Zeta potential is a surface characteristic formed on the solid surface and liquid interface. It is an interesting way to describe the surface properties of materials; thus, a series of four homemade polar embedded stationary phases that contain phosphate groups incorporated into hydrophobic ligands were investigated according to surface zeta potential. Measurements were carried out using Zetasizer Nano ZS for the stationary phases suspensions prepared in various solvent and solvent binary mixtures. The negative zeta potential values were obtained for most cases due to negatively charged residual silanols and phosphate groups. However, in some solvents: tetrahydrofuran, isopropanol, and toluene zeta potential are positive. Additionally, it was observed that the zeta potential seems to be independent of the type of silica gel used for the stationary phase synthesis.

Industrial research, including pharmaceutical research, is increasingly using liquid chromatography techniques. This involves the production of large quantities of hazardous and toxic organic waste. Therefore, it is essential at this point to focus interest on solutions proposed by so-called “green chemistry”. One such solution is the search for new methods or the use of new materials that will reduce waste. One of the most promising ideas is to perform chromatographic separation using pure water, without organic solvents, as a mobile phase. Such an approach requires novel stationary phases or specific chromatographic conditions, such as an elevated separation temperature. The following review paper aims to gather information on stationary phases used for separation under purely aqueous conditions at various temperatures.

Modern analytical chemistry techniques meet the need for greater attention to ecological and economic aspects. It is becoming necessary to seek solutions to reduce harmful waste production, especially in large quantities. High-performance liquid chromatography is a technique widely used in many industries, including mainly pharmaceuticals, and requires an approach to reduce the significant amount of organic solvent waste. One of the green chemistry solutions is using environmentally benign substitutes, such as pure water, supercritical dioxide, and ethanol. Our work focuses on the preparation and application of new stationary phases with embedded hydrophilic groups for separations using pure water in liquid chromatography. Polar-embedded stationary phases are obtained by attaching a phosphodiester group and 4 different hydrophobic molecules. The studies consisted of hydrophobicity measurements, concentration dependence of retention of the organic additive to the mobile phase, and chromatographic separations of polar and non-polar substance mixtures in RP-LC and HILIC systems. Three mixtures were studied: purine alkaloids, benzene, and polycyclic aromatic hydrocarbons and nucleosides. The stationary phases interact differently with the analytes depending on the attached hydrophobic group. It is possible to use pure water to separate each mixture under study. It is also significant that it has been possible to separate a mixture of completely non-polar compounds using pure water for the first time. The research being carried out is crucial in synthesizing new polar-embedded stationary phases, providing work versatility and high environmental performance.

Non-destructive chromatographic methods were used to determine the hold-up volumes of four self-packed columns containing embedded phosphate groups. The stationary phases are named Diol-P-C10, Diol-P-C18, Diol-P-Benzyl and Diol-P-Chol. The hydrophobicity of organic ligands bound to the phosphate group increases in the benzyl< decyl < octadecyl <cholesterol direction. Using a stochastic model of inverse size exclusion chromatography with a wide pore size distribution, the hold-up volume, interstitial volume and pore volume of the columns were determined. Using the method of minor disturbances, the thermodynamic hold-up volume of the columns was calculated and the excess isotherm was determined for acetonitrile-water mobile phases. The results show that these stationary phases can be used effectively in RPLC and HILIC. When using hold-up volume markers, it was found that the composition of the mobile phase has to be taken into account. In the case of protic solvents, inorganic salts are excluded from the pores and their elution volume is not the total hold-up volume. Rather, in the case of aprotic mobile phase, retention occurs due to the adsorbed water layer.