Liquid Chromatography - The Fixed Wavelength Detector 2

The mercury vapor lamp is the most popular as it has an emission wavelength that allows the detector to sense a wide range of solute types. The detector usually contains both a sample and reference cell and the output from the reference cell is compared to that from the sample cell The difference is fed to a non linear amplifier that converts the signal to one that is linearly related to concentration of solute in the sample cell. The fixed wavelength detector is the least expensive and, as the majority of the light is emitted at a specific wavelength(s) it has a high intensity, and thus, a higher intrinsic sensitivity than the multi-wavelength UV detectors. However, the multi-wavelength detector can often compensate for the lower sensitivity by choosing a wavelength that has the highest extinction coefficient for the solutes of interest. Average specifications for commercially available fixed wavelength UV detectors are as follows:-

Typical Specifications for a Fixed Wavelength UV Detector


Sensitivity (toluene)

5x 10-8 g/ml

Linear Dynamic Range

5 x 10-8 to 5 x 10-4 g/ml

Response Index

0.98 - 1.02


Figure 18. The High Speed Separation of a Two Component Mixture