A. A. Ekechukwu and J. E. Young
Westinghouse Savannah River Company
Aiken, SC 29808

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Several methods have been proposed to replace the Freonä -extraction method to determine total petroleum hydrocarbon (TPH) content. For reasons of cost, sensitivity, precision, or simplicity, none of the replacement methods are feasible for analysis of radioactive samples at our facility. We have developed a method to measure total petroleum hydrocarbon content in aqueous sample matrixes using total organic carbon (total carbon) determination. The total carbon content (TC1) of the sample is measured usinl a total organic carbon analyzer. The sample is then contacted with a small volume of non-pokar solvent to extract the total petroleum hydrocarbons. The total carbon content of the resultant aqueous phase of the extracted sample (TC2) is measured. Total petroleum hydrocarbon content is calculated (TPH = TC1-TC2). The resultant data are consistent with results obtained using Freonä extraction followed by infrared absorbance.

The Savannah River Site (SRS) is a 300-square-mile US Department of Energy nuclear site located in Aiken, South Carolina. The site contains two nuclear separations facilities, nuclear waste processing facilities, environmental monitoring and remediation sites, and several laboratories located throughout the site. These labs support plant operations, Research and Development, environmental remediation, and waste treatment and characterization. The mission of the site has shifted over the last decade from nuclear material production to environmental clean-up and nuclear waste stabilization. The Savannah River Technology Center (SRTC) is the Research and Development laboratory for the site. Our laboratory provides analytical support for many different types of research programs within SRTC and throughout the Savannah River Site.

A wide variety of sample types including ground water, organics, laboratory waste, process control, sludge, soils, and others are received for many different analyses. Total petroleum hydrocarbon analysis (oil and grease) is needed for analysis of research-related samples, process monitoring and control, and waste characterization. The primary use of the analysis is for environmental compliance and waste characterization, including the waste in the SRTC high and low activity waste tanks. Without this data, waste cannot be shipped and therefore waste tanks cannot be emptied. The analysis is critical to waste management and environmental compliance for the continued operation of SRTC and SRS, and thus must be maintained.

The standard analysis method for determining total petroleum hydrocarbons (Oil and Grease Analysis or Freonä Extractable Hydrocarbon Content) has been solvent extraction of the hydrocarbons using Freonä -113 followed by quantification using infrared detection. This has been the method of choice because it was simple, rugged, inexpensive, and applicable to solid and liquid samples and radioactive samples. Due to its deleterious effect on the ozone layer, the use of Freonä and other chloro-fluorocarbons (CFCs) has been greatly restricted. Freonä has become very expensive and will soon be unavailable entirely. Freonä -113 solvent is hazardous to the environment, is difficult to obtain, and is very expensive. It also presents disposal problems, particulary when it has come into contact with radioactive material. The analysis, although relatively simple to perform, is difficult to manage and expensive (both to the laboratory and the customer).

Several methods have been proposed to replace the Freonä extraction method. These methods include solid-phase extraction, solvent extraction, and supercritical fluid extraction, all of which use gravimetric determination or infrared analysis of the extracted hydrocarbons. For reasons of cost, sensitivity, precision, or simplicity, none of the replacement methods are feasible for analysis of radioactive samples. In addition, these replacement methods focus on extracting the hydrocarbons into an organic solvent and then trying to measure the concentration of these extracted species in the solvent. This is a difficult measurement to make, and the precision and accuracy of the method therefor suffers.

The method we have developed to replace the current Freonä Extraction Method uses an existing total organic carbon (total carbon) instrument. Briefly:

• The total carbon content (TC1) of the sample is measured using the DC-190 total organic carbon analyzer (or other total carbon instrument).
• The sample is then contacted with a solvent (petroleum ether, for example) to extract the Freonä -soluble hydrocarbons.
• The resultant aqueous phase is sparged with nitrogen to remove any solvent which amy remain in solution.
• The total carbon content of the resultant aqueous phase of the extracted sample (TC2) is measured.
• Oil and Grease is calculated: Oil and Grease concentration = TC1-TC2

The method was validated on standards and customer samples. The data obtained thus far show that the results from the new method and the old Freonä method on standards and customer samples agree within 10%.

Benefits

This method will eliminate use of a hazardous solvent (Freonä -113). The cost for the analysis will be reduced by 50%. The new method uses an existing instrument. The method can be implemented with minimal analyst training (note that the method validation work was performed by a technical analyst with a written work instruction from the task supervisor). The volume of solvent used is less than that used with the Freonä method (1 milliliter as compared to 15 milliliter per sample). This solvent volume-reduction further decreases waste generation and analyst exposure.

We have developed a method to measure total petroleum hydrocarbon content in aqueous sample matrixes using total organic carbon (total carbon) determination. The sensitivity of the method is not as good as the Freonä solvent extraction method (detection limits are 20 ug/ml as compared to 1 ug/ml) but are sufficient for the majority of applications, including the most important use, waste characterization. The resultant data are consistent with results obtained using Freonä extraction followed by infrared absorbance. The method should be of great interest to manufacturers of total organic carbon (TOC) instruments. The method uses solvent extraction and a TOC analyzer to measure total petroleum hydrocarbons (TPH) in aqueous samples, thus creating a new market for manufacturers of these instruments.