Flame Photometric Detector
The Flame Photometric Detector can detect sulfur compounds, such as H2S or SO2, down to about 200 ppb and phosphorus compounds to 10 ppb. While not 100% selective, the Flame Photometric Detector is 100,000 times more sensitive to sulfur and phosphorus compounds than hydrocarbons. The phosphorus response is linear, and the sulfur response is exponential (twice the sulfur yields four times the peak area).
The Flame Photometric Detector is similar in design to the FID, except that the detector body is light-tight and a second flow of hydrogen purges the optical path between the photomultiplier tube (PMT) and the hydrogen-rich flame. A bandpass filter (at 393 nm for sulfur and 525 nm for phosphorus) mounts in front of the PMT, so only that the emissions from sulfur or phosphorus are detected while other wavelengths are rejected.