Detector response:

The response of a detector is the quantity of a signal produced through a given amount of the solute.

Noise and minimum detectable quantity

Detector sensitivity could be made as large as desired while the electrical output of a detector is increased to almost any desired value through electronic amplification. Therefore, electrical noise inherent in the detector and electronics is also amplified and a point is reached while the noise level is high sufficient to obscure the detector's response. Thus, the noise level limits the concentrations or mass flow rate of solutes which can be detected.

Figure:  Minimum detectable quantity

The low detectable quantity is that amount which provides a detector response equivalent to twice the noise level.