Total Petroleum Hydrocarbon (TPH) analysis refers to
the quantitative determination of the sum of all hydrocarbons,
degraded and non-degraded, that may be extracted from
a sediment or water sample. The analysis is performed
gravimetricly or by gas chromatography / flame ionization
detection (GC/FID).
The gravimetric technique is an inexpensive and quick
screening tool for oil spill response projects. The
gravimetric TPH method is performed by solvent extracting
hydrocarbons from a sample, concentrating the extract
by reducing the extract volume, and weighing a portion
of the extract.
The more expensive GC technique provides additional
sensitivity and information. This method takes a portion
of the concentrated extract (as above) and injects it
into a GC/FID. The resulting chromatogram is integrated,
using a straight line, between the retention time for
the n-alkane n-C15 and the retention time for the n-alkane
n-C34. This integration includes most extractable petroleum
related hydrocarbons.
Using this method, the Total Resolvable Hydrocarbons
(TRH) and the Unresolved Complex Mixture (UCM) may also
be determined. The TRH are non-degraded hydrocarbons
which appear as peaks in the chromatogram. The UCM is
the area under the chromatogram (excluding the peaks)
representing degraded hydrocarbons. As an oil degrades,
the UCM “hump” becomes larger and the TRH decreases.
TPH is the sum of TRH and UCM.
