The Flame Photometric Detector

The flame photometric detector (FPD) is a mass-sensitive detector, which is speciflc for sulfur and phosphorous. The light that is emitted from phosphorus or sulfur combustion products is measured. The detection limit is about 5 pg S s and 50-100 pg P s and the linearity is 10 -10 . Main area of use is speciflc detection of sulfur in petroleum and petrochemical samples as well as of phosphorus containing pesticides. 

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Other Detectors Two additional detectors are similar in design to a flame ionization detector. In the flame photometric detector optical emission from phosphorus and sulfur provides a detector selective for compounds containing these elements. The thermionic detector responds to compounds containing nitrogen or phosphorus. 

The flame-photometric detector (FPD) is selective for organic compounds containing phosphoms and sulfur, detecting chemiluminescent species formed ia a flame from these materials. The chemiluminescence is detected through a filter by a photomultipher. The photometric response is linear ia concentration for phosphoms, but it is second order ia concentration for sulfur. The minimum detectable level for phosphoms is about 10 g/s for sulfur it is about 5 x 10 g/s. 

Flame Photometric Detector3 With the flame photometric detector (FPD), as with the FID, the sample effluent is burned in a hydrogen/air flame. By using optical filters to select wavelengths specific to sulfur and phosphorus and a photomultiplier tube, sulfur or phosphorus compounds can be selectively detected. 

In the case of crop residues, GC determination is carried out on the hydrolyzed product, i.e., methomyl oxime, instead of alanycarb to make effective use of its substantially higher response to the flame photometric detector. In order to prevent vaporization loss of methomyl oxime, ethylene glycol must be added prior to concentration in Section 6.3. In all other concentration operations, full account must also be taken of the high volatility of both alanycarb and methomyl oxime, especially in the process of removal of the last traces of solvents. Alanycarb residue in the sample is stable under storage condition at -20 °C for at least 100 days. 

The chemiluminescent reaction with chlorine dioxide provides a highly sensitive and highly selective method for only two sulfur compounds, hydrogen sulfide and methane thiol [81]. As in the flame photometric detector (FPD), discussed below, atomic sulfur emission, S2(B3S -> ) is monitored in the wave-... 

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. 

Reliable flame photometric detector quantification of organosulphur compounds requires careful optimization of the gas chromatograph parameters. Although the relative response of the flame photometric detector to various sulphur compounds remains somewhat controversial [7], analysis of organosulphur compounds by flame photometric detector is now relatively straightforward. 

Brody and Chaney in 1966, were the first and foremost to describe the flame photometric detector (FPD) which unfortunately could not get enough recognition in the field of gas chromatographic analysis due to the following reasons, namely ... 

The presence of naphthalene masks the HD response in the flame photometric detector used for both MINICAMS and DAAMS methods. 

The amount transformation process is illustrated with data for chlorpyrifos in the flame photometric detector, phosphorus mode, and shown in Table VI. Level 1 transformations were calculated where the amount power was increased by 0.03 units for each step. At an amount power of 0.20 the F statistic of 32.7 showed a minimum but at a confidence level of 95% did not satisfy the F test for linearity. Power steps changed by only 0.01 and 0.001 units in the vicinity of the minimum were then calculated as shown in levels 2 and 3. The best linearity was found in this case at a power transformation of 0.182 although the F statistic of 8.33 did not indicate linearity when compared with the critical F of 2.99 at P=.95. Calculations at these second and third levels were not always necessary and even when performed did not always lead to a satisfactory condition of linearity. 

There is one final observation using the bandwidth information The data of Tables IX and X suggest that the flame photometric detector (chlorpyrifos) produces more consistent data than the electron capture detector. The chlorpyrifos data clearly had the narrowest bandwidth yet both the range and sample size of this set were comparable to the others studied. The range of chlorpyrifos was 500 to 1 whereas those of fenvalerate and chlorothalonil were 2000 to 1 and 1000 to 1, resp. Chlorpyrifos had 30 samples whereas the other two had 36 and 30, resp. Chlorpyrifos had 5 analysis levels while the other two had 6 each. More data of this sort is needed to compare various detector systems. 

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. 

The responses of these three detectors to a variety of organophosphorus molecules have often been compared the results seem to vary from compound to compound165,179,217,238,289. In many instruments the stream is split and passes through several detectors for parallel measurements184,187,298. The flame photometric detectors are the most selective for phosphorus, yield less extraneous peaks and make the identification work easier188. 

Sulfur Dioxide. Both flame photometric and pulsed fluorescence methods have been applied to the continuous measurement of S02 from aircraft. In the flame photometric detector (FPD), sulfur compounds are reduced in a hydrogen-rich flame to the S2 dimer. The emission resulting from the transition of the thermally excited dimer to its ground state at 394 nm is measured by using a narrow band-pass filter and a photomultiplier tube. 

The flame photometric detector, which is sensitive to sulfur or phosphorus, shows diminished response to sulfur compounds, if large amounts of hydrocarbons are eluted simultaneously. This happens even though there is no significant response on the chromatogram from the interfering hydrocarbons. The opposite effect can also occur. In some of the newer types of electron... 

The impact of the flame photometric detector (FPD) resides in its simultaneous sensitivity and specificity for the determination of sulfur and phosphorus. It is inherently compatible with the FID and as such affords the analytical chemist a discriminating ability beneficial to many analyses. In 1966, Brody and Chaney published data on their design of an FPD (26)(Figure 5.18). 

The flame photometric detector has been found to be versatile in pesticide analysis, food putrefaction, air pollution, and for fuel analysis. 

It is obvious from the FTIR and NMR analyses of these extracts that in order to positively identify organosulfur structures we need an analytical technique that is sulfur selective. That is, a technique that responds to sulfur uniquely. One such technique, applicable to the problem in hand, is GLC-FID/FPD where the flame photometric detector is set in the sulfur selective mode. 

It should be noted that the flame photometric detector is more sensitive to thiophenes than it is to benzothiophenes (22). Studies in our laboratory have shown that the flame photometric detector response to thiophene is approximately 25% greater than that for the corresponding quantity of benzothiophene. Hence a consequence of this non-linearity of response is that the thiophenes are not as quantitatively dominant as suggested by some of the FPD pyrograms. 

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). 

B. Ehrlich, R. Hall, et al., Sulfur detection in hydrocarbon matrices. A comparison of the flame photometric detector and the 700A Hall electrolytic conductivity detector, J. Chromatogr. Sci., 79 245-249 (1981). 

Standards of typical meat flavor sulfur aliphatics and heterocyclics were made from 5 ng/pl to 500 ng/pl in hexane to determine response factors as well as reproducibility in the flame photometric detector. Background sulfur compounds were checked in concentrated reagent blanks. 

The use of the Fractosil 200 produced a flat almost noise free baseline with the flame photometric detector. 

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