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Bilharzia is the world's second parasitic endemic and its genito-urinary lesions are well described. Ectopic pregnancies on tubal obstruction by bilharzia eggs are reported in African populations. Through a case of clinical observation we report an exceptional case of tubal erythema tubal bilharziasis in a French woman of origin but particularly affectionate by the African woman Africa south of the sahara. where she carries out humanitarian activities in countries in conflits (Democratic Republic Of Congo, Ivory Coast, and Mali).La bilharziose est la seconde endémie parasitaire mondiale et ses atteintes génito-urinaires sont bien décrites. Les grossesses ectopiques sur salpingite bilharziennes ont rapportées dans les populations Africaines. Nous vous rapportons un cas exceptionnel. de grossesse extra-utérine sur bilharziose tubaire chez une française d'origine mais particulièrement affectionnée par l'Afrique au sud du saharienne où elle mène des activités humanitaires dans les pays Africains en conflits armées (République Démocratique Congo, Côte d'Ivoire, et Mali).

The IUPAC-IUGS joint Task Group “Isotopes in Geosciences” recommends a value of (49.61 ± 0.16) Ga for the half life of 87Rb, corresponding to a decay constant λ87 = (1.3972 ± 0.0045) × 10−11 a−1.

Consistency of observed oceanographic salinity data is discussed with respect to contemporary metrological concepts. The claimed small uncertainty of salinity measurement results traceable to the conductivity ratio of a certified IAPSO Standard Seawater reference is not metrologically justified if results are compared on climatic time scales. This applies in particular to Practical Salinity SP, Reference Salinity SR, and the latest estimates of Absolute Salinity using the TEOS-10 formalism. On climate time scales an additional contribution to the uncertainty that is related to unknown property changes of the reference material must be accounted for. Moreover, when any of these measured or calculated quantity values is used to estimate Absolute Salinity of a seawater sample under investigation, another uncertainty contribution is required to quantify the accuracy of the equations relating the actually measured quantity to the Absolute Salinity. Without accounting for these additional uncertainties, such results cannot be used to estimate Absolute Salinity with respect to the International System of Units (SI), i.e. to the unit chosen for the mass fraction of dissolved material in the sample, which is "g kg−1". From a metrological point of view, such deficiencies in the calculations involving other quantities will produce SI-incompatible results. We outline how these problems can be overcome by linking salinity to primary SI measurement standards.

A basic measurement model and corresponding measurement function for measuring isotope amount ratios on various gases is described and discussed, as the measurand is different from the one used in differential measurements ( δ values). Performed on similar types of ‘hardware’ (a gas isotope ratio mass spectrometer) Isotope Amount Ratio Measurements (‘IARM’) are not intended to replace the traditional (delta) isotope measurements but to complement them: providing “absolute” isotope amount ratio values when there is a need for them. The basic theory is discussed while in a subsequent paper, illustrations by experimental values will be described. The measurement functions used in performing ‘IARM’ describe a transparent and metrologically traceable relationship between an isotope amount ratio of an element (the quantity intended to be measured i.e. the ‘measurand’) to its measured ion current ratio (the quantity subject to measurement), based on the gas flow dynamics in the gas inlet system of the mass spectrometer and due consideration of isotope fractionation effects.

The power of the theoretical formalisms based on concepts from kinetic gas theory described in Part I of this series, is demonstrated in isotope measurement results obtained for three different gases: CO 2 , SiF 4 gas highly enriched in the 28 Si isotope and a high purity neon gas of natural isotopic composition. The measurement procedure as described in this paper enables to detect various (small) anomalies in the gas mass spectrometer during the ion current measurements thus creating the opportunity to correct for them. Using these concepts which govern the isotope fractionation of the gas in the mass spectrometer and performing a calibration by means of synthesized values for isotope amount ratios, SI traceable values in terms of the derived measurement unit mol/mol can be obtained.

The current state of knowledge on the half-lives of the long-lived U radionuclides has been reviewed by the IUPAC-IUGS joint Task Group “Isotopes in Geosciences”. 238 U is assigned a half-life of (4.4683 ± 0.0096) Ga, i.e . a decay constant λ 238 = (0.155125 ± 0.000333) Ga −1 . The coverage factor is k = 2 for this and all other estimates presented here. The 238 U half-life can be used as a reference for the half-lives/decay constants of all other isotopic geochronometers. A revision of the half-life of 235 U based on intercomparison of natural geological samples is premature. The improved repeatability of mass spectrometric measurements has revealed Type B uncertainties that had been dismissed as subordinate in the past. The combined uncertainty of these as yet incompletely charted and quantified sources of Type B uncertainty may be no smaller than the currently accepted uncertainty of the α counting experiments. A provisional value for the 234 U half-life can be calculated with the assumption of secular equilibrium in the analyzed natural samples. This assumption has not yet been verified independently and its metrological traceability appears sub-optimum. A Type B evaluation suggests that the ca. 0.17% offset between the N ( 234 U)/ N ( 238 U) number-ratios of the natural samples used to estimate the 235 U half-life and those of the four samples used to estimate the 234 U half-life should be compounded into the standard measurement uncertainty of the latter. The resulting provisional uncertainty interval ( k = 2) for the 234 U half-life is (244.55–247.77) ka, corresponding to λ 234 = (2.8203–2.8344) Ma −1 .

Different sets of synthetic isotope mixtures for the calibration of carbon and oxygen ion current ratio measurements obtained by mass spectrometry have been prepared by mixing carbon dioxide isotopically enriched in O-18 ((CO2)-C-nat-O-18) and natural carbon dioxide (CO2)(nat), and by mixing different natural CO2 gases with slightly different carbon and oxygen isotopic compositions. These mixtures act as Primary Standards to the Sl for carbon and oxygen isotope amount ratio measurements in CO2. They will help to anchor existing carbon Isotope Reference Samples (i.e., NBS 19, IAEA-CO-9) and therefore offer the basis for comparability of carbon (and oxygen) isotope measurement results, without any assumptive correction for the oxygen isotopes. Through such 'absolute' isotope amount ratio measurements of carbon and oxygen on CO2 produced from the Primary Standard for carbon to the VPDB-scale, NBS19(CO2), calibrated by means of synthetic isotope mixtures, 'absolute' isotope amount carbon and oxygen ratios for the zero point of the VPDB conventional scale were calculated to be R-13/12 = (111,376 +/- 116) x 10(-7) and R-18/16 = (208,824 +/- 148) x 10(-8), respectively. This approach makes these values traceable to the derived SI unit mol/mol. (C) 2007 Elsevier B.V. All rights reserved.

A model has been developed enabling to quantify the degree of scrambling of carbon and oxygen isotopes in mixtures of CO 2 gases with different isotopic compositions. If such isotope mixtures are quantitatively prepared (‘synthesized’) they are ‘embodiments’ (‘realizations’) of SI units, and can serve as ‘calibrators’ of measurements of C and O isotope amount ratios, thus establishing metrological traceability of the measurement results to the SI. Absence of complete equilibrium will cause further isotope scrambling reactions during the isotope amount ratio measurements in the mass spectrometer until the realization of full isotopic equilibrium, but biasing the measurement results continuously before the equilibrium is attained. The concept of isotope ratio space has been conceived to describe this process. This model fits the experimental data adequately and enables to determine the degree-of-isotopic-equilibrium in the gaseous mixture at any time during the mixing process. This creates the possibility to verify the achievement of the isotopic equilibrium prior to the (ion current ratio) measurements.

The definitions of some units of the Systeme International are likely to be revised as early as 2011 by basing them on fixed values of fundamental constants of nature, provided experimental realizations are demonstrated with sufficiently small uncertainties. As regards the kilogram, experiments aiming at linking it to the Planck constant and the atomic mass constant are under way in several laboratories. The other units likely to be redefined are the ampere, the kelvin and the mole. We discuss the advantages and disadvantages of different alternatives for revised definitions of the kilogram and the mole. From physical considerations, metrological consequences and ease of understanding, a definition of the kilogram based on the mass of a particle, such as an atom or the electron, is favoured. One of the proposed definitions fixes the value of the Planck constant through the Compton frequency of a material, though unphysical, particle. Finally, a redefinition of the mole, the counting unit of the amount-of-substance, is proposed which fixes the Avogadro constant as a dimensionless number.

SI-traceable (qabsoluteq) values have been obtained for sulfur isotope amount ratios n(S-33)/n(S-32) and n(S-34)/n(S-32), in two batches of high purity SO2 gas (IRMM-2012 and IRMM-2013). The SO2 gas was converted at IMR-Beijing to Ag2S, then fluorinated to SF6 gas both at IMR-Beijing and at IPMM-Geel. Yields of different conversion methods exceeded 99%. The sulfur amount-of-substance measurements were performed by gas mass spectrometry on SF5+ ions using qIRMM's amount comparator IIq. These isotope amount ratios were calibrated by means of gravimetrically prepared synthetic mixtures of highly enriched sulfur isotopes (S-32, S-33 and S-34) in Ag2S form. The ratio values in the SO, Secondary Measurement Standard are traceable to the SI system. They can be used in the calibration of field sulfur isotope measurements thus making these metrologically traceable to the SI. (c) 2004 Published by Elsevier B.V.

The Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry completed its last review of the isotopic compositions of the elements as determined by isotope-ratio mass spectrometry in 2001. That review involved a critical evaluation of the published literature, element by element, and forms the basis of the table of the isotopic compositions of the elements (TICE) presented here. For each element, TICE includes evaluated data from the “best measurement” of the isotope abundances in a single sample, along with a set of representative isotope abundances and uncertainties that accommodate known variations in normal terrestrial materials. The representative isotope abundances and uncertainties generally are consistent with the standard atomic weight of the element Ar(E) and its uncertainty U[Ar(E)] recommended by CAWIA in 2001.

A value for the Avogadro constant, NA, was derived from new measurements of the lattice parameter, the density and the molar mass of a silicon single crystal. The result NA = 6.022 135 3 × 1023 mol−1 has a relative measurement uncertainty and is in excellent agreement with other published data based on the x-ray crystal density molar mass method, indicating the high repeatability of these experiments. The value differs significantly from the Committee on Data for Science and Technology's most recent recommended value of 6.022 141 99 × 1023 mol−1 by more than 1 × 10−6 NA.

A number of measurement institutes are working together toward a determination of the Avogadro constant with a relative combined standard uncertainty of 10/sup -8/. This will enable a definition of the kilogram based on the mass of a specific number of /sup 12/C atoms rather than an artefact. In order to bring together all the data obtained in the various laboratories and maintain accountability and traceability across the collaborating institutes, a Web-based database has been set up. This database forms part of the BIPM website, although access is currently limited to project participants. Any data used in publications on the Si-route, together with supporting evidence, can be found in this database.

A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to ethical, legal, and international standards. The standard atomic weights of the elements are regularly evaluated, recommended, and published in updated tables by the Commission on Atomic Weights and Isotopic Abundances (CAWIA) of the International Union of Pure and Applied Chemistry (IUPAC). These values are invariably associated with carefully evaluated uncertainties. Atomic weights were originally determined by mass ratio measurements coupled with an understanding of chemical stoichiometry, but are now based almost exclusively on knowledge of the isotopic composition (derived from isotope-abundance ratio measurements) and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled to a numerical value of exactly 12 for the mass of the carbon isotope of mass number 12. Technological advances in mass spectrometry and nuclear-reaction energies have enabled atomic masses to be determined with a relative uncertainty of better than 1 ×10−7 . Isotope abundances for an increasing number of elements can be measured to better than 1 ×10−3 . The excellent precision of such measurements led to the discovery that many elements, in different specimens, display significant variations in their isotope-abundance ratios, caused by a variety of natural and industrial physicochemical processes. While such variations increasingly place a constraint on the uncertainties with which some standard atomic weights can be stated, they provide numerous opportunities for investigating a range of important phenomena in physical, chemical, cosmological, biological, and industrial processes. This review reflects the current and increasing interest of science in the measured differences between source-specific and even sample-specific atomic weights. These relative comparisons can often be made with a smaller uncertainty than is achieved in the best calibrated “absolute ” (=SI-traceable) atomic-weight determinations. Accurate determinations of the atomic weights of certain elements also influence the values of fundamental constants such as the Avogadro, Faraday, and universal gas constants. This review is in two parts: the first summarizes the development of the science of atomic-weight determinations during the 20th century; the second summarizes the changes and variations that have been recognized in the values and uncertainties of atomic weights, on an element-by-element basis, in the latter part of the 20th century.

An isotopic reference material (IRM), IRMM-010, was prepared as a metallic platinum wire and certified for isotopic composition of platinum. The measurements were carried out with a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) in peak jumping mode using a secondary electron multiplier as detector. Five synthetic isotope mixtures with certified isotope amount ratios of n(196Pt)/n(195Pt) were prepared in order to calibrate the measurements. The synthetic isotope mixtures, the natural platinum reference material as well as the isotopically enriched materials were measured in a 2% HNO3 and 2% H2O2 matrix in order to reduce memory effects during the measurements. These measurements resulted in certified isotope amount ratios and isotopic composition of a platinum reference material with natural isotopic composition. The relative abundances of the different platinum isotopes were determined as: 0.0117±0.0012 amount % of 190Pt, 0.782±0.016 amount % of 192Pt, 32.86±0.27 amount % of 194Pt, 33.77+0.16 amount % of 195Pt, 25.21+0.23 amount % of 196Pt, and 7.356±0.087 amount % of 198Pt. This lead to an atomic weight equal to 195.0844±0.0058 for this material. The purity of IRMM-010 was measured, the total impurity was found to be 140±140 μg·g−1. Uncertainties are expanded combined uncertainties expressed with a coverage factor k=2.

The EFQM (European Foundation for Quality Management) model offers a structure to describe and characterize one’s organization and allows the user to adapt the model to a great extent to the local working environment. Using five organization oriented enablers and four result oriented focused criteria, any organization, or substantial part of it, can be characterized. This accounts certainly for a medical laboratory in a hospital setting. The model tries to encourage practical usefulness and self-guidance, continuous improvement in a natural, stepwise way, and change management focused on the positive things within the organization. Application leads to consciousness of the quality of the entire operation, diagnoses, and advises for quality improvement and managerial control, i.e., through indicators. As the work of Islin and Thystrup illustrated, the EFQM model can be very elegantly and effectively applied to medical laboratories [1]. This paper is a compilation of nine lectures given in sequence to elaborate on each of the nine EFQM criteria. The following compilation explores the possibilities of using in a dedicated laboratory service this general quality management model by each of the criteria.

Calibrated values have been obtained for sulfur isotope abundance ratios of sulfur isotope reference materials distributed by the IAEA (Vienna). For the calibration of the measurements, a set of synthetic isotope mixtures were prepared gravimetrically from high purity Ag2S materials enriched in32S, 33S, and 34S. All materials were converted into SF6 gas and subsequently, their sulfur isotope ratios were measured on the SF5+ species using a special gas source mass spectrometer equipped with a molecular flow inlet system (IRMM’s Avogadro II amount comparator). Values for the 32S/34S abundance ratios are 22.650 4(20), 22.142 4(20), and 23.393 3(17) for IAEA-S-1, IAEA-S-2, and IAEA-S-3, respectively. The calculated 32S/34S abundance ratio for V-CDT is 22.643 6(20), which is very close to the calibrated ratio obtained by Ding et al. (1999). In this way, the zero point of the VCDT scale is anchored firmly to the international system of units SI. The 32S/33S abundance ratios are 126.942(47), 125.473(55), 129.072(32), and 126.948(47) for IAEA-S-1, IAEA-S-2, IAEA-S-3, and V-CDT, respectively. In this way, the linearity of the V-CDT scale is improved over this range. The values of the sulfur molar mass for IAEA-S-1 and V-CDT were calculated to be 32.063 877(56) and 32.063 911(56), respectively, the values with the smallest combined uncertainty ever reported for the sulfur molar masses (atomic weights).

An "absolute" value for the molar volume of Si in Si single crystals is presented as 12.058 820 7(54) cm/sup 3/ mol/sup -1/ with a relative standard uncertainty of 4.5/spl middot/10/sup -7/. It is argued that the consistency of most of the molar volume determinations is useful for evaluating the quality of the Si single crystals involved. A value for the Avogadro constant is derived as 6.022 133 9(27)/spl middot/10/sup 23/ mol/sup -1/ having a relative standard uncertainty of 4.6/spl middot/10/sup -7/.

Isotope amount ratios of krypton were measured on subsamples from one large batch of high purity krypton separated from the atmosphere. Synthetic mixtures of enriched krypton isotopes were used to "calibrate" the measurements with small uncertainties. The result is a primary isotopic gas standard (PIGS) IRMM-2030 with certified values for isotope ratios, isotopic composition, and molar mass of krypton with small combined uncertainties u(c), evaluated according to the ISO/BIPM Guide (GUM). It is commercially available from IRMM-Geel or from MESSER (Duisburg, D). The certified krypton isotope amount ratios in the PIGS IRMM-2030 are as follows: n(Kr-78)/n(Kr-84)=0.006 232 5(55), n(Kr-80)/n(Kr-84)=0.040 107(17), n(Kr-82)/n(Kr-84)=0.203 43(17), n(Kr-83)/n(Kr-84)=0.201 79(11), and n(Kr-86)/n(Kr-84)=0.303 205(59) with expanded uncertainty U=ku(c) and coverage factor k=2, The molar mass of Kr in this sample is M(Kr)=83,798 02(16) g/mol. These values are in good agreement with published measurements of atmospheric krypton but have smaller combined uncertainties and are "calibrated" by means of synthetic isotope mixtures. The values of the PIGS are traceable to the SI. Measurements of isotope amount ratios of krypton in other samples can be linked to SI using this PIGS. (Int J Mass Spectrom 206 (2001) 129-136) (C) 2001 Elsevier Science B.V.

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. "traceable" to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be "external" to the measurement laboratories which are being evaluated. This is realized in IRMM's International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using "metrology", the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be "demonstrated" rather than just "designated" and this can be shown to both customers and regulators. It inspires more confidence.

Five synthetic isotope mixtures were prepared from isotopically enriched and purified platinum solutions to obtain accurately known isotope amount ratios n(196Pt)/n(195Pt). Two metallic platinum powders enriched in isotopes 195Pt and 196Pt, respectively, were dissolved in aqua regia. The resulting hexachloroplatinic acid was reduced under hydrogen to transform it into a metallic platinum sponge. The level of impurities contained in the sponges, as well as their stoichiometry were estimated and taken into account in all calculations carried out with the isotopically enriched materials. The prepared isotope amount ratios, n(196Pt)/n(195Pt), of the five mixtures were 0.099 57, 0.397 34, 0.738 00, 3.9976, and 10.005 with expanded relative uncertainty (coverage factor k = 2) varying from 1 × 10−3 to 2.8 × 10−3. These mixtures were used to calibrate isotope amount ratio measurements of a platinum sample of natural isotopic composition by inductively coupled plasma mass spectrometry. Keywords: Atomic weight; Platinum; Inductively coupled plasma mass spectrometry; Isotopic reference material; Synthetic isotope mixtures

The performance of four commercially available ICPMS instruments of three different types was compared by means of uranium "isotopic measurements". Examined were two quadrupole sector (different generation, different manufacturer), one single detector double focusing magnetic sector and one multiple collector double focusing magnetic sector instruments. The same samples of the IRMM-072 series were used under routine conditions to measure the 233U/235U and the 233U/238U ratios which, in these samples, vary over almost three orders of magnitude from approximately 1 to approximately 2 x 10(-3). Within expanded (k = 2) uncertainties, good agreement was observed between the certified values and the data internally corrected for mass-discrimination effects. The magnitude of the evaluated uncertainties was different for each type of instrument. With the multiple collector instrument, expanded uncertainties varied from +/- 0.04% to +/- 0.24% for the 233U/235U ratio, and from +/- 0.08% to +/- 0.27% for the 233U/238U ratio. They were approximately 1 to 5 times larger with the single detector magnetic sector instrument, and approximately 10 to 25 times larger with both quadrupole sector instruments. With the multiple collector instrument, repeatability of the measurements seemed to be limited by the difficulty of correcting properly for instrumental background, whereas with the single detector magnetic sector instrument the counting statistics was the only limitation (on smallest ratios). Apparent mass-discrimination was clearly found to be larger but more reproducible (and hence easier to correct for) in the case of magnetic sector instruments than for both quadrupole sector instruments. If space charge effects were the main source of mass-discrimination for all instruments, these results are in contradiction with the hypothesis of the size of mass-discrimination decreasing with the acceleration voltage. With the single detector magnetic sector instrument in particular (when operated by changing the ion energy only), our results pointed at more than only one major source of mass-discrimination, with variable size depending on the ratios measured.

The meaning of calibration in general and in the field of isotopic measurements in particular is described, stressing the fundamental difference between calibration as an aim and tools to achieve calibration. The role of proper uncertainty budgeting as a prerequisite for establishing a “calibrated” measurement is explained. It leads to the recommendation that the quality of the uncertainty statement should be heavily weighed when ranking or judging “calibrated” isotopic measurement results evaluated by the Commission on Atomic Weight and Isotopic Abundances.

Two synthetic isotope mixtures for the calibration of sulfur isotope amount ratio measurements were gravimetrically prepared from high purity Ag2S materials enriched in 32S, 33S, and 34S. The mixtures were made so as to closely resemble the (natural) isotopic composition of the materials to be “calibrated”. This allowed a totally independent evaluation, on the same samples, of the relative combined uncertainty of: (a) the procedure to perform direct measurements of the amount of substance ratios of gas isotopes in the redetermination of the Avogadro constant and (b) the gravimetric preparation procedure. The result of both procedures, mass spectrometry and gravimetry, agree to a relative uncertainty of 3 × 10−4 for sulfur amount ratio measurements of the major abundant isotopes. Thus it seems that a direct measurement of isotopic gas mixtures (e.g. of natural isotopic composition) is now possible for sulfur—and probably also for other gaseous isotopes—without necessarily having to rely on “calibration” by means of values provided by measurements of gravimetrically prepared isotope mixtures. However, synthetic mixtures may be needed for validation and verification purposes, in particular for quality assurance.

A batch of SF6 gas prepared by Messer (Germany) was metrologically certified for absolute isotope abundance ratios and molar mass (atomic weight) of sulfur following the ISO/BIPM Guide to the expression of uncertainties in measurements. The certification is based on the "Avogadro II Measurement Procedure" using the "Avogadro II amount comparator," which was developed in the framework of the redetermination of the Avogadro constant. For the correction of small remaining systematic effects of unknown nature, synthetic isotope mixtures of Ag2S converted to SF6 were used in order to obtain "calibrated" or "absolute" values with small combined uncertainty. The values for this sulfur primary isotopic gas standard (PIGS) are traceable to the Systeme International d'Unites (SI) in the shortest possible way and can therefore serve as a link to SI when used in differential measurements. The PIGS is now commercially available. (Int J Mass Spectrom 193 (1999) 1-8) (C) 1999 Elsevier Science B.V.

Two methods are described for the preparation of GeF 4 from Ge and GeO 2 for isotopic measurements: a direct reaction with elemental fluorine and a wet chemical procedure. Germanium isotope amount ratios were obtained using the same measurement procedures and instruments as developed in the framework of the redetermination of the Avogadro constant and taking all significant sources of uncertainty into account. The repeatability of measurements on an individual sample was 5 × 10 −5 relative. The results on the abundance ratios for different sample materials and preparation techniques agree to within 7 × 10 −5 relative. All uncertainty statements were made following the ISO/BIPM Guide to the Expression of Uncertainty in Measurements (Geneve, 1993). The calibrated isotope abundance ratios are calculated to be n ( 70 Ge)/ n ( 74 Ge) = 0.5635 (29); n ( 72 Ge)/ n ( 74 Ge) = 0.7519 (38); n ( 73 Ge)/ n ( 74 Ge) = 0.2123 (11); n ( 76 Ge)/ n ( 74 Ge) = 0.2118 (11) resulting in an atomic weight A r (Ge) = 72.6276 (32). These results are compared to values previously published for the isotopic composition and atomic weight of Ge.

The half-life of 241Pu for β decay has been determined on an initially 93 % isotopically enriched material by measuring the decreasing amount ratio n(241Pu)/n(240Pu) as a function of time over more than twenty years. Over the same period the decrease of this ratio was measured relative to the amount ratio n(240Pu)/n(239Pu) in a "ratio-of-ratio" measurement which allowed for correction of isotopic effects in the ion source, taking into account the decay of 240Pu (half-life = 6553 a) and 239Pu (half-life = 24110 a). A regression procedure of the ratio-of-ratio measurements as a function of time resulted in a value for the 241Pu half-life of (14.290 ± 0.006) a (expanded uncertainty with coverage factor k = 2). The slight difference found in the half-life value as measured by the authors on the same material in the period 1976 to 1981 is discussed.

The aim of the International Measurement Evaluation Programme (IMEP) is to give an objective picture of state-of-the-practice analytical measurements by comparing them to a reference value obtained by a primary method of measurement. The referencevalue is therefore as traceable to the SI system of measurements as can presently be achieved and is independent of human or political decisions. Thus a large scale field test is made to achieve (international) comparability of measurements by comparing them with an independent metrologically established value. In the fourth measurement round, IMEP-4, three trace elements, Li, Cu and Zn, at three different levels in (bovine) serum were measured by about 12 participating laboratories using their routine methods. The (coded) results are graphically reported and compared to certified reference values established by an isotope-specific method, isotope dilution mass spectrometry, defined as a primary method of measurement by the Consultative Committee on Amount of Substance. Results indicate a spread of more than ±50%, asymmetrically distributed around the reference value with its own uncertainty range, although the self-declared accuracy of the laboratories was 5–10%. Self-assessment by participants of their analytical capabilities does not show a high correlation between self-rating ("more experienced" or "less experienced") and actual performance. In the way they have been applied, all methods seem to produce results of approximately the same quality.

The first interlaboratory study of the Consultative Committee for Amount of Substance (CCQM) focused on the determination of lead concentration in a synthetic water sample. In the framework of the CCQM activities, only leading metrology institutes participated in the study. The prescribed analytical method was double isotope dilution mass spectrometry (IDMS) as a primary method of measurement (PMM). At the Institute for Reference Materials and Measurements (IRMM) the material was additionally analysed by direct IDMS as a primary method of measurement using, completely independently, a certified spike reference material. The work described in this paper concerns direct IDMS. Conclusions are drawn on the use of IDMS as a PMM, on the comparison of the results with those of double IDMS, on the use of a certified spike reference material and on the calculation of uncertainty.

Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li2CO3 compounds. The starting materials, 99.9981% enriched 6Li, and 99.9937% enriched 7Li, were purified by ion exchange, and the purified materials converted from LiOH to Li2CO3 by reaction with CO2. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li2CO3 carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(6Li)/n(7Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.

Preparation of two Isotopic Reference Materials of thorium has been performed, starting from highly enriched 232Th (99.99%) and 230Th (99.8%). After full characterization (chemical and isotopic) of these purified base materials the thorium nitrate was transformed to thorium dioxide. Accurately weighed amounts of the two isotopes in the dioxide form were subsequently dissolved in nitric acid and resulted in solutions with amount ratios n(230Th)/n(232Th) close to 10–5 (IRMM-035) and 3 · 10–6 (IRMM-036). These gravimetrically prepared ratios were finally verified by means of Thermal Ionization Mass Spectrometry (TIMS). The purpose of the Reference Materials is to calibrate thorium isotope amount ratio measurements.

One of the routes to re-determine the Avogadro constant requires ultra-high accuracy isotopic measurements of amount ratios of Si isotopes to 10 -5 reproducibilities on the ratio measurements and calibrating the results by synthetic isotope mixtures prepared to 2 10 -5 relative combined uncertainty. The route to these results is described. followed by a description of the improvement of out knowledge of the Avogadro constant N A through these measurements. The same route has recently been opened for other gases and has opened the way to the establishment of Primary Standards of Measurements' for gas isotopic measurements. It is described how these highly accurate measurements of ratios of amount of substance have considerably contributed to clearer thinking about concepts for measurements of amount of substance. The acquired expertise in measurement instrumentation and measurement procedures can now be extended to a more general use in measurements of isotope amount ratio (i.e. in other elements). It can also be combined with isotope dilution. This latter combination opens up a new route towards a realization of traceability of an amount-of-substance measurement to the SI and to the (measurement procedure and instrumentation leading to) Avogadro constant.

Procedures developed for accurate measurement of amount of substance ratios for gas isotopes, as used to improve our knowledge of the Avogadro constant and checked for quantitative conformity against kinetic gas theory, were used to measure synthetic mixtures of enriched xenon gas isotopes, prepared by (micro)-gravimetry as is usual in the preparation of synthetic gas compound mixtures. This allowed a totally independent evaluation, on the same samples, of the relative combined standard uncertainty of (a) the procedure to perform direct measurements of amount of substance ratios of gas isotopes in the redetermination of the Avogadro constant and (b) the gravimetric preparation procedure. The results of both procedures, mass spectrometry and gravimetry, agree to a relative uncertainty of 2 × 10-3 for amount measurements of the major abundant isotopes. Thus it seems that a direct measurement of isotopic gas mixtures (e.g. of natural isotopic composition) is now possible for xenon isotopes- and probably also for other gaseous isotopes- without necessarily having to rely on ''calibration'' by means of values provided by measurements of gravimetrically prepared isotope mixtures. However, synthetic mixtures may be needed for validation and verification purposes, in particular for quality assurance (QA).

A series of synthetic mixtures of thorium isotopes was prepared on a gravimetrical basis. The starting compounds consisted of natural thorium Th-232 (99.99%) and highly enriched Th-230 (99.8%). These materials were chemically purified and characterized for isotopic composition and chemical purity. Thorium dioxide (ThO2) was demonstrated to be a suitable compound for gravimetrical blending. The isotope amount ratios in the mixtures ranged from 10(-2) to 3 x 10(-6). These synthetic isotope mixtures are to our knowledge, the first ever prepared for thorium and may serve for calibration purposes. Published by Elsevier Science B.V.

A metrological certification measurement was made on a large batch of xenon separated from the terrestrial atmosphere by Messer Griesheim (Duisburg, Germany). The measurements were performed using the same procedure for measurements of amount ratios as developed for the improvement of the Avogadro constant N-A. During the measurement, the gas effusion from the expansion vessel into the ion source was continuously monitored by measuring experimental values for [m(E-i)/m(E-j)](-(empty set)) to enable correction for mass discrimination. Synthetic mixtures were made of enriched Xenon isotopes and measured. They did not reveal a significant correction factor for residual unknown errors within the measurement uncertainty of 5 x 10(-4). Thus, an isotopic composition and a molar mass (atomic weight) value M(Xe) = 131.29276 +/- 0.00033 g mol(-1) for xenon in this batch was established by procedures confirmed by kinetic gas theory at this level. The measured isotope amount ratios were compared to previous measurements on atmospheric xenon. They are in good agreement but now have considerably smaller relative combined uncertainties: n(Xe-124)/n(Xe-132) = 0.003536(12); n(Xe-126)/n(Xe-132) = 0.0033077(72); n(Xe-128)/n(Xe-132) = 0.070989(29); n(Xe-129)/n(Xe-132) = 0.98112(41); n(Xe-130)/n(Xe-132) = 0.151290(47); n(Xe-131)/n(Xe-132) = 0.789055(76); n(Xe-134)/n(Xe-132) = 0.387819(69); n(Xe-136)/n(Xe-132) = 0.32916(17). Published by Elsevier Science B.V.

The isotope abundance ratio of lithium in the Li isotopic reference material IRMM-016 was redetermined by thermal ionisation mass spectrometry by means of synthetic isotope mixtures. This resulted in an absolute ratio n(6Li)/n(7Li) of 0.08212 ± 0.00028, and corresponding isotope abundances of 7.589 ± 0.024 amount % 6Li, 92.411 ± 0.024 amount % 7Li and an atomic weight of lithium of 6.94005 ± 0.00024. Uncertainties are expanded uncertainties using a coverage factor of two.

The meaning of traceability to SI and how this can be achieved by using primary methods is demonstrated in this paper, using the example of the certification for Cd and Pb concentration in the candidate reference material, MURST ISS A1 Antarctic sediment. The analytical method used was inductively coupled plasma mass spectrometry (ICP-MS) in combination with isotope dilution (ID). ID is recently recognised as a primary method, and its advantages are presented. Microwave pressure digestion and separation (anion exchange) were applied. The uncertainty budget calculation is performed according to the EURACHEM and ISO guidelines, and some useful considerations about other approaches are given.

Basic principles for traceability of measurements to the Systeme International d'Unites (SI) in general, and for measurements of amount of substance in particular, are described. Analogies with long-standing traceability schemes in physical measurements are given and an attempt is made to show the probable development of traceability for amount-of-substance measurements, a process now in its early stages.

An Ultra-Clean Chemical Laboratory (UCCL) has been built at IRMM to allow reliable, contamination-free chemical treatment of samples prior to inorganic elemental or isotopic analysis. The concept is intended to guarantee a dust-free environment as well as resistance to corrosion even if hot concentrated mixtures of acids are continuously used, thus establishing not a clean or dust-free room but a clean laboratory. The excellent air quality is demonstrated both by particle measurements and the analysis of acids purified by subboiling distillation in the UCCL.

Progress in science is often achieved by modifications of hypotheses imposed by reliable results of measurements with small uncertainty. The application of the discipline of metrology to chemistry, based on the SI and the estimation of uncertainties, is illustrated by suggested refinements of the presentation of molar-mass values of the elements as recommended, and biennially revised, by the International Union of Pure and Applied Chemistry (IUPAC). All these values from 1969 to 1995 are tabulated here with attributed uncertainties, and the changes achieved in all these uncertainties are presented pictorially. Molar mass is the factor that converts, with its entity-specific uncertainty, the mass of that specified entity in a given sample from a value expressed as a mass quantity to one in the amount-of-substance SI base quantity. An element with two or more isotopes may exhibit differences in isotope abundances. A small range of molar-mass values may exist even in normal terrestrial materials. The IUPAC combines, with only one-digit precision, such ranges with experimental uncertainties. Nevertheless, the IUPAC values in the past have proved highly reliable for use in chemistry. For anticipated improvements in the accuracy of some chemical measurements, two-digit uncertainties, evaluated and published separately from normal terrestrial ranges of molar mass, are proposed.

A new 15N-enriched nitrate species-specific spike isotopic reference material IRMM-627 has been prepared in the form of KNO3 in NaOH solution (pH = 10). It is a 64.6% enriched 15N-nitrate material, certified for its nitrogen isotope ratio (in nitrate species) n(14NO3−)/n(15NO3−) = 0.548 ± 0.012 and its nitrate concentration c(NO3−)/mmol kg−1 = 3.124 ± 0.080 (expanded uncertainty, coverage factor k = 2). The isotopic composition was determined using negative thermal ionisation mass spectrometry and the concentration via reverse isotope dilution mass spectrometry (IDMS). The mass fractionation of the mass spectrometric procedure was determined using synthetic isotope mixtures. Isotopic homogeneity, stability and impurity content of IRMM-627 were investigated. Orthodox uncertainty evaluation was done by examining the different uncertainty contributions. The species specific spike isotopic reference material can be used to perform isotope dilution analysis of nitrate with c(NO3−)/mmol kg−1 > 0.016. It is available in quartz ampoules containing approximately 4.5 g of solution.

The isotopic composition of atomic nitrogen and its molar mass (numerically equal to its atomic weight) M(N) were re-measured using recently improved accurate gas isotope-ratio mass spectrometry. We found in one sample of pure nitrogen, M(N) = 14,006 721 4 g mol-1 with a combined uncertainty uc = 0,000 001 8 g mol-1 (an average of four partially independent values). Another sample, atmospheric nitrogen, similarly from four values, yielded M(N) = 14,006 727 8 g mol-1 with uc = 0,000 001 5 g mol-1 corresponding to an isotope substance ratio n(14N) /n(15N) = f(14N)/f(15N) = 271,87 with uc = 0,11. The latter is in good agreement with the currently accepted IUPAC value of 272,0 with uc = 0,3. The measurements were carried out by means of the same rigid measurement procedures and instrumentation which are used in the isotopic measurements for ongoing redeterminations of the Avogadro constant. Although the measurements were not calibrated against synthetic N-isotope mixtures, the results compare favorably, within quoted uncertainties, with those selected by the International Union of Pure and Applied Chemistry (IUPAC) as the hitherto "best measurements from a specific source" and those representative of terrestrial compositions. They suggest a new standard of reliability for molar-mass determinations. They also establish the best realization so far of traceability of nitrogen isotopic measurements to the mole in the Systeme International d'Unites (SI), as well as to the Avogadro constant.

The evolution of trace concentrations (sub ng·g−1) of uranium in aqueous reference solutions was followed over time by isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). Blank levels and detection limits needed to be determined prior to the actual investigations. Accuracy and precision of the method were determined on the basis of results obtained for uranium reference materials under similar experimental conditions. Reference solutions, certified for uranium concentration were prepared on gravimetrical basis. Analyses were performed over a period of 2 years. Taking into account the accuracy and the precision achieved, no significant change of the concentration is observed with time. Therefore, the mid and long term stability of the concentration of such reference materials was successfully demonstrated.

As a result of the reprocessing of nuclear fuel, the fission products xenon and krypton are released to the atmosphere. Due to their different isotopic composition as compared to natural atmospheric xenon (krypton) the dilution process in air results in isotopic alterations in the blend. The isotopic compositions of fission noble gases were calculated for two scenarios. Subsequently blending calculations were carried out in order to simulate the mixing of the fission off-gases with atmospheric noble gases. In order to estimate the detection limit of the alternations occurring, the calculated isotope ratios in the blend were compared to the ratios of natural xenon (krypton) as measured using the highly developed ultra-accurate measurement facilities for isotopic mass spectrometry at the Institute for Reference Materials and Measurements. The calculated sensitivity of this method lies within a range of some 10 9 m 3 of air g −1 fission gas. Finally the potential application of stable isotope measurements of xenon (krypton) as a supplementary method for detecting reprocessing activities is discussed.

Under favorable conditions, a retrospective test for reliability of published sets of physical property data becomes possible. The test and the necessary conditions for its use are discussed. The test is applied, by example, to well-documented, periodically republished nuclidic (atomic) masses of nine low atomic number nuclides. An index of reliability is suggested and evaluated for the example.