Natural Matrix Reference Materials Research Articles

A comparative analysis of different hair matrixes and matrix reference materials for quantitative hair analysis in drug tests

The proposal of the concept of Precision Science and the rapid development of technology have raised expectations for a higher demand for accurate quantitative analysis, including hair analysis in drug tests. Many details are presently constraining improvements in precision, so there is a greater need for standardized methods to control and improve the analytical process in the laboratory. Hair matrix reference materials may become a feasible option. In the present study, 34 drug-free hair samples from healthy volunteers were collected and compared with 2 certified standard hair samples. It was observed that the hair matrix of different origins did have a significant impact on hair analysis. Three reference materials were prepared using spiking and two soaking methods, and one natural reference material was collected from real cases. A total of 57 authentic hair samples were measured from March to August 2022 using these 4 reference materials. Differences in the origins of samples were found to have a significant impact on the hair analysis results. The reference material soaked in water and methanol at a 1:1 ratio (v/v) appeared to be an excellent tool for daily quality control, as it gave results closest to those of the natural matrix reference material in all aspects and supported the law principle of the Presumption of Innocence.

A New Reference Material for Tritium Organic Molecules in Sediment: Results of an International Intercomparison Exercise

Solid matrix 3H reference materials are challenging to prepare given the volatile nature of 3H and are often unrepresentative of the range of 3H forms that may be encountered during routine analysis. As a result, few 3H reference materials are currently available, undermining verification of analytical techniques for environmental 3H measurement. To address this, an International Working Group on Organically‐Bound Tritium Analysis determined to produce a tritium natural matrix reference material (NMRM). The reference material comprises marine sediment blended with sewage sludge contaminated with 3H‐organic species arising from authorised discharges from a radiopharmaceutical manufacturing site. Previous studies have demonstrated that the 3H species have persisted in the environment over three decades providing valuable supporting data to underpin the characterisation of the NMRM. The preparation and characterisation of the NMRM are described along with the subsequent application of the reference material in an international intercomparison exercise involving nineteen laboratories from nine countries. A reference value of 168 ± 22 Bq kg−1 was derived from the data arising from the proficiency test.

Food safety measurement issues: way forward

Ensuring food safety (FS) is a persistent concern frequently faced by many countries. Safeguarding the quality of food that is fit for human consumption is the primary responsibility of the governmental regulatory agencies. For most part, agro-industries and food processors assume voluntary leadership for producing safe food. However, in the event of FS breach, the regulatory responsibility kicks into identify and rectify the situation. Notwithstanding whether it is the regulator or the industry that institutes the remedial action (e.g. improved hygiene and refined agricultural and manufacturing practices), the role of laboratory measurements is central in safeguarding the integrity of a functioning FS system. There are many analytical tools available to implement this task, such as validated analytical methods, natural matrix reference materials, field tested monitoring systems (proactive assessment) and effective surveillance systems (constant vigilance to prevent repeat safety violations). Way forward: existing FS tools are insufficient and should be strengthened with innovative approaches. Examples are: assembling swift intervention logistics to face FS breaches; rapid response systems including communication; robust metrology based measurement systems located at strategic locations in the country; and inter-disciplinary human resource to match the need for capacity development. These issues are discussed.

Preparation and certification of a fish oil natural matrix reference material for organochlorine pesticides

The mass fractions of six organochlorine pesticides in a fish oil certified reference material (CRM) have been determined using multiple methods of analysis. Fish oil was extracted from the filet of Tilapia fish collected from the River Nile, and this CRM was recently issued by the National Institute of Standards (NIS). It can be used as natural matrix CRM for organochlorine pesticides determination in fish and for marine environmental measurement purposes. The analytical methods used are described, and the obtained results were combined to calculate the mass fractions of the six detected organochlorine pesticides and their associated uncertainty values. It has been concluded that mass fractions of four pesticides are certified values. These are 1,1-(dichloroethylidene)bis[4-chlorobenzene](4,4′-DDE), 1,1-(2,2,-dichloroethylidene)bis[4-chlorobenzene] (4,4′-DDD), 1-chloro-2-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene (2,4′-DDT) and 1,1-(2,2,2-trichloroethylidene)bis[4-chlorobenzene] (4,4′-DDT). Meanwhile, mass fractions of two pesticides were reference values. These are heptachlor and 1-chloro-2-[2,2-dichloro-1-(4-chlorophenyl)ethyl]benzene (2,4′-DDD).

Measurement of Strontium Isotopic Ratio in Natural Matrix Sample Containing Strontium-90

Strontium isotopic ratios in a natural matrix reference material (IAEA-A-12) containing strontium-90 were measured by means of a thermal ionization mass spectrometer with a multi-collector system (MC-TIMS). There was significant difference in the measured isotopic ratios between the IAEA-A-12 and a standard reference material of the strontium isotopes (SRM 987), and 88Sr/86Sr and 87Sr/86Sr of the IAEA-A-12 were smaller and 84Sr/86Sr was larger than those of the SRM 987. 90Sr/86Sr ratio was estimated, by calculating the number of atoms of the strontium-90 from its activity, to be 3.55 × 10−10.

Metrological concepts for enhancing the reliability of food and nutritional measurements

Metrology is a specialized discipline that deals with the science of measurements, irrespective of the field of application and regardless of the size of the measurement uncertainty. Incorporating metrological approaches into the measurement process enhances the reliability of analytical findings. These developments include: high-quality reference standards, validated methods, robust sampling practices, proven calibration approaches, natural matrix reference materials, speciation chemistry, assessment of measurement uncertainty and establishment of traceability links, certified reference materials to facilitate one aspect of traceability, and proficiency testing, among others.

The natural matrix reference material database of the International Atomic Energy Agency: Reference materials in support of dietary investigations

Certified reference materials (CRMs) are the recognized tools to make the results of analytical measurements comparable and traceable to international standards. The use of CRMs in quality control and quality assurance of analytical determinations and in development of newer analytical methodologies is widely recognized. The International Atomic Energy Agency (IAEA) maintains a database on internationally available CRMs of natural matrices. This database is periodically updated, and presently documents about 2700 reference materials. Several food and clinical natural matrix materials certified for nutritionally essential substances are included. The IAEA database serves as a useful indicator of the status of current developments in natural matrix CRMs in this field. This article provides an account of the available data on natural matrix reference materials related to diet and create an awareness among the prospective end-users to enable the wider adaptation of these CRMs for validation purposes.

Determination of self-absorption corrections for gamma analysis of environmental samples: comparing gamma-absorption curves and spiked matrix-matched samples

Accurate determination of the massic activity of gamma-emitting radionuclides in environmental samples, particularly sediments and soils, cannot be achieved without taking into account sample self-absorption. The extent of self-absorption in the sample will depend on a number of factors including sample composition, density, sample size and gamma-ray energy. The preferred method for correcting for this effect is to use spiked or natural matrix reference materials that match each sample type to be analysed. However, for laboratories that must measure a wide variety of sample matrices this method is too costly and time-consuming. Another technique commonly used is to make direct gamma-ray transmission measurements for each sample. This method, while more practical, still requires a minimum of three measurements to be made for each sample analysed. A more convenient method is to prepare sets of gamma-absorption curves. This approach involves making a series of direct transmission measurements for samples of varying densities but similar type. Sets of matching samples, both spiked and unspiked, were prepared and density correction factors determined using the direct transmission method and the spiked sample approach. It was found that, for soil and sediment samples, these two methods typically differed by 5–9% for higher energy gamma rays and by 12–15% for the 59.54 keV 241Am peak. Gamma-absorption curves were also derived and, for the admittedly limited dataset, 95% confidence intervals of ±7% for the curve generated using the spiked samples method were obtained.

Determination of total mercury in environmental and biological samples using k0-INAA, RNAA and CVAAS/AFS techniques: Advantages and disadvantages

The accuracy and precision of the results obtained for total mercury in various environmental and biological samples and certified reference materials (CRMs) by various analytical methods, including k 0-instrumental neutron activation analysis (k 0-INAA), radiochemical neutron activation analysis (RNAA) and cold vapour atomic absorption (and atomic fluorescence) spectrometry (CVAAS/AFS) used in routine analysis in our laboratory, were investigated. Three natural matrix reference materials (RMs) from the International Atomic Energy Agency (IAEA), five CRMs from the Institute for Reference Materials and Measurements (IRMM), six CRMs from the National Institute of Standards and Technology (NIST) and one from the Jožef Stefan Institute (IJS) were analyzed. The results obtained show good agreement between certified or assigned values, and between the methods used, except for some data obtained by k 0-INAA in biological samples. This can be explained by losses during irradiation in semi-open systems (irradiation in plastic ampoules) and/or spectral interferences.

K0-NAA quality assessment by analysis of different certified reference materials using the KAYZERO/SOLCOI software

A suite of natural matrix reference materials (RMs) were used to assess the quality of analytical results obtained by k0-instrumental neutron activation analysis (k0-INAA) at the Jožef Stefan Institute (IJS). Five certified reference materials (CRMs) from the Institute for Reference Materials and Measurements (IRMM), two standard reference materials (SRMs) from the National Institute of Standards and Technology (NIST), three RMs from the International Atomic Energy Agency (IAEA) and one RM from IJS were analyzed. Altogether, results for twenty-four elements in inorganic matrices and twenty-nine elements in organic matrices, obtained by k0-INAA, were compared to certified values. Results obtained show good agreement with certified or assigned values except for Fe, La, Nd, Sm and U in inorganic matrices, and Ag, Al and Cr in organic matrices.

Database of natural matrix reference materials (NMRM) for organic constituents.

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 1,700 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, 1,682 (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.

Particle size determination of some IAEA and NIST environmental and biological reference materials

Particle size distributions in fifteen International Atomic Energy Agency (IAEA) and sixteen National Institute of Standards and Technology (NIST) reference materials (RMs) were measured with the basic aim to investigate the potential of these materials to be used as reference or quality control materials in analyses where a small sample mass is required (< 100 mg). Most of the investigated materials are commercially available environmental or biological natural matrix RMs with certified values for trace elements, radionuclides, or organometallic compounds. The laser diffraction technique was used in all measurements. From the point of particle size distribution, materials IAEA-390 (Algae, a set of three materials), IAEA-396m (Urban Dust, 3x air jet milled), NIST-SRM 1515 (Apple Leaves), NIST-SRM 1547 (Peach Leaves), NIST-SRM 1566a (Oyster Tissue), NIST-SRM 1570a (Spinach), NIST-SRM 1573a (Tomato Leaves), and NIST-SRM 1648 (Urban Particulate) can be considered appropriate for small sample mass analysis. However, additional analytical tests are needed to confirm the appropriate homogeneous distribution of chemical composition, the level of heterogeneity for individual elements, at this sample mass level.

A synopsis of different approaches to the certification of reference materials

Proliferation of Biological and Environmental Reference Materials (RMs), agencies and individuals preparing and characterizing them for a wide variety of inorganic and organic chemical constituents, makes it pertinent to look at the various certification approaches followed. This synopsis presents amalgamated versions of several of the major certification approaches, for natural-matrix RMs, alluding to some of the many factors that significantly affect the conduct and outcome of the analytical characterization exercises.

Two New Multi-element Reference Materials Of Coal Ash Composition†

Two reference materials of coal ash (ZUK-1 and ZUA-1) developed at the Institute of Geochemistry, Irkutsk, and their place in the collection of natural matrix reference materials, are described. The paper provides sampling conditions, mineralogical features and a description of the processing of reference materials. The two samples have been certified for 49 and 31 major, minor and trace elements, respectively; additionally, information values are proposed for about 20 trace elements in each

Micro-homogeneity of Candidate Reference Materials Characterized by Particle Size and Homogeneity Factor Determination

T. Sonntag and M. Rossbach, Analyst, 1997, 122, 27 DOI: 10.1039/A605396C

IAEA Programme of natural matrix reference materials for the determination of radionuclides

The International Atomic Energy Agency has been providing analytical quality control services (AQCS) to its Member States since the 1960's. The AQCS programme distributes reference materials (RMs), organizes intercomparison runs, and provides training courses for quality assurance in chemical analysis and radioactivity measurements of food, biological, environmental and marine materials. This paper focusses on those aspects of the subject dealing with reference materials and intercomparison runs for the determination of radionuclides. Nineteen natural matrix reference materials are available for the determination of radionuclides. Twelve new intercomparison and reference materials are in preparation or under consideration. The radionuclides of interest include: K-40, Mn-54, Co-60, Sr-90, Tc-99, Ru-106, Ba-133, Cs-134, Cs-137, Pb-210, Ra-226, Th-228, Th-232, Pu-238, Pu-239+240.

Preliminary assessment of homogeneity of new candidate agricultural/food reference materials

In an effort to bring to the analytical community new natural matrix reference materials (RM's) for elemental composition quality control, ten new agricultural/food candidate reference materials prepared previously, were characterized for homogeneity. The materials include bovine muscle powder, whole egg powder, corn bran, microcrystalline cellulose, wheat gluten, whole milk powder, corn starch and three wheat flours representing a wide range of matrix types and elemental composition. Characterization was for up to some twenty five major, minor, trace and ultratrace elements of nutritional, toxicological and environmental significance. Solid sampling electrothermal atomic absorption spectrometry was applied to the determination of copper and lead in sub-milligram subsamples. A variety of other analytical techniques via an interlaboratory cooperative effort was used to determine many other elements in 100–2000 mg subsample sizes. Good material homogeneity was observed for virtually all materials and analytes with the exception of Cr and Pb in limited instances. The materials were thus deemed suitable for detailed characterization of elemental concentration to lead to recommended values and to bring these biological products to reference material status.

An intercomparison exercise on the determination of neptunium-237 in an environmental material

An intercomparison exercise has been carried out on the measurement of237Np in a sample of sea-born sediment taken from the estuary of the River Esk in Cumbria, United Kingdom. The sediment had been contaminated by radioactive liquid discharges from the nuclear fuels reprocessing plant at Sellafield. The measure of agreement between the submitted values was such that one would accept with confidence237Np analyses reported by the participating laboratories. The exercise was arranged by the Analysts' Informal Working Group (AIWG). The AIWG is a small group of chemists from several Government laboratories in the United Kingdom having an interest in radionuclides in the environment. From time-to-time the Group arranges intercomparison exercises; these exercises are in addition to the members' normal quality assurance schemes, and in addition to intercomparison exercises arranged by other organizations. So far as the authors are aware, there has been no report of such an exercise involving237Np, and there appear to be no natural matrix reference materials available for environmental237Np.

Primary standards in activation analysis

The availability of natural matrix reference materials evaluated for trace element content has resulted in their widespread use as standards (i.e., calibration materials; comparators) for instrumental neutron activation analysis (INAA). Due to the uncertainties associated with their certified values, the limited number available, and the relative matrix independence of INAA, these reference materials are more properly utilized as quality assessment materials, after calibration of the INAA analytical system with true primary standards. Terminology is defined, the use of matrix reference materials to evaluate the analytical system is discussed, techniques for the accurate preparation of primary standards for trace element analyses are reviewed, and necessary precautions in the accurate comparison of samples to standards are presented.

Natural matrix radioactivity standards and reference materials

Although the precise definitions of Natural Matrix Standard (NMS) and Natural Matrix Reference Material (NMRM) remain somewhat unclear, few doubt their extreme usefulness in virtually all programs involving measurements of radioactivity. Rigorous quality assurance/quality control is difficult, if not impossible, particularly in studies requiring radiochemical/radiometric analyses of environmental matrices, when lacking good NMSs and NMRMs. A fairly comprehensive range of these materials is now available internationally, at a reasonable cost. Progress on the National Bureau of Standards NMS program as well as EML's Quality Assessment Program are discussed. In addition 99Tc in vegetation is presented as a specific example of the methodology of preparing a NMRM.