In the present study, electromembrane extraction (EME) and pulsed electromembrane extraction (PEME) coupled with high-performance liquid chromatography (HPLC) were compared for the extraction of two acidic drugs including diclofenac (DIC) and mefenamic acid (MEF).

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In this work, the conventional reactions were used to functionalize the silica surface with amide and hydrocarbon chain groups affording two different mixed‐mode stationary phases (Sil‐amide‐C11 and Sil‐C12‐amide). The prepared stationary phases were analyzed by elemental analysis and thermogravimetric analysis. The retention of benzene, phenol, pyridine, and aniline was investigated and compared with synthesized and commercial columns, and this led to prove the existence of different interactions on the synthesized stationary phases. The mixed‐mode stationary phases showed multiple interactions, and different chromatography modes were found under distinct chromatographic conditions. According to the type of amide group (either free or within the hydrocarbon chain), different interactions can be made on the columns. The alkylbenzenes and polycyclic aromatic hydrocarbons, as nonpolar hydrocarbons, were chromatographed under reversed‐phase liquid chromatography modes, in which amide groups on the silica could efficiently separate polar analytes under hydrophilic interaction liquid chromatography mode in both prepared stationary phases. The performance of the columns was compared by the separation of the carboxylic acid group and biological samples. The bonding method and the type of amide group showed different interactions leading to different separation and performance.

A modified C18 column (Silpr‐2MI‐C18) was prepared using 2‐methylindole and C18 reagent. The extent of C18 hydrocarbon chain, conjugative rings and anion exchange site provided multiple retention mechanisms, including reversed‐phase liquid chromatography (RPLC), π–π interaction, hydrophilic interaction liquid chromatography (HILIC) and anion exchange chromatography (AEC). The separation of protected amino acids was investigated on the commercial C18 and Silpr‐2MI‐C18 columns, while the chromatographic conditions, including methanol content and pH of the mobile phase, were studied. The separation arrangement of the hydrophilic amino acids was different on the Silpr‐2MI‐C18 column compared to the commercial C18 column under RPLC mode. Furthermore, these amino acids were separated on the Silpr‐2MI‐C18 column under HILIC mode. The modified C18 column was employed to separate amino acids, alkylbenzenes and polycyclic aromatic hydrocarbons under RPLC mode and inorganic anion under AEC mode. The results confirm that this new stationary phase of RPLC/HILIC/AEC has multiple interactions with different analytes. Effective retention of biological samples was found on the Silpr‐2MI‐C18 column by comparing the results obtained from the commercial C18 column.