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 FPD 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 FPD 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.
The dual FPD detector is equipped with two PMTs and filters for the simultaneous detection of sulfur and phosphorus.
|The three chromatograms at left show the FID/Dual FPD combination detector responses to a 50 ppm malathion sample.|
Both the single or dual FPD can be equipped with an FID collector electrode and electrometer, which will detect the hydrocarbon peaks at the same time the PMTs are responding to the sulfur and phosphorus compounds. The FID response is not as sensitive as a pure FID because the hydrogen-rich flame is optimized for sulfur and phosphorus detection, rather than hydrocarbon detection. Users can easily optimize the sulfur-phosphorus response versus hydrocarbons response simply by adjusting the hydrogen/air mixture with the included EPC gas controls.
|The sulfur PMT in the FID/dual FPD combination detector can detect a 5ppm malathion sample (left)|
|The phosphorus FPD can detect a 5ppb malathion sample (right).|