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Analytical and Bioanalytical Chemistry (v.370, #2-3)
Eighth International Symposium on Biological and Environmental Reference Materials (BERM-8), Bethesda, MD, September 17–22, 2000
by Thomas E. Gills; Wayne R. Wolf; M. Stoeppler (pp. 109-110).
CRMs for the 21st century: new demands and challenges by J. Pauwels; A. Lamberty (pp. 111-114).
To play their role as essential tools for the achievement of comparability and traceability of measurements, the upcoming generation of certified reference materials will continue to be the subject of increased requirements related to their preparation, characterization, monitoring, documentation, and distribution. An analysis is made of the most important aspects not only related to the physical form of future CRMs, the determination of their shelf-life, and their certification, but also to increased requirements related to their distribution, including required additional documentation. Two examples of cost breakdown demonstrate the need for improved productivity of certification projects and more efficient marketing.
Challenges from speciation analysis for the development of biological reference materials by H. Emons (pp. 115-119).
Starting with explanations for the increasing demand for speciation analysis the need of appropriate certified reference materials is justified. Specific aspects of biological reference materials for speciation QA/QC are discussed from the point of view of the total analytical process. Examples of unwanted species transformations during analysis are given and critical analytical steps are highlighted. Unchanged biological materials as CRMs and appropriate pure standard compounds are indispensable for the further development of this analytical field.
Trends in certified reference materials for the speciation of trace elements by R. Cornelis; H. Crews; O. F. X. Donard; L. Ebdon; Ph. Quevauviller (pp. 120-125).
The measurement of the chemical species of elements (instead of the total element concentration) has become an irreversible trend in analytical chemistry. The motivation lies in the fact that the biochemical and geochemical behaviour of an element is governed by its species. Quality assurance of the analytical procedures used for speciation analysis requires the analysis of representative reference materials, certified for the relevant species. Up to now the number of existing certified reference materials for trace element species is very limited. The most important ones are environmental CRMs certified for trialkyltin compounds, methylmercury, Cr(III)/Cr(VI) and food CRMs certified for arsenic species and methylmercury. Major developments are to be expected in CRMs focussed on environmental problems, including waste treatment, on bioavailability of trace elements in food and on bio-monitoring in occupational health and hygiene. It is, however, unlikely that the producers of CRMs will ever be able to cover all needs. Add to this that many, very active species are notoriously unstable and/or short living and require in-situ analysis. This will lead to different analytical developments, such as analyses in-situ, where the classical concept of CRMs may not stand firm anymore.
Some difficult problems still existing in the preparation and certification of CRMs by R. Dybczyński; B. Danko; H. Polkowska-Motrenko (pp. 126-130).
Differences between particle size measurements of CRMs by various methods are discussed and the importance of the reliability of such data for proper estimation of the homogeneity of the material is emphasized. On the basis of a very simple model, the dependence of the Ingamells’ sampling constant on the average mass of a single particle of the material is derived, and theoretical predictions are compared with the experimental results. Various approaches to the certification of the candidate RMs are briefly reviewed. The merits of the approach being used in this laboratory to evaluate data obtained in the interlaboratory comparison, and to assign certified and information values, is discussed. The conclusions are supported by results obtained for selected trace elements by use of “definitive” (primary) and “very accurate” methods. Some observations on the unusual resistance of some biological materials to wet ashing and the resulting possibility of making analytical errors are mentioned.
What’s new with the NRC certified reference material program by Scott N. Willie (pp. 131-133).
The environmental CRMs currently available from NRC Ottawa comprise four natural waters for trace elements, four biological tissues for trace elements and methylmercury, three marine sediments for major and trace elements (one sediment has certified values for butyltins) and one fish tissue for organochlorines (PCBs, dioxins). Although significant effort has been expended to maintain this suite of materials, several new initiatives have also recently been completed or are in progress. The certified value for arsenobetaine in Dogfish Muscle CRM DORM-2 has been established. The certification approaches, as well as the studies to determine extraction efficiency of this organoarsenic compound, are presented. A stability study has been completed for Hg in a natural water sample and plans are underway for production of a CRM. Assessment of micronutrient stability in seawater for the purposes of CRM production is continuing and progress on this initiative is discussed.
Recent developments in the field of environmental reference materials at the JRC Ispra by H. Muntau (pp. 134-141).
The production of reference materials for environmental analysis started in the Joint Research Centre at Ispra/Italy in 1972 with the objective of later certification by the BCR, but for obvious budget reasons only a fraction of the total production achieved at Ispra ever reached certification level, although all materials were produced according to the severe quality requirements requested for certified reference materials. Therefore, the materials not destinated to certification are in growing demand as inter-laboratory test materials and as laboratory reference materials, for internal quality control, e.g., by control charts.The history of reference material production within the Joint Research Centre is briefly reviewed and the latest additions described. New developments such as micro-scale reference materials intended for analytical methods requiring sample intakes at milligram or sub-milligram level and therefor not finding supply on the reference material market, and “wet” environmental reference materials, which meet more precisely the “real-world” environmental analysis conditions, are presented and the state-of-the-art discussed.
Recent production of candidate reference materials at IRMM by G. N. Kramer; J. Pauwels; L. Le Guern; H. Schimmel; S. Trapmann (pp. 142-146).
In the execution of its mission to promote a common European measurement system in support of EU policies, IRMM’s Reference Materials Unit is currently involved in preparation of proficiency-testing samples and candidate reference materials. Recent work related to bovine spongiform encephalopathy in cows, genetically modified organisms, and a variety of environmental materials is described.
The use of spectro(photo)metric reference materials in chemical metrology – present status in Romania by Steluţa Duţă (pp. 147-150).
This paper discusses some aspects of the use of certified reference materials (CRMs) to ensure the uniformity of results, especially through calibration and validation of spectro(photo)metric instrument performance. In this way the link between the intrinsic performance of instruments and the accuracy of measurement results is underlined. Some types of local CRM are also presented.
Reference materials and certified reference materials for spectrometry in Romania by M. Buzoianu (pp. 151-155).
Several reference materials (RMs) and certified reference materials (CRMs) are widely used in Romania as measurement standards in different spectrochemical measurements. Among them, single element standard solution certified for their mass concentration play a key role in ensuring the required traceability of results expressed in this measurement unit. A short review of the locally available elemental RMs and CRMs used in atomic spectrometry or in other analytical techniques where aqueous standard solutions are required (usually called RMs or CRMs for spectrometry) is given. The experience of the INM in preparation and certification of such materials is described. Some aspects regarding their use for ensuring the accuracy and for confirmation of the traceability of analytical measurements, especially through calibration and metrological validation of main instrument performances, are discussed.
Biological and environmental reference materials in CENAM by R. Arvizu-Torres; A. Perez-Castorena; J. A. Salas-Tellez; Y. Mitani-Nakanishi (pp. 156-159).
Since 1994, when the NIST/NOAA Quality Assurance Program in Chemical Measurements was discussed in Queretaro, CENAM, the National Measurement Institute (NMI) of Mexico, has become involved in the development of reference materials. In the field of biological and environmental reference materials, in particular, the NORAMET collaboration program with NIST and NRC, and the North-American Environmental Cooperation signed among three free-trade treaty organizations, have greatly helped the development of the materials metrology program in the newly established CENAM.This paper describes some particularly significant efforts of CENAM in the development of biological and environmental reference materials, on the basis of inter-comparison studies organized with local and governmental environmental agencies of Mexico.In the field of water pollution CENAM has developed a practical proficiency testing (PT) scheme for field laboratories, as a part of registration by local government in the metropolitan area, according to the Mexican Ecological Regulation. The results from these eight PTs in the last 5 years have demonstrated that this scheme has helped ensure the reliability of analytical capability of more than 50 field laboratories in three states, Mexico, D.F., and the States of Mexico and Queretaro.Similar experience has been obtained for more than 70 service units of stack emission measurements in the three states in 1998 and 1999, as a result of the design of a PT scheme for reference gas mixtures. This PT scheme has been accomplished successfully by 30 analytical laboratories who provide monitoring services and perform research on toxic substances (Hg, methylmercury, PCB, etc.) in Mexico.To support these activities, reference samples have been produced through the NIST SRMs, and efforts have been made to increase CENAM’s capability in the preparation of primary reference materials in spectrometric solutions and gas mixtures.Collaboration among NMIs has also successfully overcome the inability of CENAM to prepare biological tissue for mercury assessment and marine sediments for analysis of trace metals.The importance of international collaboration is stressed not only in the NORAMET region but also in the SIM, to provide help for each other and achieve mutual recognition among member countries of the region.
Reference materials – a view from a small country by John Love (pp. 160-163).
ISO/IEC 17025 has an increased emphasis on traceability and estimation of uncertainty of measurement compared with ISO Guide 25. Demonstration of traceability is a new concept in analytical chemistry and depends on access to relevant reference materials or use of reference methods. Until now most reference materials used in New Zealand have been imported, because they offered international comparability. New Zealand is currently starting to develop the required infrastructure so that it will be able to produce unique reference materials that will contribute to the total international effort in improving the reliability of analytical chemistry.
The deplorable state of the description of the use of certified reference materials in the literature by P. J. Jenks; Markus Stoeppler (pp. 164-169).
A detailed survey of 26 scientific journals showed that journal editors and a majority of authors of the reviewed papers seem unconcerned by the importance of correctly reporting their use of certified reference materials (CRMs). Only around 55% of the abstracts surveyed mention the use of CRMs described in these papers. This, however, is of key importance as the abstract of a paper is most widely available in electronic media. Many authors mentioned the use of CRMs in passing, often in incomplete form and without giving any details of the results obtained. Some are confused about the source of the reference material used, as they fail to report the type or the producer of CRMs applied. Others use materials that do not match the samples analyzed or do not see the need to use any CRM, despite the availability of suitable materials. Even in cases where correct data were given for type and producer of the CRMs, frequently the proper use and statistical evaluation are questionable. To improve this situation it is necessary that publishers should give recommendations where and how the use of CRMs should be described.
Some aspects of the evaluation of measurement uncertainty using reference materials by Mirella Buzoianu (pp. 170-177).
To ensure and to confirm the required traceability according to the definition given in the International Vocabulary of Basic and Standard Terms in Metrology, three main aspects need to be considered in practice: “stated reference”, “unbroken chain of calibration” and “stated uncertainty”. For a certain spectrochemical result, each of the aspects above mentioned is highly dependent on measurement uncertainty, both on its magnitude and how it was estimated. The paper describes the experience of the Romanian National Institute of Metrology (INM) in estimating measurement uncertainty during certification of reference materials, in metrological calibration and during specific analytical processes. Practical examples of the use of reference materials or certified reference materials issued by the INM to estimate measurement uncertainty are discussed for their applicability in spectrochemical and turbidity analysis. Some aspects of the use of analysis of variance (ANOVA) to obtain additional information on the components of measurement uncertainty and to identify the magnitude of individual random effects are presented.
Evaluation of results derived from the analysis of certified reference materials – a user-friendly approach based on simplicity by L. Jorhem; Joakim Engman; Torbjörn Schröder (pp. 178-182).
Certified reference materials (CRMs) have now been in regular use for several decades. Their production and certification are regulated by international standards. But, even today there are no agreements on procedures for evaluating results obtained by the users. As a consequence, the way CRM results are treated in the literature leaves a lot to be desired. A statistical evaluation is rarely, if ever, described in published reports. The most common approach is to compare the found mean and/or range with the certified range and then state if the mean falls within the certified range, or if the two ranges overlap. If this happens, the analyst is usually satisfied. In addition, usually no regard is paid to the fact that the certified interval is based on a 95% confidence interval (CI) and the found interval on standard deviation and that this evaluation has little, if any, statistical relevance. Long-term evaluation of a CRM often consists in nothing more than producing a control chart, which relates the found results to the certified mean and CI.This paper is an attempt to improve the situation by providing a set of easy-to-use guidelines for evaluating results from CRMs. During the process we have identified different areas in which there is a need for such guidelines:1. short-term evaluation of a single, or multiple, determination at one or several specific times;2. identification of systematic and random errors;3. evaluation of CRMs when used in a collaborative trial of a method; and4. long-term evaluation for monitoring an analytical process over extended periods of time.It is important that the guidelines do not require expert competence in statistics from the analyst. Such obstacles would probably render most guidelines unused.
Estimating the uncertainty of stability for matrix CRMs by Thomas P. J. Linsinger; J. Pauwels; Andrée Lamberty; H.G. Schimmel; Adriaan M. H. van der Veen; Lothar Siekmann (pp. 183-188).
The new version of ISO Guide 34 requires producers of certified reference materials (CRMs) to include contributions of possible instability to the overall CRM uncertainty, to obtain a value for the uncertainty in compliance with the Guide to the Expression of the Uncertainty in Measurement (GUM). A pragmatic approach to estimating the uncertainty of stability is presented. It relies on regression analysis of stability data with subsequent testing of the slope of the regression line for significance. If the slope is found to be statistically insignificant, a shelf life is chosen and the uncertainty connected with this time is estimated via the standard deviation of the slope. This uncertainty is included in the overall uncertainty of the CRM. This approach is explained with examples showing its applicability to matrix CRMs.
Water as a source of errors in reference materials by Stephan Rückold; Karl Heinz Grobecker; H.-D. Isengard (pp. 189-193).
In the field of reference materials, long-term stability is of highest importance. Particularly for biological matrices, any kind of deterioration must be avoided during shelf-life. In the production precautions are taken to prevent these, but possible alterations caused by intensive drying have been underestimated until today. This presentation discusses several mechanisms of deterioration related to water activity and water content. Comparison of the results for water and moisture for six reference materials and their water sorption isotherms serve as a base to discuss the importance of accurate dry mass corrections for certified values. It is shown that the method chosen for dry mass correction influences certified contents significantly and a method description must be given. Furthermore, it is confirmed that for biological matrices optimal ranges of water activity and water content exist, where hygroscopicity is low without significant danger of product deterioration. Additionally, handling is facilitated in the optimised ranges.
GC–FID as a primary method for establishing the purity of organic CRMs used for drugs in sport analysis by B. King; S. Westwood (pp. 194-199).
The National Analytical Reference Laboratory has synthesized and characterized 67 anabolic steroid marker metabolites, both unlabelled and deuterated, and 37 key glucuronide and sulfate steroid conjugate pure substance reference materials. Work is also in process to establish their full traceability so that they can be issued as certified and primary reference materials. Both identity and purity have been rigorously characterized using a number of techniques and a primary method for purity assessment developed, based gas chromatography combined with flame ionization detection for the parent steroids and HPLC with evaporative light scattering detection for non-volatile steroid conjugates. Strategies for establishing traceability and for estimating measurement uncertainty are reported. The strategies described are considered applicable to a wide range of organic pure substance reference materials.
Reference materials at emission levels of NH3 and HCl by J. I. T. van Wijk; Gerard Nieuwenkamp; Theo L. Hafkenscheid (pp. 200-202).
Due to instability in static mixtures, in the past only dynamic preparation techniques for mixtures of NH3 and HCl were maintained; however, recent developments of new passivation techniques for cylinder treatment and commercially available nitrogen with a very low content of impurities have opened up the possibility of preparing stable mixtures in cylinders by gravimetry. Mixtures of NH3 (300 μL/L and 30 μL/L) and HCl (300 μL/L) were prepared in nitrogen in cylinders with different passivation treatments. The mixtures were compared with dynamically prepared mixtures using Photo Acoustic detection (PAS) and FT-IR. The uncertainty is about 3.5% with PAS analysis for NH3 at the 300 μL/L level. For the analysis of HCl with FT-IR the initial uncertainty in the 300 μL/L mixtures is about 7%. Two of the HCl mixtures show significant instability; for the other three mixtures the uncertainty in the measurement is too large to discriminate between stability and instability. The NH3/N2 mixtures are stable within 3.5% for a one-year period. The stability of the 30 μL/L mixtures of NH3 cannot be underpinned by measurement results, but a systematic effect in the measurement procedure seems more likely than instability. Improvement in the measurement procedure should clarify this point.
Database of natural matrix reference materials (NMRM) for organic constituents by G. V. Iyengar; A. R. Bleise (pp. 203-207).
The International Atomic Energy Agency maintains a database of internationally available certified reference materials (CRM) of natural matrices. This database is periodically updated, and presently documents nearly 25,000 measurands in 1700 materials. The organic constituents are classified in five major groups of analytes – aliphatic and aromatic hydrocarbons (A), chlorinated hydrocarbons (B), pesticides (C), organometallic compounds (D) and other organic constituents (nutrients, etc.) (E). The matrices include natural materials such as body fluids, food products, soils, and sediments, terrestrial (e.g. plants), and anthropogenic products (e.g. dust, fly ash). These five organic groups of analytes encompass more than 2000 measurands for 420 different analytes in 230 materials. Of these measurands, 1682 (68%) are certified, and 768 (32%) are provided as informational values. Within each major group of analytes, measurands reported as informational values accounted for: A (35%); B (35%); C (26%); D (10%), and E (22%). The high proportion of informational values (i.e. non-certified values) for A, B, and C, compares well with a similar but undesirable situation faced in the nineteen-seventies in the inorganic area when simultaneous multielement techniques became available. In the case of D and E, it appears that mostly targeted analytes are measured, leading to a cohesive certification profile. Although the IAEA database is not equally comprehensive for all groups of analytes cited above, it can still serve as an useful indicator of the status of organic constituents in RMs.
Development of a reference material for routine performance monitoring of methods measuring polychorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like polychlorinated biphenyls by S. S. Selliah; S. Cussion; K. A. MacPherson; E. J. Reiner; D. Toner (pp. 208-212).
Matrix–matched environmental certified reference materials (CRMs) are one of the most useful tools to validate analytical methods, assess analytical laboratory performance and to assist in the resolution of data conflicts between laboratories. This paper describes the development of a lake sediment as a CRM for polychorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DLPCBs). The presence of DLPCBs in the environment is of increased concern and analytical methods are being developed internationally for monitoring DLPCBs in the environment. This paper also reports the results of an international interlaboratory study involving thirty-five laboratories from seventeen countries, conducted to characterize and validate levels of a sediment reference material for PCDDs, PCDFs and DLPCBs.
A review of the DNA standard reference materials developed by the National Institute of Standards and Technology by B. C. Levin; H. Cheng; M. C. Kline; J. W. Redman; K. L. Richie (pp. 213-219).
The Standard Reference Materials Program at the US National Institute of Standards and Technology (NIST) has three human DNA standard reference materials (SRM 2390, SRM 2391a, and SRM 2392) currently available1 (Orders and requests for information concerning these SRMs should be directed to the Standard Reference Materials Program, National Institute of Standards and Technology, 100 Bureau Drive, Stop 2321, Gaithersburg, MD 20899-2321, Telephone (301) 975-6776, FAX: (301) 948-3730.) [1, 2]. Both the DNA profiling SRM 2390 and the polymerase chain reaction (PCR)-based DNA profiling SRM 2391a are intended for use in forensic and paternity identifications, for instructional law enforcement, or for non-clinical research purposes and are not intended for clinical diagnostics. The mitochondrial DNA (mtDNA) SRM 2392 is to provide standardization and quality control when performing PCR and sequencing any segment or the entire 16,569 base pairs that comprise human mitochondrial DNA. SRM 2392 is designed for use by the forensic, medical, and toxicological communities for human identification, disease diagnosis or mutation detection.
EUROSOILS – A set of CRMs for comparability of soil-measurements by B. M. Gawlik; A. Lamberty; H. Muntau; J. Pauwels (pp. 220-223).
An overview is given on the development, properties, and application of the European reference soil set – the EUROSOILS. The introduction of this new type of reference material has, for the first time, enabled comparison of data related to the interaction of chemical substances with the soil, and thus, improvement of soil quality. Because of their unforeseen success, a second generation of EUROSOILS had been produced and the range of application extended to other types of measurement related to the soil matrix – soil pH, carbon and nitrogen content, particle-size distribution and cation-exchange capacity. Other fields of application include analytical method development or testing of soil decontamination techniques.On the basis of the success of the EUROSOIL concept and the need for a common basis for comparison of soil-related data in Europe and beyond, the European Commission’s Institute for Reference Materials and Measurements decided to certify several properties of the second EUROSOIL-generation, thus establishing a common QA/ QC system for soil-related data. The main features of the EUROSOILS, their origin, the necessary field and laboratory work, and some interesting background information about the project are presented in this paper.
Harmonized protocol and certified reference material for the determination of extractable contents of phosphorus in freshwater sediments – A synthesis of recent works by V. Ruban; J. F. López-Sánchez; P. Pardo; G. Rauret; H. Muntau; Ph. Quevauviller (pp. 224-228).
An analytical protocol for the determination of the extractable phosphorus contents in freshwater sediments has been harmonized through interlaboratory studies in the frame of the Standards Measurements and Testing Program of the European Commission. A homogeneous and stable sediment reference material has been prepared and certified on the basis of this protocol named SMT protocol, and will be available in spring of 2001. The SMT protocol, together with the reference material, are useful tools in the field of water management, especially at a time when quality assurance and data comparability are of paramount importance in laboratory analysis. The knowledge of the bioavailable forms of phosphorus is important not only for sediments but also for sludge and soils. Therefore, the SMT protocol could be extended to these materials and new CRMs could be prepared. The SMT protocol was used in a study of a reservoir, which allowed to calculate the P stock, therefore helping to predict the restoration delay of the lake. The paper describes the protocol and the CRM, and gives a brief outline of the case study.
Preparation and characterization of a set of IAEA reference air filters for quality control in air-pollution studies by J. Kučera; B. Smodiš; K. Burns; P. De Regge; M. Campbell; V. Havránek; M. Makarewicz; A. Toervenyi; E. Zeiller (pp. 229-233).
Several sets of reference air filters were prepared as part of an IAEA evaluation of the performance of laboratories involved in air-pollution studies. Each set comprised three polycarbonate membrane filters, two of which were loaded with urban air particulate matter (APM) obtained in Vienna or Prague, and one unloaded filter. The filters were loaded by filtration of a suspension of the APM materials in water. The homogeneity both of bulk APM materials and of the loaded filters was evaluated and found suitable by determining several elements by instrumental neutron-activation analysis (INAA), proton-induced X-ray emission (PIXE), and micro-X-ray energy-dispersive fluorescence analysis (μ-EDXRF). After evaluation of the homogeneity, INAA, PIXE, EDXRF, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP–OES), and ICP mass spectrometry (ICP–MS) were used to characterize the filter materials and establish “target values” and their associated standard deviations for 15 elements. Problems encountered during the preparation of these unique, simulated air filters and the criteria for setting both the target values and standard deviations are presented.
An alternative method for the certification of the sulfur mass fraction in coal Standard Reference Materials by M. R. Winchester; W. R. Kelly; J. L. Mann; W. F. Guthrie; B. S. MacDonald; G. C. Turk (pp. 234-240).
The S mass fractions of coal SRMs 2682b, 2684b, and 2685b are certified by direct comparison with coal SRMs 2682a, 2684a, and 2685a, respectively, using high-temperature combustion analysis with infrared (IR) absorption detection. The S mass fractions of the “a” materials used for calibration were previously determined by means of isotope-dilution thermal-ionization mass spectrometry (ID-TIMS). Therefore, the comparisons performed with the combustion–IR absorption method establish direct traceability links to accurate and precise ID-TIMS measurements. The expanded uncertainties associated with the certified S mass fractions are of approximately the same magnitude as would be expected for the ID-TIMS methodology. An important aspect of these certifications is that each “b” material is essentially identical with the corresponding “a” material, because both were produced from the same bulk, homogenized coal. As a test of the efficacy of the new certification approach when calibrant and unknown are not identical, the S mass fraction of coal SRM 2683b has been determined by direct comparison to coal SRM 2683a. These two coals, which have both previously been analyzed with ID-TIMS, are different in terms of S content and other properties. Whereas the S mass fraction for SRM 2683b determined with the new methodology agrees statistically with the ID-TIMS value, there is reason for caution in such cases. In addition to the usefulness of the alternative approach for certification activities within NIST, this approach might also be an excellent way of establishing NIST traceability during the value assignment process for reference materials not issued by NIST. Further research is needed, however, to understand better the scope of applicability.
Possibilities of low-level determination of silicon in biological materials by activation analysis by J. Kučera; Z. Řanda (pp. 241-245).
The capabilities of neutron and photon activation analysis (NAA and PAA, respectively) for low-level determination of silicon in biological materials have been examined. Sensitivities of a variety of modes of NAA and PAA with radiochemical separation have been evaluated. Results are presented for silicon in reference materials CSRM 12–2-03 Lucerne, Bowen’s Kale, NIST SRM-1571 Orchard Leaves, and NIST SRM-1515 Apple Leaves. The results were obtained by employing the 29Si(n,p)29Al reaction with fast reactor neutrons and the radiochemical procedure developed for aluminium separation. Possibilities of further improvement of the silicon determination limit down to the μg g–1 level by employing NAA and PAA with radiochemical separation are outlined.
Determination of silicon in biological samples by ICP-OES after non-oxidative decomposition under alkaline conditions by S. Hauptkorn; J. Pavel; H. Seltner (pp. 246-250).
A non-oxidative alkaline sample digestion procedure using tetramethylammonium hydroxide and a high pressure, microwave assisted autoclave digestion system was developed. The silicon concentrations of the digested samples were measured by inductively coupled axial plasma optical emission spectrometry (ICP-OES). Details of the digestion conditions as well as the optimised instrumental parameters for ICP-OES are described. The method was developed and tested using silicon-spiked ascorbic acid and applied to samples of animal tissue and organs. The total silicon content of two different reference materials, NIST 1577b Bovine liver and BCR 184 Bovine Muscle having neither certified nor informational values for Si was determined. The results obtained are compared with the results of independent methods such as wavelength dispersive x-ray fluorescence spectrometry (WDXRF) and solid sampling electrothermal atomic absorption spectrometry (ETAAS). The method described achieves a limit of detection of 2 mg kg–1 using 100 mg of solid biological or organic material and covers a concentration range of up to 500 mg kg–1.
Methodologies for the analysis of rare earth elements and their relevance to reference materials by B. Vijayalakshmy; T. Prasada Rao (pp. 251-254).
India has the third largest resources of rare earth elements (REE) in the world. These resources are essentially the monazite sand present in the beaches of south-west, south-east, and mid-eastern coasts of India. Therefore, analytical methodologies for the determination of REE in sea water and high-purity materials were developed. An overview of this work and its relevance to the preparation of standard reference materials of REE in sea water, marine sediments, and high-purity materials in the future is given.
k0-NAA, a valuable tool for reference-material producers by P. Robouch; M. Eguskiza; M. I. Maguregui; S. Pommé; J. Pauwels (pp. 255-258).
The main concern of producers of certified reference materials (CRM) is the preparation of high-quality products with demonstrated homogeneity and stability, combined with a well established set of certified characteristics. CRM producers must, furthermore, comply with other constraints imposed by the ISO Guide 34:·*production processes, production control, and certification analyses should be performed by expert laboratories, using validated protocols documented in their respective quality assurance manuals;·*laboratory mean values and the corresponding “expanded” uncertainties, must be used for the determination of the certified values, as recommended by the ISO Guide to the Expression of Uncertainties in Measurements (GUM); and·*when possible, traceability of the certified value to the SI units, using appropriately validated and/or primary methods, must be ensured.k0-NAA, i.e. neutron activation analysis with k0 standardization, is one of the analytical techniques implemented at the Reference Material Unit of IRMM; it meets the first two requirements.
Using inductively coupled plasma–mass spectrometry for calibration transfer between environmental CRMs by G. C. Turk; L. L. Yu; Marc L. Salit; William F. Guthrie (pp. 259-263).
Multielement analyses of environmental reference materials have been performed using existing certified reference materials (CRMs) as calibration standards for inductively coupled plasma–mass spectrometry. The analyses have been performed using a high-performance methodology that results in comparison measurement uncertainties that are significantly less than the uncertainties of the certified values of the calibration CRM. Consequently, the determined values have uncertainties that are very nearly equivalent to the uncertainties of the calibration CRM. Several uses of this calibration transfer are proposed, including, re-certification measurements of replacement CRMs, establishing traceability of one CRM to another, and demonstrating the equivalence of two CRMs. RM 8704, a river sediment, was analyzed using SRM 2704, Buffalo River Sediment, as the calibration standard. SRM 1632c, Trace Elements in Bituminous Coal, which is a replacement for SRM 1632b, was analyzed using SRM 1632b as the standard. SRM 1635, Trace Elements in Subbituminous Coal, was also analyzed using SRM 1632b as the standard.
Direct and precise determination of environmental radionuclides in solid materials using a modified Marinelli beaker and a HPGe detector by Bum Kyoung Seo; Kil Yong Lee; Yoon Yeol Yoon; Dae Won Lee (pp. 264-269).
A simple but precise detection method was studied for the determination of natural radionuclides using a conventional HPGe detector. A new aluminium beaker instead of a plastic Marinelli beaker was constructed and examined to reach radioactive equilibrium conditions between radon and its daughter elements without the escape of gaseous radon. Using this beaker fifteen natural radionuclides from three natural decay series could be determined by direct γ-ray measurement and sixteen radionuclides could be determined indirectly after radioactive equilibrium had been reached. Analytical results from ground water were compared with those from conventional α spectroscopy and the results agreed well within 12% difference. Nitrogen gas purge was used to replace the surrounding air of the detector to obtain a stable background and reducing the interference of radon daughter nuclides in the atmosphere. The use of nitrogen purging and the aluminium Marinelli beaker results in an approximately tenfold increase of sensitivity and a decrease of the detection limit of 226Ra to about 0.74 Bq kg–1 in soil samples.
NH4NO3 extractable trace element contents of soil samples prepared for proficiency testing – a stability study by H. Traub; Holger Scharf (pp. 270-274).
In view of its intended use as a sample for proficiency testing or as a reference material the stability of the extractable trace element contents of a soil from an irrigation field was tested using the extraction with 1 mol/L ammonium nitrate solution according to DIN 19730. Therefore, changes of the extractability of sterilized and non sterilized soil samples stored at different temperatures were evaluated over a period of 18 months. Sets of bottles were kept at –20 °C, +4 °C, about +20 °C and +40 °C, respectively. The NH4NO3 extractable contents of Cd, Cr, Cu, Ni, Pb and Zn were determined immediately after bottling and then after 3, 6, 12 and 18 months with ICP-AES or ETAAS. Appropriate storage conditions are of utmost importance to prevent deterioration of soil samples prepared for the determination of NH4NO3 extractable trace element contents. Temperatures above +20 °C must be avoided. The observed changes in the extractability of the metals (especially for Cr and Cu) most likely could be related to thermal degradation of the organic matter of the soil. There is no need to sterilize dry soil samples, because microbiological activity in soils with a low moisture content appears to be negligible with regard to trace element mobilization.
Recent developments in food-matrix Reference Materials at NIST by K. E. Sharpless; Jennifer C. Colbert; Robert R. Greenberg; Michele M. Schantz; Michael J. Welch (pp. 275-278).
Since 1996, the National Institute of Standards and Technology (NIST) has developed several food-matrix Standard Reference Materials (SRMs) characterized for nutrient concentrations. These include SRM 1544 Fatty Acids and Cholesterol in a Frozen Diet Composite, SRM 1546 Meat Homogenate, SRM 1548a Typical Diet, SRM 1566b Oyster Tissue, SRM 1846 Infant Formula, and SRM 2383 Baby Food Composite. Three additional materials – SRM 1946 Lake Superior Fish Tissue, SRM 2384 Baking Chocolate, and SRM 2385 Spinach – are in preparation. NIST also recently assigned values for proximate (fat, protein, etc.), individual fatty acid, and total dietary fiber concentrations in a number of existing SRMs and reference materials (RMs) that previously had values assigned for their elemental composition. NIST has used several modes for assignment of analyte concentrations in the food-matrix RMs, including the use of data provided by collaborating laboratories, alone and in combination with NIST data. The use of data provided by collaborating food industry and contract laboratories for the analysis of food-matrix RMs has enabled NIST to provide assigned values for many analytes that NIST does not have the resources or analytical expertise to measure.
Twenty five years of reference material activity at Agriculture and Agri-Food Canada by Milan Ihnat (pp. 279-285).
In the mid 1970s, the available RMs, notably Bowen’s Kale and Orchard Leaves and Bovine liver from National Bureau of Standards (NBS), although of great benefit, were overwhelmingly insufficiently representative, in respect of matrix and elemental composition, of the wide range of natural products submitted for analysis and in worldwide commerce. To provide additional coverage, an RM development project was initiated with input from cooperating analysts leading to an Agriculture and Agri-Food Canada/National Institute of Standards and Technology (NIST) cooperative venture and development of a total of 12 different agricultural/food RMs. With a total of 303 concentration values for 34 elements and a wide range of matrix components such as ash, silica, protein, fat, carbohydrate and fiber, these RMs significantly augment the world repertoire of biological control materials. A final material under consideration is a highly reliable, discrete, synthetic RM for quality control and calibration. This paper summarizes the research and developmental activities undertaken during the past quarter of a century related to RM development at Agriculture and Agri-Food Canada and includes a short historical background, conceptual considerations, preparation, physical characterization, homogeneity estimation, chemical characterization, calculation of recommended reference values and associated uncertainties, methodology development and application, and performance of inorganic analytical methods in a multielement, multilaboratory, collaborative characterization campaign.
Selenomethionine content of candidate reference materials by W. R. Wolf; H. Zainal; B. Yager (pp. 286-290).
Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine (Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched yeast, have been examined by use of a gas chromatography–isotope dilution mass spectrometry (IDMS) procedure, after treatment of the matrix with 0.1 mol L–1 hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results in cleavage of the CH3Se group to form volatile CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample enables estimation of the naturally occurring protein-bound 80Semet by IDMS without a protein-digestion process. We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 μg Setotal g–1. Commercial selenium yeast tablets are labeled as containing an elevated level of “organic selenium”, usually as Semet. The sample we investigated contained 210 μg Setotal g–1 sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153±21 μg SeSemet g–1; n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet and would be good candidates for further study and characterization as reference materials for determining this important food component. The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that this material is pure selenomethionine.
A natural matrix (pureed tomato) candidate reference material containing residue concentrations of pesticide chemicals by P. Armishaw; Roderick Millar (pp. 291-296).
NARL (the Australian National Analytical Reference Laboratory) is preparing a pureed tomato reference material spiked with residue concentrations of a range of pesticide chemicals relevant to the Australian horticultural industry.Traceable certified pesticide concentration values will be established using both isotope dilution mass spectrometry primary methods (developed within NARL) and measurements carried out by a number of experienced laboratories. As far as we are aware, there is no other similar CRM available anywhere in the world.The need for such a material is evident from the results of interlaboratory proficiency studies conducted by NARL among Australian and Asia-Pacific residue testing laboratories. Many participants are experiencing difficulties with the analysis of pesticide residues in fruit and vegetables at concentrations of regulatory significance. Chemicals such as methamidophos (an organophosphorus pesticide widely used on tomato crops) are causing particular problems.In a pilot study, a number of units of control (unspiked tomato) and the candidate reference material were prepared and packaged into lacquered steel cans which were sealed and sterilised by immersion in boiling water.Accelerated stability testing of the packaged material was conducted using isochronous measurement. All of the pesticides showed some degree of degradation after 4 weeks of storage at 50 °C, and after 168 days of storage at room temperature. However, all appeared to be stable after 168 days of freezer storage.Homogeneity testing involved duplicate test portions taken from every 50th unit of reference material. An experimental protocol was devised with the aim of minimising the analytical variability and assuring the quality of the data generated. There is some degree of inhomogeneity in the prepared material and a small fill trend is also indicated. Potential improvements to the spiking and preparation procedure have been identified and it is planned to prepare a second batch of both control and spiked material for further homogeneity trials and for certification of the pesticide concentrations.
Long-term stability of nutrients in a frozen mixed food control material by K. M. Phillips; A. H. Simpkins; Karen R. Amanna; Wayne Wolf; Kent K. Stewart; Seth Clark; Keun Pyo Kim; Gary R. Beecher; Joanne Holden (pp. 297-302).
A mixed food homogenate was prepared as a quality control material for two multi-center clinical feeding trials. Approximately 100 kg of homogenized human diet material was prepared under controlled conditions to maintain the stability of lipid components. More than 4800 20–25 g aliquots were prepared and stored at –60 °C in glass jars with Teflon-lined lids. The homogeneity of the composite was validated by analysis of moisture and total fat in aliquots taken throughout the dispensing sequence. A portion of the material was reserved at the National Institute of Standards and Technology and further characterized as SRM 1544-Fatty Acids in Diet Composite. Moisture, protein, ash, total lipid, fatty acids, cholesterol, sodium, potassium, calcium, and magnesium were assayed as part of routine quality-control analyses. Components were analyzed over a total time period ranging from 29 months (minerals) to 60 months (moisture), and up to 319 values per nutrient were generated. Results for all components assayed were stable over the time period studied. For example, moisture (n = 319; 60 months) ranged from 70.66 to 72.58 g/100 g with a mean, standard deviation (SD), and relative standard deviation (RSD) of 71.90, 0.27, and 0.4%, respectively. The range, mean, SD, and RSD for cholesterol (mg/100 g; n = 98; 49 months) were 13.54–17.96, 15.14, 0.64, and 4%.