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National Water Quality Laboratory

Friday December 15, 2017

USGS Water-Resources Investigations Report 03-4318

Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory — Determination of Polycyclic Aromatic Hydrocarbon Compounds in Sediment by Gas Chromatography/Mass Spectrometry

Mary C. Olson, Jana L. Iverson, Edward T. Furlong, and Michael P. Schroeder

2004

A method for the determination of 28 polycyclic aromatic hydrocarbons (PAHs) and 25 alkylated PAH homolog groups in sediment samples is described. The compounds are extracted from sediment by solvent extraction, followed by partial isolation using high-performance gel permeation chromatography. The compounds are identified and quantitated using capillary-column gas chromatography/mass spectrometry. The report presents performance data for full-scan ion monitoring. Method detection limits in laboratory reagent matrix samples range from 1.3 to 5.1 µg/kg for the 28 PAHs. The 25 groups of alkylated PAHs are homologs of five groups of isomeric parent PAHs. Because of the lack of authentic standards, these homologs are reported semiquantitatively using a response factor from a parent PAH or a specific alkylated PAH. Precision data for the alkylated PAH homologs are presented using two different standard reference materials produced by the National Institute of Standards and Technology: SRM 1941b and SRM 1944. The percent relative standard deviations for identified alkylated PAR homolog groups ranged from 1.55 to 6.98 for SRM 1941b and from 6.11 to 12.0 for SRM 1944. Homolog group concentrations reported under this method include the concentrations of individually identified compounds that are members of the group.

Organochlorine (OC) pesticidesóincluding toxaphene, polychiorinated biphenyls (PCBs), and organophosphate (OP) pesticidesócan be isolated simultaneously using this method.

In brief, sediment samples are centrifuged to remove excess water and extracted overnight with dichloromethane (95 percent) and methanol (5 percent). The extract is concentrated and then filtered through a 0.2-micrometer polytetrafluoroethylene syringe filter. The PAH fraction is isolated by quantitatively injecting an aliquot of sample onto two polystyrene-divinylbenzene gel-permeation chromatographic columns connected in series. The compounds are eluted with dichloromethane, a PAH fraction is collected, and a portion of the coextracted interferences, including elemental sulfur, is separated and discarded. The extract is solvent exchanged, the volume is reduced, and internal standard is added. Sample analysis is completed using a gas chromatograph/mass spectrometer and full-scan acquisition.

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