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R9 Laboratory SOP 380
Purgeable Aromatics and Hydrocarbons by GC PID/FID
Summary
This SOP is based on procedures contained in EPA SW-846 methods 5030B, 5035, 8015B, and 8021B. This method is used to determine benzene, toluene, ethyl benzene, the xylenes (BTEX) and purgeable petroleum hydrocarbons, including gasoline range organics (GRO's) in a variety of matrices. GRO's correspond to the range of alkanes from C610 . This method may also be used to screen for methyl tert-butyl ether, however, GC/MS is necessary for positive confirmation. This method is applicable to many types of samples, regardless of water content, including ground water, aqueous sludges, soils, and sediments.
The applicable concentration range of this method is approximately 0.5 to 200 μg/L for individual components and 50 to 2,000 μg/L for gasoline in water, and 0.05 to 20 mg/Kg for individual components and 5 to 200 mg/Kg for gasoline in soil. Determination of the structural isomers meta and para xylene is hampered by coelution and they are reported as an isomeric pair.
The identification of specific fuel types may be complicated by environmental processes such as evaporation, biodegradation, or the presence of more than one fuel type.
The quantitation limit (QL) for an individual compound is approximately 0.05 mg/Kg (wet weight) for soil/sediment samples, and 0.5 μg/L for ground water (see Table 2). QL's for gasoline are approximately 5 mg/Kg (wet weight) for soil/sediment samples, and 50 μg/L for ground water. QL's will be proportionately higher for samples that require dilution or reduced sample size to avoid saturation of the detector.
Aqueous Samples: After addition of a surrogate compound, an inert gas is bubbled through a portion of an aqueous sample at ambient temperature. The volatile components are efficiently transferred from the aqueous phase to the vapor phase. The vapor is swept through a sorbent column where the volatile components are adsorbed. After purging is completed, the sorbent column is heated and back flushed with inert gas to desorb the components onto a gas chromatographic column.
Soil Samples: A portion of the bulk soil sample is dispersed in a water-miscible solvent (methanol). After addition of a surrogate compound, an aliquot of the extract is added to organic free water and purged as an aqueous sample.
Detection is achieved by a photo ionization detector (PID) and a flame ionization detector (FID) in series. The PID signal is used to quantitate the aromatic compounds (BTEX), while GRO's are quantitated using the signal from the FID. Tentative identifications are obtained by analyzing standards under the same conditions used for samples and comparing resultant GC retention times. Confirmatory information for single response analytes can be gained by comparing the relative response from the two detectors. Concentrations of the identified components are determined by comparing the response of a compound to the average relative response of that compound in the calibration standards.