Pulsed Flame Photometric Detector (PFPD)
The PFPD can detect at least 28 elements
S, P, N, C, As, Sn, Se, Mn, B, Br, Ga, Ge, Pb, Si, Te, V, Al, Bi, Cr, Cu, Eu, Fe, Ni, Rh, Ru, W, In, Sb
Thirteen elements can be detected with infinite selectivity
S, P, N, As, Se, Sn, Ge, Ga, Sb, Te, Br, Cu, In
The Pulsed Flame Photometric Detector (PFPD) was developed in the early 1990’s by Dr. Aviv Amirav.(1-3) 燯nlike the traditional flame photometric detector which has a continuous flame, the PFPD is based on a pulsed flame for the generation of flame chemiluminescence. The detector operates with a fuel rich mixture of hydrogen and air. This mixture is ignited and then propagates into a combustion chamber three to four times per second where the flame front extinguishes. Carbon light emissions and the emissions from the hydrogen/oxygen combustion flame are complete in two to three milliseconds, after which a number of heteroatomic species give delayed emissions which can last from four to 20 milliseconds. These delayed emissions are filtered with a wide band pass filter, detected by an appropriate photomultiplier tube, and electronically gated to eliminate background carbon emission.
In a conventional flame photometric detector (FPD), a sample containing heteroatoms of interest is burned in a hydrogen-rich flame to produce molecular products that emit light (i.e., chemiluminescent chemical reactions). The emitted light is isolated from background emissions by narrow bandpass wavelength-selective filters and is detected by a photomultiplier and then amplified. The detectivity of the FPD is limited by light emissions of the continuous flame combustion products including CH*, C2*, and OH*.?Narrow bandpass filters limit the fraction of the element-specific light which reaches the PMT and are not completely effective in eliminating flame background and hydrocarbon interferences. The solution to this problem, conceived by Professor Amirav of Tel Aviv University was to set the fuel gas (H2) flow into the FPD so low that a?continuous flame could not be sustained. But by inserting a constant ignition source into the gas flow, the fuel gas would ignite, propagate back through a quartz combustor tube to a constriction in the flow path, extinguish, then refill the detector , ignite and repeat the cycle. The result was a pulsed flame photometric detector (PFPD).
The background emissions from the hydrogen-rich air:hydrogen flame (approximately 10 mL/min H2 and 40mL/min Air) is a broad band chemiluminescence. The combustion of hydrocarbons is highly exothermic, rapid and irreversible, producing a light emission by the hydrocarbon products equal to the time for the flame to propagate through the combustor or 2 to 3 milliseconds. Many of the chemiluminescent reactions of the heteroatoms such as S, P, N , etc., are less energetic and more reversible, and proceed after the temperature behind the propagating flame has dropped. These heteroatom emissions are therefore delayed from the background emissions.
?span style='font:7.0pt "Times New Roman"'> HC emission (gated at 1-3 ms)
OH* + C2 ?CH* + CO
?span style='font:7.0pt "Times New Roman"'> Sulfur emission (gated at 6-26 ms)
H + H + S2 ?S2* + H2
?/span>S + S ?S2* (second-order or quadratic response)
?span style='font:7.0pt "Times New Roman"'> Phosphorus emission (gated at 4-14 ms)
H + PO ?HPO* (first order or linear response)
By using the leading edge of the flame background emission to trigger a gated amplifier with an adjustable delay time, heteroatomic emissions can be amplified to the virtual exclusion of the hydrocarbon background emission. The selective amplification of the element-specific emissions is the basis of the PFPD’s unique sensitivity and selectivity.
Applications of PFPD
Petrochemical
Sulfur compounds in petroleum feedstocks and products
Sulfur gases in Natural gas
Arsine and phosphine in natural gas and light hydrocarbons牋牋牋?
General Chemical
Sulfur (S), phosphorus (P), nitrogen (N) and arsenic (As) in chemical warfare agents牋牋?
Organic synthetic chemistry
Food
Sulfur gases and nitrogen (N) impurities in beverage grade CO2
Sulfur flavors and aromas in beer, onion, garlic
Nitrosamines in processed foods
Pharmaceutical
Sulfur (S) drugs
Electronics
Environmental
Pesticides (P, S, N ): Organophosphorus pesticides in water, soil, sludge
Tin (Sn), nickel (Ni) and iron (Fe) residues in waste water and marine sediments牋牋牋牋?
Nitrogen (N)-containing explosive residues in soils
Manganese (Mn) and lead (Pb) anti-knock agents in gasoline and soils牋牋?
Nitrogen (N) and sulfur (S) in fuels, and N- and S-oxygenates in vehicle exhaust emissions?
Example Chromatograms
1 ppm each Sulfur gases in Natural Gas
150 pg each phosphorus pesticides
Analytical Software
Analytical software available for the PFPD permits one to view the emissions of the PFPD on a scope like window. This allows for quick set up and optimization of the detector flows. It also allows the user to view the emission profile of the background and eluting peak for qualitative information. Finally, the emission data from the complete chromatogram can be saved as a data file and viewed. The resulting data may also be manipulated to provide dual elemental chromatograms.
Emission profile of eluting Sulfur compound
PFPD Data File showing phosphorus and sulfur chromatograms |
