PAH Analysis (Alkylated PAHs & PAHs in Air)

Alpha Analytical has considerable experience with the analysis of hydrocarbons in general, and PAHs in particular. Alpha offers a unique combination of the highest quality analytical capability, as well as the required capacity to process the large numbers of samples these types of projects typically generate in accordance with the often challenging timeframes. Due to these capabilities and our vast expertise,  Alpha has supported some of the largest, most demanding and highest profile hydrocarbon investigations in the world. Alpha's PAH analyses range from the typical parent PAH compounds on the EPA Priority Pollutant list, to PAH target compounds lists which also include their respective alkyl-substituted homologs.

Alkylated PAH Analysis

The EPA has developed a two-tiered ecological risk assessment approach for contaminated sediments, and Alpha’s Alkylated PAH analysis can be used to support both  In Tier 1, the potential bioavailability of PAHs is assessed based on the analysis of whole sediments, with the PAH concentrations detected and evaluated against established equilibrium partitioning guidelines. In Tier 2, the potential PAH bioavailability is assessed based on  the analysis of the sediment pore water. The pore water analysis can be conducted on pore water samples obtained in the field, or from pore water generated in the laboratory via centrifugation of sediment. The analysis can also be performed using solid phase microextraction (SPME) analysis (ASTM D7363).

PAH Analysis of Sediment Pore Water (SPME / GCMS-SIM)

Total PAH concentrations in sediment are generally recognized in the literature to be poor predictors of benthic invertebrate toxicity. Pore water analysis provides a better indication, although the direct measurement of its PAH concentrations  has traditionally been extremely challenging.

For this application, Alpha Analytical utilizes ASTM Method D7363-13a: Determination of Parent and Alkyl Polycyclic Aromatics in Sediment Pore Water Using Solid-Phase Micro-Extraction and Gas Chromatography/Mass Spectrometry in Selected Ion Monitoring Mode. This approach provides a viable option since minimal pore water volume is required for a sample aliquot to be obtained under representative conditions from a small amount of sediment.

This method is designed to measure dissolved PAH concentrations in sediment pore water. The pore water is then separated from the bulk sediment by centrifugation and  subjected to a flocculation procedure to assure that only the dissolved fraction is determined. The sample is then analyzed by GC/MS-SIM with a solid phase micro-extraction (SPME) sample introduction technique.

PAH Analysis in Air

Air monitoring for PAHs during MGP site remediation, or  checking for a possible vapor intrusion pathway, have become increasingly  common. For MGP sites where vapor intrusion is a concern, Alpha has developed a target compound list that has the standard EPA Method TO-15 analytes, plus a number of the 'MGP Indicator' compounds:

• Thiophenes: thiophene, methylthiophene, ethyl thiophene, benzothiophene
• Alkyl-substituted benzenes: 1,2,3-trimethylbenzene, 1,2,4,5-tetramethylbenzene
• Aromatics: indane, indene, naphthalene, 1-methylnaphthalene, 2-methylnaphthalene

This list is recommended in the New York State Department of Environmental Conservation (NYSDEC) vapor intrusion guidance for MGP sites and is applicable to sites in other jurisdictions.

Alpha also offers EPA Method TO-13A analysis for PAHs in air monitoring programs and has extensive experience providing this analysis for conducting fence-line monitoring during remediation of MGP sites. As a cost-saving measure, the TO-15 SIM method may be applicable for the analysis of naphthalene if that is the only PAH compound of concern and the reporting limit meets the Perimeter Air monitoring plan (PAMP ) for off site emissions.  A number of comparison studies have been conducted, and the results for naphthalene-- via the TO-15 and TO-13 methods-- are comparable. Method TO-13 offers lower reporting levels than Method TO-15 for naphthalene.