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2 2025

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Structural and surface characterization of adsorbents applied in liquid chromatography

Lech-Przywara Regina, Galek Tomasz, Przywara Mateusz, Zapała Lidia, Zapała Wojciech

Advances in Science and Technology. Research Journal

2025

Vol. 19, no. 9

292--309

A detailed analysis of the four commercial stationary phases often applied in liquid chromatography was performed using the following: SEM-EDS techniques and specific surface area and porosity analysis methods (multipoint BET, BJH, DH and DFT). The SEM-EDS results confirmed that the main component of all adsorbents examined is silica (SiO₂), while differences in oxygen content indicate varied approaches to surface modification, ranging from the strongly hydrophilic phase of TSK Gel Amide-80 to the hydrophobic Nucleodur C18 Gravity. Besides, the presence of trace amounts of metals may influence the additional analyte-adsorbent interaction of different nature. A comparison of specific adsorbent surface area data obtained using the multipoint BET method with the manufacturers values revealed significant discrepancies in the cases of TSK Gel Amide 80 and Nucleodur C18 Gravity, which may be the result of differences in pore accessibility and measurement methods. However, the Eurospher II 100-5 HILIC and Purospher STAR NH₂ phases showed good agreement with the manufacturers data. The porous structure of the phase studied shows significant differences: TSK Gel Amide 80 is characterized by mesopores with a uniform distribution, which favor the retention of larger molecules; Eurospher II 100-5 HILIC is microporous and selective for small, polar analytes; Nucleodur C18 Gravity has a structure typical of reversed phase materials; and Purospher STAR NH₂ exhibits the highest porosity, which favors the retention of large molecules, although it can also lead to the retention of undesirable analytes.

Analysis of selected factors influencing the course of the process in liquid chromatography

Lech-Przywara Regina, Zapała Wojciech

Advances in Science and Technology. Research Journal

2025

Vol. 19, no. 6

1--16

This study examines the influence of temperature, eluent modifier type and concentration, and mobile phase flow velocity on the separation efficiency of caffeine (CAF) and phenol (PH) in Hypersil GOLD HILIC and Shodex SILICA 5NH 4D chromatographic columns. A thermodynamic analysis demonstrated that the adsorption processes of these compounds are primarily exothermic and depending on the eluent type. Acetonitrile-water (ACN:H₂O) systems provided superior selectivity between caffeine and phenol compared to methanol-water (MeOH:H₂O) systems, with selectivity improving as temperature increased in ACN:H₂O systems. Variations in eluent modifier concentration significantly impacted retention times, suggesting diverse interaction mechanisms between the analyzed compounds and the stationary phase. Furthermore, studies on column efficiency indicated that faster eluent flow reduced separation efficiency, as evidenced by HETP values. The optimal flow rates were determined to range between 0.2 and 1.25 ml/min, depending on the column tested.