Biomedical subjects

Marilyn X Zhou

Publications and source records attributed to Marilyn X Zhou.

3 recordsLinked to original sources

PubMed2006

Quantitative theory of electroosmotic flow in fused-silica capillaries using an extended site-dissociation--site-binding model.

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.

Binding Sites↗

PubMed2004

Analytical method for the quantitation of sertraline hydrochloride stereoisomers by electrokinetic chromatography.

Sertraline is a basic compound and of pharmaceutical application for antidepressant treatment. The compound has two chiral centers. Separation of the three enantiomeric impurities from the parent compound is challenging. In this study, we successfully separated all four stereoisomers by electrokinetic chromatography using highly sulfated gamma-cyclodextrin and highly sulfated alpha-cyclodextrin as the chiral selectors. The two chiral selectors provided different selectivity and therefore affected the overall separation profiles. This may be due to the size difference between the dichlorophenyl moiety end and naphthalenamine moiety end, resulting in two different types of inclusion complexes with the different cyclodextrins. For routine analysis, highly sulfated gamma-cyclodextrin was better than highly sulfated alpha-cyclodextrin. For each stereoisomeric impurity, the method using sulfated gamma-cyclodextrin provided a limit of quantitation at or lower than 0.1% of the drug substance with adequate resolution. The critical resolution at this concentration level was not less than 4.0. Experimental data suggested that an internal standard was necessary for the purpose of quantitation, and the practical linearity range for analysis of sertraline stereoisomeric impurities was of about two orders of magnitude.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2004

Dual opposite injection electrokinetic chromatography: nonionic microemulsion pseudostationary phase and novel approach to electrokinetic sampling bias.

Dual opposite injection capillary electrophoresis (DOI-CE) is a family of CE techniques in which the sample is introduced into both ends of the capillary. For the analysis of compounds with widely varying pKa values using a voltage-driven separation scheme, DOI-CE is superior to conventional CE with sample introduction at only one end of the capillary due to DOI-CE's broader elution window. To enhance the DOI-CE separation, a running buffer with a microemulsion system was developed. Since DOI-CE works best under conditions of low electroosmotic flow (EOF), the suppression of EOF via the addition of a multiply charged cation (e.g., Zn2+) to the buffer was investigated, and was found to suppress the EOF effectively at moderate concentrations (2.5-10 mM). Three different dual opposite injection modes were studied: simultaneous electrokinetic injection, sequential electrokinetic injection, and sequential hydrodynamic injection. The injection bias in the first two electrokinetic injection modes was compared with the sequential hydrodynamic injection. Corrections in the bias of the electrokinetic injections were discussed, and an improved approach was suggested. Finally, the effect of the relative concentration of the multiply charged cation in the sample plug and running buffer on the peak shape of co-electroosmotic and counter-electroosmotic ions was examined, and found to be much more influential on the latter.

Anions↗