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.