No abstract

We present a method for finely adjustable electroosmotic flow (EOF) velocity in cathodic direction for the optimization of separations in capillary electrophoresis. To this end, we use surface modification of the separation fused silica capillary by the covalently attached copolymer of acrylamide (AM) and 2‐acrylamido‐2‐methyl‐1‐propanesulfonate (AMPS), that is, poly(AM‐co‐AMPS) or PAMAMPS. Coatings were formed by the in‐capillary polymerization of a mixture of the neutral AM and anionic AMPS monomers premixed in various ratios in order to control the charge density of the copolymer. EOF mobility varies in the 0 to ∼40 × 10−9 m2 V−1 s−1 interval for PAMAMPS coatings ranging from 0 to 60 mol.% of charged AMPS monomer. For EOF in PAMAMPS‐treated capillaries, we observed (i) a negligible dependence on pH in the 2–10 interval, (ii) a minor variance among background electrolytes (BGEs) in function of their components and (iii) its standard decrease with increasing ionic strength of the BGE. Interest in variable cathodic EOF was demonstrated by the amelioration of separation of two kinds of isomeric anionic analytes, that is, monosaccharides phosphates and helquat enantiomers, in counter‐EOF mode.

Eight different stationary phases based on two aminopropyl silicas of different brands suitable for multimodal chromatography applications have been prepared by a four-component Ugi reaction. The intention was to synthesize stationary phases significantly differing in their properties hereby demonstrating flexibility of the Ugi synthetic protocol. Diverse functional groups including a nonpolar long aliphatic chain, phenyl moiety, cholic acid scaffold, phenylboronic and monosaccharide units, charged betaine, and arginine moieties were immobilized on a silica surface. The novel sorbents were extensively characterized by elemental analysis, Raman spectroscopy, and chromatography. Considering the anchored chemical structures covalently bonded to the silica surface, reversed-phase, hydrophilic, and ion-exchange separation modes were expected. The chromatographic evaluation was performed directed to map the potential of the individual columns specifically in the mentioned chromatographic modes. The Ugi synthetic protocol has proven to be a simple, feasible, and versatile tool for the synthesis of sorbents of variable properties. The newly prepared stationary phases differed considerably in hydrophobicity and ion-exchange ability. A significant influence of the supporting aminopropyl silica on the final chromatographic behavior was observed. Finally, one practical example confirming applicability of the newly prepared sorbents was demonstrated in separation of cytarabine.