ISO/IEC 17025: Clause 6.5 - Ensuring Metrological Traceability (Clause 6.5.2)

Clause 6.5.2 of ISO 17025 describe that a laboratory’s measurement results are traceable to the International System of Units (SI), which is required for maintaining accuracy, consistency, and credibility in test results.

Clause 6.5.2 Requirements :

1. Calibration by a Competent Laboratory:

Explanation: The lab can trace measurements to SI units by having its instruments calibrated by an external, accredited calibration lab. This external lab should itself be accredited to ISO 17025, ensuring its competency in providing traceable calibration.

Example: In a food testing lab, certain equipment like glassware, data loggers, or autoclaves needs to be calibrated periodically to ensure measurement accuracy. The lab must have these items calibrated by an accredited calibration lab that provides a calibration certificate, not a test certificate. A calibration certificate contains information on traceability to SI units and the calibration status of the equipment, which is required for fulfilling the requirements of ISO 17025. This calibration certificate verifies that the measurements and adjustments align with internationally accepted SI standards, thereby ensuring reliable and consistent results in food testing.

2. Certified Reference Materials (CRM) from a Competent Producer:

Explanation: The lab can use certified reference materials (CRMs) that are traceable to SI units. These CRMs should be obtained from a competent producer (ISO 17034-certified) to ensure metrological traceability.

Example: For heavy metal like lead testing in food products, the lab could use a CRM with a known lead concentration, certified by an ISO 17034-accredited producer. This CRM ensures traceability to SI units (e.g., mg/kg of lead) and allows the lab to verify its measurement methods against a known, traceable standard.

3. Direct Realization of SI Units through National/International Standards:

Explanation: Alternatively, the lab may directly or indirectly compare its measurements with national or international standards, achieving traceability through national metrology institutes (such as NIST or NPL).

Example: If the lab performs pH testing in food, it might compare its pH meter's calibration directly to a national standard solution with a certified pH value from a metrology institute. This process directly ties the pH measurements to an SI-traceable reference standard, ensuring that the lab’s measurements align with internationally accepted values.