Hybrid Materials Based on MF-4SC Membranes and Carbon Nanotubes: Transport Properties and Characteristics of DP-sensors in Hydrophobic Amino Acid Solutions

Abstract

Perfluorinated sulfonated cation-exchange membranes MF-4SC containing 0.5-3.0% of carbon nanotubes (CNTs) have been synthesized. A correlation between the water uptake and transport properties of the membranes in the K +-form and the sensitivity of DP-sensors (with the analytical signal in the form of a Donnan potential) to the analyte and interfering ions in solutions of hydrophobic amino acids (alanine, valine, and phenylalanine) has been found. Hybrid membrane samples that provide the highest sensitivity of DP-sensors to amino acid cations and zwitterions and the lowest sensitivity to hydroxonium ions at pH < 7 in a concentration range of 1.0 × 10-4-1.0 × 10-1 M have been selected. Membrane modification has led to a decrease in the relative error and the relative standard deviation in the determination of amino acid ions by a factor of 3 and 1.5, respectively.

Ionic Mobility in Ion-Exchange Membranes

“…They are used for gas separation [ 1 , 2 , 3 ], water purification [ 4 , 5 , 6 , 7 ], purification of pharmaceutical drugs and biological fluids [ 8 ]. The number of applications of membrane technologies in the chemical and petrochemical industries [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ], modern energy [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ], and sensorics [ 24 , 25 , 26 , 27 ] has significantly increased. Ion-exchange membranes are one of the most widespread and demanded membrane types [ 5 , 28 ].…”

Potentiometric Sensors Based on MF-4SC Membranes and Carbon Nanotubes for the Determination of Nicotinic Acid in Aqueous Solutions and Pharmaceuticals

“…According to [20], the modification of MF-4SC membranes with a higher amount of CNTs (up to 3.0 wt. %) leads to a significant decrease in the water uptake and the rate of transfer of cations and anions across the membrane.…”

“…Many authors deposit CNTs on graphite or glassy carbon electrodes in composites with electrically conductive and/or ion-exchange polymers [17][18][19]. The authors of [20] proposed the use of perfluorosulfonic acid membranes of Nafion type containing CNTs as the material for sensors with an internal reference solution and the analytical signal in the form of a Donnan potential (DP). According to published data, during the modification of Nafion membranes, CNTs are mostly localized in the hydrophobic perfluorinated matrix; this factor leads to an increase in the mechanical strength of the materials [21,22].…”

“…The exposure of CNTs to nitric acid during pretreatment leads to the formation of carboxyl groups on their surface and thereby contributes to the partial localization of the CNTs in the hydrophilic pores of the membranes, which changes their sorption and transport properties [23]. It was shown that the incorporation of CNTs pretreated with concentrated nitric acid into perfluorinated membranes provides a high accuracy of determination of hydrophobic amino acid cations at a pH of <7 in a concentration range of 10 -4 to 10 -1 M [20]. In this study, the possibility of using hybrid materials based on perfluorosulfonic acid membranes MF-4SC and CNTs for the potentiometric determination of nicotinic acid in aqueous solutions and pharmaceuticals was explored.…”