Flame photometric detector for

The analysis of organosulphur compounds has been greatly facilitated by the flame photometric detector [2], Volatile compounds can be separated by a glass capillary chromatographic column and the effluent split to a flame ionization detector and a flame photometric detector. The flame photometric detector response is proportional to [S2] [3-6]. The selectivity and enhanced sensitivity of the flame photometric detector for sulphur permits quantitation of organosulphur compounds at relatively low concentrations in complex organic mixtures. The flame ionization detector trace allows the organosulphur compounds to be referenced to the more abundant aliphatic and/or polynuclear aromatic hydrocarbons. 

One advantage of gas chromatography is the availability of detectors which respond specifically to certain types of compound. The best known are the electron capture detector for chlorine compounds and the flame photometric detector for nitrogen and phosphorus compounds. If one wants to detect very small molecules such as water or CSj, the standard flame ionisation detector must be replaced by a thermal conductivity detector. 

Because the FPD responds to both aerosol and gaseous sulfur species, it has also been possible to modify these instruments to continuously measure aerosol sulfur by selectively removing gaseous sulfur compounds with a lead(II) oxide-glycerol coated denuder (55). Use of such an instrument for airborne measurements of aerosol sulfur in and around broken clouds has been reported (57). In principle, speciation between aerosol sulfate, disulfate, and sulfuric acid by selective thermal decomposition (58, 59) can also be achieved. Flame photometric detectors have also been used as selective detectors for gas chromatography. Thornton and Bandy (60) reported the use of a chromatographic system with a flame photometric detector for airborne measurement of S02 and OCS with a detection limit of 25 pptrv. 

The major disadvantage of this technique is that the entire mixture must be separated and detected in the chromatographic system. All peaks must be standardized via response factors whether their analysis is needed or not. Internal normalization also requires that a detector be used that responds somewhat uniformly to all components. This technique cannot be used with electron capture and flame photometric detectors, for instance. 

Bowman, M. C., Beroza, M. A copper-sensitized, flame-photometric detector for gas chromatography of halogen compounds. J. Chromatog. Sci. 7, 484 (1969). 

Durbin, R. P. I. Characterisation of the flame photometric detector for gas chromatography. II. Thermodynamics of some metal (3-diketonates via gas-liquid chromatography. Dissertation Abstr. B 27, 710 B (1966). 

A. Amirav and H. Jing, Pulsed flame photometric detector for gas chromatography, Anal. Chem., 67, 3305-3318 (2000). 

Linearity was determined by duplicate analyses at three different sample volumes (concentrations). The results for six representative compounds are shown in Figure 8. Responses were linear within the uncertainty limits shown in Table V. The measurements were made over the range of concentrations normally encountered in the air and seawater samples. The signal-to-noise ratios (S/N) for these measurements are shown in Table VI for typical air and seawater concentrations. For OCS at 500 pptv the S/N ratio is better than the flame photometric detector. For (CH3)2S the signal strength was intentionally reduced by selecting a 0.026-s MID scan time because of its very high concentration in seawater (—10 ppbv). 

Detectors can also be grouped into concentration-dependent detectors and mass-flow-dependent detectors. Detectors whose responses are related to the concentration of solute in the detector cell, and do not destroy the sample, are called concentration-dependent detectors, whereas detectors whose response is related to the rate at which solute molecules enter the detector are called mass-flow-dependent detectors. Typical concentration-dependent detectors are TCD and GC-FTIR. Important mass-flow-dependent detectors are the FID, thermoionic detector for N and P (N-, P-FID), flame photometric detector for S and P (FPD), ECD, and selected ion monitoring MS detector. 

D. J. Freed, Flame photometric detector for liquid chromatography. Anal Chem., 47,186,1975. 

Pollutants in Water Via Simultaneous Gas Chromatography Employing Flame Ionization and Flame Photometric Detectors for Sulfur and Phosphorus, Proceedings 13th Conference, International Association Great Lakes Research, 1970 pp. 128-136. 

Hayward, T. Thurbide, K. (2009). Quendning-Resistant Multiple Micro-Flame Photometric Detector for Gas Chromatography. Ami. Chem., Vol.81, N°21, pp. 8858-8867, ISSN 01659936. 

Figure 5 Cross-sectional view of a flame photometric detector. (Reproduced with permission from Patterson PL, Howe RL, and Abushumays A (1978) Dual-flame photometric detector for sulfur and phosphorus compounds in gas chromatographic effluents. Anal cal Chemistry 50 339-344.)...

This section has been included because it is a good example of the use of selective detectors in petroleum analysis, where the need often arises to analyze for small amounts of heterocompounds in a complex hydrocarbon matrix. Another good example is the use of the flame photometric detector for the determination of small concentrations of sulfur compounds in various plant streams. The analysis of oxygenated compounds can, however, be carried out in a totally different manner using column switching instead of the selective detector. 

In 1869, Salet observed that the blue emission from sulfur compounds and the green emission from phosphorous compounds within a hydrogen flame are intensified when a cool body is introduced into the hot environment of the flame. The importance of the discovery was realized during the development of the flame photometric detector for gas chromatography and is now known as Salet phenomenon. The phenomenon is due to the stabilization of the excited molecules on the cool surface. 

Figure 10.51. GC-FPD (flame photometric detector — for sulfur only) chromatograms for three transportation fuels (Ma et al., 2001, with permission).

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