Flame photometric detector hydrocarbon

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. 

Pesticides and Fungicides. Modern pure food regulations require that the food processor be responsible for their finished products. Since so many pesticides and fungicides are used in agriculture, their detection and quantitative analysis are difficult (5, 22). Organophosphorus and chlorinated hydrocarbons are the most common pesticides. When GLC is used for halogens, electron capture or microcoulometric detectors are used for phosphorus, a thermionic flame photometric detector is required. 

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 saturated hydrocarbon fractions contain traces of sulfur. The gas-solid chromatography of the Lloydminster saturates boiling in the range of the C2s normal alkane, using a Melpar flame photometric detector, shows that the sulfur compounds are retained much longer than the hydrocarbons. This is typical for alkyl sulfides. 

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). 

The non-polar chlorinated hydrocarbon pesticides are routinely quantified using gas chromatography (GC) and electron capture(EC) detection. Alternate detectors include electrolytic conductivity and microcoulometric systems. Organophosphate pesticides which are amenable to GC are responsive to either the flame photometric detector (FPD) or the alkali flame detector (AFD). Sulfur containing compounds respond in the electrolytic conductivity or flame photometric detectors. Nitrogen containing pesticides or metabolites are generally detected with alkali flame or electrolytic conductivity detectors. 

The detection limits of a pulsed flame photometric detector (PFPD) are much better than those of any conventional FPD, and in addition the detector does not suffer the quenching of co-eluting hydrocarbon chemicals (45). The ability to also detect arsenic or nitrogen containing chemicals makes the PFPD very useful for the screening of CWC-chemicals. Frishman and Amiraw (46) used fast GC equipped with a short capillary column (1.5 m) and PFPD for the analysis of air samples. A complete analysis cycle time of 30 s was demonstrated. Killelea and Aldstadt (47) used PFPD in the arsenic selective mode for the analysis of organoarsenic chemicals. 

The emissivity detector or what is now known as the Flame Photometric detector (FPD) was originally developed by Grant (9) in 1958 but was not produced commercially at the time as it could not compete in sensitivity with the ionization detectors. The emissivity detector, however, has some unique properties that can make its response quite specific, thus giving it certain unique areas of application. Grant originally employed it to differentiate aromatic from paraffinic hydrocarbons in coal tar products by measuring the luminosity that the aromatic nucleus imparted to the flame. 

The feedstocks (straight-mn naphtha (SRN) and a blend of SRN and hydrocracked naphtha) and hydrotreated products were analysed by ASTM methods for density, carbon, hydrogen, hydrocarbon and boiling point distribution. Total sulfur was determined by ASTM D-4045 method, mercaptan sulfur by the potentiometric method (ASTM D-3227 and UOP-212), disulfides by the UOP-202 method, polysulfides by polarography [1], and elemental sulfur by the UOP-286 method. The Perkin-Elmer gas chromatograph (Model 8700), equipped with a flame photometric detector (GC/FPD) and a DB-1 fused silica capillary column (30 m x 0.53 mm), was used for identification of individual sulfur compounds [2-6]. The sensitivity of the GC/FPD technique was maximized by optimizing the gas flow rates and temperature programming as presented elsewhere [1]. 

Hydrocarbon impurities in propylene can be determined by gas chromatographic methods (ASTM D-2712, ASTM D-2163), and another test is available for determination of traces of methanol in propylene (ASTM Test Method D4864). A gas chromatographic method (ASTM D-5303) is available for the determination of trace amounts of carbonyl sulfide in propylene with a flame photometric detector. Also, sulfur in petroleum gas can be determined by oxidative microcoulometry (ASTM D-3246). 

Obviously, the chromatographic principles are the same in process and laboratory GCs and they are built up in a very similar way. Standard detectors are in each case the thermal conductivity detector (TCD), which is a universal detector for all components, and the flame ionization detector (HD), which is a specific detector for hydrocarbons. To detect sulfur gases selective detectors like an electrochemical detector, chemiluminescence detector and, most important, flame photometric detector (FPD) are used. Gaseous fuels hke natural gas, synthetic gases, and blends are complex mixtures that cannot completely be separated in a single column. Two or more different columns must be combined. To monitor the fuel quality a quasi-continuous analysis is necessary this means that very short cycle times must be realized. To do so, high-boiling components are removed... 

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. 

The flame photometric detector is the principal component in the determination of sulphur compounds for which it offers a selectivity of about five orders of magnitude with respect to hydrocarbons. The selective sulphur detection is based on the formation of electronically excited S2 molecules in a hydrogen-rich flame. These short-lived species revert to their ground state and emit characteristic molecular band spectra with peak wavelengths at 384 and 394 nm. This chemiluminescent radiation passes an optical filter and is monitored by a UV-sensitive photomultiplier. 

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. 

Lee and his co-workers (57) combined adsorption chromatography and capillary-column GC to characterize the liquid fraction from the SRCll process. A fused-silica column (20 m x 0.3 mm coated with SE-52) was used along with a flame ionization detector (FID) and either a nitrogen-phosphorous detector or a flame photometric detector. Four hydrocarbon fractions were isolated and characterized. They were found to contain the following functionalities ... 

Flame photometric detector (FPD) 2 X 10 g of sulfur compounds, 9 X 10 g of phosphorous compounds 1 X 10 for sulfur compounds lx 10 for phosphorous compounds 10 to 1 by mass selectivity of S or P over carbon Hydrocarbon quenching can result from high levels of CO in the flame Self-quenching of S and P analytes can occur with large samples Gas flows are critical to optimization Response is temperature dependent Condensed water can be a source of window fogging and corrosion... 

---