Biomedical subjects

FH Quina

Publications and source records attributed to FH Quina.

3 recordsLinked to original sources

PubMed2000

Effect of a variety of organic additives on retention and efficiency in micellar liquid chromatography

The effect of 21 organic additives (alkanols, alkane diols, dipolar aprotic solvents, alkanes) on the chromatographic behavior (retention, elution strength, efficiency) of probe solutes of widely differing hydrophobicity, such as benzene and 2-ethylanthraquinone, have been examined using a C18 stationary phase and sodium dodecyl sulfate (SDS) micellar mobile phases. The mobile-phase elution strength parallels the octanol-water partition coefficients of the additives or their ability to bind to the SDS micellar system, due to the increased solubility in the mobile phase and reduced affinity for the additive-modified surfactant-coated stationary phase. The comparison of the elution strength of micellar mobile phases with that of a reference acetonitrile-water system indicates that the elution strength is lower for micellar systems and depends on the nature of the eluted solute. The displacement of the solute-micelle and solute-stationary phase binding equilibria is quantified for several probe solutes eluted with micellar mobile phases in the presence of 1-propanol, 1-butanol, 1-pentanol, and acetonitrile. A correlation was also observed between the number of theoretical plates and the hydrophobicity of the alcohol additives: the efficiency initially increased steeply and reached a plateau. Compared to benzene, a more hydrophobic additive was needed to attain the maximum efficiency for the more hydrophobic 2-ethylanthraquinone analyte. Dipolar aprotic solvents appear to be somewhat more effective in enhancing the efficiency than alcohols. The results are rationalized in terms of the ability of the organic additives to alter the composition, structure, dynamics, and properties of the micelles and the surfactant-coated stationary phase.

Journal Article↗

PubMed1999

Growth of Cetyltrimethylammonium Chloride and Acetate Micelles with Counterion Concentration.

Time resolved fluorescence quenching measurements with pyrene as probe are employed to determine aggregation numbers for hexadecyltrimethylammonium acetate (CTAOAc) and chloride (CTACl) micelles as a function of the concentration of detergent and added common-counterion salt. The aggregation numbers, NA, of CTACl are roughly twice those of CTAOAc micelles at equivalent concentrations of detergent and salt, consistent with the known relative counterion binding affinity (chloride >> acetate). For both detergents, the increase of NA with the net concentration of counterions in the intermicellar aqueous phase ([Yaq]) follows the relationship found previously for anionic micelles: log NA = log No + gamma log[Yaq], where gamma and No are constants. However, compared to anionic micelles, for which gamma = 0.2-0.25, spherical micelles of both CTAOAc and CTACl exhibit less pronounced growth, with gamma = 0.1. Copyright 1999 Academic Press.

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PubMed1997

Counterion Exchange Selectivity in Detergent-Polymer Aggregates

In aqueous solution, the interaction between sodium dodecyl sulfate (SDS) and poly(ethylene glycol) (PEG) results in the formation of small aggregates or clusters of SDS attached to the PEG polymer chain. Selectivity coefficients for exchange of two monovalent (N -methyl-4-cyanopyridinium cation and Tl+ ) and two divalent (methylviologen cation and Cu2+ ) counterions at the surface of SDS-PEG clusters, determined employing photophysical techniques, are similar, but not identical, to those for exchange at the surface of SDS micelles in the absence of PEG. The principal factor affecting ion exchange selectivity in SDS-PEG clusters does not appear to be aggregate size or surface charge density but rather the presence of poly(oxyethylene) subunits at the aggregate surface.

Journal Article↗