ISO/IEC 17025 accreditation is widely recognised as the global benchmark for analytical laboratory competence. Whether your laboratory operates in environmental testing, mining, pharmaceuticals, food, or industrial quality control, accreditation demonstrates technical capability, impartiality, and consistent operation according to internationally accepted standards.
At the core of this framework sits one critical element: the effective use and management of Certified Reference Materials (CRMs).
CRMs provide the metrological traceability, documented uncertainty, and performance verification that auditors expect under ISO/IEC 17025. This guide explores how CRMs support compliance, highlights common audit findings, and outlines practical strategies to maintain accreditation with confidence.
Understanding ISO 17025 CRM Requirements
Metrological Traceability Obligations
ISO 17025:2017 Section 6.5.2 requires laboratories to ensure measurement results are traceable to the International System of Units (SI) through an unbroken chain of comparisons.
In most analytical chemistry laboratories, that traceability chain typically follows this structure:
- National Metrology Institutes (e.g., National Institute of Standards and Technology, Physikalisch-Technische Bundesanstalt, National Physical Laboratory)
- ISO 17034-accredited reference material producers
- Certified Reference Materials with documented uncertainty
- Laboratory working standards and calibration solutions
CRMs are the essential link between SI-traceable standards and routine laboratory measurements. Without properly certified materials and documented uncertainty, laboratories cannot demonstrate the traceability required during accreditation audits.
Documentation and Record-Keeping Requirements
Section 7.5 of ISO 17025 emphasises robust documentation of all measurement processes. For CRMs, this extends beyond simply retaining a Certificate of Analysis (CoA).
Certificate Management
Laboratories should maintain:
- Complete CoAs for every CRM lot used
- Verification of supplier ISO 17034 accreditation
- Documented uncertainty values (expanded uncertainty, typically k=2)
- Clear statements of metrological traceability
Auditors frequently examine whether laboratories have reviewed—not just filed—CRM certificates.
Inventory Control
Effective CRM control includes:
- Verification of received materials against purchase orders
- Documented storage condition monitoring
- Expiration date tracking
- Usage logs linking specific CRM lots to analytical batches
These records demonstrate control over measurement inputs, a key audit focus area.
Measurement Uncertainty: Where CRMs Directly Impact Compliance
ISO 17025 Section 7.6 requires the evaluation of measurement uncertainty for reported results. CRMs contribute significantly to uncertainty budgets through:
- Certified value uncertainty (from the CoA)
- Homogeneity uncertainty
- Stability uncertainty
- Uncertainty propagated through dilution or gravimetric preparation
One of the most common audit findings is the omission of CRM uncertainty from overall uncertainty calculations. Laboratories must explicitly incorporate these components and document their propagation through the calibration hierarchy.
CRM Selection: Fit for Purpose
ISO 17025 Section 6.6 requires verification of supplier competence.
Supplier Qualification Criteria
Qualified CRM providers should demonstrate:
- ISO 17034 accreditation
- ISO/IEC 17025 accreditation (if performing analytical certification)
- A documented quality management system
- Regular surveillance by recognised accreditation bodies
Best practice includes annual supplier reviews and documented verification that the accreditation scope aligns with your laboratory’s analytical needs.
Matrix and Concentration Matching
CRMs must be appropriate for their intended use.
Matrix considerations include:
- Acid composition compatibility
- Solvent compatibility
- Ionic strength alignment
- Absence of interfering stabilisers
The concentration strategy should include:
- Stock solutions suitable for accurate dilution
- Intermediate calibration standards
- QC standards at regulatory limits
- Spike solutions for matrix effect evaluation
Using an inappropriate matrix is a frequent source of audit findings and measurement bias.
Verification Protocols: Before a CRM Is Used
Every CRM should undergo structured verification before introduction into routine workflows.
Technical Review
- Confirm traceability statements
- Review uncertainty calculations (coverage factor, confidence level)
- Verify expiration dates and storage conditions
Analytical Verification
- Perform independent analysis using validated methods
- Compare results against certified values
- Document acceptance criteria and statistical evaluation
This independent verification step demonstrates technical due diligence during audits.
Ongoing Monitoring and Control
Control Charting
Statistical process control tools should monitor CRM performance over time. Control charts can:
- Detect systematic drift
- Establish warning and action limits
- Support uncertainty validation
Cross-Verification
Additional assurance can include:
- Lot-to-lot comparison
- Inter-laboratory comparison
- Proficiency testing participation
Consistent CRM monitoring strengthens audit defensibility and demonstrates continual quality oversight.
Common ISO 17025 Audit Findings Related to CRMs
1. Incomplete Traceability Chains
Auditors frequently identify missing links between working standards and SI-traceable certified values. Documentation gaps in dilution steps and calibration hierarchies are common.
Prevention strategy: Maintain structured calibration hierarchies and documented dilution records with uncertainty propagation.
2. Inadequate Uncertainty Evaluation
Common deficiencies include:
- Omitting CRM uncertainty from budgets
- Failing to propagate dilution uncertainty
- Underestimating storage-related variability
Best practice: Develop detailed uncertainty models incorporating all CRM-related components and validate through long-term control data.
3. Inappropriate CRM Selection
Matrix mismatches—such as using drinking water CRMs for complex wastewater analysis—are frequent audit concerns.
Solution: Establish formal CRM selection procedures based on analytical method requirements and sample matrix characteristics.
Practical Implementation Strategies
Integrating CRMs into the Quality Management System
Develop clear SOPs covering:
- Procurement and supplier qualification
- Receipt verification
- Storage and handling procedures
- Performance verification protocols
- Non-conformance investigations
Staff training is equally critical. Personnel must understand traceability concepts, uncertainty propagation, and documentation requirements.
Leveraging Technology
Laboratory Information Management Systems (LIMS) can:
- Track certificates and expiration dates
- Link CRM lots to analytical results
- Automate uncertainty calculations
- Monitor supplier accreditation status
Control charting software further enhances statistical oversight and documentation reliability.
Advanced Compliance Strategies
Optimising Measurement Uncertainty
To minimise uncertainty:
- Select CRMs with low certified uncertainty for critical methods
- Optimise dilution schemes
- Maintain temperature-controlled storage
- Conduct periodic re-verification studies
Continuous Improvement
High-performing laboratories implement:
- Regular method revalidation
- Participation in proficiency testing
- Inter-laboratory comparisons
- Ongoing staff competency development
Such initiatives demonstrate proactive quality management during accreditation reviews.
Audit Preparation: Staying Ready
Before an audit:
- Review all CRM certificates and verification records
- Confirm supplier accreditation validity
- Reassess uncertainty calculations
- Conduct internal audits focusing on CRM handling
During the audit, be prepared to:
- Explain CRM selection rationale
- Demonstrate traceability chains
- Present uncertainty evaluations
- Show evidence of monitoring and corrective action
Clear documentation and confident technical explanations are often the difference between observations and full compliance.
Conclusion
Certified Reference Materials are not simply calibration tools—they are the backbone of metrological traceability under ISO/IEC 17025. Effective CRM management supports:
- Demonstrable SI traceability
- Robust uncertainty evaluation
- Reduced audit findings
- Improved measurement reliability
- Sustained accreditation confidence
Laboratories that implement structured CRM selection, documentation, and monitoring systems are better positioned to maintain compliance while delivering defensible, high-quality analytical results.
For laboratories seeking ISO 17034-accredited reference materials, custom calibration solutions, and documentation-ready standards, Graham B Jackson (GBJ) provides technical guidance and globally recognised CRM solutions tailored to accredited laboratories.
Strong accreditation begins with strong traceability. And traceability begins with the right CRM strategy.
For Further Enquiry Contact: sales@gbjpl.com.au