Person: Vierke, Lena
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Lena
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Veröffentlichung Estimation of the Acid Dissociation Constant of Perfluoroalkyl Carboxylic Acids through an Experimental Investigation of their Water-to-Air Transport(2013) Berger, Urs; Cousins, Ian T.; Vierke, LenaThe acid dissociation constants (pKas) of perfluoroalkyl carboxylic acids(PFCAs) have been the subject of discussion in the literature; for example, values from-0.2 to 3.8 have been suggested for perfluorooctanoic acid (PFOA). The dissociatedanionic conjugate bases of PFCAs have negligible air-water partition coefficients (KAWs)and do not volatilize from water. The neutral acids, however, have relatively high KAWsand volatilization from water has been demonstrated. The extent of volatilization ofPFCAs in the environment will depend on the water pH and their pKa. Knowledge ofthe pKas of PFCAs is therefore vital for understanding their environmental transport and fate. We investigated the water-to-airtransfer of PFCAs in a novel experimental setup. We used ~1 ìg L-1 of PFCAs in water (above environmental backgroundconcentrations but below the concentration at which self-association occurs) at different water pH (pH 0.3 to pH 6.9) andsampled the PFCAs volatilized from water during a 2-day experiment. Our results suggest that the pKas of C4-11 PFCAs are <1.6.For PFOA, we derived a pKa of 0.5 from fitting the experimental measurements with a volatilization model. Perfluoroalkanesulfonic acids were not volatilized, suggesting that their pKas are below the investigated pH range (pKa <0.3).
Quelle: http://pubs.acs.org/