Limit of detection

The lowest amount or concentration of an analyte that an analytical method can distinguish from background at a specified confidence level.

Blank signal: The measured response when no analyte is present in a sample. Its variability establishes how large a response must be before it counts as detection.
Limit of quantification: The lowest analyte level that can be measured with specified precision and accuracy. An analyte can be detectable below the level at which its amount can be quantified reliably.
Analytical chemistry: The study of methods for separating, identifying, and quantifying chemical substances. Detection limits are a standard performance measure for chemical analyses.
Type I and type II errors: Errors in hypothesis testing: rejecting a true null hypothesis or failing to reject a false one. Detection limits balance false alarms against missed analyte signals.
Signal-to-noise ratio: The ratio of a measured signal’s magnitude to the background variation accompanying it. Detection depends on whether analyte response stands out from measurement noise.
Sensitivity (analytical chemistry): The change in analytical response per change in analyte amount or concentration. A steep response can improve detection, but sensitivity alone does not determine the detection limit.
Mass spectrometry: An analytical technique that identifies ions by their mass-to-charge ratios. Its detection limit depends on ionization efficiency, background ions, and instrument conditions.
Receiver operating characteristic: A curve showing how a classifier’s true-positive rate changes with its false-positive rate. It describes the trade-off behind choosing a signal threshold for detection.
Standard deviation: A measure of how widely values in a dataset vary around their mean. Blank-response spread often sets the statistical scale for the detection threshold.
Selectivity (analytical chemistry): An analytical method’s ability to measure an analyte in the presence of other substances. Interfering substances can obscure analyte response even when the instrument is highly sensitive.

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