Stripping Analysis of Nanomolar Perchlorate in Drinking Water with a Voltammetric Ion-Selective Electrode Based on Thin-Layer Liquid Membrane

Abstract

A highly sensitive analytical method is required for the assessment of nanomolar perchlorate contamination in drinking water as an emerging environmental problem. We developed the novel approach based on a voltammetric ion-selective electrode to enable the electrochemical detection of "redox-inactive" perchlorate at a nanomolar level without its electrolysis. The perchlorate-selective electrode is based on the submicrometer-thick plasticized poly(vinyl chloride) membrane spin-coated on the poly(3-octylthiophene)-modified gold electrode. The liquid membrane serves as the first thin-layer cell for ion-transfer stripping voltammetry to give low detection limits of 0.2-0.5 nM perchlorate in deionized water, commercial bottled water, and tap water under a rotating electrode configuration. The detection limits are not only much lower than the action limit (approximately 246 nM) set by the U.S. Environmental Protection Agency but also are comparable to the detection limits of the most sensitive analytical methods for detecting perchlorate, that is, ion chromatography coupled with a suppressed conductivity detector (0.55 nM) or electrospray ionization mass spectrometry (0.20-0.25 nM). The mass transfer of perchlorate in the thin-layer liquid membrane and aqueous sample as well as its transfer at the interface between the two phases were studied experimentally and theoretically to achieve the low detection limits. The advantages of ion-transfer stripping voltammetry with a thin-layer liquid membrane against traditional ion-selective potentiometry are demonstrated in terms of a detection limit, a response time, and selectivity.

All solid state chronopotentiometric ion-selective electrodes based on ferrocene functionalized PVC

“…Attractive analytical sensing characteristics were obtained by applying such dynamic electrochemistry approaches and some analytical problems, such as polyion detection in undiluted human blood have been only successfully solved in this manner [14]. Stripping ion voltammetric [15][16][17][18], thin layer coulometric [19], pulsed chronopotentiometric and chronopotentiometric flash titration protocols [14,20,21] have been developed on the basis of such approaches. In a number of cases, operationally unstable potentiometric sensors can be made much more reproducible by controlling ion fluxes by instrumental means [22].…”

“…Recently, conducting polymers such as PEDOT or POT have been also explored as solid contact ion-to-electron transducer for the detection of small hydrophilic ions by ion-transfer voltammetry [29][30][31][32]. Very low limits of detection on the order of 1 nM were obtained for potassium and perchlorate with all solid-state thin layer stripping ion voltammetry in rotating disk electrode mode [15][16][17]. The reports have focused on the lower limit of detection and therefore employed relatively mild applied currents or potentials.…”

Improved Thin-layer Electrolysis Cell for Ion Transfer at the Liquid|Liquid Interface Using a Conducting Polymer-coated Electrode

“…21,22,[42][43][44][45] In previous studies, however, the target ions in the W were not completely extracted into O. The advantage of the present flow cell for stripping analysis is that it can be used to achieve the quantitative transfer of a target ion in a flow system, which contributes to the higher efficiency of the preconcentration and determination processes without the need for a calibration curve.…”

“…The interface between W and O is the analyzing interface where the potential response in the all-solid ISE [27][28][29][30][31][32][33][34][35] or electrolytic extraction of the target ion in an electrolysis cell occurs. 13,14,[21][22][23][24][25] When the current for the transfer of the target ion at the W|O interface flows, the redox reaction of the PEDOT on the solid electrode occurs with the simultaneous doping-undoping of A -into the PEDOT. The oxidized PEDOT becomes the exchanger of A -in O.…”

“…13,14 The conducting polymer-coated electrodes have been applied to all-solid ion-selective electrodes (all-solid ISE) with a thin organic membrane, [15][16][17][18][19][20] or to working electrodes for the stripping analysis of ionic species based on ion transfer at the W|O interface. [21][22][23][24][25] We found that the poly(3,4-ethylenedioxytiophene)-coated electrode (PEDOT-E), one of the conducting polymer-coated electrode, was useful for this purpose. In order to use the PEDOT-E as a reference/ counter electrode in O, we also evaluated the electrode properties of PEDOT-E in O.…”