Ordered Media in Chemical Separations

296 Pages·1987·5.02 MB·English

by  Willie L. Hinze and Daniel W. Armstrong (Eds.)

Ordere
in Chemical Separations
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
ACS SYMPOSIUM SERIES 342
Ordered Media
in Chemical Separations
Willie L. Hinze, EDITOR
Wake Forest University
Daniel W. Armstrong, EDITOR
Texas Tech University
Developed from a symposium sponsored by
the Division of Analytical Chemistry
at the 191st Meeting
of the American Chemical Society,
New York, New York,
April 13-18, 1986
American Chemical Society, Washington, DC 1987
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Library of Congress Cataloging-in-Publication Data
Ordered media in chemical separations.
(ACS symposium series; 342)
Developed from the Symposium on Use of Ordered
Media in Chemical Separations.
Includes bibliographies and indexes.
1. Chromatographic analysis—Congresses.
2. Separation (Technology)—Congresses. 3. Surface
active agents—Congresses. 4. Cyclodextrins—
Congresses.
I. Hinze, Willie L., 1949- .
W., 1949- . III. American Chemica
Division of Analytical Chemistry
Chemical Society. Meeting (191st: 1986: New York,
N.Y.) V. Symposium on Use of Ordered Media in
Chemical Separations (1986: New York, N.Y.)
VI. Series.
QD79.C4073 1987 543'.08 87-13563
ISBN 0-8412-1402-6
Copyright © 1987
American Chemical Society
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In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
ACS Symposium Series
M. Joan Comstock, Series Editor
1987 Advisory Board
Harvey W. Blanch Vincent D McGinnis
University of California—Berkele
Alan Elzerman W. H. Norton
Clemson University J. T. Baker Chemical Company
John W. Finley James C. Randall
Nabisco Brands, Inc. Exxon Chemical Company
Marye Anne Fox E. Reichmanis
The University of Texas—Austin AT&T Bell Laboratories
Martin L. Gorbaty C. M. Roland
Exxon Research and Engineering Co. U.S. Naval Research Laboratory
Roland F. Hirsch W. D. Shults
U.S. Department of Energy Oak Ridge National Laboratory
G. Wayne Ivie Geoffrey K. Smith
USDA, Agricultural Research Service Rohm & Haas Co.
Rudolph J. Marcus Douglas B. Walters
Consultant, Computers & National Institute of
Chemistry Research Environmental Health
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Foreword
The ACS SYMPOSIUM SERIES was founded in 1974 to provide a
medium for publishing symposia quickly in book form. The
format of the Series parallels that of the continuing ADVANCES
IN CHEMISTRY SERIE
papers are not typese reproduce y
by the authors in camera-ready form. Papers are reviewed under
the supervision of the Editors with the assistance of the Series
Advisory Board and are selected to maintain the integrity of the
symposia; however, verbatim reproductions of previously pub
lished papers are not accepted. Both reviews and reports of
research are acceptable, because symposia may embrace both
types of presentation.
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Preface
ENORMOUS ADVANCES AND GROWTH IN THE USE OF ORDERED MEDIA (that
is, surfactant normal and reversed micelles, surfactant vesicles, and
cyclodextrins) have occurred in the past decade, particularly in their
chromatographic applications. New techniques developed in this field
include micellar liquid chromatography, micellar-enhanced ultrafiltration,
micellar electrokinetic capillar
products with reversed micelles
cyclodextrins as stationary and mobile-phase components in chromatogra
phy. The symposium upon which this book was based was the first major
symposium devoted to this topic and was organized to present the current
state of the art in this rapidly expanding field.
This volume resulted from the need to have a readily available
reference source to present an account of the roles and uses of ordered
media in separation science. The emphasis has been placed on chromato
graphic applications. The organization of the volume divided naturally into
two parts. The first part, consisting of 10 chapters, deals with organized
surfactant media in separation science; the second, consisting of six
chapters, details the applications of cyclodextrins in chromatography.
Emphasis has been placed on a critical assessment of recent work and an
integration of material from a wide range of sources. Although all of the
applications involving these types of ordered media in separation science
were not covered, it is hoped that all of the important recent developments
in this field have been included.
We thank the authors for their contributions and their interest in this
project. We are also grateful to the anonymous referees for their time,
invaluable comments, and constructive criticism of the manuscripts during
the review process. We also thank the ACS Books Department staff for their
help with this undertaking and for their patience.
WILLIE L. HINZE
Wake Forest University
Winston-Salem, NC 27109
DANIEL W. ARMSTRONG
Texas Tech University
Lubbock, TX 79409
IX
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Chapter 1
Organized Surfactant Assemblies in Separation Science
Willie L. Hinze
Department of Chemistry, Wake Forest University, P.O. Box 7486,
Winston-Salem, NC 27109
A brief description of the structural features and
relevant properties of different organized assemblies
formed from surfactant molecules is presented Next
the use and applicatio
systems in separatio
possible new areas for future developments employing
these ordered media are mentioned.
Many separation processes mediated by the presence of surfactant
organized assemblies (also referred to as organized or ordered media)
have been developed during the past ten years. The growing importance
and popularity of such separation techniques is demonstrated by the
fact that numerous recent review articles have been devoted to this
subject (1-10). The purpose of this overview is two-fold. First, it
is intended to provide the novice entering the field with basic,
simplified background information on organized surfactant systems
which should facilitate a better understanding of the more specific
technical articles that appear in subsequent chapters of this
monograph (or the chemical literature). Secondly, this overview will
attempt to update and summarize the previous reported work in this
area of separation science. Topics not extensively covered in the
previous reviews (or succeeding chapters of this monograph) will be
discussed in greater detail. Throughout, emphasis will be placed on
the practical applications and potential future developments. It is
hoped that this overview will paint a general picture of the
structure, properties, and role of different surfactant organized
assemblies in separation science.
Structure and Properties of Different Organized Surfactant Assemblies
Structure Formation in Surfactant Solutions. Surfactants, also
referred to as soaps, detergents, tensides, or surface active agents,
are amphiphilic molecules possessing both hydrophilic and hydrophobic
regions. They can be classified as anionic, cationic, zwitterionic,
or nonionic (neutral) depending upon the nature of the polar
0097-6156/87/0342-0002$ 18.30/0
© 1987 American Chemical Society
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
1. HINZE Surfactant Assemblies in Separation Science 3
head-group that is bound to the nonpolar hydrocarbon tail. Various
colloidal-sized organized structures can form when surfactant
molecules are dissolved in a particular solvent depending upon the
nature and concentration of the surfactant molecule, nature of the
solvent system, and exact experimental conditions U.e. temperature,
pressure, and/or presence or absence of additives) (11-16). Figure 1
shows an oversimplified representation of some of the different
surfactant species possible as the surfactant concentration is
increased in a surfactant - water two-component system. At low
concentrations above the Krafft temperature, the surfactant is present
in isolated monomeric molecular form. With further increases in
concentration, the surfactant molecules can dynamically associate to
form micellar assemblies (termed aqueous or normal micelles). The
surfactant concentration at which such aggregation occurs is referred
to as the critical micelle concentration (CMC) and the number of
surfactant molecules comprising the micellar entity is called its
aggregation number (N)
generally viewed as bein
controversy still exists concerning the exact shape and structure of
such entities (15,17). Typically, such micellar aggregates are
composed of 40 - 140 monomeric surfactant molecules such that their
hydrophobic tails are oriented inward forming a nonpolar core region
and their hydrophilic headgroups are directed toward and in contact
with the bulk aqueous solvent. Further increases in surfactant
concentration can result in the formation of other different types of
organized assemblies. Initially, there can be a transition from
spherical to rodlike or cylindrical micelles (Figure 1). Still higher
concentrations lead to formation of various liquid crystalline
aggregates (Figure 1: middle, viscous, and neat liquid crystalline
phases) (jj_, 1_5,J_8). The presence of a third component (organic
solvent) can give rise to an even larger variety of aggregated
surfactant species (j_5). Table I summarizes the structure, name, and
micellar parameters (CMC and N) of some typical long-chain alkyl
surfactants employed to form aqueous normal micellar systems (11,19).
In addition to these types of micellar-forming surfactants, there
is another class of molecules that can associate in water to form
micellar aggregates; namely, the bile salts (20). Bile salts are very
important biological detergent-like molecules. However, they differ
from the long-chain alkyl surfactants previously mentioned in that
they possess a hydrophobic and a hydrophilic face (Figure 2).
Consequently, bile salts exhibit a different type of aggregation
behavior. That is, the aggregation process is viewed as consisting of
the stepwise formation of initial primary micelles which are composed
of 2 - 8 monomers held together by hydrophobic interactions between
the bile salt nonpolar faces. At higher bile salt concentration (or
high ionic strength), the primary micelles can further aggregate to
form larger, rod-like cylindrically shaped secondary bile salt
micelles due to intermolecular hydrogen bonding between their hydroxyl
groups (2,21). Table II presents the name, structure, and micellar
parameters of some common bile salts. All surfactants and bile salts
mentioned in Tables I and II are commercially available (22). A
recent multi-volume series lists the trade name, chemical name,
manufacturer, form, properties, toxicity, composition, principal and
secondary uses, etc. for many of these surfactants (26).
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
4 ORDERED MEDIA IN CHEMICAL SEPARATIONS
TABLE I. Structure, Name, Abbreviation, and Micellar Parameters of
Some Aqueous Micellar-Forming Surfactants Employed in
Separation Science
Surfactant Structure; Name; and [Abbreviation] CMC,a'^ N^'°
mM
Anionic Micelle-Forming Surfactants of General Formula R-X M+:
R=C , X=0S0, M=Na; Sodium hexadecylsulfate [NaHDS] 0.52 100
16 3
R=C , X=0S0, M=Na; Sodium dodecylsulfate [NaLS] 8.1 62
12 3
R=C , X=0S0, M=Na; Sodium decylsulfate [NaDS] 33.0 50
1Q 3
R=C, X=0S0, M=Na; Sodium octylsulfate [NaOS] 136.0 20
g 3
R=C , X=C0, M=Na; Sodium laurate [NaL] 24.0 56
1Q 2
R=C , X=C0, M=K; Potassiu
1Q 2
R=C , X=C0, M=K; Potassiu
15 2
R=C , X=S0, M=Na; Sodium dodecylsulfonate [NaDDS] 9.8 54
12 3
Cationic Micelle-Forming Surfactants of General Formula R-N+(CH ) X~:
3 3
R=C , X=C1; Hexadecyltrimethylammonium chloride [CTAC] 1.3 78
16
R=C , X=Br; Hexadecyltrimethylammonium bromide [CTAB] 0.9 61
16
R=C , X=Br; Dodecyltrimethylammonium bromide [LTAB] 15.0 50
12
R=C , X=Br; Decyltrimethylammonium bromide [DTAB] 65.0 47
1Q
R=C, X=Br; Octyltrimethylammonium bromide [OTAB] 180
g
Mixture of R=C , C.,, and C., X=Br; Cetrimide [C] 2.0- 50-
10 c
predominately R=C^ 8.5 62
CH (CH ) N+C H Cl"; Cetylpyridinium chloride [CP] 0.9 95
3 2 15 5 5
CH (CH ) N+(CH ) (CH C H )Cl"; Hexadecyldimethyl-
3 2 15 3 2 2 6 5
benzylammonium chloride [CBzAC] 0.27
Nonionic Micelle-Forming Surfactants of General Formula R(0CH CH ) OH:
2 2 n
R=C , n=23; Polyoxyethylene(23)dodecanol [Brij-35] 0.1 40
12
R=(CH ) CCH C(CH ) C H , n=9.5; Polyoxyethylene-t-
3 3 2 3 2 6 4
octylphenol [Triton X-100 or TX-100] 0.2 143
R=CH (CH ) CH=CH(CH ) , n=10; 10 Oleyl ether [Brij-96] 0.04
3 2 7 2 g
R=mixture of C C , and C^; n=6; Neodol 91-6 0.37(wt%)-
9> 1Q
Polysorbate 80 (or Polyoxyethylene sorbitan mono-
oleate [Tween-80] 0.012 60
Zwitterionic Micelle-Forming Surfactants of General Formula
R-(CH ) N+CH X :
3 2 2
3.9
In Ordered Media in Chemical Separations; Hinze, W., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.