Gas Chromatography Detectors - The Emissivity or Photometric Detector > Page 50

The diagram includes the transmission band for the filters usedinthe Hewlett-Packard FPD together with the response of the photo-multiplier sensor. Light emitted by sulfur compounds extends over the range from 320 nm to 480 nm and that emitted by hydrocarbons alone between 390 nm and 520 nm. By choosing a filter having a transmission window between wavelengths of about 390 nm and 410 nm, the maximum emission from sulfur compounds is sensed by the photo-multiplier. Conversely, 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