Segmented flow and curtain flow chromatography: Overcoming the wall effect and heterogeneous bed structures

The development of sol-gel open-tubular column technology in capillary electrochromatography (CEC) is reviewed. Sol-gel column technology offers a versatile means of creating organic-inorganic hybrid stationary phases. Sol-gel column technology provides a general approach to column fabrication for microseparation techniques including CEC, and is amenable to both open-tubular and monolithic columns. Direct chemical bonding of the stationary phase to the capillary inner walls provides enhanced thermal and solvent stability to sol-gel columns. Sol-gel stationary phases inherently possess higher surface area, and thus provide an effective one-step alternative to conventional open-tubular column technology. Sol-gel column technology is applicable to both silica-based and transition metal oxide-based hybrid stationary phases, and thus, provides a great opportunity to utilize advanced material properties of a wide range of nontraditional stationary phases to achieve enhanced selectivity in analytical microseparations. A wide variety of stationary phase ligands can be chemically immobilized on the capillary inner surface using a single-step sol-gel procedure. Sol-gel chemistry can be applied to design stationary phases with desired chromatographic characteristics, including the possibility of creating columns with either a positive or a negative charge on the stationary phase surface. This provides a new tool to control electroosmotic flow (EOF) in the column. Column efficiencies on the order of half a million theoretical plates per meter have been reported for sol-gel open-tubular CEC columns. The selectivity of sol-gel stationary phases can be easily fine-tuned by adjusting the composition of the coating sol solution. Open-tubular columns have significant advantages over their packed counterparts because of the simplicity in column making and hassle-free fritless operation. Open-tubular CEC columns possess low sample capacity and low detection sensitivity. Full utilization of the analytical potential of sol-gel open-tubular columns will require a concomitant development in the area of high-sensitivity detection technology.

Capillary electrochromatography with macroporous particles

The general limitations on liquid chromatographic performance in isocratic and gradient elution are now well understood. Many workers have contributed to this understanding and to developing graphical methods, or plots, to illustrate the capabilities of chromatographic systems over a wide range of values of operational parameters. These have been invaluable in getting a picture, in broad strokes, about the value of changing an operational parameter or the value of one separation approach over another. Here we present a plotting approach more appropriate for determining how to use chromatography most efficiently in one's own laboratory. The axes are linear: column length vertical and mobile phase velocity horizontal. In this coordinate system, straight lines with intercept zero correspond to different values of t0. Hyperbolas correspond to values of pressure as the product of length and velocity is proportional to pressure. For a given relationship between theoretical plate height and velocity (e.g., van Deemter), the number of theoretical plates as a function of column length and mobile phase velocity is a surface (z direction) to the x and y of velocity and length. By representing the surface as contours, a two-dimensional plot results. Any point along a constant pressure hyperbola represents the best one can do given the particle diameter, solute diffusion coefficient, and temperature. The user can quickly see how to use the pressure for speed or for more theoretical plates. Sets of such plots allow for comparisons among particle diameters or temperatures. Analogous plots of peak capacity for gradient elution are equally revealing. The plots lead instantly to understanding liquid chromatographic optimization at a practical level. They neatly illustrate the value (or not) of changing pump pressure, particle diameter, or temperature for fast or slow separations in either isocratic or gradient elution. They are illustrated with a focus on maximizing plate count with a given analysis time (isocratic), the effect of volume overload (isocratic), and separations of a limited number of peptides with a peak capacity coming from statistical peak overlap theory (gradient).

Shock layer thickness and optimum linear velocity in displacement chromatography

Theoretical study of the effect of frit quality on chromatography using computational fluid dynamics

Novel biporous polymeric stationary phase for high-speed protein chromatography

Structural radial heterogeneity of a silica-based wide-bore monolithic column

Mechanistic insights into band broadening in MOF-based liquid chromatography: Role of sub-nanopore diffusion and packing heterogeneity.

Improving HPLC separation performance using parallel segmented flow chromatography

Introduction: Several analytical methods for quantitative determination of amlodipine either in pharmaceuticals or biological fluids have suffered different setbacks. Therefore, we aimed at developing a cost effective, simple, robust, and sensitive reversed phase high performance liquid chromatography (RP-HPLC- UV) method for quantification of amlodipine in dosage form and in human plasma. Method: The separation was performed on an analytical column 150 mm x 4.6 mm i.d., Agilent Eclipse XDB C18 Column packed with 5 μm particle size and protected by a guard column (30 mm x 4.6 mm i.d.). The mobile phase composition contained acetonitrile: phosphate buffer (25 mM KH2PO4) adjusted to pH 3.1 with orthophosphoric acid in the ratio of 45:55 v/v. The flow rate was 1.2 mL/min and the UV detector was set at a wavelength of 240 nm. The column was maintained at ambient temperature. Results: The calibration curve gave good linearity in the concentration range studied. The column efficiency was highly evident by high theoretical plates and small height equivalent to theoretical plate (HETP). The percent relative standard deviation (% RSD) was less than 3% in the inter- and intra-day o assay. Amlodipine, 50 ng/mL in plasma stored frozen at -80 C was stable There was no statistical difference in the precision of amlodipine assayed after 12 months when compared to the initial assay (P>0.05). The % recovery of amlodipine in human plasma was 97.79±0.17% to 99.52±0.63%. Conclusion: The new RP-HPLC method is sensitive, reproducible, precise, accurate and robust. We conclude that the method is suitable for estimation of amlodipine besylate in human plasma for pharmacokinetic studies and assay of pharmaceutical dosage form

Capillary electrochromatography: effect of electrolyte concentration on electroosmotic flow and column efficiency

The results of a study of the optimization of the experimental conditions for maximum production rate in overloaded elution and displacement chromatography are discussed. This study is based on the use of the equilibrium-dispersive model of chromatography and the competitive Langmuir isotherms to calculate individual band profiles in the elution and displacement modes, and of a simplex algorithm to optimize the production rate. The operating parameters (sample size, mobile phase velocity, and the displacer concentration in the displacement model) and the column design parameters (column length and average particle diameter) are optimized simultaneously. Binary mixtures having relative concentrations 3:1 and 1:3, and separation factors of 1.2 to 1.8 are investigated. One of our major results is that, in both modes of chromatography, the maximum production rate is achieved at very low values of the retention factors, k', much lower than those used in current practice. In all cases, unless k' exceeds greatly that optimum value, the production rate is higher in overloaded elution than in displacement chromatography. This is particularly true for the extraction of a minor component, which is eluted second.

The design of the multi-component distillation column for processing of Bonny light crude is presented using advanced process simulation software (Aspen Hysys). The steady state design models were developed from Mesh equations and were used to obtain the design parameters based on the principle of conservation of mass and energy. The design parameters were column diameter, column cross sectional area, height of the column, downcomer area, hole area, weir length, wet area and tray spacing. The equations developed are capable of predicting compositions, partial pressures and temperature of the components of interest from the mixtures of crude oil. The accuracy of the design parameters were ascertained by comparing predicted results with literature data of a distillation unit. The simulation of the design models were performed using Aspen Hysys to obtain optimum values of the most significant variables/parameters (column diameters 1.558m, column height 17.048m, cross section area 1.907m2, downcomer area 0.229m2, tray spacing 0.5m, weir length 1.200m, hole area 0.191m2 and wet area 1.678m2). The result obtained from the steady state simulation shows that the feed flow rate, temperature and pressure influence the efficiency of the distillation column.

Separation of enantiomers by capillary electrochromatography

A water distillation detritiation facility and its performance test