Flame ionization detector, hydrocarbon

This type of analysis requires several chromatographic columns and detectors. Hydrocarbons are measured with the aid of a flame ionization detector FID, while the other gases are analyzed using a katharometer. A large number of combinations of columns is possible considering the commutations between columns and, potentially, backflushing of the carrier gas. As an example, the hydrocarbons can be separated by a column packed with silicone or alumina while O2, N2 and CO will require a molecular sieve column. H2S is a special case because this gas is fixed irreversibly on a number of chromatographic supports. Its separation can be achieved on certain kinds of supports such as Porapak which are styrene-divinylbenzene copolymers. This type of phase is also used to analyze CO2 and water. 

The hydrocarbons are separated in another column and analyzed by a flame ionization detector, FID. As an example, Figure 3.13 shows the separation obtained for a propane analyzed according to the ISO 7941 standard. Note that certain separations are incomplete as in the case of ethane-ethylene. A better separation could be obtained using an alumina capillary column, for instance. 

A flame-ionization, total hydrocarbon analyzer determines the THC, and the total carbon content is calculated as methane. Other methods include catalytic combustion to carbon dioxide, which may be deterrnined by a sensitive infrared detector of the nondispersive type. Hydrocarbons other than methane and acetylene are present only in minute quantities and generally are inert in most appHcations. 

The most widely used method of analysis for methylene chloride is gas chromatography. A capillary column medium that does a very good job in separating most chlorinated hydrocarbons is methyl silicone or methyl (5% phenyl) silicone. The detector of choice is a flame ionization detector. Typical molar response factors for the chlorinated methanes ate methyl chloride, 2.05 methylene chloride, 2.2 chloroform, 2.8 and carbon tetrachloride, 3.1, where methane is defined as having a molar response factor of 2.00. Most two-carbon chlorinated hydrocarbons have a molar response factor of about 1.0 on the same basis. 

Historically, measurements have classified ambient hydrocarbons in two classes methane (CH4) and all other nonmethane volatile organic compounds (NMVOCs). Analyzing hydrocarbons in the atmosphere involves a three-step process collection, separation, and quantification. Collection involves obtaining an aliquot of air, e.g., with an evacuated canister. The principal separation process is gas chromatography (GC), and the principal quantification technique is wdth a calibrated flame ionization detector (FID). Mass spectroscopy (MS) is used along with GC to identify individual hydrocarbon compounds. 

The flame ionization detector is capable of measuring only gaseous hydrocarbons, in other words, hydrocarbons that have a low boiling point. Emission gases can, however, also contain hydrocarbons in liquid form at ambient temperature and pressure. Therefore, analyzers based on flame ionization detection are generally equipped with heating elements to keep rhe sampling line and the detector at about 200 °C. 

Dependence of Flame Species Concentrations upon Additive Concentrations. A method of determining the dependence of various ionic, neutral molecule, and excited species concentrations on the concentration of hydrocarbon added to a hydrogen/oxygen or hydrogen/air flame (based on a principle similar to that of flame ionization detectors... 

The photocatalytic experiments were performed in a horizontal quartz tube which it have TiOi. Illumination was provided by 500 W mercury lamps, located above the horizontal quartz tube. The reactant was 0.1% (v/v) ethylene in air. In case of Photo-Catalyst test, reactor effluent samples were taken at 30 min intervals and analyzed by GC. The composition of hydrocarbons in the feed and product stream was analyzed by a Shimadzu GC14B (VZIO) gas chromatograph equipped with a flame ionization detector. In all case, steady state was reached within 3 h. 

Noncondensable gases leaving the condensation vessels were depressurized (by means of an electronic back-pressure, Brooks Instrument model 5866), totalized (by means of an on-line flow gas meter, Ritter model TG05-5), and periodically analyzed with an on-line GC (Hewlett-Packard model 6890) equipped with three columns and two detectors for the analysis of Cj-C10 hydrocarbons (A1203 plot capillary column connected to a flame ionization detector), H2, CH4,... 

As the reaction temperature is increased, chemiluminescence is observed in the reactions of ozone with aromatic hydrocarbons and even alkanes. Variation of temperature has been used to control the selectivity in a gas chromatography (GC) detector [35], At room temperature, only olefins are detected at a temperature of 150°C, aromatic compounds begin to exhibit a chemiluminescent response and at 250°C alkanes respond, giving the detector a nearly universal response similar to a flame ionization detector (FID). The mechanisms of these reactions are complex and unknown. However, it seems likely that oxygen atoms produced in the thermal decomposition of ozone may play a significant role, as may surface reactions with 03 and O atoms. 

The gaseous atmosphere was then vented through a trap at -78° (to remove most of the benzene vapor) into an evacuated vessel. Samples were removed by gas-tight syringe and injected into a Hewlett-Packard 5790 gas chromatograph, equipped with a U ft, 1/8 in Porapak P column and a flame ionization detector. Use of known samples of hydrocarbons (methane and ethane) established that the minimum detectable amounts of product by this procedure were about 0.5-1 0 % (based on starting Nb complex). Several of the reactions (Mo(CO)g, W(C0)g and Ru (CO) p) gave small amounts (around 1-2 %) of these alkanes only with Cr(C0)g was a substantial yield of hydrocarbon product consistently observed (see below). 

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. 

Chromatographic columns are commonly used to determine total petroleum hydrocarbon compounds approximately in the order of their boiling points. Compounds are detected by means of a flame ionization detector, which responds to virtually all compounds that can bum. The sum of all responses within a specified range is equated to a hydrocarbon concentration by reference to standards of known concentration. 

The current individual methods differ in procedure, compounds detected, extraction techniques, and extraction solvents used. Some methods may include a cleanup step to remove biogenic (bacterial or vegetation-derived) material, while others do not. The methods have in common a boiling point type of column and a flame ionization detector. Selection of a method depends on the type of hydrocarbon suspected to be in the sample. 

A series of normal hydrocarbons were analyzed using the same chromatographic system and the Pye LCM II flame ionization detector. In Figure 6 is shown the separation of a mixture of C, ... 

A water-cooled sampling probe of internal diameter 1 mm and external diameter 5 mm with a 3-meter long heated line was used to measure concentrations of unburned hydrocarbon (flame ionization detector, Analysis Automation, 520) and NOj (chemiluminescence analyzer, Thermal Environment Instruments, 42) at the combustor exit on a wet basis. The former, measured to a precision of the order of 1 ppm, was used to ensure complete consumption of fuel within the duct, and the latter with a precision of around 0.2 ppm was used to quantify the effect of oscillations on NOj. emissions. 

Response to organic compounds is proportional to solute mass over seven orders of magnitude. The detection limit is 100 times smaller than that of the thermal conductivity detector (Table 24-5) and is reduced by 50% when N2 carrier gas is used instead of He. For open tubular columns, N2 makeup gas is added to the H2 or He eluate before it enters the detector. The flame ionization detector is sensitive enough for narrow-bore columns. It responds to most hydrocarbons and is insensitive to nonhydrocarbons such as H2, He, N2, 02, CO, C02, H2Q, NH NO, H2S, and SiF4. 

Figure 24-20 Gas chromatograms showing sulfur compounds in natural gas (o) flame ionization detector response and (b) sulfur chemiluminescence detector response. The organosulfur compounds are too dilute to be seen in flame ionization, and the sulfur chemiluminescence is insensitive to hydrocarbons. [From N. G. Johansen and J. W. Birks, Determination of Sulfur Compounds in Difficult Matrices." Am. Lob. February 1991.112.]...

The most general purpose detector for open tubular chromatography is a mass spectrometer. Flame ionization is probably the most popular detector, but it mainly responds to hydrocarbons and Table 24-5 shows that it is not as sensitive as electron capture, nitrogen-phosphorus, or chemiluminescence detectors. The flame ionization detector requires the sample to contain SlO ppm of each analyte for split injection. The thermal conductivity detector responds to all classes of compounds, but it is not sensitive enough for high-resolution, narrow-bore, open tubular columns. 

Mass Spectrometry. The use of a quadrupole mass spectrometer as a GC detector for nonmethane hydrocarbon analysis has come of age in recent years. Development of capillary columns with low carrier gas flows has greatly facilitated the interfacing of the GC and mass spectrometer (MS). The entire capillary column effluent can be dumped directly into the MS ion source to maximize system sensitivity. GC-MS detection limits are compound-specific but in most cases are similar to those of the flame ionization detector. Quantitation with a mass spectrometer as detector requires individual species calibration curves. However, the NMOC response pattern as represented by a GC-MS total ion chromatogram is usually very similar to the equivalent FID chromatogram. Consequently, the MS detector can... 

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