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To optimize separations in capillary electrophoresis, it is important to control the electroosmotic mobility of the running buffer and the factors that affect it. Through the application of a site-dissociation-site-binding model, we demonstrated that the electroosmotic mobility could be controlled qualitatively and quantitatively by the parameters related to the physical and chemical properties of the running buffer: pH, cation valence, ionic strength, viscosity, activity, and dissociation constant. Our study illustrated that the logarithm of the number of apparent silanol sites on a fused-silica surface has a linear relationship with the pH of a buffer solution. The extension of the chemical kinetics approach allowed us to obtain the thickness of the electrical double layer when multivalent inorganic cations are present with monovalent cations in a buffer solution, and we found that the thickness of the electrical double layer does not depend on the charge of anions. The general equation to predict the electroosmotic mobility suggested here also indicates the increase of electroosmotic mobility with temperature. The general equation was experimentally verified by three buffer scenarios: (i) buffers containing only monovalent cations; (ii) buffers containing multivalent inorganic cations; and (iii) buffers containing cations and neutral additives. The general equation can explain the experimental observations of (i) a maximum electroosmotic mobility for the first scenario as the pH was varied at constant ionic strength and (ii) the inversion and maximum value of the electroosmotic mobility for the second scenario when the concentration of divalent cations was varied at constant pH. A good agreement between theory and experiment was obtained for each scenario. [ABSTRACT FROM AUTHOR]

Analyzes the effect of liquid chromatographic separation on matrix-related signal suppression in electrospray ionization mass spectrometry. Induction of matrix-related signal suppression by column overload and matrix component-analyte celation; Effectiveness of on-line orthogonal liquid chromatography separations.

Studies the effect of stationary-phase pore size on retention behavior in micellar liquid chromatography. Differences in retention behavior between various solute types and stationary phases; Partitioning behavior of representative solutes; Differences in the stationary-phase characteristics between the small- and large-pore size C18 columns.

Presents the results of a study which investigated the influence of dodecyl sulfate micelles on efficiency, selectivity, retention, elution range and resolution in micellar electrokinetic chromatography. Effects of using the counterions lithium and potassium; Effect of acetonitrile; Comparisons between the counterions; Operating currents.

Longitudinal on-column thermal modulation for comprehensive two-dimensional liquid chromatography is introduced. Modulation optimization involved a systematic investigation of heat transfer, analyte retention, and migration velocity at a range of temperatures. Longitudinal on-column thermal modulation was realized using a set of alkylphenones and compared to a conventional valve-modulator employing sample loops. The thermal modulator showed a reduced modulation-induced pressure impact than valve modulation, resulting in reduced baseline perturbation by a factor of 6; yielding a 6-14-fold improvement in signal-to-noise. A red wine sample was analyzed to demonstrate the potential of the longitudinal on-column thermal modulator for separation of a complex sample. Discrete peaks in the second dimension using the thermal modulator were 30-55% narrower than with the valve modulator. The results shown herein demonstrate the benefits of an active focusing modulator, such as reduced detection limits and increased total peak capacity. [ABSTRACT FROM AUTHOR]

Studies the experimental aspects of the sampling process in relation to comprehensive two-dimensional liquid chromatography. How is the total analysis time determined; Optimization of multidimensional separation systems; Discussion of the sensitivity of the resolution with respect to the sampling phase; Indications of the findings.

A prerequisite for ordered two-dimensional (2D) separations and full utilization of the enhanced 2D peak capacity is selective exploitation of the sample attributes, described as sample dimensionality. In order to take sample dimensionality into account prior to optimization of a 2D separation, a new concept based on construction of 2D separation selectivity maps is proposed and demonstrated for ion chromatography x capillary electrophoresis (ICxCE) separation of low-molecular-mass organic acids as test analytes. For this purpose, 1D separation selectivity maps were constructed based on calculation of pairwise separation factors and identification of critical pairs for four IC stationary phases and 28 levels of background electrolyte pH in CE. The derived IC and CE maps were then superimposed and the effectiveness of the respective 2D separations assessed using an in silico approach, followed by testing examples of one successful and one unsuccessful 2D combination experimentally. The results confirmed the efficacy of the predictions, which require a minimal number of experiments compared to the traditional one-at-a-time approach. Following the same principles, the proposed framework can also be adapted for optimization of separation selectivity in various 2D combinations and for other applications. [ABSTRACT FROM AUTHOR]

Looks at fundamental developments in liquid chromatography during the period October 1995 to October 1997. Information on the theory and optimization of liquid chromatography; Analysis of the normal phase of liquid chromatography; Questions raised with regards to reversed-phase liquid chromatography; Discussion on bipolymer separations; Details on affinity and ion chromatography; Investigation and utilization of secondary chemical equilibria.

Presents information on a study which examined the electrokinetic chromatography of a novel mixed surfactant system using thermodynamically stable vesicles and mixed micelles formed from oppositely charged surfactants. What the surfactant system consisted of; Comparison of polar group selectivity, retention, and efficiency between vesicles, mixed micelles, and sodium dodecyl sulfate micelles.