Limit of Quantification (LOQ)
Definition
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 RSD below a specified threshold; only results at or above the LOQ should appear as specific concentrations in forensic chemistry reports.
- Threshold
- Signal-to-noise 10:1, or RSD below a specified limit
- Context
- Forensic chemistry concentration reporting
- Reporting rule
- Only results at or above LOQ get numeric values
Common questions
What happens to a concentration result measured below the LOQ?+
It is not reported as a specific figure. The analyst instead states the substance was detected but below the quantifiable threshold, since precision cannot be guaranteed there.
How is LOQ different from LOD in practice?+
LOD only answers whether the substance is present. LOQ is the higher threshold at which the lab can also state how much is present with acceptable confidence.
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...
- 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...
- Metrological Traceability
- A property of a measurement result whereby the result can be related to a reference (ultimately the SI system of units) through...
- 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...