Metrology In Chemistry Research Articles

On the difference between a ‘reference material’ and a ‘material reference’

At the occasion of its 50th anniversary in 2011, the Institute for Reference Materials and Measurements, IRMM, of the Joint Research Center of the European Commission, organized an International Conference on ‘The Future of Reference—Science and Innovation’ on 23–25 November at IRMM in Geel, Belgium; see a Meeting Report in Accred Qual Assur (2011) 16:327–328. The contributions to that Topical Issue of ACQUAL are related to presentations at this Conference. The opening of the Conference consisted of the inauguration of an impressively large and well-equipped new building for the production and certification of Reference Materials by EC Director-General Heinz Zourek for Enterprise and Minister-President of Flanders, Kris Peeters. Two rather important events intended to serve Metrology in Chemistry for the European Union and, in fact, for the whole world. The occasion to devote our attention to the role of (certified) reference materials. The English language has this remarkable feature in scientific as well as in daily parlance, of admitting the ‘adjectival’ use of a noun to another noun whereby a noun is used as an adjective to another noun. There are many examples of that: morning paper, London Underground, Labour party, etc. The first noun in the examples given qualifies more explicitly the meaning of the second noun. At first sight, the adjectival use of the noun ‘reference’ (entry 2.6–1 in [1]) to the noun ‘material’ indicates that ‘material’ is the most important feature of the certified reference material CRM. The (adjectival) noun indicates that the material is intended to be used as a ‘reference’. Is that what we really intend to say? To answer that question, we need to recognize the use we intend to make of the CRM. Will we use it as a ‘trueness control material’ (unfortunately not defined in the International vocabulary of metrology—VIM [2], or as a ‘calibrator’ (entry 5.12 in [2])? A trueness control material serves the purpose of applying a correction (entry 2.53 in [2]) to compensate for a systematic effect (entry 2.17 Note 2 in [2]) somewhere in the process of ‘measurement’. A calibrator serves the purpose of calibrating a measurement. Is ‘material’ the most important role we expect from a CRM? Or is it the ‘reference’? When we compensate for a systematic effect when performing a measurement, we clearly do that by way of a multiplication factor. Such a factor can be determined comparing a measurement of the value embodied in the CRM and the certified value provided by the certifying CRM producer. This is a numerical operation needing a numerical value and cannot be performed using a material. Conclusion: The really important feature of a CRM we use is the certified value embodied in (or carried by) the ‘material’. The feature ‘reference’ is more important than the feature ‘material’. The latter only serves as a carrier of the former. That does not correspond to the hierarchy in the terminology we use, and where we concluded that the material was the most important feature.

Interlaboratory comparison for the determination of pesticide residues in Chinese cabbage

The results of and findings from an interlaboratory comparison among laboratories carrying out food testing of pesticide residues in the APEC (Asia–Pacific Economic Cooperation) region are presented and discussed to show critical roles of chemical metrology infrastructure in establishing traceability of measurements and in supporting existing measurement capability in safety and quality of food trade. The study material, which was prepared and certified by Korea Research Institute of Standards and Science (KRISS), was freeze-dried Chinese cabbage powder fortified with two organophosphorous pesticides (diazinon and chlorpyrifos). Among 14 participants, 12 laboratories were accredited based on ISO/IEC17025 and one laboratory was under assessment for the accreditation at the time of this study. Though all participants demonstrated very good intra-day repeatability and inter-day intermediate precision, many of them showed a large bias from the certified values. It is suggested that in addition to the accreditation system, economies are encouraged to develop appropriate chemical metrology infrastructure, which could effectively support laboratories to assure measurement traceability to SI, for which NMIs could play significant roles through their metrological services recognized in Mutual Recognition Arrangement (MRA) of the International Committee for Weights and Measures (Comite International des Poids et Mesures, CIPM).

Novel concept for the mass spectrometric determination of absolute isotopic abundances with improved measurement uncertainty: Part 3—Molar mass of silicon highly enriched in 28Si

Abstract A novel method of isotope amount ratio measurements using state-of-the-art techniques of a double focusing sector field mass spectrometer combined with isotope dilution mass spectrometry (IDMS) has been applied connecting analytical chemistry with metrology in chemistry aiming at the determination of the Avogadro constant ( N A). The molar mass M(“Si28”) and the corresponding isotopic composition of an artificial silicon crystal material highly enriched in the 28Si isotope has been measured for the first time using a combination of a modified IDMS- and a multicollector-ICP-mass spectrometer (MC-ICP-MS) technique. A value M(“Si28”) = 27.97697027(23) g/mol has been determined. This corresponds to a relative uncertainty u rel = 8.2 × 10 −9 ( k = 1). From this silicon crystal material two 1 kg spheres were manufactured which are used by the International Avogadro Coordination (IAC) in order to reassess ( N A) with an associated relative measurement uncertainty u rel( N A) ≤1 × 10 −8. The experiment presented here is the advancement and completion of parts 1 and 2 of this series of papers, describing the theoretical and general experimental applicability of the novel method. The current work summarizes the experimental findings aiming at the determination of the molar mass of the “Si28” material with the lowest uncertainty possible so far. The experimental prerequisites and bottlenecks for examining this highly enriched silicon material as well as experimental proofs for the verification of the presented results are described in detail. The experimental results are supplemented by an uncertainty budget according to the Guide to the Expression of Uncertainty in Measurement (GUM).

Quality assurance of thermodynamic data

To promote metrology in chemistry, ACQUAL has invited a Topical Issue under the header ‘‘Quality Assurance in Chemical Thermodynamics’’. Chemical thermodynamics is an important field of experimental chemistry. Its results are widely used even outside the chemical field. Data collections of formation quotients of chemical species in aqueous solutions are compiled with the intention to simulate the behavior of ground water constituents; activity coefficients are determined in order to predict the solubility of green house gases in ocean seawater; the thermodynamic properties of newly prepared compounds are tested for their interaction in industrial processes. The initial intention has been to learn how current workers in the field assess the quality of the data published under their name. The number of possible contributors for such an issue is, however, limited. Next to the often protracted experimental work, complex numerical (e.g., chemometric) methods need to be found to obtain an appropriate model or to decide between alternative appropriate models for the interpretation of the observed data. Only a limited number of workers in chemical thermodynamics are at least willing to deal with metrological issues. Therefore, the title of this topical issue has been decided to be ‘‘quality assurance of thermodynamic data,’’ not ‘‘metrology of thermodynamic data.’’ There are multiple possible reasons. The complexity of a thermodynamic study, e.g., of metal ligand interaction in aqueous solution, is but one reason. The application of sophisticated numerical models in the analysis of experimental data confronts the researchers with multiple possible interpretations often without clear criteria to make a decision. Targeting the behavior of chemicals in the environment may raise the problem to define the measurand. Naturally occurring organic materials (NOM), for instance, form important reactants in the environment, however, without allowing a simple separation into chemically identifiable compounds with unambiguous molar masses. As long as there is no real demand, this situation will change with an only low momentum. ‘‘Chemistry is a study of complicated systems and the complexity cannot be understood at an arbitrary level of accuracy. (...) Thus any measured data has noise, uncertainties and variability’s, non-linearity’s and unrecognized features (model-deficiencies). And mainstream chemistry has still great difficulties in recognising these basic facts’’ [1]. These words might be from an ACQUAL editorial but in fact are stated 15 years ago by one of the founding fathers of chemometrics. Statistical and numerical techniques are among those methods also applied by thermodynamicians to assess variability in data. However, the reader should understand that incorporation of metrological concepts into chemical thermodynamics is a process at its beginnings—and not yet a success story. While the complete measurement uncertainty budget is a topic, the important concept of traceability, for instance, is not discussed at all. This issue, nevertheless, consists an interesting fixing point of the current state-of-the-art in metrology in chemistry. It is probably easy to understand that a reviewer from the field of thermodynamics sees little interest in a complex S. Lis (&) Department of Rare Earths, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland e-mail: blis@amu.edu.pl

Purity assessment for 17β-estradiol

Purity assessment for high-purity organic substances is regarded as one of the core competences of national metrology institutes. For this reason, Consultative Committee for Amount of Substance—Metrology in Chemistry (CCQM) regularly organized intercomparison studies to compare and demonstrate the degree of equivalence of national measurement capabilities for purity determination. This paper reports the method development work for the participation in a recent CCQM key comparison on purity assessment for estradiol. An indirect consecutive estimation approach was adopted to determine the purity of the estradiol sample, i.e., through the identification and quantification of all possible impurities present in the sample. In the course of assessment, a variety of analytical techniques were applied. The most challenging part was to identify and estimate the amount of unknown organic-related substance present in the testing material. For the moisture determination, a gas chromatography with thermal conductivity detection (GC–TCD) method was employed to supplement the results obtained using coulometric Karl Fischer titration technique. Inorganic impurities and volatile organic compounds residual were analyzed using inductively coupled plasma mass spectrometry (ICP–MS) and gas chromatography–mass spectrometry (GC–MS) techniques, respectively, and their contributions were found to be comparatively insignificant.

NIST Tools for Quality Assurance in Botanical Dietary Supplement Measurements

The accurate analysis of botanical dietary supplements presents significant challenges for the analytical laboratory. Analyte stability, extraction efficiency, the availability of calibration materials, and the use of appropriate controls are issues that must be considered in the chemical metrology of botanicals. The National Institute of Standards and Technology (NIST) has been working with the National Institutes of Health Office of Dietary Supplements (NIH/ODS) to address these challenges. NIST has developed a variety of Standard Reference Materials (SRMs) for dietary supplements, a process which includes the acquisition of appropriate materials and the characterization of their chemical composition. Mass fractions are typically reported for active and marker compounds as well as contaminants. During the certification process, NIST scientists often develop new analytical methods and generate stability and extraction data that can be useful to the dietary supplement community. In addition to the development of reference materials, NIST administers a dietary supplement laboratory quality assurance program (DSQAP); over 80 laboratories have participated in past exercises. Laboratory inter-comparison programs such as the DSQAP provide tools that allow analysts and laboratories to assess how their methods perform relative to the community and relative to an accepted value. The DSQAP identifies measurement challenges and works to bring the measurements of participants into concordance. Proper use of dietary supplement SRMs and participation in inter-comparison programs such as the DSQAP are important tools for analytical laboratories to improve and confirm method accuracy and precision.

Some metrological aspects of the comparison between two ordinal measuring systems

The usage of ordinal scales (sometimes called ‘semi-quantitative’ scales) for performing measurements in the area of applied chemical metrology and quality assurance is widespread. This paper presents a method for handling actions such as calibration, measuring systems’ capabilities comparison and reproducibility evaluation as a comparison between two measuring systems (MSs) referring to a known/unknown reference standard. The strength of the agreement between these MSs is evaluated through two known versions of Cohen’s kappa statistics (the traditional one and the modified one). The effectiveness of these statistics from the metrological point of view is examined, and the preferability of the modified kappa statistics is demonstrated via an example.

Some simple principles for basic measurement system construction

The problems created for chemical measurement by the 1971 inclusion of the thermodynamic ‘mole’ in the Systeme International (SI) measurement units are a salutary lesson to all other measurement disciplines seeking inclusion in the SI. Do not do it! By all means make units useable with the SI but do not surrender basic principles. Chemical measurement has a serious semantic problem. Most analysts, not unreasonably, regard the SI as fundamentally irrelevant as far as the thermodynamic ‘mole’ is concerned and continue to use the earlier chemical mole, understood as an Avogadro number of specified things. However, the users of their measurements do not have this understanding. They examine the SI Brochure [1] to find to their surprise that a ‘mole’ is something quite different, having to do with a thermodynamic quantity puzzlingly named ‘amount of substance’. The next edition of the brochure [2] will make the difference even starker and more inexplicable. The longstanding ambiguity of two ‘moles’ cannot continue into the twenty-first century. Analysts need to consider their options. The term ‘mole’ is unsuitable for clear communication; it has two incompatible meanings. Chemists themselves need to clear up this confusion for it is clear that the SI will not. The solution is simple for metrology in chemistry. All we need is a new name for an Avogadro number of things that cannot be confused with the thermodynamic ‘mole’ and to make it crystal clear that the quantity we measure is a number of things and not the inexplicable thermodynamic construct termed ‘amount of substance’. The new name is obvious. It is an Avogadro number of things, although the obvious common abbreviation will be the avo. It’s equally obvious symbol is Av, following wellaccepted conventions for honouring appropriate scientists, in this case Amedeo Avogadro (1776–1856). The avo is a unit that can be used with the SI but it is not of the SI. It is SI compatible. It is not a base unit. The base unit for its corresponding quantity is one specified thing. Leonard calls it the entity (symbol ent) [3]. As Leonard shows, there are many ways in practice to construct a system of measurement units, with a variety of advantages, disadvantages, and risks. There are a few essential requirements of any practical system of measurement units. The first and highest priorities are that it be simple, concise, clear, and most essential of all, comprehensible to all users. This includes especially the audience to which the measurement results are communicated. A number of things is the simplest and most comprehensible quantity there is. That cannot be said of ‘amount of substance’. The next priority is that it be well anchored. Anchoring chemical measurements in an Avogadro number of things is simple in concept and straightforward, dependent vitally on the specific measurement problem at hand. Its ultimate anchor is the notion of one thing. After four decades, we still do not know how to anchor an ‘amount of substance’ for we still do not know in clear and concise terms what it is. The next priority, and one implied by the previous, is to strive for maximum independence of the base units and quantities. This may be a counsel of perfection, but it is something to strive for. However, there is at least one measurement unit that is independent of all others. It is one thing (or entity). One thing is what it is, quite irrespective of what other measurement units one may choose. If one G. Price (&) PO box 57, Menai, NSW 2234, Australia e-mail: gzprice@ozemail.com.au

CITAC Award 2010: Three Most Interesting Papers in Metrology in Chemistry

CITAC Award 2010: Three Most Interesting Papers in Metrology in Chemistry

The US Pharmacopeia: interfacing chemical metrology with pharmaceutical and compendial science

The United States Pharmacopeial Convention (USP) is an official public standards-setting authority for prescription and over-the-counter medicines and other healthcare products manufactured or sold in the United States. USP’s standards are recognized and used in more than 130 countries around the globe. Over the last decade, USP has worked to advance measurement science for food and drug articles of commerce. Adoption of modern metrologic principles helps ensure that a measurement of one or more property values (attributes) of a food or drug article is acceptable without regard to when (time), where (space), or how (technology) the measurement was taken. The vision of USP is to achieve the international recognition, harmonization, and official acceptance for all USP reference standards based on sound scientific metrological principles. Current hot topics at USP, such as elemental impurities, adulteration, and contamination, as well as counterfeit drugs, are also discussed in this article.

Metrology in Chemistry in Germany

The system for Metrology in Chemistry in Germany is described. At the national standards level, a network of high-level chemistry institutes coordinated by the national metrology institute, PTB, provides the primary references for chemical measurements. A dissemination mechanism employs chemical calibration laboratories accredited within the framework of the German Calibration Service (DKD). They act as “multipliers” between the national standards level and the user level by providing the user with calibration means which are traceable to the SI via national standards. Traceability structures in clinical chemistry, electrochemistry, elemental analysis and gas analysis are described

Metrological traceability chain for pH measurement results

The extent to which technical barriers to international trade caused by non-acceptance of chemical measurement results can be removed, largely depends on the success in building up national and international traceability structures also in metrology in chemistry. Achieving metrological comparability of measurement results requires the definition of metrological calibration hierarchies providing metrological traceability chains which enable the establishment of metrological traceability of measured quantity values to a common metrological reference [1]. For pH, over the last decade, work has been carried out in a number of countries to build up meteorological calibration hierarchies within a national framework. An overview on the metrological traceability chain for pH is given with focus on the primary measurement procedure of pH.

Simultaneous determination of various cardiac glycosides by liquid chromatography–hybrid mass spectrometry for the purity assessment of the therapeutic monitored drug digoxin

A high performance liquid chromatography–hybrid tandem mass spectrometry (LC–MS n ) method utilising electrospray ionisation has been developed and implemented for the simultaneous determination of several cardiac glycosides (CGs) as well as their corresponding aglycones formed by and extracted from herbaceous plants of the genus Digitalis. The method has been validated in-house and its performance characteristics (linearity, repeatability, limits of detection, etc.) were assessed for use in the quantification of CGs and their corresponding aglycones. LODs from 38 to 936 pg g −1 in solution, corresponding to mass fraction impurity levels from 0.0009 (or 0.00008%) to 0.019 mg g −1 (or 0.0019%) detectable in the pure materials have been realized. Moreover, the method was used to characterize and to determine the inherent CG impurities in batches of the therapeutic monitored drug digoxin which served as candidate reference material for an organic purity assessment inter-laboratory study (CCQM-P20.f) organised by the BIPM Chemistry Section and carried out within the framework of the Organic Analysis Working Group (OAWG) of the Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM). Digoxin was selected from materials required for the establishment of reference measurement systems for clinical chemistry and laboratory medicine.

CITAC Award 2009: the three most interesting papers in Metrology in Chemistry

CITAC Award 2009: the three most interesting papers in Metrology in Chemistry

Ethanol/water solutions as certified reference materials for breath alcohol analyzer calibration

The Federal Institute for Materials Research and Testing (BAM), Germany, has issued a series of large volume ethanol in water certified reference materials (CRMs), primarily developed for the calibration of evidential breath alcohol analyzers in Germany. The certified parameter is the ethanol mass concentration at 20 °C. When used in a wet bath simulator, the solutions deliver gas samples that meet the requirements set by the Organization of Legal Metrology for calibration of breathalyzers. The materials were prepared gravimetrically by spiking of ethanol into water in single 5 L units. A complete uncertainty budget for the preparation process has been established. The purity of the commercial ethanol stock solution was identified to be the main source of uncertainty. For stability and homogeneity measurements and for the verification of the gravimetric mass concentration of the CRMs, a robust high-precision gas chromatography, with flame-ionization detection method for ethanol determination in aqueous samples was developed and validated. The good performance of this method has been demonstrated in several international comparisons organized by the Consultative Committee for Amount of Substance—Metrology in Chemistry at the International Bureau of Weights and Measures.

International Activities in Metrology in Chemistry

In today's economy goods and information are being exchanged globally, international travel is commonplace as is the cross-boarder transport of livestock and agricultural products, and this trend is set to continue. Just as important are issues that impinge on our quality of life, such as health care, the environment and food quality. A strong international measurement and standards infrastructure is critical to assure equity in trade and a high quality of life, by ensuring that products and services meet their specifications. In the field of chemical measurements, certified reference materials (CRMs), measurement standards and reference measurement results provide stated references upon which analytical laboratories can anchor their measurement results. The traceability of measurement results to internationally accepted stated references, together with their stated measurement uncertainties, as described in ISO/IEC 17025, provides the basis for their comparability and global acceptance. Recent global activities which are succeeding in developing a system for the international acceptance of chemical measurements are described, notably: activities of the National Metrology Institutes and the BIPM; the Mutual Recognition Arrangement of the International Committee of Weights and Measures (CIPM MRA) for National Calibration Certificates and Measurement Capabilities; the Inter-Laboratory Comparisons organised through the working groups of the Consultative Committee for Amount of Substance – Metrology in Chemistry (CCQM), and the activities of the Joint Committee for Traceability in Laboratory Medicine (JCTLM).

TrainMiC®: Providing a Tool for the Inter-Calibration of Technical Assessors in Europe in the Area of Chemical Measurements

The TrainMiC® (Training in Metrology in Chemistry) programme is a European programme for Life-Long Learning in metrology in chemistry, which is a truly unique system operational across many parts of Europe (19 countries) via national teams. It uses shareware pedagogic tools and the learning content has been harmonised at the European level by a joint effort of many experts across Europe working via an Editorial Board. This paper gives an overview of the activities within the TrainMiC® programme where there is an interaction with national accreditation bodies and the European Cooperation for Accreditation. It is the responsibility of the accreditation bodies to ensure that outcome of the assessments is reliable and transparent and is meeting the relevant requirements. The paper explains the potential of TrainMiC® in providing a tool for accreditation bodies to ensure a harmonised level of knowledge in a specific sector of those who are involved in technical assessments for accreditation in the field of chemical measurements. Some use the word inter-calibration to describe this process.

The Role of Reference Materials in Chemical Metrology

Reference materials play an important role in chemical metrology. Besides ensuring traceability of measurement results, they contribute to the uncertainty budget of measurement results. This paper discusses the main uses of reference materials (certified or not) and describes their impact on establishing traceability and uncertainty budgets.

Metrology in Chemistry for pH and Electrolytic Conductivity Traceability Dissemination

pH and electrolytic conductivity are important metrological quantities for several areas of industry. To get reliable results it is necessary to calibrate measuring instruments and devices regularly. For this purpose certified reference solutions are needed. DKD-K-06901 is a manufacturer of certified reference solutions and offers calibration services in the field of analytical chemistry. There are three accredited calibration procedures for the determination of pH used by ZKM - ANALYTIK - GmbH. A new calibration procedure for electrolytic conductivity was established by experts in DKD-K-06901 as the result of a development project in cooperation with National Metrology Institutes. The validation of all procedures is guaranteed by the participation in national and international comparison measurements. Furthermore DKD-K-06901 is actively involved in the work of technical and standardisation committees for developments of analytical quantities.

Traceability of Chemical Measurement Results

Traceability to recognised references, ultimately to the SI units, is an indispensable prerequisite for measurement results to be comparable and trustworthy and hence accepted worldwide. This holds also for chemical measurement results, particularly as these are often used as a basis for important decisions and agreements, for example in health care and environmental protection. The concept of traceability and the special problems associated with its application to chemical analysis as compared to metrology in general are described. Current approaches to establish traceability of chemical measurement results are reported. The most important development in the last two decades was the establishment of the Consultative Committee for Metrology in Chemistry under the Metre Convention, which provided the basis for an international reference framework for chemical measurements. In order to link up laboratory results anywhere in the world with this international reference framework, traceability structures on the national level are required. It is shown, using the demand for traceable chemical measurements in Germany as an example, how such structures can be established and efficiently used.