sensitivity
/ sen-suh-TIV-ih-tee /
Sensitivity is how strongly an instrument's signal responds when the amount of analyte changes — how steeply the needle swings for each extra bit of substance. Think of two thermometers: one whose mercury jumps a full centimetre per degree, another that barely creeps. The first is more sensitive, because the same change in temperature produces a bigger, easier-to-read response.
In analytical chemistry, sensitivity is the slope of the calibration curve: the change in signal divided by the change in concentration. A steep slope means a small change in concentration produces a large change in signal; a shallow slope means even big concentration changes barely move the reading.
It matters because a steeper slope makes it easier to tell two nearby concentrations apart and helps push down the smallest amount you can detect. But be careful with the everyday meaning: in plain speech people say "sensitive" to mean "can detect tiny amounts," which is really about the detection limit. The technical sensitivity is strictly the slope, and a sensitive method is not automatically a low-detection-limit method if its noise is high.
A calibration line of absorbance versus concentration has a slope of 0.10 per mg/L. That slope is the method's sensitivity: each extra 1 mg/L raises the absorbance by 0.10 units.
Sensitivity is the slope of the calibration curve — signal change per unit concentration.
Sensitivity (the slope) is distinct from the limit of detection (the smallest amount that can be told apart from a blank). A method can have high sensitivity yet a poor detection limit if its signal is also very noisy.