Limit of Quantification LOQ - TX
From imde.io
Limit of Quantification
LOQ means Limit of Quantification.
It is the lowest concentration of a substance that can be measured with acceptable accuracy and precision by the analytical method.
Simple explanation
- Below LOD → the lab cannot reliably detect the substance
- Between LOD and LOQ → the substance may be detected but cannot be measured accurately
- Above LOQ → the substance can be quantified and reported with confidence
Example from a PFAS lab report
| PFAS compound | Result | LOQ | Interpretation |
|---|---|---|---|
| PFOA | < LOQ | 5 µg/kg | If present, it is below 5 µg/kg and cannot be quantified reliably |
| PFHxA | 8 µg/kg | 5 µg/kg | Measured concentration is reliable |
When a lab writes < LOQ, it means:
The substance was not quantifiable above the method’s limit, but small traces might still exist below that level.
Relation with LOD
| Term | Meaning |
|---|---|
| LOD | Limit of Detection – smallest amount that can be detected |
| LOQ | Limit of Quantification – smallest amount that can be reliably measured |
Typical relation:
LOD < LOQ
Example:
- LOD = 2 µg/kg
- LOQ = 5 µg/kg
Why this matters for packaging compliance
In packaging lab reports such as PFAS, heavy metals, and migrants:
- Regulations compare limits against quantified values
- Results reported as < LOQ are usually treated as not measurable at regulatory level
This is why LOQ must always be shown in the lab report.
It can also be useful to represent LOQ in a structured compliance dataset for PPWR technical files, instead of storing only PDFs.
