ISO/IEC 17025: Clause 6.5 - Ensuring Metrological Traceability (Clause 6.5.1)

What is Metrological Traceability?

Metrological traceability is the process by which a analytical result can be related to a reference standard through an unbroken chain of calibrations, each having a known uncertainty. The reference could be an internationally or nationally recognized standard, which ensures that the analytical results made in different places and at different times are consistent and comparable.

In simple way, it ensures that a test results (for example, the weight of an object or the temperature of a solution) is accurate and can be linked back to a recognized standard through a series of well-documented steps, so that the result can be reliable.

Key Aspects of Metrological Traceability:

Unbroken Chain of Calibrations: There must be a sequence of calibrations connecting the test result to the reference standard.

Measurement Uncertainty: Each calibrations must have its uncertainty evaluated and documented to understand the potential variability or margin of error in the measurement.

Reference Standards: The test result are traced back to primary standards, such as national or international standards, which provide a reliable benchmark.

Competent Laboratories: The calibrations must be done by laboratories that have demonstrated their competence, often through accreditation to standards like ISO/IEC 17025.

Example of Metrological Traceability:

If a laboratory measures the weight of a sample using a balance, that balance should be calibrated using certified reference weights. These reference weights should have been compared to a national standard for mass (such as the mg or gm standard). The process of linking the measurement to the national standard through a series of calibrations is what provides the traceability.

Clause 6.5.1 of ISO/IEC 17025 specifies the requirements for laboratories to ensure the accuracy and reliability of their measurement results by establishing metrological traceability. The key components of this clause are:

Establishing and Maintaining Metrological Traceability: The laboratory must have system in  place to ensures all its test results are traceable to a recognized reference standard. This traceability must be maintained throughout the entire process of analysis.

Documented Unbroken Chain of Calibrations: To achieve traceability, the laboratory must document an unbroken chain of calibrations. This means that the instruments used for analysis must be calibrated, and each calibration must be traceable to a  standard (such as a national or international standard).

Measurement Uncertainty: Each calibration step in the chain contributes to the overall measurement uncertainty.

Linking to an Appropriate Reference: The calibration chain must ultimately link to an appropriate reference, such as a national or international standard. These standards serve as the benchmarks for accurate measurements, ensuring that the laboratory’s results are consistent with those obtained elsewhere using the same traceable standards.