Reference – Standard for Comparison – Standards

Introduction

Standards and reference materials serve as the foundation for reliable, accurate, and defensible analytical measurements. In aviation, pharmaceutical, environmental, and food testing laboratories, these materials are essential for calibrating instruments, validating methods, and verifying results. They facilitate traceability to internationally recognized units, meet regulatory requirements, and ensure that data are comparable across different labs, times, and jurisdictions.

Without the use of appropriate standards, laboratory results may lack accuracy, comparability, and legal validity. This glossary explores the terminology, characteristics, and hierarchy of reference standards, certified reference materials (CRMs), working standards, and general reference materials, providing practical guidance and aviation-specific context based on international standards and best laboratory practices.

Key Definitions

Standard

A standard is a material or artifact with a well-defined composition or property, used as a benchmark for calibration, measurement, or quality assurance. In laboratories, standards may be physical objects (weights, length artifacts) or chemical solutions (known concentrations of analytes) and must be stable, homogeneous, and traceable to a recognized authority (e.g., SI units through NIST).

For example, a sodium chloride solution of exactly 1000 mg/L is used to calibrate ion chromatographs, ensuring that chloride measurements in unknown samples are accurate. In aviation, standards are vital for calibrating instruments used in fuel analysis, emissions monitoring, and environmental control.

Reference Standard

A reference standard is an exceptionally pure, well-characterized substance, used as the definitive benchmark for identity, strength, quality, and purity in analytical testing. Common sources are United States Pharmacopeia (USP), European Pharmacopoeia (EP), and similar organizations. Each reference standard is accompanied by a Certificate of Analysis (CoA) specifying identity, purity (often >99.9%), impurities, and storage conditions.

In aviation, reference standards are essential for calibrating instruments used in fuel certification, emissions testing, and environmental analysis, ensuring compliance with ICAO, FAA, and EASA regulations.

Certified Reference Material (CRM)

A Certified Reference Material (CRM) is a reference material characterized by a metrologically valid procedure for one or more specified properties, with a certificate stating the value(s), uncertainty, and traceability. CRMs are produced under ISO 17034 and ISO/IEC 17025 by organizations like NIST or EDQM.

CRMs provide the highest confidence in measurement accuracy, with comprehensive documentation on value assignment, uncertainty, traceability, and intended use. In aviation, CRMs are indispensable for instrument calibration in fuel quality, water analysis, and emission monitoring.

Working Standard

A working standard is a secondary standard, prepared and validated in-house for routine calibration and quality control. Working standards are typically made by diluting a reference standard or CRM, and must be regularly calibrated against higher-level standards to maintain accuracy.

In aviation labs, working standards are used for daily calibration of instruments involved in fuel analysis and emissions monitoring. Their preparation, calibration, and storage must be carefully documented.

Reference Material

A reference material is any material sufficiently homogeneous and stable for one or more properties, suitable for calibration, method assessment, or value assignment. While not as rigorously certified as CRMs, reference materials are produced under ISO guidelines and used for routine calibration, quality control, and analyst training.

In aviation, reference materials are used for non-critical calibrations and method development, such as multi-element solutions for preliminary instrument setup.

Hierarchy of Standards

The hierarchy of standards ensures measurement traceability, accuracy, and regulatory compliance:

1. Primary Standards: Maintained by national/international metrology institutes (e.g., NIST, BIPM), providing the ultimate source of traceability.
2. Certified Reference Materials (CRMs): Produced under strict ISO accreditation, with SI traceability and certified uncertainty.
3. Reference Standards: Supplied by pharmacopeias or standards bodies; highly pure and well-characterized but may lack full SI traceability.
4. Working Standards: Prepared in-house, validated against CRMs or reference standards, and used for routine calibration.
5. Reference Materials: Used for non-critical calibrations, training, and method development.

Characteristics and Features

Reference Standards

• Purity: >99.9% and comprehensively characterized (identity, strength, impurities).
• Documentation: CoA with methods, results, storage, and expiration.
• Traceability: Linked to higher-order standards or CRMs.
• Regulatory Acceptance: Required for certification, compliance, and legal defensibility.
• Suppliers: USP, EP, BP, JP.

Certified Reference Materials (CRMs)

• Certification: ISO 17034/17025, fully traceable to SI units.
• Uncertainty: Accompanied by certified uncertainty and detailed CoA.
• Use: Calibration, method validation, and regulatory compliance.
• Producers: NIST, EDQM, BAM, accredited commercial suppliers.

Working Standards

• Preparation: In-house from high-purity materials or by dilution.
• Validation: Regular calibration against CRMs or reference standards.
• Documentation: Batch records, storage, and recalibration intervals.
• Use: Daily calibration and routine quality control.

Reference Materials

• Homogeneity and Stability: Suitable for calibration and method development.
• Certification: Basic documentation; may lack detailed uncertainty.
• Use: Training, preliminary calibration, and non-critical quality control.

Comparative Table

Selection Criteria & Best Practices

• Traceability: Use standards traceable to SI units or national/international bodies for regulatory or accreditation-critical work.
• Matrix Matching: Select standards with a matrix similar to your samples to minimize matrix effects.
• Regulatory Requirements: Follow industry and regulatory guidelines (e.g., ICAO, FAA, ISO/IEC 17025).
• Documentation: Maintain thorough records for standard preparation, calibration, and use.
• Storage & Stability: Follow supplier recommendations for storage, handling, and expiration.
• Recalibration: Regularly recalibrate working standards against higher-level standards.
• Training: Ensure laboratory staff are trained in the preparation, validation, and use of all standards.

Conclusion

Reference standards, CRMs, working standards, and reference materials are fundamental to laboratory measurement quality, regulatory compliance, and international data comparability. By understanding their definitions, characteristics, and hierarchy, and by following best practices for selection and use, laboratories in aviation and other regulated industries can ensure the integrity and defensibility of their analytical results.

For further guidance on selecting or implementing the right standards for your laboratory’s needs, contact our experts or schedule a demo .