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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.16, #8-9)
On the difference between a ‘reference material’ and a ‘material reference’
by Paul De Bièvre (pp. 391-392).
Reference materials: from CBNM to IRMM by A. Lamberty; H. Emons (pp. 393-398).
In 2010, IRMM celebrated its 50th anniversary. The institute, created as Central Bureau for Nuclear Measurements, has developed during these 50 years from a nuclear institute producing so-called reference samples to support nuclear activities worldwide to a major producer of certified reference materials covering a broad range of application sectors both in the nuclear and especially in the non-nuclear field. A short historical overview on related IRMM developments is provided here.
Keywords: CBNM; IRMM; Treaty of Rome; Euratom treaty; Reference materials; Certified reference materials; RM producer
Standardisation and reporting for nucleic acid quantification by Jim Huggett; Stephen A. Bustin (pp. 399-405).
The real-time quantitative polymerase chain reaction (qPCR) is probably the most common molecular technique in use today, having become the method of choice for nucleic acid detection and quantification and underpinning applications ranging from basic research through biotechnology and forensic applications to clinical diagnostics. This key technology relies on fluorescence to detect and quantify nucleic acid amplification products, and its homogeneous assay format has transformed legacy polymerase chain reaction (PCR) from a low-throughput qualitative gel-based technique to a frequently automated, rapid, high-throughput quantitative technology. However, the enormous range of protocols together with frequently inappropriate pre-assay conditions, poor assay design and unsuitable data analysis methodologies are impeding its status as a mature, ‘gold standard’ technology. This, combined with inconsistent and insufficient reporting procedures, has resulted in the widespread publication of data that can be misleading, in particular when this technology is used to quantify cellular mRNA or miRNA levels by RT-qPCR. This affects the integrity of the scientific literature, with consequences for not only basic research, but with potentially major implications for the potential development of molecular diagnostic and prognostic monitoring tools. These issues have been addressed by a set of guidelines that propose a minimum standard for the provision of information for qPCR experiments (‘MIQE’). MIQE aims to systematise current variable qPCR methods into a more consistent format that will encourage detailed auditing of experimental detail, data analysis and reporting principles. General implementation of these guidelines is an important requisite for the maturing of qPCR into a robust, accurate and reliable nucleic acid quantification technology.
Keywords: Real-time polymerase chain reaction; DNA; RNA; Pathogen; Quantification; FRET
The future demand for geological reference materials by T. Meisel; J. S. Kane (pp. 407-414).
Geological RMs (G-1 and W-1) were introduced in 1951 for the purpose of validating the accuracy of silicate rock analysis by dc arc spectrography. Since then the introduction of an array of other spectrographic methods has greatly enhanced research into geological processes. The range of elements that could be determined was expanded, and the detection limits for measurement was lowered repeatedly through the years. The development and use of reference materials was critically important in supporting this rapid expansion of geological research. Essentially, all RMs are of importance to the geosciences community since G-1 and W-1 have been prepared and distributed by national geological institutions, first by the USGS or the CRPG, rather than by national metrology institutions. These geological institutions are not yet certifying their RMs according to ISO Guides. The International Association of Geoanalysts (IAG) is seeking to meet this higher metrological requirement. Since the inception of the IAG certification program in 2003, five powdered silicate rock materials have been issued to meet the demand with respect to calibration, method validation, traceability, etc. for whole rock major and trace element analysis. The introduction of microanalytical techniques nearly decades ago and the more recent advent of MC-ICP-MS have become new driving forces in geochemical research. The first opened the possibility of performing in situ elemental composition studies at the μm scale. The second led to the discovery of small isotope composition variations of mass- and non-mass-dependent processes in “non-traditional” stable isotopes (e.g., Fe, Cu, Zn, Mo, W, and Hg) through cosmo- and geochemical processes. Coupling the two techniques expands in situ analysis to isotopic studies. These developments have created great demand for (certified) RMs for both isotope ratio and microanalytical measurements for the geochemical community that is not yet being met. Homogeneity at a μm scale and unmatched matrices of the natural minerals or synthetic doped glasses hamper the progress in certification of RMs for the microanalytical measurement community. A challenge for the production of isotope RMs is to prepare an RM solution with an isotopic composition similar to the natural systems under investigation. Refined cadmium and nickel metals, for example, have fractionated isotopic compositions far above the range observed in natural systems of interest. Yet, the calibration RM cannot fulfill its purpose when the uncertainty of its isotopic composition exceeds that of the unknowns being measured against it. In this regard, the IAG has recently certified a calibration solution for the determination of Os isotopic ratios. It is also working through member organizations, USGS, and MPI for Geochemistry (Mainz) to develop appropriate microanalytical standards. In addition to these current and future challenges, establishing metrological traceability of geological reference materials in the absence of starting points developed by national metrology institutions is a major issue that needs attention in all future certifications.
Keywords: Certified reference materials; Silicate rock samples; Proficiency testing
Reference system for somatic cell counting in milk by Silvia Orlandini; Harrie van den Bijgaart (pp. 415-420).
With some analytical parameters, certified reference materials are lacking and the reference method shows limited performance. Somatic cell counting in milk is a clear example. It is one of the most frequently performed measurements, estimated at over 500 000 000 tests/year world wide. It serves as an indicator for the udder health status of lactating animals, is relevant in food legislation, in payment of raw milk, and also has a considerable impact for farm management and animal-breeding programs. The analytical performance of nowadays fluoro-opto-electronic routine methods in terms of precision is superior to the reference method based on microscopy. Laboratories have therefore adopted various solutions for anchoring their counting level. It is there that a reference system approach can serve to optimally safeguard comparability of routine testing results in laboratories world wide. A reference system is characterized as a systematically developed anchoring system that is fed by different types of information from various sources, that is, measurements on reference materials, reference method analysis, and routine method results. A joint Project Group of the International Dairy Federation and the International Committee on Animal Recording has been given the task to design a workable global reference system for somatic cell counting in milk. This paper describes the structure and the functioning of such a reference system, a plan for the implementation and the responsibilities of the involved stakeholders in safeguarding its functioning. After approval in IDF and ICAR, the resulting proposal is to be offered for adoption by concerned governmental and non-governmental bodies worldwide.
Keywords: Reference system; Raw milk analysis; Somatic cell count; SCC; Reference method; Routine method; Certified reference material
Efficient production of reference materials of hazardous organics using smart calibration by nuclear magnetic resonance by Takeshi Saito; Toshihide Ihara; Tooru Miura; Yuuko Yamada; Koichi Chiba (pp. 421-428).
The accurate quantification of pesticide residues in food is an important factor in assuring the quality of life of our citizens. In general, chromatographic methods are used, which require certified reference materials (CRMs) for each analyte of interest for accurate quantitative analysis. Recently, regulation of pesticides in food, limiting the positive maximum residue (positive list system) has been brought into effect in Japan. Furthermore, ISO/IEC 17025 requires calibration and testing laboratories to program calibrations and measurements traceable to the International System of Units (SI). Accordingly, these laboratories need a suite of CRMs that are traceable to the SI. In order to address these requirements for every analyte of interest in an efficient manner, a new approach to producing SI traceable CRMs is required. Nuclear magnetic resonance (NMR) has been used widely in chemical analysis. One of the well known characteristics of NMR is the proportional relationship between peak area and the number of nuclei contributing to the peak. If accurate relative intensities of peak areas are obtained, this provides an attractive quantitative tool for organic compounds. The area of a signal from an analyte can be measured with respect to another signal originating from a comparator that has been added to the sample solution. The chosen comparator should not react with the analyte or resonate at any chemical shift similar to that of the analyte. This enables us to produce SI traceable CRMs more effectively. In this paper, we demonstrate a new approach for producing CRMs for pesticides using quantitative NMR—an SI traceable quantitative technique.
Keywords: Nuclear magnetic resonance; Quantification; Purity; Calibration; Traceability; Pesticide; Reference material
Certification of reference materials for ochratoxin A analysis in coffee and wine by Matthias Koch; Wolfram Bremser; Robert Köppen; Rita Krüger; Tatjana Rasenko; David Siegel; Irene Nehls (pp. 429-437).
Mycotoxins are important non-anthropogenic food and feed contaminants, which can be present on almost every agricultural commodity. Effective consumer protection therefore essentially depends on food surveillance by reliable quantitative analysis enabled by appropriate quality control. Certified (matrix) reference materials (CRMs) are versatile tools to support quality assurance. However, in the case of ochratoxin A (OTA), a hepato- and nephrotoxic mycotoxin, which is regulated in various foods, there is a lack of suitable CRMs. This lack has now been overcome by the development of two European Reference Materials (ERM®) for the determination of OTA in roasted coffee (ERM®-BD475) and red wine (ERM®-BD476). This article discusses the material preparation process as well as the results of homogeneity and stability testing. Furthermore, the results of the in-house certification studies carried out at BAM Federal Institute for Materials Research and Testing are presented and discussed. Interlaboratory comparison studies involving selected expert laboratories with documented expertise in the field of mycotoxin analysis were conducted to confirm the certified values determined by BAM. The certified ochratoxin A values and their corresponding expanded uncertainties (k = 2) were assigned in full compliance with the requirements of ISO Guide 35 and are as follows: (6.0 ± 0.6) μg kg−1 for roasted coffee, ERM®-BD475, and (0.52 ± 0.11) μg L−1 for red wine, ERM®-BD476.
Keywords: OTA; Coffee; Wine; Food safety and quality; European reference materials; CRM
Certification for trace elements and methyl mercury mass fractions in IAEA-452 scallop (Pecten Maximus) sample by E. Vasileva; S. Azemard; J. Oh; P. Bustamante; M. Betti (pp. 439-447).
A marine certified reference material (CRM), IAEA-452, prepared with scallop (Pecten maximus) sample was recently produced by the International Atomic Energy Agency (IAEA) and certified for trace elements and methyl mercury (MeHg). The Scallop (Pecten maximus) sample is commonly found and consumed seafood and is also used as bio-indicators for trace metal contamination in marine pollution studies. This paper presents the sample preparation methodology, material homogeneity and stability studies, evaluation of certification campaign results, the assignment of property values and their associated uncertainty. The reference values and associated expanded uncertainty for 9 trace elements (As, Cd, Cr, Cu, Fe, Hg, Mn, Pb and Zn) and MeHg in scallop sample are established. The informative value for one more element (Ni) is also given. The new CRM can be used for the development and validation of analytical methods for determination of trace elements and methyl mercury in seafood and also for quality assurance/quality control purposes.
Keywords: Trace elements; Methyl mercury; Marine biota sample; CRM; Seafood safety; Certification
Allergen determination in food: reference materials and traceability of results by Markus Lacorn; Ulrike Immer (pp. 449-452).
Food allergens are more or less denatured mixtures of non-defined proteins in complex matrices. The most common technique to measure these proteins is an antibody-based system as, e.g., a commercial ELISA system which consists of an extraction procedure, suitable antibodies and a calibrator. Until now, only a few attempts to standardize these different ELISA systems were performed and the most promising way seems to be a standardization of the calibrator. It is shown that we have currently no methods to fully characterize these calibrators, which are always complex protein mixtures. This also means that the production of reference materials containing these calibrators is not possible. It is proposed to choose a different way because we will never have an unbroken traceability chain. As described in ISO 17511:2003 for the clinical area, one possibility could be the selection of a commercial preparation (e.g. skim milk powder) to which all test kit manufacturers will relate their results on and in a second step to select a reference method.
Keywords: Allergens; Traceability; Standardization; Reference materials; ELISA
Feasibility study for the preparation of a tuna fish candidate reference material for total As determination by V. M. O. Carioni; R. Chelegão; J. Naozuka; C. S. Nomura (pp. 453-458).
This work describes the evaluation of several parameters for the preparation of a tuna fish candidate as a reference material (RM) in order to measure the total As mass fraction by slurry sampling graphite furnace atomic absorption spectrometry (SLS-GF AAS) and slurry sampling hydride generation atomic absorption spectrometry (SLS-HG AAS). The main parameters investigated were the homogeneity, analyte segregation and composition during material production. For candidate RM preparation, tuna fish was collected at a local market, cleaned, freeze-dried and treated using different procedures as follows: (1) ground in a cutting mill and separated in different particle sizes (2) ground in cryogenic mill. The mass fraction of As in the cryogenically ground sample was (4.77 ± 0.19) μg g−1 for SLS-GF AAS and (4.61 ± 0.34) μg g−1 for SLS-HG AAS. The accuracy of the procedures was checked with tuna fish certified reference material (BCR 627) with recoveries of 102 and 94% for SLS-GF AAS and SLS-HG AAS, respectively. The homogeneity factor was calculated for different pretreatment procedures and for particle sizes in the range of 500–150 μg, indicating good homogeneity, except for raw fish. There was no observed analyte segregation and no losses, no contamination and no changes in the microdistribution of material during preparation.
Keywords: Reference material; Tuna fish; Arsenic; Atomic absorption spectrometry
Uncertainty estimation in analysis of particulate-bound mercury in different size fractions of PM10 in ambient air by D. G. Gajghate; V. V. Khaparde; T. M. Pustode; P. P. Pipalatkar; C. V. Chalapati Rao (pp. 459-465).
Different size fractions with aerodynamic diameters of (9.0–10.0) μm, (5.8–9.0) μm, (4.7–5.8) μm, (3.3–4.7) μm, (2.1–3.3) μm, (1.1–2.1) μm, (0.7–1.1) μm, and (0.4–0.7) μm of PM10 were collected on glass fiber filter using 8-stage Andersen cascade impactor. Samples were extracted using microwave acid digestion, and analysis was performed by Direct Mercury Analyzer, DMA-80. Uncertainty resulted due to sampling and analytical procedure was calculated by applying bottom-up approach. Significant sources of uncertainty are estimated, and an uncertainty budget is prepared for each fraction. Repeatability showed maximum contribution to uncertainty budget followed by calibration curve and volume of air. Estimated expanded relative uncertainties at the 95% confidence interval for particulate-bound mercury in different size fractions were between 15 and 26%.
Keywords: Particulate-bound mercury (PHg); Andersen cascade impactor; DMA-80 mercury analyzer; Uncertainty budget
The mole is not an ordinary measurement unit by Ingvar Johansson (pp. 467-470).
In this paper, it is argued that the SI system has not carefully enough taken into account the differences that exist between stoichiometry and physics, and because of this neglect forced the kind-of-quantity amount of substance into a false form. The mole is not a unit such as the metre, the kilogram, and the second. It is a “unit” only in the sense in which purely mathematical scaling factors can be called units.
Keywords: Mole; SI system; Avogadro number; Avogadro constant; Stoichiometry