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The kilogram is the unit of mass and was defined in 1889 by the international prototype of the kilogram. The mole is the unit of amount of substance and was defined in 1960 by the number of atoms in 0.012 kg of 12C. These definitions were revised in May 2019. The new definitions of the kilogram and the mole are based on the Planck constant h and the Avogadro constant NA, respectively. The values of h and NA used in the new definitions were determined by summarizing measurement results of the two physical constants by several national metrology institutes around the world. In this review, the history of the two units and measurement technologies used to derive the new definitions are described. The effect of the revision on the development of new measurement technologies is also introduced.

Volatile Organic Compounds (VOCs) are widely measured at ppb and ppt level in many contexts, from therapeutic drug control in respiratory diseases to monitoring of climate change and indoor air quality. The need for accuracy is a common denominator in all these fields. The interactions between gas mixtures and solid surfaces in sampling lines and instruments play an important role in calculating the total uncertainty of the amount of VOC. The amount of substances in the gas mixture is affected by its reversible and irreversible interactions with the sampling line. The main aim of this paper is to propose and discuss a method to quantify the amount of substance segregated by reversible interactions on sampling lines. To validate the proposed method, the areic amount of a VOC (Acetone) is measured for a commercial test pipe (Sulfinert®) as the amount of substance per unit area of the internal surface of the test pipe segregated from the flowing gas mixture. Stainless steel coated by Sulfinert® was chosen as a test material because of its wide use and its limited irreversible and permeation effects. A certified gas mixture of Acetone in air with a nominal mole fraction of 10 µmol mol−1 was used for validation. Broad temperature control was used and the sensibility of the method to the temperature and the pressure has been evaluated to correct the bias due to physical condition. The sensitivity to the residence time and the Reynolds number of the gas flow has been evaluated to verify the reaching of equilibrium and the limits of the applicability of the method. The areic amount of Acetone at equilibrium on Sulfinert® coated pipe was measured as 40 nmol m−2, and an equilibrium constant value of around 0.2 m was calculated as the ratio between the superficial amount segregated on the wall and the amount concentration of Acetone in the mixture, both at the equilibrium. The observed reproducibility was better than 2.5%. This method is aimed to investigate VOC losses due to interactions for many VOC/material systems at a lower amount of substance levels.

Gravimetric preparation method is one of the most precise and accurate methods for preparing primary standard gas mixtures (PSMs). Although the principle and execution of the gravimetric method are not complicated, the uncertainty of the gravimetric method is so small that a seemingly minor error can result in an incorrect amount fraction of the PSM. Therefore, verifying the amount fraction of the PSMs is a necessary step. We perform a high-precision comparison between the PSMs of oxygen in nitrogen (∼100 µmol per mol) using a well-stabilized gas chromatograph with a thermal conductivity detector (GC-TCD) system in conjunction with high-precision pressure monitoring for sample amount correction and a quality-control cylinder technique in which the PSMs were analyzed against a reference cylinder, which leads to the cancellation of the drift in the sensitivity of the GC-TCD. After optimization of the measurement conditions, the relative expanded uncertainty reaches 0.022% (coverage factor k = 2), which is equivalent to the uncertainty of the PSMs. The Consultative Committee for Amount of Substance of the Comite International des Poids et Mesures performed a key comparison CCQM-K53, in which one of the PSMs used in this work was compared and agreed well with PSMs prepared by other National Metrology Institutes. These results show that the GC-TCD system developed in this work is sufficiently reliable, precise and accurate to verify PSMs.

We have developed a method to calculate the fractional distribution of CO2 across all of its component isotopologues based on measured δ13C and δ18O values. The fractional distribution can be used with known total CO2 to calculate the amount of substance fraction (mole fraction) of each component isotopologue in air individually. The technique is applicable to any molecule where isotopologue-specific values are desired. We used it with a new CO2 calibration system to account for isotopic differences among the primary CO2 standards that define the WMO X2007 CO2-in-air calibration scale and between the primary standards and standards in subsequent levels of the calibration hierarchy. The new calibration system uses multiple laser spectroscopic techniques to measure mole fractions of the three major CO2 isotopologues (16O12C16O, 16O13C16O, and 16O12C18O) individually. The three measured values are then combined into total CO2 (accounting for the rare unmeasured isotopologues), δ13C, and δ18O values. The new calibration system significantly improves our ability to transfer the WMO CO2 calibration scale with low uncertainty through our role as the World Meteorological Organization Global Atmosphere Watch Central Calibration Laboratory for CO2. Our current estimates for reproducibility of the new calibration system are ±0.01 µmol mol−1 CO2, ±0.2 ‰ δ13C, and ±0.2 ‰ δ18O, all at 68 % confidence interval (CI).

Following the revision of the International System of Units (SI), that takes effect on 20 May 2019, the unit mole is defined by using a fixed number of elementary entities. This number is the fixed numerical value of the Avogadro constant, which is the defining constant of the unit mole. This definition was made possible because the determination of the Avogadro constant had reached a level of relative uncertainty that allowed its value to be fixed and, at the same time, safeguard continuity of measurement results before and after the definition. The motivation for the revision of the SI and the mole in particular will be explained and the experimental work that allowed it is summarized.

A study is reported of the quantification of the amount of matter by secondary ion mass spectrometry (SIMS) when depth profiling a nominally 3.1 nm thick delta layer of FMOC-l-pentafluorophenylalanine in Irganox 1010. The depth profiles are made using 5 keV Ar2300+ cluster ions with analysis by 25 keV Bi3+ ions. Data for 89 negative secondary ions shows profiles whose integrated intensities as a function of depth, even when normalized to the intensity for the pure material, still vary over a factor of 12. This variation mainly arises from matrix effects that are measured here using separate samples with mixed layers of three intermediate compositions of the two materials. Matrix enhancements or suppressions vary widely from secondary ion to secondary ion and are not related to the energy of the analyzing Bi3+ ion. Strong effects can cause the delta layer signal to show structure that may be misinterpreted. The compositional profile is established by using trial Dowsett profiles, representing the compositi...

Free acidity of aqueous solutions was initially defined in 1909 by Søren Peter Lauritz Sørensen as pH = −lgcH+ (c/mol·dm−3 or m/mol·kg−1 of the free hydrogen ions in solution, H+) soon (1910) was changed to pH = paH+ = −lgaH+, integrating the new concepts of activity, ai and activity coefficient γi, for the ionic species i under concern, H+ in this case; it is ai = −lg(miγi). Since individual ions do not exist alone in solution, primary pH values cannot be assigned solely by experimental measurements, requiring extra thermodynamic model assumptions for the activity coefficient, γH+, which has put pH in a unique situation of not being fully traceable to the International System of Units (SI). Also the concept of activity is often not felt to be as perceptible as that of concentration which may present difficulties, namely with the interpretation of data. pH measurements on unknown samples rely on calibration of the measuring setup with adequate reference pH buffers. In this work, the assignment of pH values to buffers closely matching the samples, e.g., seawater, is revisited. An approach is presented to assess the quantity pmH+ = −lgmH+ profiting from the fact that, contrary to single ion activity coefficients, mean activity coefficients, can be assessed based on experimentally assessed quantities alone, γExp ±, thus ensuring traceability to the mole, the SI base unit for amount of substance. Compatibility between γExp ± and mean activity coefficient calculated by means of Pitzer model equations, γPtz ±, validates the model for its intended use.

Quantitative analysis is an important field in the quality control of medicinal plants, aiming to determine the amount of pharmacologically active constituents in complex matrices. Often biological effects of herbal drugs are not restricted to single compounds, but are rather caused by a number of often biogenetically related plant metabolites. Depending on the complexity of the analyzed plant extract, conflicts between accuracy, such as total content assays using photometric or colorimetric methods, and comprehensiveness, e.g. quantification of one or a few lead compounds can occur. In this study, we present a qHNMR approach determining the total amount of cycloartanoids in black cohosh (Actaea racemosa) rhizomes. Perdeuterated methanol containing 1,2,4,5-tetrachloro-3-nitrobenzene as an internal standard was used for extraction. Amounts of cycloartanoids were then measured by integrating 1H NMR signals of all cycloartenoids' H-19 exo protons. Due to their unusually low chemical shifts, these signals are well separated from all remaining signals in crude extracts. Thus, accurate (recovery rates of 99.5-102.5%) and precise (relative standard deviations below 2.5%) quantification of cycloartanoids was accomplished. To the best of our knowledge, this is the first example of a quantification of the total amount of a pharmacologically relevant compound class by integration of one 1H NMR signal characteristic for all members of this particular compound class. Additionally, we propose a new term and unit for the evaluation of medicinal plants and herbal medicinal products: the "specific partial amount of substance" of pharmacologically active constituents, indicated in mmol/g.

The possibility of using radioactive sources to measure atomic number Z and the amount of substance nD of unknown objects is considered. An experiment is performed with test samples of different materials exposed to γ-rays from Cs-137 and Co-60 sources. The range of the method’s applicability in measuring atomic number Z and amount of substance nD is shown.

The detection of steroids originating from synthetic precursors against a background of their chemically identical natural analogues has proven to be a significant challenge for doping control laboratories accredited by the World Anti-Doping Agency (WADA). The complementary application of gas chromatography–mass spectrometry (GC-MS) and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) has been demonstrated to provide specific detection of endogenous steroid misuse for improved anti-doping analysis. Markers of synthetically derived steroids are reviewed on the basis of abnormal urinary excretions and low 13C content. A combinatorial approach is presented for the interpretation of GC-MS and GC-C-IRMS data in the anti-doping context. This methodology can allow all relevant information concerning an individual's metabolism to be assessed in order to make an informed decision with respect to a doping violation. Copyright © 2012 John Wiley & Sons, Ltd.

Neutron activation analysis (NAA), based on the comparator method, has the potential to fulfill the requirements of a primary ratio method as defined in 1998 by the Comite Consultatif pour la Quantite de Matiere — Metrologie en Chimie (CCQM, Consultative Committee on Amount of Substance — Metrology in Chemistry). This thesis is evidenced in this paper in three chapters by: demonstration that the method is fully physically and chemically understood; that a measurement equation can be written down in which the values of all parameters have dimensions in SI units and thus having the potential for metrological traceability to these units; that all contributions to uncertainty of measurement can be quantitatively evaluated, underpinning the metrological traceability; and that the performance of NAA in CCQM key-comparisons of trace elements in complex matrices between 2000 and 2007 is similar to the performance of Isotope Dilution Mass Spectrometry (IDMS), which had been formerly designated by the CCQM as a primary ratio method.

Evaporation losses of organic solvents used to dissolve reference solutions and samples lead directly to errors in the measurement of amount of substance. This is due to changes in the mass fraction composition and the mass:volume concentration of solutions. We have found that measuring the amount of solute added to a solution by weighing by difference is vulnerable to negative bias in the measured amount of solute added, because solvent vapour is lost from opened vials and from syringe needles. Relative negative bias became larger with higher solvent volatility and with smaller volumes, reaching −28% for 10 µL of dichloromethane. Straightforward precautions that reduce the impact of evaporation on gravimetric operations with volatile solvents are presented.

Highly accurate measurements of the amount of substance of organic molecules in a test material can be obtained using exactly matched calibration solutions and internal standards that are labeled with stable isotope atoms by measuring the amount ratio of analyte to internal standard using mass spectrometry. Estimating the uncertainty of quantitative measurements of organic molecules is a means of evaluating accuracy and of establishing traceability to the International System of Units (SI) and requires a measurement function that fully describes the measuring system. This paper presents the derivation of the equation (measurement function) that describes this complete measurement after the internal standard has equilibrated with the test material matrix. It is similar to the equation for inorganic measurements using isotope dilution techniques, but potential biases during chemical processing arising from whole organic molecule analysis compared to inorganic atomic analysis required greater investigation of the yield factors that occur during organic molecule measurements. In the new equation, a series of ratios of proportionality factors are used to relate the amount of substance in a test material to chromatographic peak area ratios corresponding to mass spectrometer ion current ratios. All the proportionality factors are grouped together to define a measuring system factor F(X), the value of which is determined by the fundamental chemical processes affecting the yields of analyte, internal standard, and reference standard of the analyte in the measurement process. Any factors in the measurement process that affect the mole ratio of analyte to internal standard in the calibration solution differently from the test solution will result in a nonunity value for F(X) and a proportional bias to the measurement, and in this way F(X) represents the concept of recovery of the amount ratio of analyte to internal standard. Thus highly accurate measurements require F(X) or its constituent factors to be evaluated. In addition, the uncertainty in the evaluation of F(X) or of its constituent factors must be included in a complete uncertainty estimation of the analytical procedure. The many different permutations of proportionality factor ratios that may result in a unity value of F(X) are discussed resulting in a case for evaluating F(X) rather than the more common practice of evaluating individual factors for each major stage of the measurement procedure. Since the new measurement function describes the complete chemical process that constitutes the measurement, traceability to the SI is assured when all factors in the function are measured traceably and have their associated uncertainty estimated correctly. Ignoring F(X) would invalidate traceability to the SI and would prevent a complete estimation of measurement uncertainty.

This paper discusses the use of high-precision direct absorption spectroscopy to realize the amount of substance standards for ozone (O 3), a reactive species which cannot be delivered through traditional gravimetrically based gas cylinder standards. The O3 amount of substance is linked to the known concentrations of nitric oxide (NO) and nitrogen dioxide (NO2) through a gas-phase titration reaction and spectroscopic measurements using room-temperature pulsed quantum-cascade lasers. Ultimately, this approach will allow the determination of an O3 transition line strength linked to the primary gravimetric standards of NO and NO 2. The line strength can be used in future measurements to determine O3 concentrations of unknown samples

Measurement is the process of determining a correct value of a measurand; definition of the measurand is decisive for an expedient choice of a measurement method. The result of a measurement refers in principle only to the amount of substance actually contributing to the analytical signal. An appropriate definition of the measurand, however, must include a specification of the entire system, for which the result of the measurement is required to apply, i.e., which it is supposed to represent. The concept of representativity therefore assumes importance for the metrological quality of a measurement, and the process with which to ascertain representativity is proper sampling. All systems from which a sample is to be selected are inherently heterogeneous (this is only a matter of the scale of observation), and it is therefore necessary to take into account a contribution from this characteristic, when expressing the uncertainty of the reported value of the measurand. Examples are presented, where methods from metrology are combined with the Theory of Sampling to evaluate the influence of sampling on the uncertainty of results obtained by the analysis of biological materials.

The growing need for global volatile organic compounds (VOC) data at trace level for industrial applications, domestic and working health, air quality and climate change is driving research towards the preparation of traceable and accurate standards for the VOC amount of substance fraction in gas phase.The World Meteorological Organization (WMO) has implemented a worldwide VOC monitoring programme, named Global Atmosphere Watch (GAW), which data quality objectives refer to an expanded uncertainty lower than 10% for VOC measurement at amount of substance fractions lower than 100 nmol∙mol−1.Currently, gaseous standard atmospheres are prepared in high pressure gas cylinders, but they do not fulfil GAW requirements of accuracy and stability at ppb level, especially for oxygenated VOCs. Dynamic methods are proposed as an alternative to provide a stable amount of substance fraction of the mixture over time. Diffusion rate, dilution and carrier air flow rates, purity of air, VOC losses due to wall-interactions a...

At the Department of TOT, an experimental setup was created to measure the density of a binary gas system from 100 to 300 K and pressures up to 16 MPa and with any mixture compositions. Experimental density for the helium-nitrogen system were determined by the piezometer of constant volume method. The amount of substance in the piezometer was measured by volumetric method. In this setup, the mixture of He – N2 was prepared in a special mixer for a series of p-v-T experiments, the concentration was determined by calculation using the equations of state of pure components. In the experiment, mixtures were prepared with molar concentrations, lying close to the range: 0.2, 0.4, 0.6 and 0.8.

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.

This paper describes a realistic model for amount-of-substance gaseous primary standards based on absorption spectroscopy. On the basis of the results obtained using a frequency-referenced CO2 laser to probe SF6 in nitrogen in the molar fraction range of 10-4 mol/mol, an evaluation of the main systematic effects is presented and 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.

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).

Entitic quantities are quantities, such as entitic number (or number of entities) Ne(B), , entitic mass me(B) or entitic volume Ve(B), relating to a specified ''generalized molecule'' or entity B, such as H (meaning a single atom of hydrogen) or H2O or {(1 - x)H20 + xCH3OH}. Molar quantities are the quotients of an extensive quantity and amount of substance nB, such as molar number Nm {or Avogadro constant L = Ne(B)/n(B)}, molar mass mm(B) {or M(B)}, or molar volume Vm(B), also of an entity B. It is shown that there is no imperative need to retain quantities like amount of substance n, or the Avogadro constant L, or the molar gas constant R, or the SI unit: mole. All of these could be discarded from the equations of physical science, though whether it would be useful to discard them is of course open to question.

The potential role of isotope dilution (ID) in the future organization of traceability and therefore comparability of chemical measurements (amount measurements in SI terms) is described. Essential is that ID (e.g. in isotope dilution mass spectrometry IDMS), directly measuring in our SI unit for amount of substance (the mole), gives matrix-independent results and reduces a complicated chemical measurement to a simple physical measurement. It is possible to borrow from the ultra-high accuracy isotopic measurement techniques needed in the continuous improvement of the Avogadro constant in order to make high accuracy measurements of the amount of substance: both fields have in common the determination of isotope abundance ratios with small but well known total uncertainties (conditions for so-called “absolute” measurements). In addition, the use of such ratio measurements in an isotope dilution procedure for amount measurements seems to constitute a form of direct traceability of amount measurements to the “Avogadro measurement procedure” and therefore to the closest realisation of the mole so far. All of this will have far-reaching consequences: Will enriched isotopes be available in a systematic, continuous, affordable supply to ensure the possibility of isotope dilution in the future? Will simpler and, above all, cheaper isotope mass spectrometers be available for the key laboratories of future measurement networks needed in the organization of the traceability of chemical measurements? Will the difference between “chemical” and “physical” measurements not gradually fade away in the organization of traceability of amount measurements? Is further development and application of IDMS — but also of ID using other isotope-specific measurement techniques — not needed for all elements?

According to provisions of IUPAC, SI and ISO the concept of equivalence should be abandoned, due to its shortcomings. The equivalent weight of a substance cannot be uniquely defined. The equivalence law applies only to acid-base and oxidation-reduction titrations, and does not apply to complexometric and precipitation titrations. This paper presents a rule of equal amount of substance to solve the problems of the equivalence law.

Chemical measurements play a rapidly increasing role in modern society and more and more form the basis of important decisions and regulations (legal, medical, environmental, etc.). Therefore, their reliability is of the utmost importance. Environmental measurements are becoming a particular case in point with the public's and governments' growing awareness about the environment. These measurements will also have to be comparable across borders. Chemists must worry more about this reliability in order not to lose credibility and not to generate a loss of faith in chemistry. In order to achieve both credibility and comparability, the fulfilment of the following requirements seems to be needed: express all results of (environmental) measurements in the SI unit for amount of substance, the mole; ensure their traceability to the mole, our SI unit for amount of substance; assess their real performance through regular participation in external (border-crossing) quality assessment programmes using undis...

In Germany a system of primary amount of substance standards for elemental analysis is being developed, which forms the material's basis for the National Standards for element determination. The metrological concept and technical approach is briefly described. The objective of traceability in chemistry, in this case for elemental determination, is illustrated on the example of copper.

The metrological principles of neutron activation analysis are discussed. It has been demonstrated that this method can provide elemental amount of substance with values fully traceable to the SI. The method has been used by several laboratories worldwide in a number of CCQM key comparisons – interlaboratory comparison tests at the highest metrological level – supplying results equivalent to values from other methods for elemental or isotopic analysis in complex samples without the need to perform chemical destruction and dissolution of these samples. The CCQM accepted therefore in April 2007 the claim that neutron activation analysis should have the similar status as the methods originally listed by the CCQM as 'primary methods of measurement'. Analytical characteristics and scope of application are given.

cited By 12; International audience; Isotope dilution is a well-known primary ratio method of quantitative analysis that yields good-quality metrological results. Many equations have been proposed to calculate the amount of substance from the isotope ratio measurements, and these have been used successfully for more than a half-century. Decades ago, isotope dilution equations were extended to correct for analyte formation during analysis, which is especially apparent in the analysis of methylmercury or chromium(VI). Considering only methods for the determination of these two analytes, many variables that are involved must be considered (for example, the extent of analyte formation, the number of isotopes monitored for each analyte, the number of substances, or the nature of mass spectra (elemental versus molecular)). To date, no master equation that can adequately address all of these aspects of the problem has been proposed. In this manuscript, we propose a general equation for isotope dilution.

Publisher Summary This chapter provides an introduction to the technique called isotope dilution mass spectrometry (IDMS) which is recognized as a primary method of measurement by the Comite Consultatif pour la Quantite de Matiere (CCQM) or as it is named in English, the consultative committee for amount of substance. The basic principles, derived IDMS equations, and the main benefits of IDMS as well as some pitfalls are outlined and explained. The isotope dilution technique is used in many fields of analytical science, from biochemistry to geology. . A primary method of measurement is a method having the highest metrological qualities, whose operation can be completely described and understood, for which a complete uncertainty statement can be written down in terms of SI units. IDMS is the most important technique for accurate measurements of amount content and at the highest metrological level, which the key comparisons represent. IDMS is transparent and can be very precise. It is a solid technique because it works even if there are non-quantitative recoveries from digestion or separation steps.. It is also independent of instrument sensitivity.

Publisher Summary The concept of traceability is a basis of scientific work. It is well established and has a long tradition in physical measurements. This chapter explains the concept of traceability and its implications for isotopic measurements in a consistent way. Exemplified are the cases of amount of substance measurements by isotope dilution mass spectrometry (IDMS), isotope amount ratio measurements and differential measurements of so called 6- values. Traceability is a property of values of a standard or of values resulting from a measurement. It can and must be applied to isotopic measurements. It is a powerful tool to establish comparability of measurement results in time and space. In isotopic measurement lack of traceability is observed caused by lack of a correct comparison and less frequently by problems related to stated or varying references, wrong or missing uncertainty statements or broken chains. It is very desirable as it avoids dispute and confusion, thus enhances development and saves resources.

This chapter discusses the applications of thermal analysis (TA) in the study of inorganic chemicals and coordination compounds. Calorimetry is included as it complements results from TA measurements. The chapter describes mainly the solids. Some few examples of studies of fluids are known, while gases are beyond the field of thermal analysis. Binary compounds consist of two elements: A α B β . The advantages of the main thermodynamic properties measured with calorimetry or differential scanning calorimetry (DSC) are: (1) short time of measurement, (2) continuous temperature change, and (3) small amount of substance needed. In the adiabatic method the sample is isolated from heat exchange with its environment, and the remaining heat exchange is made as reproducible as possible. Measured amounts of heat are then supplied to the sample and the resulting temperature changes are measured.

The primary method for pH is based on the measurement of the potential difference of an electrochemical cell containing a platinum hydrogen electrode and a silver/silver chloride reference electrode, often called a Harned cell. Assumptions must be made to relate the operation of this cell to the thermodynamic definition of pH. National metrology institutes use the primary method to assign pH values to a limited number of primary standards (PS). The required comparability of pH can be ensured only if the buffers used for the calibration of pH meter-electrode assemblies are traceable to these primary pH standards. To assess the degree of equivalence, comparisons of primary measurement procedures for pH were organized in co-operation with EUROMET. Typical results will be presented. In 1998, the Consultative Committee for Amount of Substance (CCQM) decided to include the field of pH in its working programme. The first key comparison for this quantity was recently carried out on two phosphate buffer solutions.

High purity elements can serve as a realization of the SI unit amount of substance for the specific element. Solutions prepared from high purity metals by applying gravimetric preparation and the concept of molar mass are used as 'calibration' solutions in many fields of analytical chemistry and provide the metrological basis in elemental analysis. Since ideal purity does not exist for real materials, the actual purity of the high purity material must be known with a specified uncertainty. As required uncertainties around 10?4 relative on the purity statement are not accessible in almost all cases by a direct measurement of the element in itself, the indirect approach is followed, where all elements excepting the matrix element itself are measured and their sum is subtracted from the value for ideal purity, which is 1 kg/kg. It was the aim of this comparison to demonstrate the capability of national metrology institutes and designated institutes to determine the purity of pure elements. In order to limit the effort within this comparison, only six metallic impurities (Ag, Al, Cd, Cr, Ni, Tl) in the low mg/kg range are considered in a zinc matrix. It has to be underlined here that the task was to measure the purity of zinc based on the determination of six analytes. The task is not trace analysis of specific analytes in zinc. This subtle distinction defines different measurands. The sample, pure Zn, was cut in pieces of cubic geometry for wet chemical analysis or of pin geometry for GDMS analysis and was sent to the participants. The comparison was run under the auspices of the Inorganic analysis Working Group (IAWG) of the CCQM and was piloted by the BAM Federal Institute for Materials Research and Testing, Berlin, Germany. The majority of the participants applied ICP-MS techniques and only two participants used additionally atomic absorption spectrometry. GDMS was used only by one participant. The observed spreads for the measurement results reported by the participants were significantly lower than those of the preceding study CCQM-P107 and were well below the target uncertainty of 30% relative. As a consequence, comparability within the participating laboratories is demonstrated to be established. The individual measurement results, mean values and medians derived were in all cases very consistent with the reference values obtained by IDMS and so the accuracy of the measurement results for the participating laboratories is as well demonstrated to be established. Especially with the results of CCQM-P62 and CCQM-P107 in mind, the outcome of CCQM-K72 can be considered as a big step forward in the community. CCQM is aware of the difference between a characterization based on only six analytes and a complete characterization. Therefore, the pilot study CCQM-P149 has been initiated and already started, which focuses on the fit-for-purpose approaches for the purity determination of metals (here: zinc) to be used as primary standards in elemental analysis. Another follow-up in the form of a pilot study on non-metal impurities is mandatory, because non-metal impurities such as oxygen, nitrogen and sulfur often make up the largest contributions. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The aim of the IRMM—International Measurement Evaluation Program (IMEP) is to test out a possible realization of international measurement comparability for field laboratories through traceability of their measurements to the SI Unit for amount of substance: the mole. In IMEP-3, 10 different trace elements, B, Ca, Cd, Cu, Fe, K, Li, Pb, Rb, and Zn, were determined in a synthetic and a natural water by participating laboratories using their routine methods and graphically compared (in coded form) to certified values, established by IRMM and NIST using an isotope-specific method (Isotope Dilution Mass Spectrometry, Neutron Activation Analysis). The number of participants was 70; 64 laboratories have reported results. The results show a spread of more than 50% asymmetrically around the certified value. The Youden graphs allow evaluation of the overall performance of the laboratories in the IMEP-3 round.

Key comparison COOMET.QM-K1.a is the second key comparison in the field of gas analysis organized by the Technical Committee 1.8 'Physical Chemistry' of COOMET, and corresponds to measurements of carbon monoxide in nitrogen for nominal amount-of-substance fractions of 100 ?mol/mol and 1000 ?mol/mol. COOMET.QM-K1.a results could be linked to those of an earlier key comparison, CCQM-K1.a, carried out by the Consultative Committee for Amount of Substance, and published in 1999. The aims of this COOMET exercise were the recognition of national measurement standards of Belarus and Ukraine in view of entering calibration and measurement capabilities (CMCs) of BelGIM and Ukrmetrteststandard in the KCDB of the BIPM in accordance with the Mutual Recognition Arrangement (CIPM MRA) for national measurement standards and for calibration and measurement certificates issued by NMIs; and to improve the CMCs of those laboratories which previously participated in the key comparison CCQM-K1a: BAM and VNIIM. All the laboratory results stand within ?0.6% relative to the gravimetric value obtained by the coordinating laboratory for the nominal value 100 ?mol/mol, and within ?0.3% relative to the gravimetric value for the nominal value 1000 ?mol/mol. This represents a satisfying output. For all the laboratories the observed difference between the gravimetric and reported values does not exceed its combined uncertainty. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

In clinical chemistry and medical diagnostics, the reliability of the results obtained by numerous testing protocols has a major impact on the critical decision-making processes. Considerable efforts are made by international institutes to promote and give guidance on measurement comparisons and metrological traceability using appropriate certified reference materials. The concentration values or amount of substance contents are usually assigned to chemical analytical results. In contrast, the most relevant quantity is the activity of ions in clinical chemistry. Activity corresponds to the available biologically active part of these components in a mixture. Many measurement methods and instruments currently in use do not differentiate between the total substance concentration and its biologically active component. In physiological solutions, such as blood plasma, the chemical activity makes a clear difference between ion or substrate concentration. Ion selective electrodes (ISE) are widely used to directly measure the activity of ions. Measurement by means of ion-selective electrodes is a standard method in point of care testing units (POCT) for continuous monitoring for e.g. haemodialysis, cardiac surgery and in intensive care units. A metrological approach to ISE potentiometric measurements is proposed, to determine the activity with their uncertainty. A prerequisite is to develop an activity calibration scale for complex electrolyte solutions with known and traceable ion activities.

This workshop explored why, despite 150 years experience of carrying out chemical analysis, we are not clear about some of the underpinning concepts and still do not have an adequate organizational infrastructure to ensure that measurements made in different countries can agree. Over 60 chemical measurement experts from Western Europe, with observers from Eastern Europe, Russia and the USA, took part in plenary sessions and group discussions. The topics considered included: measurement traceability/comparability, calibration, measurement uncertainty, measurement validation, interlaboratory comparisons and accreditation. Over 50 conclusions and recommendations were reported to the EURACHEM Committee for action. From these the Workshop Technical Committee have prepared 15 composite recommendations which are reported in this paper.

It is shown from the analysis of metrological validation of all physical quantities measured in chemistry that only for ‘concentration’ and ‘amount of substance’ is there no admitted measurement compatibility system like that for other physical quantities. Based on the fundamental notions of metrology, an attempt is made to derive a general concept of traceability and reliability of the measurement of concentration. Special attention is paid to metrological uses of standard samples and reference materials. Specific features of the quantity ‘amount of substance’ and its unit, the mole, are discussed in terms of metrology.

New isotope abundance and relative atomic mass (atomic weight) values — with low, hitherto unattained uncertainty—are reported for two previously described silicon reference materials using a well-known method with an improved isotope-ratio mass spectrometer. These new values are directly traceable to the SI, more specifically to the unit for amount of substance, the mole, and independent of the SI unit of mass and of the Avogadro constant. Besides the residual mass-spectrometric uncertainties, these new values depend in effect only on a recently published direct comparison of the cyclotron frequency in a Penning trap of ^"Si'* with that of

Because of high labour costs, a prerequisite for economic running of an organic elemental analysis laboratory was the development of rapid methods for the most frequently determined elements, which in our case are N, C, H, O, halogens and S. The methods must be capable of automation to the fullest extent, and the analytical results available in the shortest possible time. The data must therefore be presented in digital form for processing by computer, which can (in a fully automated version) print out a complete analytical record. To avoid dependence on physical calibrations, the end-determination methods should yield physical values strictly proportional to the amount of substance. Titration or gas volume measurement seems to fulfil this condition most closely. The methods developed and used at BASF has been reported, along with some new techniques and modifications to apparatus. A crucial point is the possibility of automating the different methods of analysis, and the economics of different degrees of automation have been discussed.

Mass spectrometry of nonvolatile substances by laser-induced-ionization with the laser microprobe mass analyzer (LAMMA®1000), is applied to analytical chromatographic techniques by means of the electrospray technique. As typically resulting from chromatographic analysis, substance amount in the picogram range (preparation included) and concentration of the substance in the range of 10−6 to 10−8 mole·l−1 is sufficient for mass spectroscopic determination. However, the amount of substance needed to produce each mass spectrum is found to be in the femtogram range.

The design and calibration of a passive sampler operating according to the diffusion principle and its application to the analysis of indoor air are described. Taking aliphatic and aromatic hydrocarbons as representative pollutants, it is demonstrated that at constant concentration, the amount of substance trapped by the sampler is a linear function of the time of exposure. An equation is given relating this amount of substance to the mean pollutant concentration. The detection limit is of an order of 300μg/(m3.h). For test gas atmospheres variation coefficients of between 5 and 10%, were determined for a 24-hour exposure in an atmosphere with concentrations of the individual hydrocarbons between 150 and 600 μg/m3.

The amount of substance that can be separated per unit time (the production rate) and the purity of the isolated compounds are the determining quantities in preparative chromatography. Basing the design and operation of a preparative system on the optimal production rate means optimizing the latter with respect to time, solvent consumption and the smallest possible dilution of the sample in the effluent. Equations describing the influence of the process variables are derived showing as the most important and striking result that the production rate is not a linear function of the column length. They predict that working under conditions where the contribution to mass dispersion of the injected volume and the column itself are about equal is to be preferred. The influence of the pressure limitation and pumping capacity of a chromatographic system on the production rate is discussed.

The theory of Kubelka and Munk is evaluated for simultaneous measurement of reflectance and transmittance as a densitometric method. A relation yielding the amount of substance in a t.l.c. spot, as a function of its reflectance and transmittance, is derived. A densitometer operating according to this relation is described. To check the validity of the derived relation, measurements were made on spots of Sudan yellow developed with chloroform on silica layers. The results show a satisfactory proportionality between apparatus response and amount of substance applied.