochemistry, may be relegated to specialized applications.

Precise lead isotope ratios in Australian galena samples by high resolution inductively coupled plasma mass spectrometry

High resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) was used to measure Pb isotope ratios in standard solutions and Pb mineral digests. The RSD values obtained for208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, 208Pb/206Pb and 207Pb/206Pb were 0.13, 0.11, 0.11, 0.046 and 0.048%, respectively (values as 1σ). These values were obtained from 30 analyses of three different standard sample types (multi-element standard, NIST SRM 981 and a Broken Hill galena digest). Based on 39 analyses of 11 galena samples from different locations around Australia, the difference between HR-ICP-MS and conventional TIMS values for 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, 208Pb/206Pb and 207Pb/206Pb ratios was generally better than±0.2%. This paper outlines a very simple and rapid analytical method for the measurement of Pb isotope ratios, and is one of the first studies to use HR-ICP-MS to measure Pb isotope ratios in galena and galena-bearing ores.

Modulus—An experiment to measure precise stable isotope ratios on cometary materials

Modulus is the name given to a measurement philosophy that involves the determination of light element, stable isotope ratios to high levels of accuracy within a self-contained, space-compatible experiment. In its inaugural form Modulus has been selected for implementation on the international Rosetta mission to comet P/Wirtanen. The principal isotope ratios of interest are 18O/ 16O, 17O/ 16O, 13C/ 12C, 15N/ 14N and D/H (although this could be extended to sulfur isotope ratios and the noble gases). There are two fundamental aspects of Modulus that distinguish it from other related experiments. Firstly, the elements of interest are converted into specific gases for analysis, i.e. O 2 for oxygen, CO 2 for carbon (and oxygen), N 2 for nitrogen, and CH 4 or HF for hydrogen. The conversion steps are accomplished by utilisation of small quantities of solid-state reagents. The consequence of utilising low molecular weight species produced by chemical processing is that a mass spectrometer of only low mass range and, indeed, limited mass resolution is needed (making the overall package simpler and smaller). Secondly, the mass spectrometer is calibrated in-situ using reference gases of known isotopic compositions (and thus, results can be related to the international standardisation procedure used by the entire ground-based community). The benefits of in-situ calibration are results of high levels of accuracy. The entire experiment (mass spectrometer, gas processing system, ancillary control supplies, reference materials etc.) can be built with a mass of <3 kg; the total power requirement is <5 W. Two variants of Modulus have been selected for Rosetta — one experiment on the Orbiter, the other on the RoLand Lander. This combination will not only allow a detailed investigation of ices, volatiles, refractories etc. from cometary nuclear materials, but also characterisation of any chemical and isotopic effects produced by gases within the coma (since measurements of equivalent species can be made on the nucleus surface and at some distance from the comet). Ultimately this procedure may allow future comets to be explored by remote means only, with the certainty that any isotopic effects caused after volatiles leave the comet's surface can be corrected for on the basis of the Modulus (Rosetta) results.

Precision and accuracy in isotope ratio measurements by plasma source mass spectrometry

Precise and accurate isotope ratio measurements are an important task in many applications such as isotope dilution mass spectrometry, bioavailability studies or the determination of isotope variations in geological and cosmic samples. There is much more interest in ICP-MS for isotope ratio determinations at present compared with GDMS, which is preferred for the direct measurement of the isotopic composition of metallic solid samples. Spectroscopic interferences and a limited abundance sensitivity can influence the accuracy of isotope ratio determinations by GDMS and ICP-MS. In addition, in ICP-MS the space charge effect always influences the accuracy and a nozzle separation effect may also contribute to the total mass bias. Using a quadrupole ICP-MS the mass discrimination per mass unit can be >10% for elements with mass numbers <10, about 1–5% for mass numbers in the range of 20–120 and only <1% for heavier elements. Mass discrimination is strongly dependent on the potential of the different lenses of the ion optics and on the nebulizer gas flow. Even in magnetic sector field ICP-MS instruments a distinct mass discrimination is observed. Different procedures such as calibration by substances of consistent natural isotopic composition of the same or a neighbouring element and by isotopic standard reference materials, respectively, in combination with various mathematical functions, linear and exponential ones, are used for mass bias correction. In addition to the ion counting statistics, stability of the ion current is one of the most important topics which influences the precision of isotope ratio determinations. Magnetic sector field instruments, producing flat topped peak shapes, coupled with a multi-collector system for simultaneous measurement of different isotopes achieve the best relative standard deviation in the range of typically 0.005–0.02%, which is only comparable with precisions obtained by TIMS. However, ICP-TOFMS also has the potential for similar results. Typical relative standard deviations for other types of plasma source mass spectrometers for isotope ratio determinations are as follows: GDMS 0.1–1, quadrupole ICP-MS 0.1–0.5, and high resolution ICP-MS 0.05–0.2%.

In situaccurate and precise lead isotopic analysis of ultra-small analyte volumes (10–16m3) of solid inorganic samples by high mass resolution secondary ion mass spectrometry

A sensitive high mass resolution ion microprobe (SHRIMP) SIMS instrument was used to analyse the Pb isotopic composition of ultra-small analyte volumes (10–16 m3) of NIST SRM 610, an in situ technique applicable to any solid inorganic sample. The accuracy and precision of multiple analyses are comparable to those attained by TIMS and double focusing multiple collector ICP-MS. The international standard NIST SRM 610 was used to demonstrate the technique. No instrumental mass fractionation correction is necessary for these SIMS analyses, although a correction for the isobaric interference of 204Hg on 204Pb in NIST SRM 610 is necessary for accuracy of the 204Pb measurement, and is estimated to be 0.8%. With consideration of our values with respect to those from other techniques, we propose a set of ‘preferred’ values for Pb isotope ratios in NIST SRM 610, and support its usefulness as an international Pb isotope standard: 206Pb:204Pb 17.050±0.026; 207Pb:206Pb 0.908 56±0.000 68 and 208Pb:206Pb 2.1663±0.0015 (2s uncertainty). The advantage of being able to perform in situ accurate and precise Pb isotope analyses on ultra-small volumes allows the application of this SIMS technique to areas in the forensic and environmental sciences, archaeology and geochemistry where, in the last case, important isotopic information is obtainable on thin or shallow micro-structures such as melt films at grain boundaries and shallow internal structures in individual mineral grains. Such applications are not possible using dissolution techniques and are difficult or impossible with current laser ablation ICP-MS instruments. An application of the technique to the measurement of Pb isotopes in 5 µm sulfide crystals included within a large natural Ca(Mg,Fe2+)Si2O6 (diopside) crystal is presented. The results suggest that the source of the host rocks to the sulfides was an enriched mid-ocean ridge basalt. This result is consistent with a previous study of major and trace elements of the same sample.

Ultratrace and precise isotope analysis by double-focusing sector field inductively coupled plasma mass spectrometry

Double-focusing sector field inductively coupled plasma source mass spectrometry with its capability of providing a very sensitive multi-element analysis has been established for the determination of trace and ultratrace elements in high-purity materials, environmental samples and radioactive waste materials. Some applications of double-focusing sector field ICP-MS for the multi-element analysis of trace and ultratrace impurities in high-purity inorganic materials are described. A matrix separation procedure for ZrO2 by liquid–liquid extraction after microwave-induced dissolution in an acid mixture is proposed in order to determine ultratrace impurities. The detection limits of ICP-MS reached after matrix separation in solid samples are in the low ng g–1 concentration range. The detection limits in ICP-MS (determined by the blank values of the chemicals used) are comparable to those of solid-state mass spectrometry, which allows the direct determination of trace impurities in high-purity solids. Isotope ratio measurements of Mg, K and Ca were performed to investigate the transport phenomena of nutrient solutions in plants by tracer experiments using highly enriched 25Mg, 26Mg, 41K, 42Ca and 44Ca isotopes. In order to separate the 38ArH+ and 40ArH+ ions from the 39K+ and 41K+analyte ions for potassium isotope ratio measurements, double-focusing sector field ICP-MS with an ultrasonic nebulizer was used at a mass resolution of 9000. The precision of potassium isotope ratio measurements was 0.7% (at a potassium concentration of 100 µg l–1). Isotope ratios of Mg and Ca (each at a concentration of 50 µg l–1) were determined at a mass resolution of 3000 with a precision of 0.4 and 0.5% on real biological samples. The accuracy of isotope ratio measurements of K and Mg was determined using isotopic standard reference materials with natural isotope composition (NBS SRM 985 and 980). The results of isotope ratio measurements of K, Mg and Ca on real biological samples doped with enriched stable isotopes are discussed.

Identification of ground water contaminations by landfills using precise boron isotope ratio measurements with negative thermal ionization mass spectrometry

Precise boron isotope ratio measurements with negative thermal ionization mass spectrometry were used for the identification of ground water contaminations by leakages of landfills. BO 2 - thermal ions were produced to determine the 11 B/ 10 B isotope ratio, which was expressed as δ 11 B value in ‰ normalized to the standard reference material NIST SRM 951. For example, household waste influences the boron isotope ratio by specific components such as washing powder. In the case of one investigated landfill low δ 11 B values correlate well with high boron concentrations in contaminated seepage water samples and vice versa for uncontaminated ground water samples. Possible boron contributions of rainwater were taken into account, determining a boron content of 2.3 μg/L and a δ 11 B value of 13.1‰ for a representative sample. Such low boron concentrations were determined by isotope dilution mass spectrometry (detection limit 0.3 μg/L) whereas higher contents were also analyzed by a spectrophotometric method. However, different sources of contamination could only be identified by the isotope ratio and not by the concentration of boron.

Use of stable isotopes to study fatty acid and lipoprotein metabolism in man

Tracer studies have long been an important tool for lipid metabolism research. Recent advances and availability of high performance mass spectrometers (MS) and improved stable isotopically labeled tracers contribute to an increase in stable isotope tracer studies in humans. We briefly review recent studies and discuss advances in high sensitivity methods and applications. GC/MS analysis. Tracer studies with gas chromatography/mass spectrometry (GC/MS) usually rely on D labeling, where labeling with more that three D atoms shifts the analyte mass above that of the natural abundance envelope, and the MS monitors selected masses representing the isotopimers of interest. Recent examples are the work of Emken and coworkers, who investigated the desaturation of 18:0 and 16:0, and 18:2n-6 and 18:3n-3 elongation/desaturation, in adults, with oral doses of about 3 g of d 2,4,6 fatty acids. They showed modest levels of 18:0 and 16:0 desaturation over 2 days and an influence of dietary 18:2n-6 on elongation. In premature infants, Salem, Uauy and coworkers recently have used d 5-18:2n-6 and d 5-18:3n-3 doses of 50–100 mg/kg body weight to show that infants as small as 1980 g and 32 weeks gestation elongate and desaturate both precursors within 24 h. Most fatty acid metabolites including 20:4n-6, 20:5n-3, and 22:6n-3 were easily detected in serum. High precision isotope ratio MS (IRMS). In 1992, we introduced a high sensitivity fatty acid tracer method based on [U- 13C] tracers and GC-combustion-IRMS (GCC-IRMS). The combustion interface facilitates carbon-by-carbon tracer detection; with U- 13C tracers all GC peaks are detected with highest precision. Rhee et al have quantified the desaturation of 18:0 and 16:0 in lipoproteins of adults using 30 mg oral doses (0.5 mg/kg). In the first 12 h, conversion of 18:0 to 18:1 was 7% in chylomicrons and 17% in VLDL, showing that both intestine and liver desaturate 18:0. Plasma conversion of 18:0 over 144 h was 14%, while that for 16:0 was 2%, showing that combined intestine and liver desaturation is minor compared with normal fluctuations in dietary levels. Carnielli applied GCC-IRMS to 8:0 elongation in very-low-birth-weight infants. Significant conversion products of 8:0 were 14:0 (5%), 16:0 (8%) but not 10:0 or 12:0.

Strontium isotopic, chemical, and sedimentological evidence for the evolution of Lake Lisan and the Dead Sea

Precise strontium isotope ratios, combined with chemical analyses and sedimentological information, are used to monitor the water sources and the evolution of the Dead Sea and its late Pleistocene precursor, Lake Lisan (70-18 kyr B.P.). The materials analyzed include bulk aragonite, water-leached soluble salts, and residual aragonite and gypsum from the Lisan Formation in the Perazim Valley (near the SW shore of the Dead Sea). The residual aragonite and the associated soluble salts display systematic fluctuations in 17 Sr 86 Sr ratios between 0.70803 and 0.70806 and from 0.70805 to 0.70807, respectively. In individual soluble salt-residual aragonite pairs, the soluble salt displays a higher 87 Sr 86 Sr ratio. Gypsum samples yield 17 Sr 86 Sr ratios similar to the soluble salts from adjacent layers in the section. This shows that, in individual samples, the source of Sr in aragonite was distinct from that in soluble salts and the gypsum. The sterility of the Lisan sediments, their strictly nonbioturbated fine lamination, and their high content of chloride salts indicate that Lake Lisan was a saline, or even hypersaline water body. In the absence of alternative sources of HCO 3 − and S0 4 2− the abundance of primary aragonite and gypsum in the Lisan column reflects an import of very large volumes of freshwater into the otherwise saline lake, resulting in a density stratification of this water body. The history of the upper water layer and that of the lower brine is reflected in the chemical and strontium isotope composition of the aragonite and in that of the associated soluble salts and in the gypsum samples, respectively. Whereas the bicarbonate and much of the Ca 2+ required for aragonite crystallization were supplied by the freshwater, the complementary Ca 2+ (and Sr 2+) were added by the lower brine. The upper water layer of Lake Lisan acted as a SO 4 2− capacitor during the lake's rise periods. It was removed therefrom, as prominent gypsum beds, upon climatic-induced (drier period) mixing or even complete overturn of the lake. The evolution of Lake Lisan took place between two distinct modes. The first was characterized by an extensive supply of freshwater and resulted in a rise of the lake's level, a (density) layered structure, and precipitation of aragonite. The second mode was marked by a diminishing freshwater input, resulting in mixing or complete overturn of its water, and precipitation of gypsum. These two modes reflect the climatic evolution of the region in the late Pleistocene which fluctuated between drier and wetter periods. The transition to the Holocene is accompanied by the dry up of Lake Lisan and its contraction to the present Dead Sea.

Negative thermal ion mass spectrometry of oxygen in phosphates

A novel technique for the precise measurement of oxygen isotopes by negative thermal ion mass spectrometry (NTIMS) is presented. The technique is ideally suited to the analysis of oxygen isotopes in phosphates which form intense P03 ion beams. Since P is monoisotopic, the mass spectrum for P0 3 − at 79, 80, and 81 corresponds to 1660, 170, and 180. Natural and synthetic phosphates are converted and loaded on the mass spectrometer filament as Ag 3PO 4 precipitated directly from ammoniacal solution. To lower the work function of the filament, BaCl, is added in a 1:1 molar ratio of PO 4:Ba. Using these procedures, Br − mass interference (at 79 and 81 amu) is eliminated for typical analyses. Experiments with 180-enriched water show less than 1 % O-exchange between sample PO 4 and adsorbed water, and there is no O-exchange with trace OZ present in the mass spectrometer source chamber. The ionization efficiency of PO 4, as P0 3 − is >10% compared to 0.01% for both conventional dual inlet Gas Isotope Ratio Mass Spectrometry (GIRMS) and secondary ion mass spectrometry (SIMS). Therefore, NTIMS offers exceptional sensitivity enabling routine and precise oxygen isotope analysis of sub-microgram samples of PO 4, (<21 nmoles equivalent CO 2 gas) without need for lengthy chemical pre-treatment reproducibility of the sample. Overall external precision is ±1%c (2σ) for 18 O 16 O and 17 0 15 O with of instrumental isotope fractionation (calculated from 18 O 16 O of ±0.5%c amu −1. Small phosphate samples including single mineral grains from meteorites, or apatite microfossils, can be analyzed by this technique.