Voltammetric studies of hexachromic anion transfer reactions across micro-water/polyvinylchloride-2-nitrophenyloctylether gel interfaces for sensing applications

The transfer reactions of various anionic hexavalent chromium species across a polarized water/polyvinylchloride-2-nitrophenyloctylether (PVC-NPOE) interface featuring a 66 microhole array are described for the development of selective and sensitive Cr(VI) sensors. The transfer of hydrophilic hexachromic anions across a liquid/liquid interface typically involves setting the potential window in a negative region. Therefore, a highly hydrophobic tetraoctylammonium tetrakis(pentafluorophenyl)borate (TOATB) salt was synthesized and incorporated into the PVC-NPOE gel phase as an organic supporting electrolyte to provide a larger potential window at the negative end. The transfer of different hexachromic anions across the microhole array interface between the aqueous and PVC-NPOE gel phase containing TOATB was first characterized by voltammetric measurements. Since Cr(VI) ion species can hold different anionic forms such as Cr ₂O ₇ ^2-, HCrO ₄ ^-, and CrO ₄ ^2- depending upon the pH and the Cr(VI) concentration, the effect of these two parameters on the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) responses was also investigated. In order to utilize the ion transfer reaction across the microhole array interface for the selective and sensitive detection of Cr(VI) ions, the assisted transfer of HCrO ₄ ^- anion by an Aliquat 336 ionophore incorporated into the PVC-NPOE gel phase was investigated using CV and differential pulse stripping voltammetry (DPSV). An excellent detection limit of 0.5 μM (26 ppb) with a wide linear dynamic range extending from 0.5 μM to 10 μM was achieved.