Controlling retention, selectivity and magnitude of EOF by segmented monolithic columns consisting of octadecyl and naphthyl monolithic segments – applications to RP‐CEC of both neutral and charged solutes

Abstract

Monolithic capillaries made of two adjoining segments each filled with a different monolith were introduced for the control and manipulation of the electroosmotic flow (EOF), retention and selectivity in reversed phase-capillary electrochromatography (RP-CEC). These columns were called segmented monolithic columns (SMCs) where one segment was filled with a naphthyl methacrylate monolith (NMM) to provide hydrophobic and π-interactions, while the other segment was filled with an octadecyl acrylate monolith (ODM) to provide solely hydrophobic interaction. The ODM segment not only provided hydrophobic interactions but also functioned as the EOF accelerator segment. The average EOF of the SMC increased linearly with increasing the fractional length of the ODM segment. The neutral SMC provided a convenient way for tuning EOF, selectivity and retention in the absence of annoying electrostatic interactions and irreversible solute adsorption. The SMCs allowed the separation of a wide range of neutral solutes including polycyclic aromatic hydrocarbons (PAHs) that are difficult to separate using conventional alkyl-bonded stationary phases. In all cases, the k' of a given solute was a linear function of the fractional length of the ODM or NMM segment in the SMCs, thus facilitating the tailoring of a given SMC to solve a given separation problem. At some ODM fractional length, the fabricated SMC allowed the separation of charged solutes such as peptides and proteins that could not otherwise be achieved on a monolithic column made from NMM as an isotropic stationary phase due to the lower EOF exhibited by this monolith.

Capillary electrochromatography of proteins and peptides (2006–2015)

“…3.1.1.1 Reversed-phase separation Karenga and El Rassi introduced a series of monoliths for reversed-phase CEC [54][55][56][57][58].…”

Recent advances in nonpolar and polar organic monoliths for HPLC and CEC

“…Furthermore, Karenga and El Rassi also developed a series of segmented monolithic columns (SMC) [13] and demonstrated their applications in CEC. These SMCs were made up of two adjoining segments each filled with a different monolith in the aim of controlling and manipulating the EOF, retention and selectivity in RP-CEC.…”

Monolithic stationary phases with a longitudinal gradient of porosity

“… used sequential filling of capillary with polymerization mixtures varying in hydrophobicity. By using the same approach, Karenga and El Rassi prepared monolithic column combining hydrophobic and π‐interactions . Currivan et al.…”