Subnanomolar limits of detection (LODs) are obtained for stripping voltammetry based on ion transfer at the interface between the aqueous sample and the thin polymeric membrane supported with a solid electrode. It has been predicted theoretically that a lower LOD can be obtained for a more lipophilic analyte ion, which can be preconcentrated at a higher equilibrium concentration in the solid-supported thin polymeric membrane to enhance a stripping current response. This study is the first to experimentally confirm the general theoretical prediction for both cationic and anionic analytes. Proof-of-concept experiments demonstrate that a subnanomolar LOD of (8 ± 4) × 10-11 M tetrapropylammonium is significantly lower than a LOD of less lipophilic tetraethylammonium. Importantly, stripping voltammetry of the cationic analytes is enabled by newly introducing an oxidatively doped poly(3,4-ethylenedioxythiophene) film as the intermediate layer between a plasticized poly(vinyl chloride) membrane and a Au electrode. On the other hand, an undoped poly(3-octylthiophene) film is used as an intermediate layer for voltammetric detection of a lipophilic inorganic anion, hexafluoroarsenate, an arsenical biocide found recently in wastewater. A LOD of (9 ± 2) × 10-11 M hexafluoroarsenate thus obtained by ion-transfer stripping voltammetry is comparable to a LOD of 80 pM by inductively coupled plasma mass spectrometry with anion-exchange chromatography. Great sensitivity for a lipophilic ion is potentially useful for environmental analysis because high lipophilicity of an ion is relevant to its bioaccumulation and toxicity.
All Science Journal Classification (ASJC) codes
- Analytical Chemistry