Optimization of a sensitive and robust strategy for micellar electrokinetic chromatographic analysis of sofosbuvir in combination with its co-formulated hepatitis C antiviral drugs.

Based on our previous work with "pseudostationary-ion exchanger sweeping", we use this strategy to develop a sensitive, reliable and robust method for the analysis of the newly-FDA approved hepatitis C antiviral drugs namely; sofosbuvir (SOV), daclatasvir (DAC), ledipasvir (LED) and velpatasvir (VEP) in their pure forms and co-formulated pharmaceutical dosage forms using micellar electrokinetic chromatography (MEKC) as a separation method. For the first time, a successful separation of all the investigated compounds was achieved in less than 8 min using a basic background electrolyte (BGE) composed of 25 mmol L SDS + 20% (v/v) ACN (acetonitrile) in 10 mmol L disodium tetraborate buffer (final apparent pH is 9.90).

Determination of the Exact Particle Radius Distribution for Silica Nanoparticles via Capillary Electrophoresis and Modeling the Electrophoretic Mobility with a Modified Analytic Approximation.

In this study, we use aqueous dispersions of amorphous silica nanoparticles of various sizes to investigate whether electropherograms recorded from capillary electrophoresis experiments can be converted directly into exact number-based particle radius distributions, provided that there is a relaxation effect-based size selectivity of the electrophoretic mobility and provided that the electrokinetic potential ζ of the particles can be regarded to be homogeneous over the surface of the particles, independent of the particle size. The results of this conversion procedure are compared with number-based particle radius distributions obtained from a large set of transmission electron microscopy (TEM) data. For this specific example, it is shown that the modified analytic approximation developed by Ohshima adequately describes the mobility-dependent relaxation effect and the electrophoretic mobility of the particle as a function of the reduced hydrodynamic radius and electrokinetic potential, which is a prerequisite for the presented procedure.

Mixed-mode acrylamide-based continuous beds bearing tert-butyl groups for capillary electrochromatography synthesized via complexation of N-tert-butylacrylamide with a water-soluble cyclodextrin. Part I: Retention properties.

With the aim to improve the understanding of morphology and efficiency properties, we investigate in this series the impact of the complex formation constant of the hydrophobic monomer with respect to statistically methylated-β-cyclodextrin (Me-β-CD) on the electrochromatographic properties of highly crosslinked amphiphilic mixed-mode acrylamide-based monolithic stationary phases. Based on our previous work on amphiphilic mixed-mode monolithic stationary phases for capillary electrochromatography (CEC) using N-(1-adamantyl)acrylamide (Ad-AAm) as hydrophobic monomer that forms an extremely strong water-soluble inclusion complex with Me-β-CD, we now selected N-tert-butylacrylamide (NTBA) as hydrophobic monomer forming an inclusion complex with Me-β-CD with a much lower value of the formation constant. Mixed-mode monolithic stationary phases are synthesized by in-situ free radical copolymerization of cyclodextrin-solubilized N-tert-butylacrylamide, a water soluble crosslinker (piperazinediacrylamide), a hydrophilic neutral monomer (methacrylamide), and a negatively charged monomer (vinylsulfonic acid) in aqueous medium in bind silane pre-treated fused silica capillaries.

Elucidation of the Enantiodiscrimination Properties of a Nonracemic Chiral Alignment Medium through Gel-based Capillary Electrochromatography: Separation of the Mefloquine Stereoisomers.

Enantiodiscrimination and enantioseparation are two highly important processes in chemistry, often performed by using NMR spectroscopy and chromatography. For a better understanding of the mechanistic details, the same system should be studied by both methods. In addition, isotropic and anisotropic NMR parameters should be obtained, the latter using alignment media so that residual dipolar couplings and chemical-shift anisotropies can be measured.

In-capillary derivatization with o-phthalaldehyde in the presence of 3-mercaptopropionic acid for the simultaneous determination of monosodium glutamate, benzoic acid, and sorbic acid in food samples via capillary electrophoresis with ultraviolet detection.

For the rapid simultaneous determination of monosodium glutamate (MSG), benzoic acid (BA), and sorbic acid (SA) in canned food and other processed food samples, we developed a method that combines in-capillary derivatization with separation by capillary electrophoresis. This method employs the rapid derivatization of MSG with o-phthalaldehyde (OPA) in the presence of 3-mercaptopropionic acid (3-MPA) and enables the detection of the resulting OPA-MSG derivative and of non-derivatized BA and SA at 230nm. The composition of the background electrolyte and the parameters of derivatization and separation are as follows: 25mM borax containing 5mM OPA and 6mM 3-MPA, separation voltage 25mV, injection at 30mbar for 20s, and column temperature 25°C.

Characterization of hydrophilic coated gold nanoparticles via capillary electrophoresis and Taylor dispersion analysis. Part II: Determination of the hydrodynamic radius distribution - Comparison with asymmetric flow field-flow fractionation.

In the first paper of this series we have shown for hydrophilic coated Au nanoparticles that capillary electrophoresis in combination with Taylor dispersion analysis in fused silica capillaries with an inner diameter of 75 μm allows for the unbiased precise determination of the number-weighted mean hydrodynamic diameter, the zeta potential and the effective charge number, although mobility corrected double layer polarization has to be taken into account. In this second paper we investigate whether the modified approximate analytic expression developed by Ohshima (2001) permits the calculation of calibration lines and the concomitant conversion of electropherograms into number-weighted particle radius distributions. We show that with the method developed size distributions are obtained which are independent of the measurement conditions.

Characterization of gold nanoparticles with different hydrophilic coatings via capillary electrophoresis and Taylor dispersion analysis. Part I: determination of the zeta potential employing a modified analytic approximation.

Taking gold nanoparticles with different hydrophilic coatings as an example, it is investigated whether capillary electrophoresis in combination with Taylor dispersion analysis allows for the precise determination of mean electrophoretic mobilities, electrophoretic mobility distributions, and zeta potentials in a matrix of exactly known composition and the calibration-free determination of number-weighted mean hydrodynamic radii. Our experimental data confirm that the calculation of the zeta potential for colloidal nanoparticles with ζ>25 mV requires to take the relaxation effect into account. Because of the requirement to avoid particle-wall interactions, a solution of disodiumtetraborate decahydrate (borax) in deionized water had been selected as suitable electrolyte.

Boronate affinity-assisted MEKC separation of highly hydrophilic urinary nucleosides using imidazolium-based ionic liquid type surfactant as pseudostationary phase.

In this work, we extend our investigations regarding the separation of urinary nucleosides by MEKC with the ionic liquid type surfactant 1-tetradecyl-3-methylimidazolium bromide (C14MImBr). We study the impact of adding alkyl- and arylboronic acids (in the presence of C14MImBr micelles) to the separation of these highly hydrophilic metabolites and investigate the mechanism of interaction between the negatively charged nucleosides (the negative charge is acquired either due to deprotonation of the amidic group and/or complexation with boronate) and the positively charged pseudostationary phase. This interaction is not only due to electrostatic (Coulombic) forces, but also due to hydrophobic interaction of the alkyl or aryl group of the boronate that forms a complex with the cis-diol group of the nucleoside.

Determination of urinary nucleosides via borate complexation capillary electrophoresis combined with dynamic pH junction-sweeping-large volume sample stacking as three sequential steps for their on-line enrichment.

The combination of dynamic pH junction, sweeping (using borate complexation), and large volume sample stacking (LVSS) is investigated as three consecutive steps for on-line focusing in the sensitive quantitation of urinary nucleosides by CE-UVD. A low conductivity aqueous sample matrix free from borate and a high conductivity BGE (containing borate, pH 9.25) are needed to fulfill the required conditions for dynamic pH junction, LVSS, and sweeping.

Adamantyl-group containing mixed-mode acrylamide-based continuous beds for capillary electrochromatography. Part IV: investigation of the chromatographic efficiency dependent on the retention mode.

In our previous work we have described the synthesis, characterization, and optimization of the chromatographic efficiency of a highly crosslinked macroporous mixed-mode acrylamide-based monolithic stationary phase synthesized by in situ free radical copolymerization of cyclodextrin-solubilized N-adamantyl acrylamide, piperazinediacrylamide, methacrylamide and vinylsulfonic acid in aqueous medium in pre-treated fused silica capillaries of 100μm I.D. In the present work, we study with different classes of neutral analytes (with varied hydrophobicity) the impact of the type of retention mode (influenced by the type of analyte and the mobile phase composition) and the impact of the solute functionality on the chromatographic efficiency and peak symmetry with a monolith synthesized under optimized synthesis parameters.

Adamantyl-group containing mixed-mode acrylamide-based continuous beds for capillary electrochromatography. Part II. Characterization of the synthesized monoliths by inverse size exclusion chromatography and scanning electron microscopy.

In our previous article we have described the synthesis of a new amphiphilic monolithic stationary phase by in situ free radical copolymerization of cyclodextrin-solubilized N-adamantyl acrylamide, piperazinediacrylamide, methacrylamide and vinylsulfonic acid in aqueous medium in pre-treated fused silica capillaries of 100μm I.D. In the present work, we study the morphology of different monolithic stationary phases synthesized under variation of the concentration of ammonium sulfate in the polymerization mixture.

Processes involved in sweeping as sample enrichment method in cyclodextrin-modified micellar electrokinetic chromatography of hydrophobic basic analytes.

Sweeping is an enrichment method in MEKC, which includes following steps: stacking/destacking of the micelles, sweeping of analyte by the stacked/destacked micelles, destacking/stacking of the swept analyte zone and additional focusing/defocusing due to the retention factor gradient effect (RFGE). In this study, we investigate additional processes, regarding online focusing in cyclodextrin-modified MEKC (CD-MEKC) of hydrophobic basic analytes: dynamic pH junction (sample with pH different from that of BGE) and adsorption of analyte onto the capillary wall within the sample zone. It is demonstrated that the developed method for the assessment of the sweeping efficiency is also applicable to CD-MEKC taking ethylparaben as an example of acidic analytes and desloratadine as an example of basic analytes using different types of β-cyclodextrin.

Adamantyl-group containing mixed-mode acrylamide-based continuous beds for capillary electrochromatography. Part III. Optimization of the chromatographic efficiency.

In a previous article we described the synthesis of amphiphilic monolithic stationary phases by in situ free radical copolymerization of cyclodextrin-solubilized N-adamantyl acrylamide, piperazinediacrylamide, methacrylamide and vinylsulfonic acid in aqueous medium in pre-treated fused silica capillaries of 100μ.m I.D.

Imidazolium-based ionic liquid-type surfactant as pseudostationary phase in micellar electrokinetic chromatography of highly hydrophilic urinary nucleosides.

Ionic liquid (IL)-type surfactants have been shown to interact more strongly with polar compounds than traditionally used quaternary ammonium cationic surfactants. The aim of this study is to provide an alternative micellar electrokinetic chromatographic method (MEKC) for the analysis of urinary nucleosides in their ionic form at low surfactant concentration. This approach could overcome the use of high surfactant concentrations typically associated with the analysis of these highly hydrophilic metabolites as neutral species, which is frequently accompanied by high electric current, Joule heating and long analysis time.

Robust analysis of the hydrophobic basic analytes loratadine and desloratadine in pharmaceutical preparations and biological fluids by sweeping-cyclodextrin-modified micellar electrokinetic chromatography.

The analysis of hydrophobic basic analytes by micellar electrokinetic chromatography (MEKC) is usually challenging because of the tendency of these analytes to be adsorbed onto the inner capillary wall in addition to the difficulty to separate these compounds as they exhibit extremely high retention factors. A robust and reliable method for the simultaneous determination of loratadine (LOR) and its major metabolite desloratadine (DSL) is developed based on cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) with acidic sample matrix and basic background electrolyte (BGE). The influence of the sample matrix on the reachable focusing efficiency is studied.

Sweeping as a multistep enrichment process in micellar electrokinetic chromatography: the retention factor gradient effect.

The application of a new method developed for the assessment of sweeping efficiency in MEKC under homogeneous and inhomogeneous electric field conditions is extended to the general case, in which the distribution coefficient and the electric conductivity of the analyte in the sample zone and in the separation compartment are varied. As test analytes p-hydroxybenzoates (parabens), benzamide and some aromatic amines are studied under MEKC conditions with SDS as anionic surfactant. We show that in the general case - in contrast to the classical description - the obtainable enrichment factor is not only dependent on the retention factor of the analyte in the sample zone but also dependent on the retention factor in the background electrolyte (BGE).

Adamantyl-group containing mixed-mode acrylamide-based continuous beds for capillary electrochromatography. Part I: study of a synthesis procedure including solubilization of N-adamantyl-acrylamide via complex formation with a water-soluble cyclodextrin.

A new synthesis procedure for highly crosslinked macroporous amphiphilic N-adamantyl-functionalized mixed-mode acrylamide-based monolithic stationary phases for capillary electrochromatography (CEC) is investigated employing solubilization of the hydrophobic monomer by complexation with a cyclodextrin. N-(1-adamantyl)acrylamide is synthesized and characterized as a hydrophobic monomer forming a water soluble-inclusion complex with statistically methylated-β-cyclodextrin. The stoichiometry, the complex formation constant and the spatial arrangement of the formed complex are determined.

Processes involved in sweeping under inhomogeneous electric field conditions as sample enrichment procedure in micellar electrokinetic chromatography.

Sweeping under inhomogeneous electric field conditions has been described as a process that includes stacking or destacking of the micelles when entering the sample zone, sweeping of analytes by the stacked or destacked micelles, and destacking or stacking of the swept analyte zone. However, there is ongoing debate that not only the retention factor of the analyte but also the electric conductivity of the sample solution or the concentration of an added salt can have an impact on the enrichment efficiency. Revisiting the equations describing sweeping, a factor θ (phase ratio shift factor) is defined to quantitatively describe the change of the retention factor between the sample and separation zones.

Sensitivity enhancement in near-field photothermal-lens detection in capillary electrophoresis using laser-induced online precipitation.

This paper reports simultaneous photoinduced precipitation-based online preconcentration of target analytes at the inner walls in capillary zone electrophoresis (CZE) and surface-enhanced near-field crossed-beam photothermal-lens detection of the preconcentrated analytes. A simple technique using online readjustment of the optical scheme of the thermal-lens detector in the course of the separation for gaining optimum sensitivity for both water-soluble and precipitated analytes is proposed. It provides a considerable decrease in the limits of detection (LOD) with good concordance with the previously developed theoretical approach to this combination (D.

Regulation of the retention factor for weak acids in micellar electrokinetic chromatography with cationic surfactant via variation of the chloride concentration.

For tetradecyltrimethylammonium bromide in boric acid/borate or acetic acid/acetate buffer and NaCl or CaCl₂ as the added salt, it is investigated whether the retention behaviour of weak acids in MEKC with cationic surfactant can be modelled by assuming for the deprotonated species predominantly electrostatic interaction with the micelles acting as a pseudostationary ion-exchanger. The retention of (partially) charged solutes by oppositely charged micelles is analyzed by applying the classical theory of IEC (plotting lg k against lg(c(Cl⁻)) assuming a fixed concentration of ion-exchange sites. When plotting the absolute slopes of the regression lines against the absolute effective charge numbers of the analytes, correlation coefficients of 0.

Diffusion as major source of band broadening in field-amplified sample stacking under negligible electroosmotic flow velocity conditions.

Theory of field-amplified sample stacking (FASS) also called field-enhanced sample stacking is reevaluated considering the early work of Chien, Burgi and Helmer. The classical theory presented by Chien, Helmer and Burgi predicts the existence of maxima, which are ascribed to the counteracting principles of zone focusing and hydrodynamic dispersion. In contrast to their work, we here focus on cationic analytes separated in an acidic background electrolyte providing a very low electroosmotic flow velocity.

Characterization of nanoparticles by capillary electromigration separation techniques.

Considering the large number of papers presented in the last years in the field of CE and plate gel electrophoresis (PGE) of nanoparticles and nanoparticle-biomolecule conjugates, this review article gives an overview on the application of capillary electromigration separation techniques for the separation of nanoparticles and nanoparticle-biomolecule conjugates according to differences in size and/or zeta potential and for the determination of several physicochemical parameters characterizing a population of nanoparticles. A brief introduction is given into the theoretical background of the size-selective electrophoretic separation of nanospheres in free-solution and sieving media including involvement of interparticle interactions. Some aspects of colloidal system stability are discussed.

Calibration-free concentration determination of charged colloidal nanoparticles and determination of effective charges by capillary isotachophoresis.

Although colloidal nanoparticles show an electrophoretic heterogeneity under the conditions of capillary electrophoresis, which can be either due to the particle-size distribution and/or the particle shape distribution and/or the zeta-potential distribution, they can form correct isotachophoretic zones with sharp-moving boundaries. Therefore, the technique of isotachophoresis permits to generate plugs in which the co-ions and counter ions of the original colloidal solution are removed and replaced by the buffering counter ions of the leading electrolyte. It is shown that analytical isotachophoresis can be used to measure directly, without calibration, the molar (particle) concentration of dispersed ionic colloids provided that the transference number and the mean effective charge number of the particles (within the isotachophoretic zone) can be determined with adequate accuracy.

Sensitivity enhancement of thermal-lens spectrometry using laser-induced precipitation.

The possibility of thermal lensing of dynamically emerging light-absorbing layers at cell surfaces was investigated. Analyte accumulation at a cell surface determines long-term changes in the thermal-lens signal that was used as a source of analytical information to enhance sensitivity of thermal lensing. Considering the rate of accumulation as an additional analytical signal, we achieved a threefold decrease in the limits of detection for 4-aminoazobenzene to the level of 7 microM in a batch mode with the same level of reproducibility.

Separation of very hydrophobic analytes by micellar electrokinetic chromatography IV. Modeling of the effective electrophoretic mobility from carbon number equivalents and octanol-water partition coefficients.

It is investigated whether those relationships derived within an optimization scheme developed previously to optimize separations in micellar electrokinetic chromatography can be used to model effective electrophoretic mobilities of analytes strongly differing in their properties (polarity and type of interaction with the pseudostationary phase). The modeling is based on two parameter sets: (i) carbon number equivalents or octanol-water partition coefficients as analyte descriptors and (ii) four coefficients describing properties of the separation electrolyte (based on retention data for a homologous series of alkyl phenyl ketones used as reference analytes). The applicability of the proposed model is validated comparing experimental and calculated effective electrophoretic mobilities.