Semivolatile and Nonvolatile Hydrocarbons

More sophisticated detection methods for gas chromatography are also employed in the analysis of hydrocarbons gas chromatography-mass spectrometry (EPA 8270C) and gas chromatography-Fourier transform infrared spectroscopy (EPA 8410). These procedures have a significant advantage in providing better characterization of the contaminants and thus are of particular use where some environmental modification of the hydrocarbons has taken place subsequent to soil deposition. 

A superior approach to determination of total petroleum hydrocarbons in soil is the summation of areas for specific ranges of hydrocarbons. This allows a better profiling of the contaminants and also confers the ability to trace the source of the pollutant. Typical ranges for the hydrocarbon profiles are n-Cio to n-Ci4, n-Cis to n-C2o, n-C2i to n-C26, and n-C2i to n-Css. However, one must be cautious in the application of statistical methods to the determination, insofar as such methods are only as good as the information and assumptions used. Recall Garbage in, garbage out  

One of the major problems associated with profiling of hydrocarbons at contaminated sites is the phenomenon of weathering, which relates to a change 

Of particnlar significance in the study of petroleum weathering are the biomarker molecules (e.g., pristane, phytane, the hopanes and steranes). Historically, the biomarkers have been employed as crude oil signatures in prospecting and characterization. More recently, such molecules have also been employed in the environmental field, both for the determination of pollutant source and estimation of the degree of weathering. 

The biomarker molecules are particularly resistant to microbial attack, and thus the ratio of other hydrocarbon components to the biomarker will decrease as the crude oil is biodegraded (Wang et al., 1994). In the case of an ongoing oil discharge into the soil, this ratio will be highest nearest the source and will decrease with increasing distance from the source. Thus, the ratio may be used to locate the source of the contaminant (Whittaker et al., 1995). 

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