Ion-Transfer Voltammetry of Perfluoroalkyl Sulfonates and Carboxylates: Picomolar Detection Limit and High Lipophilicity.

Analytical chemistry

PubMedID: 25313994

Garada MB, Kabagambe B, Kim Y, Amemiya S. Ion-Transfer Voltammetry of Perfluoroalkyl Sulfonates and Carboxylates: Picomolar Detection Limit and High Lipophilicity. Anal Chem. 2014;.
Here we report on ion-transfer voltammetry of perfluoroalkyl sulfonates and carboxylates at the interface between a plasticized polymer membrane and water to enable the ultrasensitive detection of these persistent environmental contaminants with adverse health effects. The ion-transfer cyclic voltammograms of the perfluoroalkyl oxoanions are obtained by using the ~1 ┬Ám-thick poly(vinyl chloride) membrane plasticized with 2-nitrophenyl octyl ether. The cyclic voltammograms are numerically analyzed to determine formal ion-transfer potentials as a measure of ion lipophilicity. The fragmental analysis of the formal potentials reveals that the 10(4) times higher lipophilicity of a perfluoroalkyl sulfonate in comparison to the alkyl sulfonate with the same chain length is due to the inductive effect of perfluorination on lowering the electron density of the adjacent sulfonate group, thereby weakening its hydration. The fragmental analysis also demonstrates that the lipophilicity of perfluoroalkyl and alkyl groups with the same length is nearly identical and varies with the length. Advantageously, the high lipophilicity of perfluorooctane sulfonate allows for its stripping voltammetric detection at 50 pM in the presence of 1 mM aqueous supporting electrolytes, a ~10(7) times higher concentration. Significantly, this detection limit for perfluorooctane sulfonate is unprecedentedly low for electrochemical sensors and is lower than its minimum reporting level in drinking water set by the US Environmental Protection Agency. In comparison, the voltammetric detection of perfluoroalkyl carboxylates is compromised not only by the lower lipophilicity of the carboxylate group but also by its oxidative decarboxylation at the underlying poly(3-octyl thiophene)-modified gold electrode during voltammetric ion-to-electron transduction.