Performance and selectivity of cationic nanoparticle pseudo‐stationary phases in electrokinetic chromatography

Abstract

Electrokinetic chromatography (EKC) is a powerful analytical technique that uses an ionic pseudo-stationary phase (PSP) to separate neutral compounds. Although anionic surfactants are the most common choice for PSP, cationic latex nanoparticles are an attractive alternative. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize several types of diblock copolymers that self-assemble into latex nanoparticles, which were characterized by a variety of techniques including diffusion NMR. The performance of each nanoparticle as a PSP was studied by using a homologous series of ketones and linear solvation energy relationships (LSER) analysis. A cationic homopolymer coating was found to be necessary to prevent band broadening caused by analyte interactions with nanoparticles adsorbed to the capillary surface. No significant difference in methylene selectivity or LSER parameters was observed between nanoparticles with different cationic shells, but differences were observed between nanoparticles with different hydrophobic cores. Cationic latex nanoparticles behaved more like anionic latex nanoparticles than like cationic surfactants, suggesting that selectivity is primarily driven by the hydrophobic portion of a PSP. Cationic latex nanoparticles in combination with a homopolymer cationic capillary coating are an excellent choice for EKC analyses where an anodic electroosmotic flow is required.

Determination of lipid bilayer affinities and solvation characteristics by electrokinetic chromatography using polymer‐bound lipid bilayer nanodiscs

“… also suggested that EKC could be used to characterize PSPs. Numerous materials have been developed as PSPs, and the solvent characteristics of a variety of PSP materials, including micelles , polymers ,vesicles , microemulsions , liposomes , bicelles and nanoparticles have been studied by EKC. The solvent characteristics of liposome PSPs composed of zwitterionic and anionic lipids have frequently been studied as models of lipid bilayer membranes and as a means to determine octanol water partition coefficients (P o/w ) .…”

Evaluation of poly([2‐(acryloyloxy)ethyl]trimethylammonium chloride) cationic polymer capillary coating for capillary electrophoresis and electrokinetic chromatography separations

“…The application of interest in the current study for these coatings is the separation of neutral compounds by EKC using a cationic PSP. In previous work we described the synthesis and evaluation of cationic latex nanoparticles formed from amphiphilic diblock copolymers containing a cationic block and a hydrophobic block . As presented above, these cationic nanoparticles adsorb to the capillary surface and form a cationic coating, creating an anodic EOF.…”

“…Diblock copolymer nanoparticles containing an AETMAC hydrophilic block and ethyl acrylate hydrophobic block (hereafter referred to as EAAETMAC) were synthesized in a two‐step process . AETMAC macroCTA was synthesized in the same manner as the PAETMAC capillary coating.…”

“…The most common PSP is the anionic surfactant SDS, but cationic PSPs can also be used with an anodic EOF. In recent work utilizing cationic latex nanoparticles as a PSP for EKC, we discovered that it was necessary to modify the capillary wall to render it cationic before introducing the PSP . Failure to do this resulted in the PSP forming a hydrophobic cationic coating on the capillary wall, and adsorption of analytes to the PSP‐modified surface resulted in poor separation efficiency and performance for small neutral hydrophobic analytes.…”