Fundamentals and Applications of Chemical Sensors
New! Dennis Schuetzle and Robert Hammerle, Editors Ford Motor Company Presents the first comprehensive collection of articles on the fundamentals and applications of a wide variety of chemical sensors. Discusses a range of topics from the development of new sensor concepts to improvements in sensors that have been mass produced for several years. Specific types of sensors discussed include oxygen, electrochemical, microbial, drug, and glucose sensors. CONTENTS Chemically Sensitive Electronic Devices · Gas Sensors in Japan · Tin Oxide Microsensors · Tin(IV) Oxide Gas Sensors · Perovskite-Type Oxides · Zirconium Oxide Oxygen Sensors · Microsensor Vapor Detectors · Chemical Microsensors · Solid State Gas Sensors · Amperometric Proton-Conductor Sensors · Atmospheric Gas Composition Determinations · Chemically Modified Electrode Sensors · Coated-Wire Ion-Selective Electrodes · Chemical Sensing · Detection of Airborne Chemicals · AmidoximeFunctionalized Coatings · Optical Waveguide Devices · Microbial Sensors · Stabilized Lipid Membranes · Design of Sensitive Drug Sensors · Subcutaneous-Type Glucose Sensors Developed from a symposium presented at the Congress of Pacific Basin Societies, Honolulu, Hawaii ACS Symposium Series No. 309 395 pages (1986) Clothbound LC 86-86-3518 ISBN 0-8412-0973-1 US & Canada $74.95 Export $89.95 Order From: American Chemical Society Distribution Office Dept. 16 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE 800-424-6747 and use your credit card!
Focus based detectors have great potential in this area, as discussed by Ed Yeung (Iowa State University) and Milos Novotny (Indiana University). Yeung described the use of indirect detection methods in which one probes the environment of the species rathex than the species itself. In polarimetry, for example, the signal-to-noise ratio of the background is sufficiently high that very sensitive measurements can be made. Because fluorescence detection is already highly sensitive and selective, derivatization of nonfluorescing solute molecules with fluorescing moieties is another approach to achieving sensitivity. In this way, the solute is modified to suit the detection system; usually it is the detection system that is modified to suit the solutes of interest. Because of the current interest in the newly emerging technology of SFC, several papers were given on the interfacing of SFC with spectroscopy. Dick Smith (Battelle Pacific Northwest Laboratory) described in detail the problems associated with restriction and decompression at the SFC column outlet. Jack Henion described the modification of a bench-top mass
spectrometer for SFC/MS. For FT-IR detection, deposition of the effluent on a solid surface (a moving ZnSe window, for example) before detection provides the same sensitivity advantages as noted previously for L C / F T IR. Steven Goates (Brigham Young University) presented recent results obtained from introducing the SFC column effluent into a supersonic jet for fluorescence measurements. The narrow-line fluorescence spectra obtained as a result of rotational cooling in the jet expansion region offer great improvement in the selectivity of coupled SFC/fluorescence spectroscopy. Development of modern analytical measurement techniques is driven by the desire to improve detection limits and to increase the information content of measurements. This year's Summer Symposium primarily addressed the second of these two goals. With the current interest in chromatography-spectroscopy combinations and with the rapid advancements being made in this area, there is every reason to expect that this topic will again be the central focus of a Summer Symposium in the not-too-distant future.
Cell Separations Aqueous two-phase partitioning, counter current chromatography, and field flow fractionation can be used to fractionate cell populations In the past several years, biochemists and cell biologists have become increasingly interested in obtaining viable, relatively homogeneous cell fractions for use in studies of cellular structure and function as well as for biotechnology applications, such as cloning and the production of monoclonal antibodies. Because of the fragile nature of cells, none of the common organic-solvent-based separatory techniques (such as solvent extraction or preparative chromatography) can be used. But three analytical techniques originally developed for separation of macromolecules—aqueous two-phase partitioning, countercurrent chromatography (CCC), and field flow fractionation (FFF)—are now being successfully applied to the fractionation of cell populations, as described recently at the 10th International Symposium on Column Liquid Chromatography (HPLC '86) in San Francisco, Calif.
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Aqueous two-phase partitioning Aqueous solutions of dextran (Dx) and polyethylene glycol (PEG), when mixed above certain concentrations, form immiscible liquid two-phase systems consisting of a PEG-rich top layer and a Dx-rich bottom layer. These aqueous polymer systems have been found useful not only for fractionation of proteins and nucleic acids, but also for fractionation of cells, as described at the symposium by Harry Walter of the Veterans Administration Medical Center in Long Beach, Calif. "Particles usually partition between one of the phases and the interface (unlike soluble materials, which partition between the bulk phases)," Walter explains. "The normal position of cells in a two-phase polymer system is at the interface, so whenever you see partitioning it indicates that something is acting on the cells to pull them out of the interface and into one
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of the phases." By manipulating the physical properties of the polymer sys tem, either by choice of polymer con centration, salts, or ligands, cells can be separated on the basis of surfacecharge-associated properties, noncharge-related properties, or ligand affinity. Although aqueous two-phase parti tioning is often used for actual prepar ative cell separations, it can also be used as an analytical tool to trace sub tle differences in cell surface charac teristics that occur as a function of normal in vivo processes or in vitro treatments. "Because the parameters that determine the partition coeffi cient (K) are exponentially, rather than linearly, related to the Κ value," says Walter, "partitioning often yields separation and information on physi cal properties of biomaterials that are not readily obtained by other means." For example, Walter has been able to detect charge-associated surface dif ferences between red blood cells that are indiscernible by electrophoresis. He has also been able to establish the heterogeneity of certain cell popula tions where other methods have shown only homogeneous populations. In addition to Walter's work with red blood cells, two-phase partitioning has been used to separate other types of mammalian cells, plant cells, bacte rial cells, and viruses and phages. It has also been used to study red blood cells from individuals with diseases in which red blood cell surface alter ations have been reported or are sus pected, such as chronic alcoholism and multiple sclerosis. (See Walter's re cent review article, Anal. Biochem. 1986,155, 215-42, for a detailed de scription of partitioning in aqueous two-phase systems.) Countercurrent chromatography
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Countercurrent chromatography (CCC) is a form of liquid-liquid chro matography that uses low-speed centrifugation to hold one phase of an im-
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miscible liquid pair stationary while the other is eluted through it. Epicyclic rotation of a coil sets up alternating mixing and settling bands of the two immiscible phases, and these bands then travel through the coil, giving up to 50,000 partitioning steps per hour. Sample material is usually injected with the mobile phase using a conventional liquid chromatographic sample loop; sample components that partition toward the mobile phase will elute early, while those favoring the stationary phase or interface will be retained. Applications of CCC, including purification of natural products, peptides, and drugs, have mainly concentrated on aqueous-organic phase systems using the multilayer coil planet centrifuge developed by Yoichiro Ito of the National Heart, Lung, and Blood Institute. (For a description of the development of this technique, see Ito's REPORT in the April 1984 issue of A N A L Y T I C A L C H E M I S T R Y . ) This
process has now been extended for use with double aqueous-phase systems similar to those used for two-phase partitioning, as reported by Ian Sutherland of the National Institute for Medical Research in London at HPLC '86. Because of the high-viscosity and low-density differences of aqueous polymer phases, the methods developed for use with the Ito machine cannot be directly applied. "The multilayer coil works very well with aqueous/organic phase systems," says Sutherland, "but with aqueous/aqueous phase systems, the interfacial tension is too low and the phases emulsify." Consequently, special toroidally wound coils that enhance retention of the viscous polymer phases must be used for aqueous two-phase CCC. Sutherland has used the toroidal coil machines with PEG-Dx polymer systems to fractionate rat liver organelles and for an affinity-based purification of Torpedo electroplax membranes enriched in nicotinic cholinergic receptors. These particles are relatively small (less than a micrometer) and separate well using the toroidal coil system. But larger particles, such as bacterial cells, require an extremely complicated version of the Ito machine, the nonsynchronous coil planet centrifuge. Although Sutherland has used this technique to separate red blood cells, he doesn't believe that the results necessarily justify the sort of effort required to achieve such separations. CCC has a number of potential advantages for cell separations, including very rapid separations and suit-
Computer Applications in the Polymer Laboratory
Focus ability for preparative-scale fraction ations, such as those required in the biotech industry. The use of CCC for cell separations, says Sutherland, is still an emerging technique that is far from perfect. It should move forward, however, with the identification of new biocompatible phase systems that are more appropriate for use with CCC than the current aqueous poly mer systems. Field flow fractionation
New! Theodore Provder, Editor Glidden Coatings and Resins Reports on the impact the technolog ical revolution is having on the re search worker in polymer chemistry. Reviews the impact of computer technology in the polymer laboratory, and speculates on future trends in task automation. Concentrates on three important areas: Laboratory information generation, manage ment, and analysis tools; instrument automation for polymer characteriza tion; and polymerization cure proc ess modeling and control. Helps bridge the gap between technical and office tools for all scientists and technologists working in the field of polymer research. CONTENTS Laboratory Automation: A New Perspective · Economic Considerations of LIMS · Applica tions of Computer Data Base Management · Advances in Scientific Software Packages · Computer-Assisted Polymer Design · Sili cone Acrylate Copolymers · Constrained Mixture-Design Formulations · Analysis of Isochronal Mechanical Relaxation Scans · Automated Rheology Laboratory: Part I · Automated Rheology Laboratory: Part II · Automated Analyses for the Tensile Tester · Data Collection for a Size-Exclusion Liquid Chromatograph · X-ray Pole Figure Studies of Polymers · Computers and the Optical Microscope · Simulation Activities in a R&D Laboratory for Coatings · Flexible Control of Laboratory Polymer Reactors · Control of a Polystyrene Reactor · The Modeling of Polymerization Kinetics · Mathematical Modeling of Emulsion Polymerization Reac tors · Kinetics Analysis of Consecutive Reactions · Optimization of Bake Conditions for Thermoset Coatings · An AnhydrideCured Epoxy Polymerization · Investigation of Self-Condensation of 2,4-Dimethyol-Ocresol Developed from a symposium sponsored by the Division of Polymeric Materials Science and Engineering of the American Chemical Society ACS Symposium Series No. 313 321 pages (1986) Clothbound LC 86-10831 ISBN 0-8412-0977-4 US & Canada $69.95 Export $83.95 Order from: American Chemical Society Distribution Office Dept. 20 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE 800-424-6747 and use your credit cardl
Steric field flow fractionation (steric FFF), an elution-based technique that sorts particles according to their size, can also be used for cell fractionation, according to Karin Caldwell of the University of Utah. FFF has a large fractionation range (baseline separa tion of a seven-component mixture of polystyrene latex spheres with diame ters ranging from 2 to 45 μτη has been performed in less than 5 min), making it particularly useful for fractionation of cells with diameters in the l-20-μπι range. The fractionator is a thin ribbonshaped channel that is exposed to a centrifugal field perpendicular to the major walls. Sample particles settle at one of the channel walls, and the flow of carrier forces the particles to move downstream at rates proportional to their size. This is a highly efficient process, and separations can be ac complished in a matter of minutes. One advantage of FFF, says Cald well, is that the choice of carrier has little influence on the separation, al
lowing use of a carrier with maximum compatibility with the cells, such as aqueous buffers or growth medium. "Generally, when you work with live materials such as cells, the less bizarre an environment they are exposed to, the better off you are," she explains. "If cells are separated in a polymer phase, then you have to move them very carefully from the polymer medi um to a growth medium so as to avoid osmotic and other shocks. But because FFF can be performed directly in the growth medium, no such transfers are necessary." This carrier flexibility, combined with the short separation times, makes FFF particularly suitable for handling cell samples in which viability follow ing separation is important. Hela cells, neurons, and glial cells have all shown good growth in tissue culture after passage through a sedimentationbased steric FFF system. Like the aqueous polymer-based techniques, FFF can be used to detect small differences in cell populations (although in the case of FFF, these are differences in size rather than in cell surface characteristics), as well as for preparative separations. For example, retention differences can be seen be tween cells of the same type from dif ferent species and between cells of the same line grown in different environ ments. FFF can also be used to sepa rate cells for use in cloning and pro duction of monoclonal antibodies and to obtain growth-synchronized cell populations. M.D. W.
Instrumentation Growth Areas Environment, process control, and biotechnology are seen driving the market Although the worldwide analytical instrument industry is currently esti mated to be generating more than $3 billion in annual revenues, it has never enjoyed high visibility among investment analysts. This lack of visi bility probably has something to do with the title of a recently published analysis of the industry by Nancy E. Pfund of Hambrecht & Quist Inc. (San Francisco, Calif.): "The Quiet Revolution: Analytical Instrumenta tion Extends Its Reach." For, despite the fact that revolutionary advances have been made in analytical instru
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mentation over the past decade, this revolution has heretofore obtained lit tle recognition on Wall Street. Investment analyses of PerkinElmer Corporation, for example, fre quently focus on the company's semi conductor chip-making equipment, despite the fact that analytical instru mentation constitutes a larger seg ment of Perkin-Elmer's gross reve nues. Recognition of the scientific in strument industry as a quintessentially high-technology enterprise has devel oped slowly, which makes increased attention to the industry by an invest-
