LOD (Limit of Detection)
The lowest concentration an instrument can reliably distinguish from background noise.
Limit of Detection (LOD) is the minimum concentration at which an analyte can be identified with a defined confidence level, typically 3σ above background.
LOD varies by element, matrix, and measurement time. Light elements (C, O, N) have poor LOD in XRF; transition metals in alloy matrices are typically detectable at ppm to percent levels depending on the detector and calibration.