A. V. Parshina

Determination of amino acids, vitamins, and drug substances in aqueous solutions using new potentiometric sensors with Donnan potential as analytical signal

Basic principles of a new potentiometric sensor are considered. Its analytical signal is the Donnan potential at the ion-exchange polymer/studied solution of electrolyte interface. Assessments of potential drops at individual interfaces are presented, same as estimates of diffusion potentials in the electrochemical circuit for measurement of the sensor response. It is shown that the overall contribution of the values of all potentials to EMF of the electrochemical circuit, except for the Donnan potential, at the ion-exchange polymer/studied solution interface are negligibly low as compared to the experimental values of the circuit EMF in the studied systems. Certain regularities of the Donnan potential formation are studied in the systems with the polymers of different structure and solutions containing inorganic ions and organic electrolytes in different ionic forms. The possibility is shown of using a sensor with such an analytical signal as the Donnan potential for assay of amino acids, vitamins, and drug substances in aqueous solutions. The sensor was used as a selective electrode for determination of lysine in aqueous solutions with neutral amino acids in the range of pH 5.0–7.0 and glycine in aqueous alkali solutions in the range of pH 9.00–11.00. The developed sensor is introduced as a cross-sensitive electrode into the array of multisensor systems for multicomponent quantitative analysis of the lysine monohydrochloride, thiamine chloride, novocaine hydrochloride, lidocaine hydrochloride solutions containing potassium and sodium chlorides. The measurement error of electrolytes in aqueous solutions did not exceed 10%.

A new type of potentiometric sensors based on perfluorinated, sulfonated cation-exchange membranes for quantitative analysis of multicomponent aqueous solutions

The organization principles of a new type of sensors were developed whose analytical signal is the Donnan potential at the ion-exchange polymer/test solution interface (PD-sensors) for the determination of organic and inorganic electrolytes in multicomponent aqueous solutions. It was found that the cross sensitivity of PD-sensors based on perfluorinated, sulfonated cation-exchange polymers (PSPs) in the initial inorganic forms depends on the potential-determining reactions of protolysis and ion exchange at the PSP/multicomponent test solution interface. The effects of the hydrophilicity, moisture capacity, and ionic form of the ion-exchange polymer on PD-sensor sensitivity were investigated. It was found that treatment of PSP with ethylene glycol at the glass-transition temperature of the polymer makes it possible to obtain modified PSPs in organic forms, which differ from the initial materials by a larger concentration of dissociated counterions, and thus lead to enhanced PD-sensor response and sensitivity to an appropriate organic component. Potentiometric multisensor systems including cross-sensitive PD-sensors, ion-selective electrodes (ISEs), and algorithms for the processing of multidimensional data for the quantitative determination of lysine, novocaine, lidocaine, thiamine, pyridoxine, nicotinic acid, and alkali and alkaline earth metal cations in multicomponent solutions were developed.

Hybrid perfluorosulfonated membranes with zirconia(IV) nanoparticles as an electrode-active material for potentiometric sensors

The effect that modifying MF-4SC and Nafion membranes with ZrO2 nanoparticles has on the sensitivity of PD-sensors (devices with an analytical signal in the form of a Donnan potential) to bulky organic ions in acid solutions of novocaine and lidocaine hydrochlorides and in alkaline solutions of glycine and cysteine is studied. The hybrid membranes are in situ synthesized by introducing dopant particles into the matrix of a finished membrane. An examination of the diffusion permeability of the membranes reveals that modification with ZrO2 nanoparticles leads to a deceleration of the anion transport rate and an improvement in the cation transport selectivity when compared to the original membranes. Potentiometric measurements show that the sensitivity of PD-sensors based on hybrid membranes to cations in acid solutions of NovHCl and LidHCl significantly increases compared to sensors based on unmodified membranes. An increase in the ZrO2 concentration in the membrane matrix results in a considerable increase in the sensitivity of PD-sensors to anions in alkaline solutions of amino acids, while the sensitivity to cations exhibits a tendency to decrease. The results show that hybrid membranes can be used in potentiometric sensors as electrode-active materials that are highly sensitive to various ions.

Determination of glycine, alanine, and leucine at different solution ph with the aid of donnan potential sensors based on hybrid membranes

The cross sensitive sensors whose analytical signal is the Donnan potential (PD-sensors) were developed for the determination of the amino acids glycine, alanine, and leucine in acidic and alkaline solutions. Hybrid materials based on perfluorinated sulfo cation-exchange membranes Nafion and MF-4SC with incorporated zirconium dioxide and silicon dioxide nanoparticles, including those with modified surfaces containing proton-acceptor groups, were used in the PD-sensors. The sensitivity of the PD-sensors to hydronium ions, which interfere with the determination of amino acids at pH < 7, was considerably decreased due to the use of the membranes obtained by an in situ method that contained silicon dioxide nanoparticles with amine-containing groups. The greatest sensitivity of the PD-sensors to the anions of amino acids at pH > 7 and the smallest sensitivity to the cations K+ were observed in hybrid membranes, which combined an increased rate of anion transfer and a low moisture capacity. The use of the PD-sensors based on hybrid membranes makes it possible to determine the cations, anions, and zwitterions of amino acids over a wide range of pH with a sufficiently high accuracy.

Effect of proton acceptor ability of dopants on the characteristics of PD-sensors based on hybrid perfluorinated membranes in a mixed aqueous solution of lidocaine and novocaine

The results of a study of the effect of proton acceptor ability and size of dopants incorporated into a matrix of perfluorosulfonic membranes, as well as the method of producing and the sensitivity of PD-sensors to novocaine, lidocaine, and hydroxonium cations simultaneously present in solution, are shown. Hydrated zirconia and hydrated silica with a functionalized surface containing hydrocarbon amino-containing groups are used as dopants. Depending on the method by which the hybrid membranes were produced, the dopant nanoparticle was either 3–5 or 6–18 nm. It was possible to increase the sensitivity of PD-sensors to lidocaine cations in the presence of novocaine cations using membranes obtained by casting. Due to the selection of a pair of membranes providing maximum sensitivity for PD-sensors to novocaine and lidocaine ions, the lowest sensitivity to hydroxonium ions, and a lack of correlation between the sensor responses, we achieved a high accuracy in the codetermination of organic ions in the mixed solution.

DP-sensors based on perfluorinated membranes modified with ZrO2 for the determination of novocaine and lidocaine in polyionic solutions

Cross-sensitive DP-sensors based on perfluorinated sulfonated cation-exchange membranes containing hydrated ZrO2 nanoparticles are used for the simultaneous determination of NovH+, LidH+, and K+ ions in aqueous solutions. A significant increase in the sensitivity of DP-sensors to NovH+ and LidH+ in solutions of NovHCl + LidHCl, NovHCl + KCl, and LidHCl + KCl compared to sensitivity to H3O+ ions interfering with the determination of corresponding organic cations is achieved by varying the concentration of ZrO2 in the membranes.

Sensors based on zirconia-modified perfluorinated sulfonic acid membranes sensitive to organic anions in multiionic aqueous solutions

The effect of modification of perfluorinated sulfonic acid membranes with zirconia on their conducting properties and electrode-active properties for potentiometric sensors whose analytical signal is the Donnan potential (DP) has been studied. It has been found that the incorporation of ZrO2 particles into the membrane matrix results in an increase in the ionic conductivity, as compared with unmodified membranes, and the proton diffusion coefficient changes nonmonotonically. Membranes with a gradient dopant distribution along the sample length provide for a partial decrease in the cation-exchange function of DP sensors because of a decrease in the concentration of fixed cation-exchange groups and due to the sorption of coions. This results in an increase in the sensor sensitivity to organic and sulfur-containing anions in multiionic aqueous solutions. Multivariate calibration methods with a nonorthogonal experimental design were used to evaluate the effects of the concentrations and nature of counterions and coions and pH in the test solutions on the characteristics of DP sensors.

A potentiometric multisensor system for determining lysine in aqueous solutions containing potassium and sodium chloride

A potentiometric multisensor system has been developed for the determination of lysine in aqueous solutions containing sodium and potassium chlorides. The sensor array includes a cross-sensitive sensor, the response of which is the Donnan potential at the ion-exchange polymer/test solution interface, a set of ion-selective electrodes, and a silver-silver chloride reference electrode. Multidimensional regression analysis has been employed for the calculation of component concentrations. The relative error of determining lysine, potassium, and sodium did exceed 10% in the tested solutions.

Effect of modification of the MF-4SC membranes in the potassium form with acid salts of heteropolyacids on membrane properties and characteristics of dp sensors based on them

Hybrid materials based on perfluorinated sulfo cation-exchange MF-4SC membrane and nanoparticles of cesium hydrogen phosphotungstate and silicotungstate heteropolyanions were obtained. These membranes with a gradual dopant distribution along the length were used to develop potentiometric sensors for determination of amino-containing organic cations in aqueous solutions at pH < 7. A relationship between the membrane transport characteristics and sensing properties was elucidated.

DP-sensors based on MF-4SC membrane and silica with hydrophobic surface for determination of phenylalanine, valine, and methionine cations

The influence of modification of MF-4SC membranes with silica (or surface-hydrophobized silica) nanoparticles on their ionic conductivity and diffusion permeability as well as the response stability and sensitivity of the membrane-based DP-sensors for cations of amino acids containing hydrophobic fragment has been studied. The membranes modified with surface-hydrophobized silica exhibited the 2–5 times reduced relative error of determination of the hydrophobic amino acids as compared to the initial membranes.