Matrix Certified Reference Materials
Definition
:1. Introduction
2. The Process of Manufacturing Materials for Matrix CRMs
- Planning and material selection (defining the need);
- Material processing and preparation;
- Homogeneity testing;
- Stability testing;
- Characterization (value assignment);
- Certification and documentation;
- Post-certification monitoring.
3. Process of Statistical Assessment
4. A Systematic Approach to the Production of Certified Reference Materials
5. Conclusions and Prospects
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Gaseous mCRMs [9,10,11,12] | Liquid mCRMs [9,13,14,15,16,17] | Solid-State mCRMs [9,18,19,20,21,22] | |
---|---|---|---|
Matrix | Gas phase (e.g., nitrogen, synthetic air). | Water, organic solvents, oils. | Metals, polymers, organic mattery or inorganic substances. |
Preparation Methods |
|
| Mixing, melting, casting, machining, physical homogenization, grounding, polymerization. |
Homogeneity | Achieved by rolling cylinders or using internal mixers; verified by statistical assessment. | Achieved by stirring, shaking, or sonication; verified by analysis and statistical assessment. | Achieved thorough mixing and/or casting, polymerization in special conditions etc.; verified by sampling (procedure suitable to materials form), analysis, and statistical assessment. |
Stability | Sensitive to temperature and pressure changes; short-term and long-term stability studies according to ISO 17034 [1]. | Short-term and long-term stability studies according to ISO 17034 [1]. | Short-term and long-term stability studies according to ISO 17034 [1]. Testing long-term stability under storage conditions is crucial, while short-term stability has a lower impact on materials. |
Characterization | Based on comparison with primary standards. Single laboratory strategy is more often, with mass-/volume-based characterization | Ideally uses definitive (direct) methods; ;single-lab reference procedures and value transfer from higher-order CRMs are often used strategies. For more complex liquid matrices, laboratory networks and multi-method approaches may be used. | Multi-lab and multi-method approaches are often used as a strategies. Uses of multiple analytical techniques (e.g., spark-OES, XRF, volumery, gravimetry, etc.) to decrease bias impact on the certified results; |
Certified Parameters | Composition, e.g., volatile organic compounds (e.g., benzene, toluene), gases as O3, CO2, CH4, N2O, SF6, NO2, and others. | Concentrations of organic/inorganic analytes in liquid matrix. | Elemental and compounds content (main elements/components and impurities). |
Equipment Requirements | Specialized gas handling systems, gas chromatography, permeation devices. | Calibrated balances, volumetric flasks, filtration systems, higher-order CRMs. | Technological equipment, e.g., mixers, grinders, furnaces, and polymerization reactors. As the materials are usually industrial materials, industrial or pilot scale equipment for routine industrial processing may be necessary. |
Traceability | Primary and secondary standards defined; primary standards are directly SI-traceable. | Traceable to SI units via calibrated instruments and primary standards or existing CRMs. | Traceable to SI units through calibrated analytical methods, higher-order CRMs or direct analysis. |
Challenges | Gas–surface interactions, leakage, reactivity, gas operating difficulties. | Volumetric errors, analyte solubility, filtration, reactivity of components. | Inhomogeneity, segregation, mechanical treatment. |
Homogeneity [20,23,24,25,26,27,28] | |
---|---|
Reason for Importance | Ensures consistent distribution of certified properties and matrix components across mCRM units. |
Approach to Determination | Empirical testing involves selecting representative units from the batch (typically ≥10 or cube root of total units) and analyzing them using one-way ANOVA to partition variance into between- and within-unit components. The F-statistic and p-value are used to test the null hypothesis of homogeneity. If inhomogeneity is detected, it is quantified and included in the uncertainty budget. The standard uncertainty is calculated from the mean square values. Random sampling and repeated measurements are essential. ISO 33405 [4] provides detailed procedures. Previous methods like the F-Snedecor test only assessed variance consistency without quantifying uncertainty. |
Short-Term Stability [28,29,30,31,32] | |
Reason for Importance | Confirms that CRM properties remain unchanged during transport and short-term storage. |
Approach to Determination | Stability is tested by storing CRM units at various conditions simulating transportation conditions for several days or weeks, e.g., temperatures (e.g., −20 °C to 40 °C). Linear regression analysis is often used to assess trends over time. If the slope is statistically insignificant (e.g., assessed via Student’s t-test), the material is considered stable. ISO 33405 [4] and ISO 17034 [1] provide guidance. |
Long-Term Stability [28,29,30,31,32] | |
Reason for Importance | Ensures CRM properties remain stable over the product’s shelf life. |
Approach to Determination | Long-term stability is assessed over months or years of storage or via accelerated testing (e.g., using high temperature or humidity). Linear regression is used to model changes over time, and the significance of the slope is tested. If the slope is significant, a trend is present and must be accounted for. The standard stability uncertainty is calculated from the slope’s standard error and the time interval. ANOVA may also be used to compare values across time points. Real-time monitoring is also practiced by some producers. ISO 33405 [5] and reference [32] describe these methods. |
Certified Value Determination [33,34,35,36] | |
Reason for Importance | Provides the official value for CRM users, minimizing bias and ensuring traceability. |
Approach to Determination | Several strategies are used, as follows: (1) single-lab reference procedures, (2) value transfer from another CRM, (3) mass-/volume-based characterization, (4) operational/non-operational definitions. For matrix CRMs (mCRMs), multi-lab and multi-method approaches are preferred to reduce bias. Each lab analyzes random units multiple times, and averages are calculated. Outliers are removed only with technical justification supported by statistics (e.g., Grubbs or Q-Dixon tests). The final certified value is the average of lab-level averages. This approach is used by major producers like BAM, NMIJ, JRC, and LGC. ISO 33405 [5] and ISO 17034 [1] provide detailed protocols. Determination of the certified value is also a process which brings uncertainty. Therefore, the characterization uncertainty has to be estimated. For the mentioned strategy, the standard uncertainty of characterization is equal to the standard deviation of the datasets used for characterization over the root square of the number of datasets [5]. |
Document | Title | Scope and Application |
---|---|---|
ISO 17034:2016 [1] | General requirements for the competence of reference material producers | Specifies general requirements for the competence of producers of reference materials, including certified reference materials (CRMs). |
ISO/TR 33402:2025 [43] | Good practice in reference material preparation | Provides guidance on best practices for preparing reference materials. |
ISO 33403:2024 [44] | Reference materials—Good practice in using reference materials | Describes good practices for using RMs and CRMs in measurement processes. |
ISO 33406:2024 [45] | Approaches for the production of reference materials with qualitative properties | Offers guidance for producers on creating RMs with assigned qualitative properties. |
ISO/TR 79:2015 [46] | Reference materials—Examples of reference materials for qualitative properties | Provides examples of reference materials with qualitative properties. |
ISO/TR 10989:2009 [47] | Reference materials—Guidance on and keywords used for RM categorization | Offers recommendations on how to categorize reference materials and defines related terminology. |
ISO/TR 11773:2013 [48] | Global distribution of reference materials | Discusses the international distribution landscape of reference materials. |
ISO/TR 16476:2016 [49] | Reference materials—Establishing and expressing metrological traceability of quantity values assigned to reference materials | Covers how to establish and express metrological traceability for values assigned to RMs. |
ISO/Guide 30:2015 [3] | Reference materials—Selected terms and definitions | Defines selected key terms related to reference materials. |
ISO 15194:2009 [50] | In vitro diagnostic medical devices—Measurement of quantities in samples of biological origin—Requirements for certified reference materials and the content of supporting documentation | Specifies requirements for CRMs used in in vitro diagnostics and the required supporting documentation. |
ISO Guide 99:2007 [41] | International vocabulary of metrology—Basic and general concepts and associated terms (VIM) | Provides standardized terminology and definitions used in metrology, forming the conceptual basis for all reference material standards. |
ISO 33407:2024 [51] | Guidance for the production of pure organic substance certified reference materials | Provides guidance on preparing certified reference materials based on pure organic substances. |
ISO/DIS 33408 [52] | Guidance for the production of pure inorganic substance certified reference materials | Covers the production of CRMs from pure inorganic substances. |
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Gorewoda, T.; Kostrzewa, J.; Wolska, M.; Jamroz, E.; Anyszkiewicz, J. Matrix Certified Reference Materials. Encyclopedia 2025, 5, 76. https://doi.org/10.3390/encyclopedia5020076
Gorewoda T, Kostrzewa J, Wolska M, Jamroz E, Anyszkiewicz J. Matrix Certified Reference Materials. Encyclopedia. 2025; 5(2):76. https://doi.org/10.3390/encyclopedia5020076
Chicago/Turabian StyleGorewoda, Tadeusz, Justyna Kostrzewa, Marta Wolska, Ewa Jamroz, and Jacek Anyszkiewicz. 2025. "Matrix Certified Reference Materials" Encyclopedia 5, no. 2: 76. https://doi.org/10.3390/encyclopedia5020076
APA StyleGorewoda, T., Kostrzewa, J., Wolska, M., Jamroz, E., & Anyszkiewicz, J. (2025). Matrix Certified Reference Materials. Encyclopedia, 5(2), 76. https://doi.org/10.3390/encyclopedia5020076