Polycyclic Aromatic Hydrocarbons (PAH) in Shellfish
Columbia Analytical Services, Inc. has extensive experience testing for low levels of Polycyclic Aromatic Hydrocarbons (PAH) in shellfish. Sensitive and selective techniques were developed over ten years ago and have been refined and improved on a continuing basis. In addition to the analysis for the common parent compounds, levels of the associated alkylated homologs can also be determined.
This analysis is typically performed using Gas Chromatography/Mass Spectrometry (GC/MS) operated in the Selective Ion Monitoring (SIM) mode. Key to the analytical procedure is proper sample preparation, which begins with shucking, compositing (as appropriate to the project plan), and homogenization via mechanical mixing. The preliminary preparation must be performed under clean laboratory conditions to prevent common PAH contamination. Decontamination of sample preparation equipment is performed and monitored closely to assure clean conditions. The sample homogenate is a homogenous slurry when prepared correctly. The homogenization techniques performed by Columbia Analytical have been inspected and approved by various organizations (e.g. US EPA, other federal government and state regulatory agencies, private industries, consultants, etc.) The data results for these projects were subjected to thorough government, public and private scrutiny.
After homogenization, samples are solvent extracted and subjected to cleanup procedures via silica gel to remove interfering matrix components. Again, careful control of laboratory conditions and equipment is critical to assure valid results. Cleanup is essential to remove interfering background components that mask target compounds. Insufficient cleanup may lead to potential false positive results and/or elevated detection limits that can render the data useless.
The SIM mode is used to further improve selectivity, but also increases sensitivity. Typical reporting limits for shellfish range from 0.5 nanograms per gram (ng/g) or parts per billion (ppb) to 5 ng/g (ppb), depending on the data quality objectives outlined in the project plan. The associated method detection limits (MDLs) are on the order of five to ten times lower than the reporting limit. When performing low range determinations, the reporting limit of 0.5 ng/g (ppb) is derived from the lowest standard in the calibration curve.
The inclusion of alkylated homologs is critical to the forensic aspect of the determinations as this provides the connection to the source of the PAHs. The ratios of the various PAHs with substituted low molecular weight alkyl groups provide unique chemical characteristics that relate to the source of the contamination.
The testing conducted by Columbia Analytical conforms to all requirements necessary for production of legally defensible data packages. Every operation related to the processing of samples from receipt at the laboratory to final review of the report is recorded in the package, so the entire process can be re-created at a later time. Any anomalies associated with the analysis of the samples are discussed in narrative form. A standard data deliverable includes full summaries of all quality assurance and quality control (QA/QC) operations associated with the analysis. Also of significance is the use of self-validating reporting software, which means the reporting systems perform QA/QC checks that automatically document any anomaly in the data. This assures that the issue can be addressed prior to releasing final reports.
For more information or oil spill support please contact the Columbia Analytical Team Lead, Greg Salata, at 360-501-3376.
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Tags: alkylated homologs, Aromatic, cleanup, contamination, Decontamination, EPA, Gas chromatography, Gas Chromatography/Mass Spectrometry, GC/MS, GC/MS SIM, homogenous, Hydrocarbons, mass spectrometry, MDL, Method Detection Limits, nanograms, PAH, PAH in Shellfish, PAHs, Polycyclic, ppb, selective ion monitoring, selectivity, sensitivity, Shellfish, silica gel, SIM, SIM mode, USEPA