Hydrocarbon extractables with freon

The ASTM method for total petroleum hydrocarbons (ASTM book) is similar to the standard EPA method (EPA 418.1) and calls for extraction with Freon. The estimated variability of the test method is quesUonable and may leave room for serious errors in the calculation of total petroleum hydrocarbons. 

A soil sample was soxhlet extracted with freon and the extract was analyzed for petroleum hydrocarbons (PHC) by IR spectrometry. The concentration of PHC in the sample was found to be 285 mg/kg. A 40 g portion of this sample was spiked with 2 mL of 1000 mg/L PHC standard. The concentration of the spiked sample was measured as 326 mg/kg. Determine the accuracy of the analysis as the percent recovery of the amount spiked. 

Total petroleum hydrocarbons — Freon extraction followed by IR spectroscopy or extraction with methanol or methylene chloride and determination by GC-F1D. 

Commonly used methods for the determination of petroleum hydrocarbon contamination in soil are modifications of Environmental Protection Agency method 418.1, which use sonication or a Soxhlet apparatus for analyte extraction and either infrared spectrometry [5] or gas chromatography with flame ionization detection [6-7] for extract analysis. Regardless of the analytical method following the extraction, both modifications use Freon-113, which has been implicated as a cause of ozone depletion. Therefore, alternative methods are being sought for the determination of hydrocarbon contamination in environmental samples that reduce the need for this halogenated solvent. 

Freon-extractable material is reported as total organic material from which polar components may be removed by treatment with silica gel, and the material remaining, as determined by infrared (IR) spectrometry, is defined as total recoverable petroleum hydrocarbons (TRPHs, or total petroleum hydrocarbons-IR). A number of modifications of these methods exist, but one particular method (EPA 418.1 see also EPA 8000 and 8100) has been one of the most widely used for the determination of total petroleum hydrocarbons in soils. Many states use or permit the use of this method (EPA 418.1) for identification of petroleum products and during remediation of sites. This method is subject to limitations, such as interlaboratory variations and inherent inaccuracies. In addition, methods that use Preon-113 as the extraction solvent are being phased out and the method is being replaced by a more recent method (EPA 1664) in which n-hexane is used as the solvent and the n-hexane extractable material (HEM) is treated with silica gel to yield the total petroleum hydrocarbons. 

In interpreting the data for the total petroleum hydrocarbons in a sample, the amount of moisture cannot be ignored because moistme blocks the extraction of petroleum hydrocarbons by another hydrocarbon (Freon). Potentially, sulfm or phthalate compounds also interfere with total petroleum hydrocarbons analyses. This is similar to the problem of strong interferences from phthalate esters or chlorinated solvents when one is using electron capture methods to look for chlorinated compounds such as polycholorbiphenyls or pesticides. 

Examples of the practical use of solvent extraction are the use of water to remove water-soluble components from organic mixtures (the remaining organic phase is analyzed), the use of methanol with mineral oils or polymers to remove polar additives, the use of compound-selective solvents on powdered mixtures, and the use of Freon for the extraction and measurement of hydrocarbons and organics from soil and environmental water... 

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