Detection Limit
Definition
The lowest concentration an analytical method can reliably distinguish from background noise. Data below the detection limit are censored, and combining datasets with different detection limits requires careful treatment to avoid comparing incompatible data.
- Field
- Analytical chemistry / forensic geology
- Definition basis
- Lowest concentration reliably distinguished from background noise
- Data handling term
- Values below it are censored
- Common pitfall
- Combining datasets with different detection limits without adjustment
Common questions
Why can't censored below-limit results simply be treated as zero?+
Treating a non-detect as zero understates the true concentration range and can distort statistical comparisons between samples, so analysts typically use methods built for censored data, such as substitution conventions or survival-analysis techniques, rather than plugging in zero.
What goes wrong when datasets with different detection limits are pooled?+
A sample analysed with a more sensitive method may report a trace value while an otherwise identical sample analysed with a less sensitive method reports a non-detect, so a naive comparison can read as a real difference in composition when it is actually a difference in instrument sensitivity.
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