Comparison Table of Certified Reference Materials (CRMs) and Reference Materials (RMs)
In analytical chemistry, standard substances are essential for measurement accuracy, precision and traceability. There are two of these, Certified Reference Materials (CRMs) and Reference Materials (RMs), which are distinct yet complementary. They both are calibrators, methods validaters, and quality control systems, but they are quite different in certification, traceability, and use. In this article, I explain the main differences between CRMs and RMs, which helps you determine which one is right for which use case.
Definitions and Key Characteristics
| Aspect | Certified Reference Materials (CRMs) | Reference Materials (RMs) |
| Definition | Materials with certified property values and documented measurement uncertainty and traceability. | Materials with well-characterized properties but without certification. |
| Certification | Produced under ISO 17034 guidelines with detailed certification. | Not formally certified; quality depends on the producer. |
| Documentation | Accompanied by certificates specifying uncertainty and traceability. | Typically lacks detailed documentation or traceability. |
| Traceability | Traceable to SI units or recognized standards. | Traceability is not always guaranteed. |
| Uncertainty | Includes measurement uncertainty evaluated through rigorous testing. | May not specify measurement uncertainty. |
Production and Certification Processes
CRMs: Produced by accredited organizations (e.g., NIST, BAM) following ISO 17034. The process includes:
- Homogeneity testing to ensure consistency across samples.
- Stability studies to guarantee the material's properties over time.
- Measurement uncertainty evaluation, ensuring reliable data.
- Traceability to recognized international standards.
RMs: Typically produced by manufacturers or laboratories without stringent certification processes. Characterization of properties may vary, with no formal traceability or uncertainty evaluation.
Applications and Use Cases
| Application | CRMs | RMs |
| Calibration | High-accuracy instrument calibration requiring traceability (e.g., mass spectrometers). | Routine instrument calibration where traceability is not critical. |
| Method Validation | Validating methods for regulatory compliance or interlaboratory comparisons. | Developing and optimizing analytical methods. |
| Quality Control | Critical quality control in fields such as pharmaceuticals or environmental analysis. | Routine quality control for less critical processes. |
| Regulatory Compliance | Used in applications requiring traceable, certified measurements. | Generally not suitable for regulatory purposes. |
Quality and Traceability
| Aspect | CRMs | RMs |
| Quality Assurance | Guaranteed through adherence to ISO 17034 and ISO Guide 35. | Quality depends on the producer; variability is possible. |
| Traceability | Always traceable to SI units or other recognized standards. | Not always traceable; may lack formal documentation. |
Regulatory and Standards Requirements
CRMs:
- Used in applications where strict compliance to ISO 17034, ISO/IEC 17025, and ISO Guide 35 is necessary.
- Adopted in the environment of regulation like environmental testing, food and pharmaceutical quality assurance.
RMs:
- Less regulated and suitable for general laboratory use.
- Commonly applied in routine analyses and method development.
Selection Guidelines
It's a matter of which Certified Reference Materials (CRMs) or RMs you use depending on the specific needs of the application, level of accuracy, traceability, regulatory compliance, and budget. Here are some general rules to provide labs with guidance:
| Criteria | When to Use CRMs | When to Use RMs |
| Accuracy Needs | High-accuracy applications, such as trace-level analysis in pharmaceuticals or environmental testing. | Routine analyses where extreme precision is not required. |
| Regulatory Compliance | Mandatory for meeting regulatory standards (e.g., FDA, EPA, ICH) and accreditation requirements. | Suitable for non-regulated environments or internal quality assurance. |
| Traceability | Required when measurements must be traceable to SI units or internationally recognized standards. | Not essential; often used when traceability is not a critical factor. |
| Documentation | Includes certified values, uncertainty, and traceability; essential for audits and reporting. | Typically lacks detailed documentation, sufficient for internal use or non-critical applications. |
| Application Complexity | Used in interlaboratory comparisons, proficiency testing, and high-stakes measurements. | Commonly applied in method development, instrument calibration, and routine quality control. |
| Research and Development | Serves as benchmarks in cutting-edge research and validation of new analytical methods or technologies. | Ideal for exploratory research or as preliminary materials during method optimization. |
| Training and Education | Provides certified benchmarks for training in highly regulated settings. | Cost-effective option for training new personnel or demonstrating basic analytical techniques. |
| Cost Considerations | Higher cost due to rigorous certification and production standards. | Economical alternative for labs with high-volume routine testing or budget constraints. |
| Supplier Reliability | Produced by accredited organizations under ISO 17034 guidelines, ensuring quality and traceability. | May vary by supplier; choose reputable sources to ensure reliability. |
Case Studies
Real-world scenarios provide valuable insight into the practical applications and distinctions between Certified Reference Materials (CRMs) and Reference Materials (RMs). Below are detailed examples showcasing their use in diverse analytical contexts.
Case Study 1: CRMs in Environmental Testing
An environmental laboratory has the job of analysing heavy metal contamination in water samples. Regulators like the Environmental Protection Agency (EPA) require precision and traceability in such assessments. Our lab uses CRMs certified with high levels of heavy metals (lead, cadmium, arsenic):
- Instrument Calibration: CRMs make sure the ICP-MS (Inductively Coupled Plasma Mass Spectrometer) reads properly and can be traced.
- Method Validation: Validating the method of analysis with CRMs allows the lab to be compliant with EPA guidelines and reduce errors.
- Regulatory Reporting: The certificate accompanying the CRMs provides documentation on uncertainty and traceability, which is critical for audits and reporting to regulatory bodies.
This case highlights the indispensable role of CRMs in high-stakes regulatory environments where precision and documentation are paramount.
Case Study 2: RMs in Pharmaceutical Method Development
One pharmaceutical company is in the process of establishing a new High Performance Liquid Chromatography (HPLC) process for testing active pharmaceutical ingredients (APIs) in a drug composition. At this stage:
- The laboratory uses RMs with known but uncertified concentrations of the API.
- The focus is on optimizing chromatographic parameters, such as the mobile phase composition, column type, and detector settings.
- The RMs are cost-effective for the extensive trial-and-error approach typical of method development.
Once the method is optimized and ready for validation, CRMs may be introduced to ensure compliance with regulatory requirements.
Conclusion
CRMs and RMs are essential tools in analytical chemistry, each serving specific purposes. CRMs provide traceability, certification, and rigorous quality assurance, making them indispensable for high-stakes and regulatory applications. Conversely, RMs offer flexibility and practicality for routine analyses and method development. By understanding their differences, laboratories can select the appropriate material to meet their analytical needs effectively.
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