Paul De Bièvre

Validation of the analytical linearity and mass discrimination correction model exhibited by a multiple collector inductively coupled plasma mass spectrometer by means of a set of synthetic uranium isotope mixtures

A set of commercially available synthetically prepared mixtures of uranium isotopes (IRMM 072) were used to assess the linearity and mass discrimination exhibited by a multiple collector ICP-MS instrument. Measurements of eight uranium isotopic reference materials with 233U : 235U isotope abundance ratios ranging from 1 to 0.01 were made. Linear, power law and exponential relationships between instrumental mass discrimination and mass difference were evaluated. The power law and exponential function resulted in the best correction. The corrected isotope abundance ratios for 233U : 235U and 233U : 238U did not differ significantly from the certified values at the 3 × 10–4 level.

Present Status of the a Vogadro Constant Determination from Silicon Crystals with Natural Isotopic Composition

The determination of the Avogadro constant from two selected silicon crystals is described. The density, molar mass, and lattice spacing of the two crystals were measured at NMU, PTB, IRMM, IMGC, and NIST. When all the data are combined, it leads to the Avogadro constant of 6.022 1353 (21) times 1023 mol-1 with a relative combined standard uncertainty of 3.4 times 10-7

Traceability in chemical measurement

P. De Bievre: Editorial/Introduction to this volume.- P. De Bievre, R. Kaarls, H.S. Peiser, S.D. Rasberry, W.P. Reed: Measurement principles for traceability in chemical analysis.- P. De Bievre: et al.: Protocols for traceability in chemical analysis, Part 1.- P. De Bievre et al.: Protocols for traceability in chemical analysis, Part 2.- R. Dybkaer: Metrological traceability in laboratory medicine.- F. Adams: Traceability and analytical chemistry.- P. De Bievre: Do interlaboratory comparisons provide traceability?.- R. Dybkaer: From total allowable error via metrological traceability to uncertainty of measurement of the unbiased result.- M. Buzoianu: Practical considerations on the traceability to conventional scales.- P. De Bievre: Traceability of (values carried by) reference materials.- A. Williams: What can we learn from traceability in physical measurements?.- W. Richter: How to achieve international comparability for chemical measurements?.- P. De Bievre: The key elements of traceability in chemical measurement: agreed or still under debate?.- B. King: The practical realization of the traceability of chemical measurements standards.- M. Mariassy et al.: Link to the SI via primary direct methods.- A. Zschunke: The role of reference materials.- B. Belanger: The measurement assurance concept in calibration and traceability at NBS/NIST.- I. Kuselman et al.: Lifetime of the traceability chain in chemical measurement.- St. Rasberry: Proficiency evaluation as a traceability link in chemical metrology.- P. Armishaw, B. King, R.G. Millar: Achieving traceability in chemical measurement - a metrological approach to proficiency testing.- A. Wallard: Traceability issues in physics.- W. Richter: Comparative study of the presentations at the CCQM Workshop on Traceability.- M. Muller: Traceability in Laboratory Medicine.- M. Lipp: Testing for foods derived from modern biotechnology: Opportunities and limitations for metrology.- W. Richter, Guttler: A nationaltraceability system for chemical measurements.- L. Siekmann: Establishing Measurement Traceability in Clinical Chemistry.- M. Kimberly: Clinical laboratory reference networks.- Ph. Taylor: One way of disseminating Reference Values with demonstrated Traceability and demonstrated Uncertainty to Field Laboratories: IMEP.- E. Volkert: Implementation of Traceability - Needs and Perspective of the IVD Industry.- G. Holcombe, R. Lawn, M. Sargent: Improvements in efficiency of production and traceability for certification of reference materials.- M. Buzoianu, H.Y. Aboul-Enein: Traceable measurement in clinical laboratories.- Ch. M. Beck: A traceability protocol to the SI by gravimetric analysis.- V.P. Antipin, A.A. Grigorieva: Reference Samples for analysis of gas impurities in aluminium and titanium alloys: Features of production, certification and usage to ensure traceability of results.- S. Duta: The use of certified reference materials in the Romanian traceability scheme.- P. Spitzer: Traceable measurements of pH.- P.E. Holland et al.: The development of gas standards and calibration techniques for measurement of vehicle, aircraft and industrial emissions, natural gas, occupational exposure and air quality.- I. Sperlingova et al.: Problems of traceability of total protein and catecholamine determinations in human urine.- M. Sega: Traceability in routine chemical measurements: an example of application in the determination of CO2 at atmospheric concentration.- Glavic-Cindro et al.: Traceability of measurement results of the effective acquisition time in gamma-ray spectrometry implemented by the pulser method.- Y. Mitani et al.: Traceability and Practice in Metrology in Chemistry.- P. Charlet, A. Marschal: Benefits of the implementation of a metrological structure for water analyses.- L. Bruggemann, R. Wennrich: Traceability of results of chemical measurements concerning a linear calibration.- W.P. Reed: Traceability, is it what we really want in our

Evaluation of the molar volume of silicon crystals for a determination of the Avogadro constant

For a determination of the Avogadro constant N/sub A/ by the X-ray crystal density (XRCD) method, the molar volume M//spl rho/ of three different silicon crystals, NRLM1, NRLM2, and NRLM4, have been analyzed systematically by measurements of their densities /spl rho/ and molar masses M. Details on the sample preparations and the result of measurement are presented.

The definition of primary method of measurement (PMM) of the ’highest metrological quality’: a challenge in understanding and communication

Abstract Problems with understanding, explaining and communication of the present definition of primary method of measurement are described and amendments put forward for discussion. The conclusion is drawn that in many cases more attention should be given to the measurement result and its uncertainty statement, rather than to a method. Some cases are discussed where methods might have a fundamental characteristic that other methods do not have, a condition for the epitheton ’primary’.

Adsorption in gas mass spectrometry. I. Effects on the measurement of individual isotopic species

The adsorption-desorption process of gas molecules on the walls of the mass spectrometer inlet system was studied in order to assess quantitatively its influence on measurement results. The effects on individual isotopic species in SiF4 measurements required for the re-determination of the Avogadro constant are discussed in this paper, while the effects on isotope amount ratio determinations will be discussed in a companion paper. A model based on the Langmuir adsorption isotherm is developed, which fits well the experimental observations and provides the means to investigate adsorption and desorption kinetics in the inlet system. A parameter called the ‘apparent leak-rate coefficient’ is introduced; this represents the relative variation with time of any isotopic species in the inlet system. All the adsorption parameters appearing in the balance equations are derived from the apparent leak-rate coefficient. Application of the model to long mass-spectrometric measurements of SiF4 yields a rate constant of 6.5 × 10−5 s−1 for SiF4 effusion through the molecular leak of the inlet system. Adsorption and desorption rate-constants are equal to 20–25% of the leak rate-constant, and the adsorption sites are about two orders of magnitude lower than the number of Ni and Cu atoms present on the inlet system walls.

Adsorption in gas mass spectrometry II. Effects on the measurement of isotope amount ratios

Abstract Gas adsorption in the mass spectrometer inlet system (equipped with molecular leak) causes a deviation from linearity of the measured ln R i 1 data versus time, which affects the extrapolation to time t = 0 required to obtain the isotope amount ratios of a sample. The model first presented in (R. Gonfiantini, S. Valkiers, P.D.P. Taylor, P. De Bievre, Adsorption in gas mass spectrometry. I. Effects on the measurement of individual isotopic species, Int. J. Mass Spectrom. Ion Proc. (1997) in press) is further developed in order to show the effects of adsorption on the data obtained in long measurements of SiF 4 samples and improve the extrapolation InR i /1 values to t = 0. The model enables to estimate the isotope fractionation factors for the processes of gas effusion through the molecular leak, and for adsorption and desorption on the inlet system walls. The fractionation factors obtained for gas effusion and adsorption are close to the expected value of ( M 1 / M i ) 1/2 , where M 1 and M i are the molar masses of the isotopic species considered. The isotope fractionation factor for desorption, which can be evaluated only indirectly from the data fitting, indicates that the heavy isotopes are preferentially retained in the adsorbate. Model extrapolation of data obtained during the first 10 hours of measurement gives values of R i /1 0 which are slightly but significantly smaller than those given by linear extrapolation of the first two hour data. The difference is, in relative terms, −(1.88 ± 0.23) × 10 −4 for the 29 Si/ 28 Si ratio and −(3.25 ± 0.47) × 10 −4 for the 30 Si/ 28 Si ratio. The resulting molar mass for silicon is (1.0 ± 0.1) × 10 −6 parts lower than that obtained with the isotope amount ratios of the linear extrapolation. This effect is not negligible but it cancels by using synthetic isotope mixtures for the measurement calibration. The model does not match the data after 15 h of measurement. This may imply that more than one adsorption mode occurs. Effects related to molecule fragmentation and the space charge distribution in the ion source are discussed.

Stability studies and purification procedure for nitrite solutions in view of the preparation of isotopic reference materials.

The lack of reference materials, accurately certified for nitrite, is a problem in view of the importance of this species for environmental and medical reasons. This work outlines a plan for the preparation of nitrite isotopic reference materials (IRMs) in the form of high purity solutions, certified for their nitrite-nitrogen isotopic composition and nitrite concentration. To achieve the desired accuracy (expanded uncertainty U with a coverage factor k=2 of </=2%), primary methods of measurement such as isotope dilution mass spectrometry (IDMS), gravimetry, and titrimetry must be used. The main difficulty is the stability of nitrite. Other problems expected in the preparation and certification of nitrite IRMs are described. Results from long term stability studies (up to 1.5 years) and a procedure for the purification of the candidate nitrite IRMs are presented. The purpose is to use these IRMs for high accuracy method calibrations and as anchor points for SI-traceable nitrite concentrations. Reference values linked to the SI system are useful to demonstrate the degree of international comparability of nitrite measurements in intercomparison programmes such as the IRMM-International Measurement Evaluation Programme (IMEP).

Using isotopic disequilibrium of CO2 to model gas adsorption in mass spectrometric measurements

Abstract Mass spectrometric measurements were carried out on a CO2 sample prepared by mixing known amounts of ‘natural’ CO2 with CO2 enriched in 13C and, to a lesser extent, in 17O and 18O. The sample was in isotopic disequilibrium, i.e. with the isotopic species distribution not obeying the statistical probability. The results indicate that isotope scrambling reactions occur during the measurement which tend to shift the gas isotopic composition towards the equilibrium. The isotope exchange reactions take place via gas adsorption in the mass spectrometer inlet system. A Langmuir-type adsorption model, developed independently to describe SiF4 adsorption in the mass spectrometer inlet system, is applied to the CO2 scrambling reactions. The model is capable of fitting the experimental data adequately, and sets of values for the isotope exchange kinetics can be derived from it. Small deviations from the model prediction may be due to isotope fractionations which have not been taken into account and require further investigation.

Second opportunity for chemists to re-think the mole

Since several years, the seven base units, m (metre), kg (kilogram), s (second), A (ampere), K (kelvin), mol (mole), and cd (candela) of the SI, are under revision and re-definitions are being proposed by the CCU (the Consultative Committee on Units to the CIPM, the International Committee on Weights and Measures) [1]. The mechanism of such a re-definition is lengthy and not that well known, certainly not in the chemical measurement community. In essence, CCU prepares proposals to the CIPM that passes a final recommendation for decision to the CGPM (the General Conference on Weights and Measures). CGPM is convened every 4 years: 2003, 2007, 2011, then exceptionally after 3 years in 2014, then, presumably, in 2018. It decides in virtue of the powers given to it by the Diplomatic Treaty on the Metre, ‘Convention du Metre’, signed in 1875. To that effect, CCU informs (and collects opinions of) other Consultative Committees to the CIPM on units in various fields such as: Electricity and Magnetism (CCEM), Photometry and Radiometry (CCPR), Thermometry (CCT), Length (CCL), Time and Frequency (CCTF), Ionising Radiation (CCRI), Units (CCU), Mass and Related Quantities (CCM), Amount of Substance: metrology in chemistry (CCQM), Acoustics, Ultrasound, and Vibration (CCAUV).