Stripping Voltammetry of Nanomolar Potassium and Ammonium Ions Using a Valinomycin-Doped Double-Polymer Electrode

Abstract

Here, we report on the first application of an ionophore-doped double-polymer electrode for ion-transfer stripping voltammetry (ITSV) to explore the nanomolar limit of detection (LOD) and multiple-ion detectability. We developed a theoretical model for ITSV at a thin ionophore-doped membrane on the solid supporting electrode to demonstrate that its LOD is controlled by the equilibrium preconcentration of an aqueous analyte ion as an ionophore complex into the thin polymer membrane and is lowered by the formation of a more stable ion-ionophore complex. The theoretical predictions were confirmed using valinomycin as a K(+)-selective ionophore, which forms a ∼60 times more stable complex with K(+) than with NH(4)(+), as confirmed by cyclic voltammetry. A LOD of 0.6 nM K(+) was achieved by ITSV using commercial ultrapure water as a K(+)-free media, where NH(4)(+) contamination at a higher concentration was also detected by ITSV. The dependence of the ITSV response on the preconcentration time was monitored under the rotating-electrode configuration and analyzed theoretically to directly determine ∼100 nM NH(4)(+) and ∼5 nM K(+) contaminations in commercial ultrapure water and laboratory-purified water, respectively, without the background ITSV measurement of an analyte-free blank solution.

Voltammetric Characterization of Ion–Ionophore Complexation Using Thin Polymeric Membranes: Asymmetric Thin-Layer Responses

“…Noticeably, the quantitative analysis of the backgroundsubtracted voltammogram indicates the uniform broadening of the voltammogram due to the polarization of the PVC/ PEDOT-C 10 /Au junction. 29−32 A good fit between experimental and theoretical voltammograms in Figure 3B was obtained by correcting this broadening effect using the following empirical equation as experimentally validated in our previous work: 30,31 …”

“…The gold electrode was electrochemically modified with an oxidatively doped film of PEDOT-C 10 by two potential cycles and then spin-coated with an oNPOEplasticized PVC membrane by using a spin-coating device (model SCS-G3-8, Cookson Electronics, Providence, RI). 30 A thin oNPOE-plasticized PVC membrane was obtained from a 2 μL THF solution of membrane components (ionophore, 4.0 mg of PVC, 16.0 mg of oNPOE, and 2.2 mg of (TDDA)-(TFAB) in 1 mL of THF), where a low PVC content ensures a negligible ohmic potential drop across the membrane. 35 The amount of the ionophore in the THF solution was selected to yield an ionophore concentration of 5.0 mM, unless otherwise mentioned, in the PVC membrane with a density of 1 g/mL.…”

Ion transfer stripping voltammetry for the detection of nanomolar levels of fluoxetine, citalopram, and sertraline in tap and river water samples

“…Electrochemical methods have several advantages over other analytical methods due to their simplicity and low cost. Electrochemical sensors have short response time, excellent selectivity and sensitivity, and have the capability to measure directly analytes in complex matrices [8][9][10][11][12][13][14][15]. The toxicity of selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, sertraline, and citalopram were initially reported a decade ago [16][17][18][19].…”

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.…”