Limit of Detection

The limit of detection (LOD) is the lowest concentration that is just distinguishable from zero (Blank Run Sample). One way to calculate this is when the signal-to-noise ratio is 3; that is, the signal height of a peak is 3 times the signal Noise. The lower the noise is during analysis, the lower are the detection limits. Unlike the sensitivity, the detection limit depends on the instruments used.

There are three different limits: Limit of Detection (LOD), Limit of Determination (LODn), and Limit of Quantification (LOQ). The LODn is reached when the signal height is 6 times the signal noise. The LOQ is reached when the signal height is 10 times the signal noise.

With a blank reading b <> 0, the three limits are determined as follows considering the standard deviation of the blank value (s):

It is also possible to determine the limit of detection by means of the confidence range of the calibration curve (also, refer to Confidence Interval/Confidence Range).