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Posts Tagged ‘Gas Chromatography/Mass Spectroscopy’

PFOA and Related Compounds

Wednesday, April 30th, 2008

PFOAs may adversely affect the liverIn the early 2000s, the EPA began to investigate the synthetic compound Perfluorooctanoic Acid (PFOA or C8) and its salts, primarily Ammonium Perfluorooctanate (APFO) and other fluoropolymers that may metabolize or degrade into PFOA. These compounds are of interest because of their similarity to another compound known as Perfluorooctyl Sulfonate (PFOS). PFOS was designated a persistent organic pollutant and the primary worldwide manufacturer ceased making it in 2001.

There is still controversy over PFOA’s toxicity, though the compound is persistent (doesn’t biodegrade, hydrolyse or photolyse), bioaccumulates in human and animal tissue (binds to proteins in the blood and liver), and biomagnifies up the food chain. In 2007, the Center for Disease Control and Prevention published the results of two studies on the levels of 11 different polyfluorochemicals in humans. In those studies PFOS, PFOA and Perfluorohexane Sulfonic Acid (PFHS) were found in 98% of those tested, confirming widespread exposure to these compounds. Exposure may occur through consumption of contaminated food or water or through the use of products containing these compounds, but not all sources are known or understood.


GC/MS-Full Scan vs GC/MS-SIM

Friday, February 15th, 2008

GC-MS-Full-Scan-vs-GC-MS-SIMIf you’ve had your laboratory run low-level polyaromatic hydrocarbons (PAHs) or other low level analyses, chances are you have heard of Gas Chromatography/Mass Spectroscopy- Selective Ion Monitoring (GC/MS-SIM). Over the years clients have asked us “What’s the difference between GC/MS-Full Scan and GC/MS-SIM?” To address this question we must start with the basics. (For our example we will be talking about a standard quadrupole mass spectrometer using electron ionization.)

GC/MS is an instrumental analytical technique comprised of a gas chromatograph and a mass spectrometer. In general, the GC is used to separate complex chemical mixtures into individual components. Once separated, the chemicals can be identified and quantified by the mass spectrometer.