Utilizing TPH Methods Effectively?
A lot of misconceptions still exists about total petroleum hydrocarbon (TPH) analysis. Unfortunately, this prevalent area of environmental laboratory analysis remains the least consistent among laboratories. For ten years this has been a predominant area of focus for Phase.
TPH determined by Gravimetric (weight-based) method (EPA 1664) Heavier hydrocarbons above # 6 fuel oil do not resolve well on the gas chromatograph used for the 8015B TPH methods. Consequently, the TPH 1664 method remains the optimal choice when the quantitation of heavier hydrocarbons is required. The limitations of this method are three fold. First, this method provides quantitation information only, no hydrocarbon identification information is available. Second, due to the hexane solvent extraction method utilized, lighter gas range hydrocarbons are usually lost. Third, on soil samples this method is susceptible to some interferences due to the chemical/physical nature of the soil that can yield false positive results.
TPH by Gas Chromatograph (EPA 8015B) is the predominant test currently utilized for petroleum hydrocarbon analysis. There are two basic versions of this test employed by laboratories (with many variations on the theme). Both versions utilize a sensitive instrument called a gas chromatograph (GC) to provide quantification as well as hydrocarbon identification information. The GC is not subject to interferences common to the TPH 1664 method.
The two basic versions of the 8015B method are:
So, which do you use? This choice is usually easy. If gasoline or kerosene contamination is suspected, use TPH 8015B GRO. The TPH 8015B DRO method is appropriate for diesel to # 6 fuel oil. If fuel oil above # 6 or, heavier lubricating hydrocarbons are suspected, use TPH 1664. In many cases a combination of methods must be applied to address the entire range of contamination.
For soils, be cautious when using TPH 1664 due to the methods inherit interference problems. We recommend collecting a reference sample, of the same soil type, a safe distance from the suspected contamination to determine if an interference exists due to soil type.
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