Willie L. Hinze

A Critical Review of Surfactant-Mediated Phase Separations (Cloud-Point Extractions): Theory and Applications

Abstract The general concept of using the unique phase separation behavior of some surfactant micelle solutions as a means for extractive separation is outlined and described. Next, the specific micellar parameters and phase separation behavior of nonionic and zwitterionic charge-type surfactant solutions are summarized. In addition, the phase behavior of some derivatized B-cyclodextrin solutions is briefly described. The specific applications of such systems and their phase behavior for the extractive preconcentration, separation, and/or purification of metal chelates, biomaterials, and organic compounds are summarized and discussed. The potential use of affinity ligands in conjunction with the cloud-point approach for selective bioextractions is also mentioned. The experimental protocols, advantages, and limitations of the different cloud-point extraction techniques are outlined. The use of zwitterionic as opposed to nonionic surfactant media in such separations is compared and contrasted. In addition, ...

Bile salt surfactants in micellar electrokinetic capillary chromatography. Application to hydrophobic molecule separations

Abstract Bile salt surfactants are used in the micellar electrokinetic capillary chromatography (MECC) separation of various hydrophobic compounds. The use of methanol in the mobile phase allows the separation of previously intractable compounds including polyaromatic hydrocarbons. The effects of methanol on critical micelle concentration is investigated for sodium dodecyl sulfate (SDS) and the bile salt sodium cholate. It is determined that the unique structure of the bile salt micelle is much more tolerant to the addition of organic solvents than SDS, thereby increasing the scope of applications of MECC to include hydrophobic compounds.

Applications of Cyclodextrins in Chromatographic Separations and Purification Methods

Abstract Cyclodextrins have been utilized as biomimetic models for a wide variety of processes ranging from enzymatic catalysis and membrane transport to protein ac tive-site-substrate binding interactions. As a consequence, numerous articles characterizing cyclodextrins as well as delineating their unique properties pervade the chemical literatur e.22–148 Even though the results of those studies promise great potential in terms of analytical chemistry, especially as they pertain to chromatographic separations, relatively few articles concerning their applications have been published. In view of the present inadequacy, this article is dedicated to the systematic reviewing of the use of cyclodextrins in chromatography and chemical separations. The topics to be covered include the use of cyclodextrins as selective isomeric precipitating agents, their use and role in chromatographic stationary or mobile phases, and their ability to enhance chromatographic detections. As a prerequisite to this discussion, a d...

Thin Layer Chromatographic Separation of Ortho, Meta, and Para Substituted Benzoic Acids and Phenols with Aqueous Solutions of α-Cyclodextrin

Abstract The use of aqueous solutions of α-cyclodextrin as the mobile phase in thin layer chromatography (TLC) is described. A series of eighteen substituted benzoic acid compounds were chromatographed on polyamide thin layer sheets. The Rf values were dependent on the concentration of α-cyclodextrin in the mobile phase as well as the structure and size of the individual molecules. Possible advantages of this technique over those which use pure or mixed solvent systems as the mobile phase are discussed.

New Perspectives in Micellar Liquid Chromatography

Abstract This paper will summarize several new findings obtained in our laboratory on the use of micellar mobile phases in liquid chromatography. The topics to be addressed include (i) stationary phase modification by the mobile phase surfactant in micellar liquid chromatography, (ii) investigation of the retention mechanism in micellar liquid chromatography (MLC) using an alkyl-benzene homologous series, (iii) evaluation of the effects of organic additives upon retention and efficiency in MLC, and (iv) preliminary characterization of several new classes of surfactant molecules for use in MLC. The information gained from these studies provides new insights into the dynamics of MLC and demonstrates their potential usefulness in several new separation applications including the resolution of optical isomers.

Micellar Enhanced Spectrofluorimetric Methods: Application to the Determination of Pyrene

Abstract The effects of cationic hexadecyltrimethylammonium chloride (CTAC), nonionic polyoxyethylene (9.5)p-1, 1, 3, 3-tetramethylbutylphenol, Triton X-100 (TX-100), and anionic sodium dodecylsulfate (NaLS) surfactant micelles upon the spectrofluorimetric determination of pyrene is described. It was found that the intensity of the pyrene fluorescence is enhanced from 3 to 16 times in the presence of the micellar systems. Possible reasons for this micellar induced enhanced fluorescence are discussed. The spectral parameters, fluorescence lifetimes, quantum yields, lower detection limits, and analytical figures of merit for pyrene in CTAC, NaLS, TX-100, ethanol, and water are compared. The detection limit of pyrene in the presence of micelles (∼1.0 × 10−10 M) is about an order of magnitude lower than that possible in alcohol alone. A brief discussion on the predicted general applicability of this new technique in fluorimetric analyses is also given.

Use of surfactant-mediated phase separation (cloud point extraction) with affinity ligands for the extraction of hydrophilic proteins

The feasibility of utilizing a zwitterionic surfactant, 3-(nonyldimethylammonio)propylsulfate, or nonionic surfactant, Triton X-114, mediated phase separation in conjunction with affinity ligands was studied for hydrophilic protein extractions. Below (or above) its critical temperature (so-called cloud point), aqueous solutions of zwitterionic (or nonionic) surfactants separate into two immiscible phases, a surfactant-rich phase and an aqueous phase. Avidin was successfully extracted into the zwitterionic surfactant-rich phase when a small amount of the affinity ligand, N- biotinoyl)dipalmitoyl- l -alpha- phosphatidyl ethanolamine, was added to the system. It was not possible to extract hexokinase into the surfactant-rich phase of the nonionic surfactant, Triton X-114, even if a considerable amount of octyl-beta-d-glucoside was added to the solution as an affinity ligand. In contrast, the use of the zwitterionic surfactant and octyl-beta-d-glucoside as an affinity ligand proved to be effective for the extraction of hexokinase. The hexokinase extraction efficiency was found to depend upon the solution pH and the concentration of the affinity ligand in the system. The results clearly indicate that hydrophilic proteins can be successfully extracted with surfactant mediated phase separations (cloud point extractions) via use of the zwitterionic surfactant, 3-(nonyldimethylammonio)propylsulfate, and appropriate affinity ligands. Some advantages of zwitterionic surfactants in such extractive processes relative to that of nonionic surfactants are delineated.

Enantiomeric Separations in Chromatography

I. INTRODUCTION The resolution of enantiomers (nonsuperimposable, mirror-image isomers) has traditionally been considered one of the more difficult problems in separation science. Enantiomers have identical physical and chemical properties in an isotropic environment except that they rotate the plane of polarized light in opposite directions. A mixture containing equal amounts of enantiomers is referred to as a racemic mixture. Neither racemic mixtures nor solutions of achiral compounds are able to rotate the plane of polarized light.

Separation of mycotoxins, polycyclic aromatic hydrocarbons, quinones, and heterocyclic compounds on cyclodextrin bonded phases: An alternative lc packing

Abstract β-Cyclodextrin and γ-cyclodextrin chiral bonded phases were previously shown to be useful in the separation of enantiomers, diastereomers and structural isomers. In this work it is demonstrated that these stationary phases are also useful in more routine separations. As such, they provide an alternative to the popular reverse phase packings. Because the selectivity of cyclodextrin packings is often unique they can be used to compliment conventional columns, particularly when separating complex mixtures where peak overlap is a problem. The separation of several important classes of compounds is used to demonstrate the general utility of this packing.

Facile Separation of Enantiomers, Geometrical Isomers, and Routine Compounds on Stable Cyclodextrin LC Bonded Phases

The effectiveness of employing stationary phases composed of chemically bonded cyclodextrin molecules in the high performance liquid chromatographic separation of a variety of different types of compounds is summarized. Over one hundred compounds, including optical, geometrical, and structural isomers, diastereomers, and epimers were successfully separated from each other via use of beta- or gamma-cyclodextrin bonded phases and aqueous methanolic mobile phases. The mechanism of separation is based upon inclusion complex formation between the compounds being separated and the cyclodextrin molecules bonded to the stationary phase. The effects of temperature, mobile phase composition and flow rate upon the chromatographic selectivity and resolution are described. The results indicate that the cyclodextrin columns may be more versatile, flexible, and effective compared to the conventional normal or reversed phase columns.