Metrological Traceability
Definition
A property of a measurement result whereby the result can be related to a reference (ultimately the SI system of units) through a documented, unbroken chain of calibrations, each contributing a stated uncertainty; the foundation of the CRM chain and of all quantitative forensic chemistry results.
- Ultimate reference
- SI system of units
- Requires
- Documented, unbroken calibration chain
- Each link carries
- A stated uncertainty
- Underpins
- CRM chain, quantitative forensic chemistry
Common questions
Why does an unbroken calibration chain matter more than a single accurate-looking measurement?+
A measurement is only defensible if every instrument and reference material used to obtain it can be traced back through documented calibrations to the SI unit definitions, since a single undocumented step breaks the chain and leaves the reported uncertainty unverifiable.
What happens to a quantitative forensic result if metrological traceability cannot be demonstrated?+
The result can still be reported, but its defensibility in court is weakened because the uncertainty on the measurement cannot be properly justified, which opposing experts can challenge as an unverified or unsupported number.
Related terms
- Certified Reference Material (CRM)
- A sample with one or more analyte concentrations established by an accredited body and traceable to a national metrology institute. NIST SRM...
- Internal Standard (IS)
- A compound chemically near-identical to the analyte, often a deuterated isotopologue (d3-morphine, d5-EDDP, d5-alprazolam, pyrene-d10), spiked into every sample at a known...
- ISO 17034
- The international standard specifying general requirements for the competence of reference material producers; an ISO 17034-accredited producer has demonstrated the technical competence...
- Limit of Detection (LOD)
- The lowest concentration of analyte that produces a signal reliably distinguishable from the instrument noise, conventionally three times the standard deviation of...
- Limit of Quantification (LOQ)
- The smallest concentration that can be quantified with acceptable precision and accuracy, typically corresponding to a signal-to-noise ratio of 10:1 or an...
- Linearity
- The range of analyte concentrations over which an analytical method produces instrument responses that are proportional to concentration (the calibration curve is...
- Measurement Uncertainty (MU)
- A quantified parameter associated with a result that characterises the dispersion of values reasonably attributable to the measurand. Estimated by the GUM...
- NIST SRM (Standard Reference Material)
- A reference material issued by the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, whose property values are established...
- System Suitability Test
- A pre-run check in which a standard mixture is injected into the analytical instrument and key parameters (retention times, peak widths, signal-to-noise...