Abstract
Potentiometric plasticizer-free solid-contact Pb2+-selective electrodes based on copolymer methyl methacrylate-n-butyl acrylate (MMA-BA) as membrane matrix and multi-walled carbon nanotubes (MWCNTs) as intermediate ion-to-electron transducing layer have been developed. The disposable electrodes were prepared by drop-casting the copolymer membrane onto a layer of MWCNTs, which deposited on golden disk electrodes. The obtained electrodes exhibited a sub-ppb level detection limit of 10−10 mol·L−1. The proposed electrodes demonstrated a Nernstian slope of 29.1 ± 0.5 mV/decade in the linear range from 2.0 × 10−10 to 1.5 × 10−3 mol·L−1. No interference from gases (O2 and CO2) or water films was observed. The electrochemical impedance spectroscopy of the fabricated electrodes was compared to that of plasticizer-free Pb2+-selective electrodes without MWCNTs as intermediated layers. The plasticizer-free MWCNTs-based Pb2+-selective electrodes can provide a promising platform for Pb(II) detection in environmental and clinical application.
Highlights
Potentiometry with ion-selective electrodes (ISEs) is attractive for practical applications in many fields, for example, medical diagnosis and environmental monitoring [1,2,3]
The detection limit for most traditional liquid-contact electrodes based on plasticized poly(vinyl chloride) membrane was limited to micromolar range mainly due to the primary ion leaching from the inner filling solutions [4,5]
Since a low Tg of the copolymer is critical to the functional polymeric ion-sensing membranes, the Fox equation was utilized to calculate the approximate Tg of the copolymer based on the weight fractions and Tg of the respective monomers (Tg = 378 K, Tg = 218 K) [40]
Summary
Potentiometry with ion-selective electrodes (ISEs) is attractive for practical applications in many fields, for example, medical diagnosis and environmental monitoring [1,2,3]. A large number of Pb2+ -selective electrodes reported are based on plasticized poly(vinyl chloride) membranes, reducing the diffusion coefficient of the sensing membrane can suppress the transmembrane ion flux, which is beneficial to the lower detection limit. Various factors should be considered on improving the lower detection limit of the SC-ISEs, such as the ion-sensing membrane (reduced diffusion coefficients), ion-to-electron conducting layer [29,30], and conditioning procedure [31,32]. The proposed potentiometric sensor is designed based on the following principles: (a) Reducing the diffusion coefficient by the employment of plasticizer-free copolymer methacrylate-n-butyl acrylate (MMA-BA), (b) the utilization of hydrophobic MWCNTs as a transducing layer deposited by solution-casting, (c) the dispersion of MWCNTs in plasticizer instead of surfactants to reduce the surfactants’ interference. The results suggest that the proposed sensor is promising for environmental and clinical Pb(II) determination
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