Total Petroleum Hydrocarbon Methodologies

Methodologies for Total Petroleum Hydrocarbon (TPH) analysis have changed over time, causing confusion around which type of tests are most appropriate. The initial methodology used was US Environmental Protection Agency (EPA) Method 418.1 [1]. However, methods using CFC-113 as an extraction solvent were withdrawn by the EPA in 2007. Similarly, the American Public Health Association (APHA), Standard Methods for the Examination of Water and Wastewater, 5520C [2] was also withdrawn. 

In response to the banning of fluorocarbons, the EPA developed gravimetric hydrocarbon methods, Method 1664A for waters [3] and Method 9071B for solids [4]. Notably, they refer to “n-hexane extractable material” instead of TPH. These are essentially equivalent to APHA 5520B [2] and E + F (silica gel treatment).

The issue has been further complicated with the introduction of ASTM method, D7678 – 11 [5]. In this method, an acidified 900 mL sample of water or wastewater is extracted with cyclohexane. The extract is treated with sodium sulphate and Florisil to remove traces of water, as well as polar substances. This produces a solution containing non-polar material (TPH), which is analyzed by mid-infrared laser spectroscopy. 

The common feature among each of these methods is that silica gel treatment is required to remove polar hydrocarbons in order to obtain a TPH (non-polar hydrocarbon) result. TPH is synonymous with Mineral Oil & Grease (MOG).

In 1996, a fundamentally different approach was developed by the EPA employing gas chromatography with flame ionization detection (GC-FID) to determine gasoline range organics (GRO) and diesel range organics (DRO). Based on EPA Method 8015D [6], a purging or headspace method was used to measure C₆-C₁₀ volatile hydrocarbons (GRO) and extraction to determine C₁₀ – C₂₈ hydrocarbons (DRO). Quantitation is achieved by comparison to gasoline and diesel standards. TPH is the sum of the two fractions.

Method Comparability

Gravimetric methods determine extracted hydrocarbons (approximately C₁₃ and greater), and lighter hydrocarbons are lost in the solvent evaporation process. Extraction IR methods lose some volatile hydrocarbons and silica gel treatment during the extraction, but the loss is much less relative to the gravimetric tests. Thus, depending on the hydrocarbons present, one would expect IR results to be the same or higher than gravimetric. In practice, when only heavier hydrocarbons are present, the opposite may be the case.

The EPA GC-FID method is superior in determining the light hydrocarbons because the sampling and analysis protocols prevent volatilization losses. Extractable hydrocarbons are also accurately determined, although specialized techniques are required to detect the very heavy hydrocarbons in the C₆₀ – C₁₀₀ range. The major advantage of the GC technique is that the FID chromatogram provides information on the type of product, whereas the other techniques do not.

Current Status / Recommendations

In Canada, the original GRO / DRO procedure has evolved into a number of regional methods as tabulated below. In every case, the Provincial and Federal Hydrocarbon Guidelines are based on the pertinent GC procedure.

REGION	METHOD	CARBON RANGES	CALIBRATION STANDARDS	SILICA GEL TREATMENT
USEPA	GRO / DRO	C6 – C10 C10 – C28	Gasoline (C6 – C10) Diesel (C10 – C28)	No
BC	VH EPH	C6 – C10 C10 – C19 C19 – C32	Toluene (C6 – C10), 7 n alkanes; C10 – C32, 3 PAH	Organic soils only
Federal, AB, SK, MB, ON	CCME F1-F4	C6 – C10 C10 – C16 C16 – C34 C34 – C50	Toluene (C6 – C10) nC10 nC16 nC34	Yes
QC	C10 – C50*	C10 – C50	#2 Diesel	Yes
TPH**	C6 – C36	MAH #2 Diesel
Atlantic	Atlantic PIRI	C6 – C10 C10 – C16 C16 – C21 C21 – C32	9 Aromatics 4 n-alkanes, MTBE (C6 – C10) Alkanes C10 – C32 6 PAH	Optional
Modified TPH***	C6 – C32	PIRI

* MDDELCC procedure. Pentane extract, silica gel, GC-FID, used for product identification

** Pentane extract, silica gel, GC-FID, used for product identification only

*** Guidelines for gasoline, diesel / fuel, oil. Chromatogram examined to determine hydrocarbon type and Modified TPH compared to the guideline

Bureau Veritas currently uses all three method types: gravimetric, IR (using tetrachloroethylene instead of Freon as the extraction solvent) and GC-FID. In addition, calculations of customized hydrocarbon ranges can be provided on request.

As the GC-FID methods provide accurate C₆ – C₁₀ data and are usable for comparison against remediation guidelines, the pertinent regional method is the recommended procedure for TPH requests. Due to different calibration standards, carbon ranges and the applications of silica gel, regional GC methods are not directly comparable. Techniques that do not employ silica gel treatment may be highly biased if biogenic (polar) hydrocarbons are present. Either gravimetric or IR methods may be required by some customers for historical purposes or for comparison to local guidelines such as sewer use bylaws.

References

[1] EPA Oil and Grease Measurements.

[2] Standard Methods for the Examination of Water and Wastewater. 2012, 22nd ed. Rice, E.W., Baird, R. B., Eaton, A.D., & Clesceri, L.S., eds. American Public Health Association, American Water Works Association, & Water Environment Federation, 5520B Liquid-Liquid, Partition-Gravimetric Method; 5520C Partition-Infrared Method; 5520E Extraction Method for Sludge Samples; 5520F Hydrocarbons.

[3] US Environmental Protection Agency Method 1664, Revision A: N-Hexane Extractable Material (HEM; Oil and Grease) and Silica Gel Treated N-Hexane Extractable Material (SGT-HEM; Non-polar Material) by Extraction and Gravimetry, February 1999.

[4] US Environmental Protection Agency Method 9071B, n-Hexane Extractable Material (HEM) for Sludge, Sediment, and Solid Samples, April 1998.

[5] ASTM D7678-11, Standard Test Method for Total Petroleum Hydrocarbons (TPH) in Water and Wastewater with Solvent Extraction using Mid-IR Laser Spectroscopy, ASTM International, West Conshohocken, PA, 2011

[6] US Environmental Protection Agency Method 8015D, Nonhalogenated Organics Using GC/FID, SW-846, June 2003.