To avoid mass interferences on analyte ions caused by argon ions and argon molecular ions via reactions with collision gases, an rf hexapole filled with helium and hydrogen has been used in inductively coupled plasma mass spectrometry (ICP-MS), and its performance has been studied. Up to tenfold improvement in sensitivity was observed for heavy elements (m > 100 u), because of better ion transmission through the hexapole ion guide. A reduction of argon ions Ar+ and the molecular ions of argon ArX+ (X = O, Ar) by up to three orders of magnitude was achieved in a hexapole collision cell of an ICP-MS ("Platform ICP", Micromass, Manchester, UK) as a result of gas-phase reactions with hydrogen when the hexapole bias (HB) was set to 0 V; at an HB of 1.6 V argon, and argon-based ions of masses 40 u, 56 u, and 80 u, were reduced by approximately four, two, and five orders of magnitude, respectively. The signal-to-noise ratio 80Se/ 40Ar2+ was improved by more than five orders of magnitude under optimized experimental conditions. Dependence of mass discrimination on collision-cell properties was studied in the mass range 10 u (boron) to 238 u (uranium). Isotopic analysis of the elements affected by mass-spectrometric interference, Ca, Fe, and Se, was performed using a Meinhard nebulizer and an ultrasonic nebulizer (USN). The measured isotope ratios were comparable with tabulated values from IUPAC. Precision of 0.26%, 0.19%, and 0.12%, respectively, and accuracy of 0.13% 0.25%, and 0.92%, respectively, was achieved for isotope ratios 44Ca/ 40Ca and 56Fe/57Fe in 10 microg L(-1) solution nebulized by means of a USN and for 78Se/80Se in 100 microg L(-1) solution nebulized by means of a Meinhard nebulizer.

A new version of the ''modified total evaporation'' (MTE) method for isotopic analysis of uranium samples by multi-collector thermal ionization mass spectrometry (TIMS), with high analytical performance and designed in a more user-friendly and routinely applicable way, is described in detail. It is mainly being used for nuclear safeguards measurements, but can readily be applied in other scientific areas like geochemistry. The development of the MTE method was organized in collaboration of several ''key nuclear mass spectrometry laboratories'', namely the New Brunswick Laboratory (NBL), the Safeguards Analytical Laboratory (SAL, now SGAS-Safeguards Analytical Services) of the International Atomic Energy Agency (IAEA), the Institute for Transuranium Elements (ITU/JRC), and the Institute for Reference Materials and Measurements (IRMM/JRC), with IRMM taking the leading role. Due to the use of the ''total evaporation'' (TE) principle the measurement of the ''major'' ratio n( 235 U)/n( 238 U) is routinely being performed with an accuracy of 0.02%. In contrast to the TE method, in the MTE method the total evaporation process is interrupted on a regular basis to allow for correction for background from peak tailing, internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, peak-centering, and ion source re-focusing. Therefore, the most significant improvement using the MTE method is in the measurement performance achieved for the ''minor'' ratios n( 234 U)/n( 238 U) and n( 236 U)/n( 238 U). The n( 234 U)/n( 238 U) ratio is measured using Faraday cups only with the result that the (relative) measurement uncertainty (k ¼ 2) is better than 0.12%, which is an improvement by a factor of about 5-10 compared to TE measurements. Furthermore, the IAEA requirement for the ''measurement performance'', defined here as the sum of the (absolute) deviation of the measured from the true (certified) value plus the (absolute) measurement uncertainty (k ¼ 2), for n( 236 U)/n( 238 U) ratio measurements is 1 Â 10 À6 , but the MTE method provides a measurement performance which is, depending on the ratio, by several orders of magnitude superior compared to this limit and to the TE method. For routine MTE measurements a detection limit of 3 Â 10 À9 was achieved using an SEM detector for detecting the isotope 236 U. The MTE method is now routinely being used at all collaborating laboratories with the hope that more laboratories will implement this capability in the future as well. Additional applications for the MTE method are presented in this paper, e.g., for absolute Ca isotope measurements. 238U are usually considered as the major isotopes, whereas 234 U and 236 U are called minor isotopes. Natural uranium variations

Mass spectrometry is currently being implemented in a wide spectrum of research and industrial areas, such as materials science, cosmo-and geochemistry, biology and medicine, to name just a few. Research and development in nuclear safeguards is closely related to the general field of "Peace Research", representing a specific application area for analytical sciences in general and for mass spectrometry in particular. According to Albert Einstein "peace cannot be kept by force. It only can be achieved by understanding". Understanding implies a realistic estimation of potential challenges and threats, which is based on the ability to obtain timely, reliable and independent information. A particular task of international nuclear material safeguards is reducing threats that are posed by the proliferation of nuclear weapons. An important part of the International Atomic Energy Agency (IAEA) safeguards system is the "analytical laboratory", with mass spectrometric techniques, such as thermal ionization mass spectrometry (TIMS), secondary ion mass spectrometry (SIMS), and inductively coupled plasma mass spectrometry (ICP-MS) belonging to the most powerful methods for the analysis of nuclear material and environmental samples collected during inspections. Each of the currently applied techniques provides definite merits (e.g. precision, accuracy, timeeffectiveness, high sensitivity, spatial resolution, reduced molecular interference, etc.) for a specific safeguards related application. Thus, taking advantage of each technique helps the analyst to gain a larger quantity of safeguards-relevant information. Along with the analysis of element amounts and isotopic compositions of uranium and plutonium in nuclear material the challenging applications of mass spectrometry include isotopic analysis of micro-samples, age determination of nuclear material as well as identification and quantification of elemental and isotopic signatures of inspection samples in general.Analysis of inspection samples implies strict quality control procedures and it demands the production of suitable certified isotopic reference materials which are used as calibration standards or as quality control samples. This manuscript discusses merits and limitations of presently available mass spectrometric

This work focuses on testing and application of Sr isotope signatures for the fast and reliable authentication and traceability of Asparagus officinalis originating from Marchfeld, Austria, using multicollector inductively coupled plasma mass spectrometry after optimised Rb/Sr separation. The major sample pool comprises freeze-dried and microwave-digested asparagus samples from Hungary and Slovakia which are compared with Austrian asparagus originating from the Marchfeld region, which is a protected geographical indication. Additional samples from Peru, The Netherlands and Germany were limited in number and allowed therefore only restricted statistical evaluation. Asparagus samples from Marchfeld were harvested within two subsequent years in order to investigate the annual variation. The results show that the Sr isotope ratio is consistent within these 2 years of investigation. Moreover, the Sr isotope ratio of total Sr in soil was found to be significantly higher than in an NH4NO3 extract, reflecting the mobile (bioavailable) phase. The isotope composition in the latter extract corresponds well to the range found in the asparagus samples in Marchfeld, even though the concentration of Sr in asparagus shows no direct correlation to the concentration of Sr in the mobile phase of the soil. The major question was whether the 'Marchfelder Spargel' can be distinguished from samples from the neighbouring countries of Hungary and Slovakia. According to our findings, they can be clearly (100%) singled out from the Hungarian samples and can be distinguished from the Slovakian asparagus samples with a probability of more than 80%.

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Environmental monitoring of actinides and evaluation of the contamination source (nuclear weapons tests, nuclear power plant and nuclear reprocessing plant accidents, etc.) requires precise and accurate isotopic analysis of actinides, especially uranium and plutonium. Double-focusing sector-field inductively coupled plasma mass spectrometry (ICP-SFMS) using a low-flow microconcentric nebulizer with membrane desolvation, ''Aridus'', was applied for isotopic measurements of uranium and plutonium at the ultratrace level. The detection limit (3s) for 236 U and 239 Pu after chemical extraction was 0.2 pg l 21 in aqueous solution and 0.04 pg g 21 in soil, respectively. 235 U/ 238 U, 236 U/ 238 U and 240 Pu/ 239 Pu isotope ratios were measured in soil samples collected within the 30 km zone around the Chernobyl nuclear power plant. The average 240 Pu/ 239 Pu isotope ratio in contaminated surface soil was 0.396 ¡ 0.014. The burn-up grade and the portion of spent uranium in the spent uranium/natural uranium mixture in soil were calculated using the iteration method. A slight variation in the burn-up grade of spent reactor uranium was revealed by analyzing 235 U/ 238 U and 236 U/ 238 U isotope ratios. A relationship between the 240 Pu/ 239 Pu isotope ratio and burn-up of spent uranium was observed.

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