Pulsed Flame Photometry

In a pulsed flame photometric detector (PFPD), the combustion of hydrocarbon molecules is fast and irreversible, and heteroatom species such as S2, HPO, and HNO emit light after the flame is extinguished and thus under cooler temperatures. Consequently, their respective emissions can be electronically gated and separated from the hydrocarbon emission. Thus, PFPD can provide selectivity against hydrocarbon interference during detection analysis. PFPD sensitivity was reported to be superior to FPD. Moreover, N and As could be also detected. The PFPD is currently available for use in benchtop instruments, such as the MINICAMS from O. I. Analytical and other GC detector manufacturers. 

The PFPD has much lower LOD and better sensitivity than FPD technology. The MDL of sulfur and phosphorous is in the 10 to lO- g/sec area (see Aviv Amirav et al. on www.tau.ac.il/chemistry/amirav/pfpd.shtml). In addition, the PFPD can simultaneously detect several element combinations using only one photomultiplier. Element identification can be achieved through the dual-gate-response ratio method. This detection technique is capable of identifying sulfur, phosphorous, nitrogen, arsenic, and many other elements with no interference from hydrocarbons. Thus, the PFPD would be very suitable for TIC detection. 

MINICAMS-FPD has also been placed at various sites where toxic chemical exposure may occur to serve not only as an analytical tool but also as a continuous safety monitoring device. The usefulness of this device has been repeatedly demonstrated in monitoring the potential escape of CWA vapor from engineering controls in a workplace. It can detect CWA vapors at sub-AEL concentrations. 

GC manufacturers such as Tracor and PerkinElmer have developed FPDs. The detector is located behind a GC column to identify elution peaks after separation take place as the sample migrates through the column. Proper installation of optical filters permits the FPD to detect various target compounds. For CWAs, filters for phosphorus or sulfur detection are used for nerve agents and HD detection, respectively. Some users deploy two separate detectors, one installed with the phosphorus detection filter while the other uses the sulfur detection filter to achieve simultaneous detection of nerve agents and HD should the sample contain either or both. 

Tracor has developed a CWA detector, the HyFED , which draws an air sample directly into the FPD for analysis. The instrument requires connection to compressed hydrogen and air cylinders to provide the hydrogen flame for sample ionization. The instrument provides the means to sample continuously and analyze an airstream in real-time fashion. This detector has proven useful in monitoring vapor concentrations generated in laboratories. Because the targeted sample is known in laboratory conditions, there is no need to use a GC column for sample separation. Therefore, detection is direct and output instantaneous. Relative response signals can be correlated to provide a quantitative determination. 

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