Your calibration certificate says “traceable.” Your CALA auditor wants to know: traceable to what?
ISO 17025:2017 §6.5 requires that calibration be traceable to the International System of Units (SI) through an unbroken chain of comparisons, each with stated measurement uncertainty.
“Traceable to NRC” written on a certificate does not satisfy §6.5. The auditor needs:
The specific NRC reference standard used (Standard pH Solution, NIST-traceable, lot number, expiry). The calibration uncertainty of that standard (typically ±0.005 pH at k=2). Your electrode uncertainty budget — which must include junction potential uncertainty.
That last one is where labs fail CALA audits.
Junction potential uncertainty in pH measurement is 0.03 to 0.08 pH units depending on the sample matrix. Most labs never quantify it. They calibrate in KCl-balanced buffers and then measure samples with high ionic strength, high dissolved solids, or non-aqueous components — and assume the junction potential is constant.
It is not. And a CALA technical assessor who understands electrochemistry will write it as a non-conformance.
Schrödinger supplies:
NRC-traceable pH reference solutions (certified lot-by-lot, uncertainty ±0.005 pH, k=2). Junction potential uncertainty estimates for common Alberta lab matrices: produced water, tailings pond, OSPW. Calibration uncertainty budget templates formatted for ISO 17025 quality documentation.
Your certificate can say “traceable” and actually mean it.
schrodinger.ca