This column traditionally has focused on practical aspects of how mass spectrometers function and has explored related topics
like spectral interpretation. Yet, as the instruments and our practice with them evolve, we occasionally find important topics
in which mass spectrometry (MS) plays a central role. PFCs are such a topic, and it warrants closer scrutiny.
As part of the Office of Research and Development National Exposure Research Laboratory (ORD/NERL), the Perfluorinated Compounds
group develops analytical methods that reduce the uncertainty associated with human exposure to pollutants. Along with the
health effects laboratory, which investigates traditional toxicology, the group investigates such issues as how people are
exposed to pollutants and seeks to establish how to reduce that exposure. At CoSMoS in July 2007, Mark Strynar, a physical
scientist in the Methods Development and Application Branch (MDAB) of the Human Exposure and Atmospheric Sciences Division
(HEASD), discussed his group's efforts.
Figure 1
As a class, PFCs sprang to the forefront of issues at the EPA about eight years ago. These fully fluorinated compounds demonstrate
qualities that make them useful for industrial and consumer product applications. At the molecular level, they possess a particularly
stable carbon–fluorine bond, a bond comparable in its strength to carbon–carbon, carbon–nitrogen, carbon–oxygen, or carbon–chlorine
bonds, all of which are very strong (Figure 1). PFCs resist atmospheric and biological degradation, which largely accounts
for their commercial desirability. Nevertheless, they have attracted the interest of the EPA because they could prove to be
bioaccumulative and toxic. In particular, the Organization for Economic and Cooperative Development (OECD) hazard assessment
of PFOS reported carcinogenicity in lab animals and the Science Advisory Board to the EPA recently classified PFOA as "a likely
human carcinogen."
Table I: Representative perfluorinated compounds
PFCs (Table I) are manufactured in various ways. The electrochemical fluorination process, no longer in use in the US for
PFOS based chemistry, was one way. It employed a straight chain alkane in the presence of hydrogen fluoride (HF) and electricity.
This fairly low-yield process led to not only even and odd numbered chains. but also to branched isomers, a fairly complex
mixture of components. Until 2000, 3M (St. Paul, Minnesota) used this process to make the chemical backbone for Scotchgard,
a coating for materials such as paper, upholstery, and carpet that makes such items impervious to damage from liquid spills.
Another PFC manufacturing method uses a telomerization process, where a telogen and a taxogen react to produce the telomer
iodide. A benefit of this process is that it typically leads only to even-numbered chains.
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