Standard reference materials (SRMs) for determination of organic contaminants in environmental samples

For the past 25 years the National Institute of Standards and Technology (NIST) has developed certified reference materials (CRMs), known as standard reference materials (SRMs), for determination of organic contaminants in environmental matrices. Assignment of certified concentrations has usually been based on combining results from two or more independent analytical methods. The first-generation environmental-matrix SRMs were issued with certified concentrations for a limited number (5 to 10) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Improvements in the analytical certification approach significantly expanded the number and classes of contaminants determined. Environmental-matrix SRMs currently available include air and diesel particulate matter, coal tar, marine and river sediment, mussel tissue, fish oil and tissue, and human serum, with concentrations typically assigned for 50 to 90 organic contaminants, for example PAHs, nitro-substituted PAHs, PCBs, chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs). Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Certified reference material for quantification of polycyclic aromatic hydrocarbons in sediment from the National Metrology Institute of Japan

The National Metrology Institute of Japan has issued a certified reference material (CRM) of freshwater lake sediment for polycyclic aromatic hydrocarbon (PAHs) analyses. The certification used three extraction techniques: pressurized liquid extraction (PLE) with toluene, PLE with dichloromethane/ethyl acetate (1:1 by volume), and alkaline extraction (1 M KOH in methanol) in combination with microwave-assisted extraction. Both gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/dopant-assisted atmospheric pressure photoionization/MS (LC/DA-APPI/MS) analyses were used. Certified values are provided for 18 PAHs at 1–25 μg kg⁻¹ except for perylene (2.08 × 10³ μg kg⁻¹), and information values are provided for two. Since the values of PAHs in the CRM are much lower than those in other CRMs and are comparable to those found at sites with little human influence, the CRM is suitable for PAH monitoring in sediment and soil samples.     

Matrix certified reference materials for environmental monitoring from the National Metrology Institute of Japan (NMIJ)

Matrix certified reference materials (CRMs) are playing an increasingly important role in environmental monitoring in Japan. The National Metrology Institute of Japan (NMIJ)/National Institute of Advanced Industrial Science and Technology (AIST) has been developing matrix CRMs for environmental monitoring since 2001, and has issued nine kinds of CRMs as NMIJ CRMs. The development of the CRMs was conducted in NMIJ in cooperation with candidate material producers. The isotope dilution mass spectrometry (IDMS) was principally adopted to give reliable certified values. Meanwhile, two or more analytical methods, whose levels of accuracy were well evaluated, were applied to avoid any possible analytical bias. Two typical certification processes, the certification of river water CRMs for trace element analysis and that of marine sediment CRMs for PCB and organochlorine pesticide analysis, are outlined as examples. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA.     

Preparation and characterization of organic calibration solutions for development of certified reference materials at the National Metrology Institute of Japan

Certified reference materials (CRMs) are playing an increasingly important role in environmental monitoring in Japan. The National Metrology Institute of Japan (NMIJ)/National Institute of Advanced Industrial Science and Technology (AIST) has been developing CRMs of organic calibration solutions since 2003, and has issued several NMIJ CRMs. The development of these materials was conducted at the NMIJ in cooperation with candidate material producers. The freezing-point depression method was principally adopted for assessment of the purity of starting materials to give reliable certified values. Gas chromatography with flame ionization detection (GC–FID) and/or high-performance liquid chromatography (HPLC), which are based on independent principles and whose levels of accuracy are well evaluated, were applied in combination with other methods to avoid any possible analytical bias. Purity assessment is outlined for two typical examples, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDD) and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDT), which were used as starting materials for a CRM under development. Methods adopted for gravimetric preparation and ampouling of solutions were qualified and optimized to reduce the uncertainties of certified values due to these factors. Furthermore, a new experimental scheme for assessment of stability and preparation variation is proposed for the proper estimation of uncertainties. Presented at BERM-11, October 2007, Tsukuba, Japan.     

Evaluation of uncertainty of reference materials

 Certification of reference materials is far more than just characterisation of a selected homogeneous batch of material. From the perspective of the ISO Guide on the Expression of Uncertainty in Measurement (GUM) all uncertainty sources relevant to the user of an individual certified reference material (CRM) sample at a moment in time should be part of the CRM uncertainty. This not only includes the full uncertainty of the batch characterisation (rather than the statistical variation), but also all uncertainties related to possible between-bottle variation, instability upon long-term storage and instability during transport to the customer. Received: 21 April 1999 · Accepted: 24 September 1999     

Availability of reference materials: COMAR the database for certified reference materials

COMAR is the international database for certified reference materials. A new user-friendly web-based version, COMAR², has been developed by BAM and CONET Consulting AG which will be available in December 2002. The advantages of COMAR² are briefly explained.Presented at the International ILAC/IAF Conference on Accreditation in Global Trade, 23-25 September 2002, Berlin, Germany     

Certified reference materials for organic contaminants in sewage sludge: a feasibility study

As an answer to the re-evaluation of the European sludge directive, two novel reference materials for organic components in municipal sludge have been produced and test certified for AOX (absorbable organic halogens), PAH (polycyclic aromatic hydrocarbons), NPE (nonylphenol and nonylphenolethoxylates), DEHP (di(2-ethylhexyl)phthalate), bisphenol A, and BFR (brominated flame retardants). The materials were prepared from raw sludge without spiking or mixing of different sludges. The study demonstrated that the technique for the preparation of a suitable reference material, sufficiently homogenous and stable, and with concentration levels that answer the needs of the laboratories and the relevant authorities, can now be presented in detail. The results, furthermore, show there is a need for method validation and standardisation of the measurements of NPEs and certain BFR congeners, and that the development of the laboratory structure in Europe, with fewer and more specialised laboratories, might become a major obstacle when trying to find a sufficient number of laboratories being appropriately proficient for this kind of study in the future.     

Homogeneity and stability of reference materials

 Homogeneity and stability are two crucial characteristics of any certified reference material (CRM). Utmost care must be taken during preparation to create materials as homogeneous and stable as possible. Degradation can generally be minimised by reducing the water activity of the material to a level between 0.15 and 0.35. However, careful preparation by itself is not enough. Positive demonstration of homogeneity and stability is required from the perspective of implementing uncertainty calculus according to the Guide to the Expression of Uncertainty in Measurement (GUM). In many cases, homogeneity and stability studies fail to give sufficient quantitative information on homogeneity and stability, mainly because of a lack of measurement repeatability and insufficient number of replicates. In this work, some solutions to these problems and their implications are presented. Received: 25 April 2000 / Accepted: 12 September 2000     

Feasibility studies for the preparation and certification of reference materials Part II: mineral oil contaminated waste materials

The 2-year international joint project HYCREF (Contract-No. G6RD-CT-2002-00854), funded by the European Commission in the 5th Framework programme, aimed to develop methods to prepare homogenous and stable water-, soil- and waste reference materials contaminated with mineral oil hydrocarbons and to test certify the mineral oil content by gas chromatographic methods. As mineral oil products are important sources for environmental contaminations, appropriate reference materials certified by using the new gas chromatographic methods (soil: ISO/FDIS 16703, waste: prEN 14039 and KW/04, water: ISO 9377-2) are highly needed. Additional to the HYCREF-results presented in part I–mineral contaminated soils–this second paper gives an overview of the feasibility study for the preparation and test certification of three waste reference materials (offshore marine sediment, building material and industrial waste). The following specifications, which had been defined in the project work plan, were reached successfully: uncertainty of the mineral oil content resulting from the certification exercise ≤5% and a between-bottle inhomogeneity of ≤3%. All three materials have been evaluated for long- and short term stability. They contain different levels and types of mineral oil and cover the full application range of ISO/FDIS 16703 and prEN 14039 (100–10,000 mg/kg). The expanded uncertainties U _cert of the three materials are about 6%. In this way, they are comparable to ERM^®-CC015a (U _cert=7.1%, mineral oil in a river sediment) and are suited to close the present gap of commercially available CRM for mineral oil determination in waste.     

Determination of polybrominated diphenyl ethers in environmental standard reference materials

Standard reference materials (SRMs) are valuable tools in developing and validating analytical methods to improve quality assurance standards. The National Institute of Standards and Technology (NIST) has a long history of providing environmental SRMs with certified concentrations of organic and inorganic contaminants. Here we report on new certified and reference concentrations for 27 polybrominated diphenyl ether (PBDE) congeners in seven different SRMs: cod-liver oil, whale blubber, fish tissue (two materials), mussel tissue and sediment (two materials). PBDEs were measured in these SRMs, with the lowest concentrations measured in mussel tissue (SRM 1974b) and the highest in sediment collected from the New York/New Jersey Waterway (SRM 1944). Comparing the relative PBDE congener concentrations within the samples, we found the biota SRMs contained primarily tetrabrominated and pentabrominated diphenyl ethers, whereas the sediment SRMs contained primarily decabromodiphenyl ether (BDE 209). The cod-liver oil (SRM 1588b) and whale blubber (SRM 1945) materials were also found to contain measurable concentrations of two methoxylated PBDEs (MeO-BDEs). Certified and reference concentrations are reported for 12 PBDE congeners measured in the biota SRMs and reference values are available for two MeO-BDEs. Results from a sediment interlaboratory comparison PBDE exercise are available for the two sediment SRMs (1941b and 1944).     

Two new marine sediment standard reference materials (SRMs) for the determination of organic contaminants

Two new marine sediment standard reference materials (SRMs), SRM 1941b Organics in Marine Sediment and SRM 1944 New York/New Jersey Waterway Sediment, have been recently issued by the National Institute of Standards and Technology (NIST) for the determination of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, and chlorinated pesticides. Both sediment SRMs were analyzed using multiple analytical methods including gas chromatography/mass spectrometry (GC/MS) on columns with different selectivity, reversed-phase liquid chromatography with fluorescence detection (for PAHs only), and GC with electron capture detection (for PCBs and pesticides only). SRM 1941b has certified concentrations for 24 PAHs, 29 PCB congeners, and 7 pesticides, and SRM 1944 has certified concentrations for 24 PAHs, 29 PCB congeners, and 4 pesticides. Reference concentrations are also provided for an additional 58 (SRM 1941b) and 39 (SRM 1944) PAHs, PCB congeners, and pesticides. SRM 1944, which was collected from multiple sites within New York/New Jersey coastal waterways, has contaminant concentrations that are generally a factor of 10–20 greater than SRM 1941b, which was collected in the Baltimore (Maryland) harbor. These two SRMs represent the most extensively characterized marine sediment certified reference materials available for the determination of organic contaminants.Electronic Supplementary Material Supplementary material is available in the online version of this article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

Use of uncertainty information for estimation of certified values. Comparison of four approaches using data from a recent certification exercise

Four approaches for estimation of reference values and their respective uncertainties of characterisation were compared using data from the recently finalised certified reference materials ERM-EC680k and ERM-EC681k, elements in plastics. Reference values and uncertainties of characterisation were estimated as mean of laboratory means and their respective standard deviations, using equal weights and the weighting procedure of Mandel–Paule. In addition, two approaches taking into consideration uncertainty information reported by the participants, namely the consistency check and simulation procedure proposed by Cox for CCQM Key comparisons and an approach suggested by Pauwels et al. (Accred Qual Assur 3:180–184, 2000) were used. No difference between the equally-weighted and Mandel–Paule consensus means was observed and the reference value from the Cox approach was in all cases within ±2 u _char of each consensus mean. Uncertainties varied between the three approaches. Uncertainties derived from equally-weighted mean of means approach are on average 14% above uncertainties using the Mandel–Paule consensus mean, 36% above the uncertainties estimated by Pauwels et al., and 54% above the uncertainties from the Cox approach. Robustness of the uncertainty estimation against incorrect estimation of uncertainties was assessed. Assumption of a 50% uncertainty of the individual uncertainties resulted in an uncertainty of 30% of the uncertainty of characterisation. Differences between the four approaches are negligible for this dataset when combined with the uncertainty contribution from heterogeneity and stability as prescribed in ISO Guide 35. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Filling the AOAC triangle with food-matrix standard reference materials

Well-characterized reference materials are needed by laboratories in the food testing and nutrition communities to facilitate compliance with nutritional labeling laws, to provide traceability for food exports needed for acceptance in many foreign markets, and to improve the accuracy of nutrition information that is provided to assist consumers in making sound dietary choices. As a result of the enactment of the Nutrition Labeling and Education Act of 1990 and the Infant Formula Act of 1980, the National Institute of Standards and Technology (NIST) has developed a suite of 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, SRM 1946 Lake Superior Fish Tissue, SRM 2383 Baby Food Composite, SRM 2384 Baking Chocolate, SRM 2385 Spinach, and SRM 2387 Peanut Butter. Many of these materials were developed at the request of the food industry to populate a nine-sectored fat-protein-carbohydrate triangle developed by AOAC International. With the completion of SRM 2387, SRMs representing each sector of the triangle are now available. These food-matrix reference materials are intended primarily for validation of analytical methods for the measurement of proximates, fatty acids, vitamins, minerals, and so on in foods of similar composition. They may also be used as "primary control materials" in the value-assignment of in-house, secondary, control materials to confirm accuracy as well as to establish traceability to NIST.     

Update on COMAR: the Internet database for certified reference materials

This paper describes the COMAR database for certified reference materials (CRMs). The Web-based version of COMAR is freely accessible via the Internet. COMAR was established to assist laboratories in finding the CRMs needed. The database is maintained in a collaboration of the world’s major CRM producers. The planned changes in the database as agreed at the last COMAR council meeting in Prague in May 2006 are indicated.

Reference materials in environmental trace organic analysis

 The paper reviews the application of reference materials (RMs) in environmental analysis of trace organic pollutants. The problems related to RM preparation, stability, use, etc. are critically discussed. Importance of analytical quality assurance and the role RMs play in the process are emphasised. Received: 18 May 1999 · Accepted: 27 December 1999     

The role of reference materials in food analysis

Reliability and accuracy of measurements in food and agricultural materials are essential both for implementation of the legislation concerning public health and consumer protection and for the elimination of disputes arising from trade requirements and technical barriers. In such process the crucial step is represented by the programmes aimed at the quality assurance of analytical data produced by laboratories involved in food analysis. In this framework a major role is played by the proper use of reference materials. This report provides an overview on relevance, availability, use, certification procedures and perspective of reference materials in food analysis. Measurement harmonization procedures are also discussed.     

Method validation and reference materials

For implementation of food and feed legislation, there is a strong need for development and harmonisation of reliable, validated and if possible, robust and simple analytical methods. In addition, precise methods used for measuring the exposure of humans to certain types of food contaminants and residues (natural, man-made or produced during technological treatment) such as, e.g. mycotoxins, acrylamide, pesticides and allergens have to be available, in order to compare results derived from monitoring studies. Methods should be validated (in-house or in a collaborative trial) according to harmonised protocols and good laboratory practice must be in place in order to be compliant with internationally harmonised standards. The way in which this is implemented depends strongly on the analyte, interference within the food matrix and other requirements that need to be met. Food and feed certified reference materials, when matrix matched and containing the appropriate concentration of the certified substance, are an extremely useful tool in validation of measurements.Presented at BERM-9—Ninth International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany.     

XRF检验标准物质中痕量元素的匀性

本文讨论了用Ｘ射线荧光光谱检验标准物质中痕量元素的均匀性时，可根据峰和背景强度确定能否用ＸＲＦ进行检验，以及相应于一定精度度要求的浓度下限（可检浓度），并以大米和岩石标准物质为例，计算了Ｃ－的可检浓度。还指出，作为均匀性检验量应采用浓度或净强度，尤其是对于痕量元素，最后说明了样品基体对可检浓度和最小样品量的影响。     

Primary reference materials and traceability chain for gas composition

This article briefly describes research on the development of primary reference gases and the traceability system of gas measurement at the National Research Center for Certified Reference Materials, China.     

The NIH analytical methods and reference materials program for dietary supplements

Quality of botanical products is a great uncertainty that consumers, clinicians, regulators, and researchers face. Definitions of quality abound, and include specifications for sanitation, adventitious agents (pesticides, metals, weeds), and content of natural chemicals. Because dietary supplements (DS) are often complex mixtures, they pose analytical challenges and method validation may be difficult. In response to product quality concerns and the need for validated and publicly available methods for DS analysis, the US Congress directed the Office of Dietary Supplements (ODS) at the National Institutes of Health (NIH) to accelerate an ongoing methods validation process, and the Dietary Supplements Methods and Reference Materials Program was created. The program was constructed from stakeholder input and incorporates several federal procurement and granting mechanisms in a coordinated and interlocking framework. The framework facilitates validation of analytical methods, analytical standards, and reference materials.