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Posts Tagged ‘selective ion monitoring’

Polycyclic Aromatic Hydrocarbons (PAH) in Shellfish

Friday, May 28th, 2010

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.

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Selective Ion Monitoring (SIM) for Low Level Applications in Vapor Samples

Friday, October 3rd, 2003

Selective-Ion-Monitoring-for-Low-Level-Applications-in-Vapor-SamplesGas chromatography/mass spectrometry (GC/MS) is the method of choice for the identification of volatile organic compounds (VOCs) in vapor samples (e.g. EPA methods TO-14A and TO-15). As various state and federal agencies more frequently require facilities to address risk-based concentrations, such as the low level preliminary remediation goals (PRGs), they find that the standard method is not able to reach the ultra-low levels needed. To address these requirements, CAS’ Simi Valley, California lab has developed a method using selective ion monitoring (SIM) to measure the compounds. SIM is a sensitivity enhancement technique, where the mass spectrometer is programmed to scan for only those ions that are pertinent to the compounds of interest (2-3 mass ions scanned per compound) while ignoring non-essential ions. The mass spectrometer becomes a highly sensitive compound-specific detector.

The driving force for the lower limits has been health risk assessment activities in the indoor and ambient air arena. The exposure criteria for many compounds are being re-evaluated constantly. A recent symposium sponsored by the Groundwater Resources Association (GRA) on subsurface vapor intrusion to indoor air has recommended that the SIM analytical technique be used. For example, trichloroethene (TCE) will have a reporting limit of 1.0 mg/m3 (0.19 ppbv) using the standard full scan method. In contrast, the reporting limit of 0.05 mg/m3 (0.0093 ppbv) for TCE will be achieved with the SIM technique. This meets or exceeds most risk-based concentration criteria. Lower limits are occasionally requested and are reviewed on a case-by-case basis.

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