Infrared spectroscopy aliphatic hydrocarbons

Infrared spectroscopy has been applied to the determination of particulate organic carbon in non-saline sediments, aliphatic hydrocarbons and total organic carbon in saline sediments and mixtures of organics in sludges. 

Concawe [8] have described a method for the determination of aliphatic hydrocarbons in soil based on carbon tetrachloride extraction followed by infrared spectroscopy or gas chromatography. 

A fiber-optic device has been described that can monitor chlorinated hydrocarbons in water (Gobel et al. 1994). The sensor is based on the diffusion of chlorinated hydrocarbons into a polymeric layer surrounding a silver halide optical fiber through which is passed broad-band mid-infrared radiation. The chlorinated compounds concentrated in the polymer absorb some of the radiation that escapes the liber (evanescent wave) this technique is a variant of attenuated total reflection (ATR) spectroscopy. A LOD for chloroform was stated to be 5 mg/L (5 ppm). This sensor does not have a high degree of selectivity for chloroform over other chlorinated aliphatic hydrocarbons, but appears to be useful for continuous monitoring purposes. 

For aliphatic hydrocarbons, the first overtones of C-H stretching are observed in the 1600-1800 nm range, the second overtones at 1150-1210 nm and the third overtones at 880-915 nm. NIR spectroscopy may be used to study unsaturated hydrocarbons. Although bands due to C=C and C=C bonds are not directly observed in the near infrared, the bands due to the adjacent C-H bonds may be differentiated from saturated hydrocarbons. 

With the demonstration of supercritical fluid extraction, an obvious extension would be to extract or dissolve the compounds of interest into the supercritical fluid before analysis with SFC.(6) This would be analogous to the case in HPLC, where the mobile phase solvent is commonly used for dissolving the sample. The work described here will employ a system capable of extracting materials with a supercritical fluid and introducing a known volume of this extract onto the column for analysis via SFC. Detection of the separated materials will be by on-line UV spectroscopy and infrared spectrometry. The optimized SFE/SFC system has been used to study selected nonvolatile coal-derived products. The work reported here involved the aliphatic and aromatic hydrocarbon fractions from this residuum material. Residua at several times were taken from the reactor and examined which provided some insight into the effects of catalyst decay on the products produced in a pilot plant operation. 

Figure 7. Infrared spectrum, and chemical profiling hydrocarbon fluid inclusion in fluorite (inclusion A), (a) Typical infrared spectrum recorded with an aperture of 3 3 pm2, hemical profiling is reported for the band located at 3697 cm-1 attributed to hydroxyl (b), for the C02 band (c), and for the aliphatic compounds (d). [Used by permission of the Society for Applied Spectroscopy, from Guilhaumou et al. (1998), Appl Spectroscopy, Vol. 52, Fig. 3, p. 1031.]...

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