TPH Analysis GC Chromatogram Interpretation

Ask the Expert Question: 
Is there a way to distinguish whether TPH hits in a sample are from diesel, gasoline or mineral oil?

Expert Response:
The product causing the positive TPH results can generally be identified from the pattern of contamination present in the chromatogram provided the TPH was analyzed by method SW846 8015B or a similar Gas Chromatograph (GC) analysis.

Each of the petroleum products will show analytes in a generally well defined Carbon Number range (for example, gasoline is primarily from C4-C12, Diesel Fuel from C10 to C28, etc), and each of these products also have a very distinct distribution pattern within that carbon range. Identification is then based on both the carbon range and the actual distribution within that carbon range (there can be some overlap of the carbon number range for the various products). Our petroleum chemists are very experienced in evaluating these patterns and establishing the petroleum product present, and can evaluate the GC chromatograms from the analysis for identification.

It is also possible that the results are due to something other than petroleum products. The GC TPH methods are not necessarily specific for only petroleum products, but will include any compounds that elute within a defined Carbon Number range. Again, an evaluation of the chromatographs by a trained chemist can usually identify the cause of the positive results.

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