Effects of organic modifiers on solute retention and electrokinetic migrations in micellar electrokinetic capillary chromatography

Influences of seven organic modifiers, including urea, methanol (MeOH), dioxane (DIO), tetrahydrofuran (THF), acetonitrile (ACN), 1-propanol (1-PrOH) and 2-propanol (2-PrOH), on the solute retention and the electrokinetic migrations in micellar electrokinetic capillary chromatography (MEKC) are investigated with sodium dodecyl sulfate (SDS) micelle as pseudostationary phase. It is observed that in the limited concentration ranges used in the MEKC systems the effect of organic modifier concentration on the retention can be described by the equation logk'=logk'(w)-SC for most binary aqueous-organic buffer, but deviations from this retention equation are observed at ACN and particularly THF as organic modifiers. With parameter S as a measure of the elutropic strength, the elutropic strength of the organic modifiers is found to follow a general order urea

Theoretical study of the separation mechanism of ionizable compounds in capillary electrochromatography

The migration mechanism of ionizable compounds in capillary electrochromatography (CEC) is more complicated than in high performance liquid chromatography (HPLC) due to the involvement of electrophoresis and the second chemical equilibrium. The separation mechanism of ionizable compounds in CEC has been studied theoretically. The electrochromatographic capacity factors of ions (k *) in CEC and in the pressurized CEC are derived by phenomenological approach. The influence of pH, voltage, pressure on k* is discussed. in addition, the k * of weak acid and weak base are derived based on acid-base equilibrium and the influence of pH on k * is studied theoretically.

Separation of neutral compounds by high speed capillary electrochromatography

With using short capillary column packed with porous and non-porous ODS stationary phases, high speed separation of 6 neutral aromatic compounds within 36 s by capillary electrochromatography (CEC) has been performed. Good reproducibility of the migration times for those solutes in high speed CEC was observed with RSD less than 1%. Both the linear velocity of EOF and the current linearly increases with the applied voltage, which means that the thermal effect by Joule heating was small. However, the capacity factor of solutes was found to decrease with the increase of the applied voltage, which was caused by the fact that about several seconds needed for the increase of voltage from 0 to applied value on a commercial CE instrument made larger contributions to the migration times of the early eluted compounds than those of lately eluted ones during high speed CEC, and voltage effect would increase with the higher applied voltage used. The linear relationship between the logarithm of capacity factor and the number of carbon for homologous compounds was observed, and positive value of slope means that the hydrophobicity of solutes is one of the main contribution factors to retention in high speed CEC packed with ODS stationary phases.

Determination of total iron binding capacity of serum by capillary electrophoresis

A capillary electrophoresis (CE) technique for determining total iron binding capacity (TIBC) of serum has been developed. The optimum serum pretreatment involves the following major steps: at first, saturate serum transferrin with Fe+3; then, dissociate them completely after removing excess unbound Fe. Finally, complex the released iron with phenanthroline, a chromophore, to make suitable for the CE analysis. Ammonium acetate (pH = 5.0) was used as CE background electrolyte solution. In this system, a good linear correlation coefficient was maintained over the range 0.5 similar to 10 mu M (r = 0.9979, n =12). Seven adult serum samples were studied and the TIBC parameters measured. In the present system, 10 similar to 30 mu L serum is sufficient for determination. The study shows that the CE technique described is a powerful method for rapid, efficient, sensitive and reliable analysis and hence particularly suitable for clinical application.

Capillary electrophoresis study of human serum albumin binding to basic drugs

The applicability of capillary electrophoresis/frontal analysis (CE/FA) for determining the binding constants of the drugs propranolol (PRO) and verapamil (VER) to human serum albumin (HSA) was investigated. After direct hydrodynamic injection of a drug-HAS mixture solution into a coated capillary (32 cm x 50 mu m i.d.), the basic drug was eluted as a zonal peak with a plateau region under condition of phosphate buffer (pH 7.4; ionic strength 0.17) at 12 kV positive running voltage. The unbound drug concentrations measured from the plateau peak heights had good correlation coefficients, r > 0.999. Employing the Scatchard plot, the Klotz plot and nonlinear regression, the drug protein binding parameters, the binding constant and the number of binding sites on one protein molecule, were obtained. The binding constant obtained was compared to a reported equilibrium dialysis result and they are basically in good agreement.