Polymer-based anion exchanger with adsorbed graphene oxide layer: analytical and thermodynamic characterization

Abstract

The aim of this work was to obtain a novel stationary phase for ion chromatography with an adsorbed graphene oxide and to study its properties. For this purpose, a copolymer of styrene and divinylbenzene was modified by adsorbing a layer of graphene oxide onto its surface followed by its reduction. A copolymer of a primary amine with a diepoxide obtained in situ and electrostatically fixed on the surface of the modified substrate served as a basement layer. The positively charged ion-exchange centers were obtained by alkylating the tertiary amino groups of the basement layer with diepoxide and further aminating with a tertiary amine.

The retention mechanism of some analytes was studied by constructing bilogarithmic dependences of ion retention factors on the eluent concentration. It was shown that the approach used in the work to the synthesis of anion exchangers leads to the implementation of a predominantly ion-exchange mechanism of retention of not only polarizable (Br^-, NO₃^‑, ClO₃^-), but also strongly polarizable anions (I^-, SCN^-, ClO₄^-). For the studied analytes, the apparent ion-exchange constants or corrected equilibrium coefficients were calculated, and the closeness of the retention times calculated with their help to the experimental data was shown.

The obtained stationary phase showed a significant decrease in selectivity in NO₃^-/Cl^- and NO₃^-/Br^- pairs and an increase in the efficiency of the bromide and nitrate peaks (N(NO₃^-) = 42000 TP/m) relative to the chemically modified resins described in the literature with a similar structure of the ion-exchange layer. This indicates the prospects of preliminary adsorption of graphene oxide followed by electrostatic attachment of an ion-exchange layer on its surface in order to increase the hydrophilicity of the stationary phase and the shielding degree of the polymer substrate. The possibility of rapid separation of 7 standard inorganic anions (F^-, Cl^-, NO₂^-, Br^-, NO₃^-, SO₄^2-, PO₄^3-) in 7 min in the gradient elution mode using a hydroxide eluent was demonstrated. The obtained resin was successfully used for the analysis of drinking water and soil: high intra- and inter-day reproducibility was demonstrated and the accuracy was confirmed by the spike recovery experiment.