# Gas Chromatography Detectors - Detector Linearity > Page 4

A linear
detector will provide a *normal*
response and follow the Gaussian concentration profile of the eluted peak as
shown in figure 1. If the normal signal is electronically integrated with
respect to time then an integral output is obtained. Similarly if the normal
output is differentiated then the *differential*
of the Gaussian curve is produced. In a normal response the area of the peak is
proportional to the total mass eluted whereas with the integral response the
step height of the integral curve is proportional to the total mass eluted. The
differential curve is often used to identify the retention time which is the
point where the signal crosses from positive through zero to negative.

# The Dynamic Range of the Detector

A detector has two response ranges, the *dynamic range* and the *linear dynamic range* and the two range
are not synonymous. The dynamic range of a detector is that concentration range
over which a concentration dependent output is produced. The minimum of the
range will be the concentration at which the output is equivalent to twice the
noise level and the maximum that concentration where the detector no longer
responds to a concentration increase. The dynamic range is usually given as a
concentration ratio and is thus, dimensionless.

# Detector Linearity

The linear dynamic range of a detector is that concentration range over which the detector output is linearly related to solute concentration.

Thus, y= Ac

(c) is the concentration of solute in the mobile phase passing

and (A) is a constant.