Lancaster Laboratories Environmental

Environmental NEWS - Spring 2009

The importance of GC/MS analysis of Alkylated Polycyclic Aromatic Hydrocarbons

Polycyclic Aromatic Hydrocarbons (PAHs) is a class of compounds that has appeared on priority pollutant lists since the early days of site remediation because they can pose a risk to human health and are very slow to degrade. More recently, there has also been interest in detecting alkylated PAHs, which contain an alkyl chain bonded to the carbon in an aromatic ring. For each parent PAH, there is a homologous series of alkylated PAHs with an increasing number of attached carbon molecules. PAHs and their homologs can originate from petrogenic sources, meaning they occur naturally in petroleum compounds, or pyrogenic sources, which are created upon combustion. In areas impacted by oil spills, these compounds are of concern for aquatic life, especially sediment dwelling biota. Both USEPA and the National Oceanic and Atmospheric Administration (NOAA) have conducted studies on the concentrations and effects of these compounds in marine sediments.

In addition to the basic health concerns about the bioavailability of these compounds to organisms, data on these compounds can have a forensic application. Alkylated PAHs are more abundant than their parent PAH compounds in oil, so information about the relative concentrations of these two species can provide a clue to their source. For example, contamination from a specific spill can be differentiated from background pyrogenic sources.

Analysis for PAHs can be accomplished using USEPA method 8270, which uses a GC/MS to identify and quantitate the target compounds. A reference standard is used for each PAH compound to be reported. The applicability of method 8270 to homologs of PAHs is limited by the lack of reference standards. However, Lancaster Laboratories has been successful in adapting this method to provide semi-quantitative data for the alkylated PAHs. The GC/MS provides a mass spectroscopic “fingerprint” of the parent PAH that can also be used to identify PAH homologs, and the instrument response factor from the parent PAH can then be used to estimate the concentration of PAH homologs. This method can be applied to extracts from aquatic sediment, tissue, water and soil samples.

For more information about alklyated PAH analysis, call Environmental Client Services at 717-656-2300.