Sensitivity

Detector sensitivity is one of the most important properties of a LC detector. Sensitivity of the detector is a measure of its ability to discriminate between small differences in analyte concentration. So, it is actually the slope of the calibration curve. It is also dependent on the standard deviation of the measurements. The higher the slope of your calibration curve the higher the sensitivity of your detector for that particular component, but high fluctuations of your measurements will decrease the sensitivity.

Sensitivity of a detector is not the minimum amount that can be detected. This value is influenced by the chromatographic conditions. Early eluting peaks are usually sharp, whereas the ones with long retention times are broad and sometimes difficult to discern from the noise.

Selectivity

Selectivity is another highly desirable property of HPLC detectors. A selective detector allows one to see only components of interest despite of their co-elution with any others.

Refractive index is an example of almost nonselective detector. Any component could make a response, but in case of poorly resolved mixture analyst will not be able to distinguish components.

Fluorescence and electrochemical detectors are the most selective among the common detectors. Only about 10% of organic compounds are able to fluoresce, and by choosing excitation and emission wavelength specific for the particular compound one can detect only this compound.

Usually, the more selective the detection, the lower signal noise, and the higher the sensitivity.