Free Books and Brochures

nbsp; 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-

, the emission from the background hydrocarbons is very small (albeit around a minor transmission maximum). Similarly, the light� emit by phosphorus compounds lies between 480 nm and 580 nm. Thus, a filter having a transmission window between 520 nm and 560 nm, phosphorus compounds can be selectively sensed, and the emission from the background hydrocarbons will, again, be almost negligible. Thus, sulfur and phosphorus compounds can be selectively detected. A diagram of the Hewlett-Packard flame photometric detector is shown in figure 26.     Courtesy of the Hewlett�Packard Corporation   Figure 26 The Hewlett�PackardFlame Photometric Detector