Chiral Separations Using Polymeric Surfactants and Polyelectrolyte Multilayers in Open-Tubular Capillary Electrochromatography

Abstract

In this study, fused-silica capillaries are modified using a polyelectrolyte multilayer (PEM) coating procedure in open-tubular capillary electrochromatography. The PEM coating was constructed in situ with alternating rinses of positively and negatively charged polymers. The quaternary ammonium salt poly (diallyldimethylammonium chloride) was used as the cationic polymer, and the polymeric surfactant poly (sodium N-undecanoyl-l-leucylvalinate) was used as the anionic polymer. Previous studies have shown that the PEM-coated capillaries used for achiral separations have excellent reproducibilities and high stabilities against extreme pH values. In the current study, this PEM coating approach was applied to chiral separations of 1,1'-binaphthyl-2,2'-dihydrogenphosphate (BNP), 1,1'-bi-2-naphthol, secobarbital, pentobarbital, and temazepam. However, the PEM coating procedure used in the achiral studies needed to be significantly modified in order to achieve chiral separations. Optimal conditions were established by varying the additives (sodium chloride, 1-ethyl-3-methyl-1H-imidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate) in the polymer deposition solutions, the salt concentration, the column temperature, and the bilayer number. Reproducibilities were evaluated by use of the relative standard deviation (RSD) values of the electroosmotic flow (EOF) and the first peak ((R)-(+)-BNP). In all cases, the run-to-run and capillary-to-capillary RSD values of EOF were less than 0.5%, and the run-to-run RSD values of the (R)-(+)-BNP peak were less than 1%. In addition, more than 230 runs were performed on a single PEM-coated capillary.

Method Development by Use of Capillary Electrophoresis and Applications in Pharmaceutical, Biological and Natural Samples

“…In 1994, Wang and Warner [70] were the first to report the use of a polymeric surfactant added to the BGE in MEKC. Polymeric surfactants offer several distinct advantages over conventional micelles [63,[71][72][73]. Firstly, polymerization of the surfactant eliminates the dynamic equilibrium due to the formation of covalent bonds between the surfactant aggregates.…”

“…This usually provides higher efficiencies and rapid analysis. They have, over the years, been extensively used in a BGE [74][75][76][77][78][79][80], in a polyelectrolyte multilayer coating [63,74,[81][82][83], and in a CE-MS system [84][85][86].…”

“…The most common modes of chiral CE are electrokinetic chromatography (EKC) in the presence of a chiral selector, MEKC, capillary electrochromatography (CEC), where the chiral selector can be either used as a coating (OT-CEC), a packing (P-CEC) or a monolithic material (M-CEC) in the capillary, and others [55][56][57][58][59][60][61][62][63]. The prerequisite for separation of enantiomers in CE, as in every chromatographic system, is the formation of either stable diastereoisomers by the use of a chiral derivatization agent or reversible diastereoisomeric complexes with the addition of a chiral substance, (chiral selector).…”

Recent accomplishments in the field of enantiomer separation by CEC

“…In their studies, the authors utilized poly(diallyldimethylammonium chloride) (PDADMAC) as cationic polymer and poly(sodium N-undecanoyl-L-leucine-valinate) (poly(L-SULV)) as anionic polymer (Fig. 1) [37]. Different experimental parameters influencing the enantioselective separation of 1,1 0 -binaphthyl-2,2 0 -dihydrogenphosphate (BNP), 1,1 0 -bi-2-naphthol (BOH), secobarbital, pentobarbital and temazepam were investigated.…”

Capillary Electrophoretic Screening for the Inhibition of Homocysteine Thiolactone-Induced Protein Oligomerization

“…These novel coatings allow for facile column fabrication and exceptional separation performance for both chiral and achiral analytes. [23][24][25][26][27] Herein, we report the development of a rapid CE method for studying in vitro post-translational modification-induced protein oligomerization. Capillaries coated with poly (diallyldimethylammonium chloride) (PDADMAC) were used to separate homooligomeric cytochrome c species.…”