Marker compounds for the determination of retention factors in EKC

Potential of liposomes and lipid membranes for the separation of β-blockers by capillary electromigration and liquid chromatographic techniques

β-Blockers belong to a frequently used class of drugs primarily used to treat heart and circulatory conditions. Here we describe the use of lipid vesicles and liposomes as cell membrane biomimicking models in capillary electromigration (CE) and liquid chromatography (LC) techniques for the investigation of interactions between lipid membranes and β-blockers. In addition to liposomes, the use of commercial intravenous lipid emulsions, and their interactions with β-blockers are also discussed. Different CE and LC instrumental techniques designed for these purposes are introduced. Other methodologies for studying interactions between β-blockers and lipid membranes are also briefly discussed, and the different methodologies are compared. The aim is to give the reader a good overview on the status of the use of liposomes and lipids in CE and LC for studying β-blocker interactions.

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Effect of liposome composition on β-blocker interactions studied by capillary electrokinetic chromatography

Liposome capillary electrokinetic chromatography was used to investigate the interactions between three β-blockers of different hydrophobicity and various liposome solutions. The studied β-blockers comprised alprenolol, propranolol, and carvedilol. The composition of the liposome solutions, containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycero-3-phos-phoethanolamine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine, and cholesterol in various molar ratios, was designed by a response surface methodology-central composite design approach. Subsequently, after conducting the liposome capillary electrokinetic chromatography experiments and determining the retention factors from the electrophoretic mobilities of the compounds, and further calculating the distribution coefficients, an analysis of variance was performed. After extracting the statistical models, optimal operational conditions were obtained based on the developed models. To further investigate the interactions between the β-blockers and the liposomes, nanoplasmonic sensing experiments were carried out on two different liposome systems. The overall results demonstrate the strong influence of cholesterol and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine on the distribution coefficients.

Separation of polystyrene nanoparticles bearing different carboxyl group densities and functional groups quantification with capillary electrophoresis and asymmetrical flow field flow fractionation

Two sets of polystyrene nanoparticles (PSNPs) with comparable core sizes but different carboxyl group densities were made and separated using asymmetric flow field flow fractionation (AF4), capillary electrophoresis (CE), and the off-line hyphenation of both methods. Our results revealed the significant potential of two-dimensional off-line AF4-CE hyphenation to improve the separation and demonstrated for the first time, the applicability of CE to determine the functional group density of nanoparticles (NPs). Compared to the result acquired with conductometric titration, the result obtained with synthesized 100 nm sized PSNPs revealed only a slight deviation of 1.7%. Commercial 100 nm sized PSNPs yielded a deviation of 4.6%. For 60 nm sized PSNPs, a larger deviation of 10.6% between both methods was observed, which is attributed to the lower separation resolution.

Distribution of local anesthetics between aqueous and liposome phases

Liposomes were used as biomimetic models in capillary electrokinetic chromatography (EKC) for the determination of distribution constants (K_D) of certain local anesthetics and a commonly used preservative. Synthetic liposomes comprised phosphatidylcholine and phosphatidylglycerol phospholipids with and without cholesterol. In addition, ghost liposomes made from red blood cell (RBC) lipid extracts were used as pseudostationary phase to acquire information on how the liposome composition affects the interactions between anesthetics and liposomes. These results were compared with theoretical distribution coefficients at pH 7.4. In addition to 25°C, the distribution constants were determined at 37 and 42°C to simulate physiological conditions. Moreover, the usability of five electroosmotic flow markers in liposome (LEKC) and micellar EKC (MEKC) was studied. LEKC was proven to be a convenient and fast technique for obtaining data about the distribution constants of local anesthetics between liposome and aqueous phase. RBC liposomes can be utilized for more representative model of cellular membranes, and the results indicate that the distribution constants of the anesthetics are greatly dependent on the used liposome composition and the amount of cholesterol, while the effect of temperature on the distribution constants is less significant.

Physicochemical characterization of a PEGylated liposomal drug formulation using capillary electrophoresis

In this work, the applicability of using CE to perform a physicochemical characterization of a PEGylated liposomal drug formulation of the anti-cancer agent oxaliplatin was examined. Characterization of the liposomal drug formulation using CE instrumentation encompassed: determination of the electrophoretic mobilities, size determination by Taylor dispersion analysis and interaction studies. Electrophoretic mobilities determined by CE were compared with the results obtained by laser Doppler electrophoresis, which were found to be subject to larger variation. Average hydrodynamic diameters of the liposome preparations, as determined by Taylor dispersion analysis, were in the range of 61-84 nm and were compared with the results obtained by dynamic light scattering. Interactions between oxaliplatin (and paracetamol) and the PEGylated liposome were non-detectable by CE frontal analysis as well as by liposome electrokinetic chromatography. In contrast, for the more lipophilic compound propranolol, apparent liposome-aqueous phase distribution coefficients (D(lip) ) were successfully determined by both electrokinetic chromatography (log D(lip) =2.10) and by CE frontal analysis (log D(lip) =2.14). It is envisioned that CE and capillary-based techniques, including Taylor dispersion analysis, will be useful tools for the characterization of nanoparticulate (e.g. liposomal) drug formulations.