Flame ionization detection alkanes

Hydrocarbon Anomalies in Soils Soil samples were collected at 200 to 500 m intervals over the Lisbon and Lightning Draw fields and analyzed for thermally desorbed Ci to C12 alkanes by Flame Ionization Detection Gas Chromatography (GC-FID) and solvent-extractable Ce to C36 aromatics by UV-fluorescence spectrophotometry. 

A Shimadzu GC 9A equipped with a flame ionization detection (FID) and a 0.25 /rm DB-5 coated fused sihca capillary column (30 m X 0.25 mm i.d., J W Scientific) was used to identify and quantify the products. The GC oven temperature was programmed from 100 to 250°C at 5°C/min. The C21 n-alkane was used as an internal standard. 

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). 

An IGC method for the analysis of divided solids and fibers has been initiated by Gray et al. (2 ) It is illustrated here by the results obtained from the precipitated silica sample (PI). Injecting a series of n -alkanes at infinite dilution (at the limit of detection by the flame ionization detector) usually results in a linear variation of the logarithm of the net retention volumes (V ) with the number of carbon atoms in the n-alkanes. This is illustrated in Figure 1 for measurements performed between 71 and 130°C. Thermodynamic considerations show that and the standard free energy of adsorption of the alkanes are related by... 

All petroleum-derived waxes, including blends of waxes, from n-Cn to n-C44 can be separated by capillary column chromatography (ASTM D-5442). In this method, the sample is diluted in a suitable solvent with an internal standard, after which it is injected into a capillary column meeting a specified resolution, and the components are detected with a flame ionization detector. The eluted components are identified by comparison with a standard mixture, and the area of each straight-chain and branched-chain alkane is measured. 

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