Gas Chromatography Detectors - The Emissivity or Photometric Detector > Page 49


Virtually all the basic drugs contain nitrogen and thus can be specifically detected among a large number of other unresolved compounds not containing nitrogen.

The Emissivity or Photometric Detector

The emissivity detector or, the Flame Photometric detector (FPD), was described by Grant (10) in 1958 but as it could not compete in sensitivity with the ionization detectors, did not raise any commercial interest. The emissivity detector, however, has some unique properties that could make its response quite specific and giving it certain unique areas of application. It was originally used to differentiate aromatic from paraffinic hydrocarbons by measuring the luminosity that the aromatic nucleus imparted to the flame. Contemporary photometric detectors do not usually monitor the total light emitted only light emitted at specific wavelengths. For example, phosphorus and sulfur containing hydrocarbons generate chemi-luminescence at specific wavelengths when burnt in the hydrogen flame. The wavelengths of the light emitted by carbon and hydrocarbons containing sulfur and phosphorus are shown in figure 25.


Courtesy of the Hewlett–Packard Corporation


Figure 25 Light Emission Wavelengths of Carbon and Hydrocarbons Containing Sulfur and Phosphorus