New ionic liquid based stationary phase for 2D gas chromatography with high selectivity to aromatic analytes

Abstract

Ionic liquids are a unique class of substances that combine the properties of organic and inorganic matter. They exhibit the properties of organic polar solvents, and due to the ionic structure of the molecules, they have such properties as high viscosity and low vapour pressure, which are usually characteristic of inorganic compounds. Recently, a number of ionic liquids have been shown to have characteristics that allow them to be used as stationary liquid phases for capillary gas chromatography. In particular, one of the directions in the development of new columns was the creation of a stationary liquid phase based on an ionic liquid, which demonstrates increased resolution in the separation of aromatic and oxygen-containing compounds. This study was performed by conducting research devoted to the creation and study of a new high-polarity capillary column with a stationary liquid phase based on benzyl-acridinium ionic liquid. It was shown that this column has high rates of hydrogen bonding and π-π interactions in terms of the Abraham model. At the same time, acridinium ionic liquid, which is, like similar phases based on ionic liquids, highly polar, exhibits increased selectivity in retaining aromatic compounds (aromatic hydrocarbons, phenols and similar compounds) and most oxygen-containing compounds and bases in comparison with aliphatic hydrocarbons. This allows the separation of complex mixtures, including aromatic hydrocarbons, and oxygen-containing compounds. The high thermal stability of the developed column was also shown, comparable to analogues based on quinolinium ionic liquids, but unlike them, it has a different selectivity due to higher values of π-π interactions and hydrogen bonding according to the donor mechanism. This opens up new prospects for the use of this column and, probably, its analogues, for the separation of complex mixtures containing polar aromatic and oxygen-containing compounds, especially in two-dimensional chromatography. These features were shown based on the example of the separation of a complex mixture by two-dimensional gas chromatography, where this column acted as the second column.