UPCOMING RESEARCH Prereduction of Arsenic(V) to Arsenic(lll), Enhancement of the Signal, and Reduction of Interferences by L-Cysteine in the Determination of Arsenic by Hydride Generation L-Cysteine reduces arsenic(V) to arsenic(III) at low acid concentrations. Coupled with signal enhancement and reduction of interferences from transition elements, t h e method can be used for a variety of matrices. Hengwu Chen, Department of Chemistry, Hangzhou Univer sity, Hangzhou, Zhejiang, People's Republic of China and Ian D. Brindle* and Xiao-chun Le, Chemistry Department, Brock University, St. Catherines, Ontario L2S 3A1, Canada The Predominant Role of Swelling-Induced Modulus Changes of the Sorbent Phase in Determining the Responses of Polymer-Coated Surface Acoustic Wave Vapor Sensors Comparisons of polymer-coated SAW sensor responses with GLC partition coefficients demonstrate t h a t gravi metric effects account for only a small fraction of the to tal sensor response. A model based on swelling effects is derived to explain the observed responses and is com pared with models for modulus effects. Jay W. Grate* and Mark Klusty, Chemistry Division, Naval Research Laboratory, Washington, DC 20375-5000, R. Andrew McGill, Geo-Centers, Inc., 10903 Indian Head Highway, Fort Washington, MD 20744, and Michael H. Abraham, Gary Whiting, and Jenik Andonian-Haft van, Chemistry Depart ment, University College London, London WC1H OAJ, U.K. In Vivo Calibration of Microdialysis Probes for Exogenous Compounds In vivo calibration of microdialysis probes for exogenous compounds by three different methods is described. Re covery for cocaine in the brain is 8.9 ± 0.68% compared with a n vitro recovery of 5.1 ± 0.18% a t 24 °C and 7.4 + 0.18% a t 37 °C. Stanley Menacherry, Walt Hubert, and Joseph B. Justice, Jr.*, Department of Chemistry, Emory University, Atlanta, GA 30322 Model Analysis of Enzyme Monolayer- and Bilayer-Modified Electrodes: The Steady-State Response A systematic analysis of heterogeneous processes, facili tated by the simple surface configuration, has unraveled the contributions of elementary factors to t h e steadystate sensor response, in good agreement with experi mental results. Tetsu Tatsuma* and Tadashi Watanabe, Institute of Indus trial Science, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan
Model Analysis of Enzyme Monolayer- and Bilayer-Modified Electrodes: The Transient Response Elementary steps and the overall process of the transient amperometric response are analyzed by numerical simu lation and give results in good agreement with experi mental observations. Tetsu Tatsuma* and Tadashi Watanabe, Institute of Indus trial Science, University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan and Yusuke Okawa, Department of Image Science, Faculty of Engineering, Chiba University, Yayoi-cho, Chiba 260, Japan Overoxidized Polypyrrole Films: A Model for the Design of Permselective Electrodes Overoxidized polypyrrole-based polymer-modified carbon electrodes a r e further characterized. The results shed light on the design of permselective electrodes. Allan Witkowski and Anna Brajter-Toth*, Department of Chemistry, University of Florida, Gainesville, FL 32611-2046 Microscopic Organic Analysis Using Two-Step Laser Mass Spectrometry: Application to Meteoritic Acid Residues The spatial resolution of two-step laser desorption/laser ionization MS is extended to 40 μπι, and the technique is applied to the organic analysis of six meteoritic acid res idues. Laurie J. Kovalenko, Claude R. Maechling, Simon J. Clemett, Jean-Michel Philippoz, and Richard N. Zare*, Department of Chemistry, Stanford University, Stanford, CA 94305 and Conel M. O'D. Alexander, McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130 Interpretation of Retention Behaviors of Transition-Metal Cations in Micellar Chromatography Using an Ion-Exchange Model Reversed-phase micellar chromatographic behavior of transition-metal ions is interpreted on t h e basis of an ion-exchange model. Quantitative interpretation facili tates the prediction and optimization of the separation. Tetsuo Okada, Faculty of Liberal Arts, Shizuoka University, Shizuoka 422, Japan Sensitivities of Inductively Coupled Plasma Optical Emission Spectrometry for Dry and Wet Aerosols Mixing a dry silver aerosol with HN0 3 /water droplets re sults in a 43.1% decrease in the ICP signal because of scavenging processes in the nebulizer, whereas the exci tation temperature remains constant. The efficiency of the ultrasonic nebulizer is 5.2%, as determined by cali bration with neutron activation analysis. Alfred P. Weber, Rolf Keil, Leo Tobler, and Urs Baltensperger*, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
These articles are scheduled to appear in AC RESEARCH in the near future. * C o r r e s p o n d i n g author ANALYTICAL CHEMISTRY, VOL. 64, NO. 5, MARCH 1, 1992 • 305 A
UPCOMING RESEARCH Expert System Based on Principal Components Analysis for the Identification of Molecular Structures from Vapor-Phase Infrared Spectra. 2. Identification of Carbonyl-Containing Functionalities Principal components analysis is used to classify vaporphase IR spectra of carbonyls. The tree structure necessary for this expert system is described. In 96% of our trials this tree yielded a correct classification. Erik J. Hasenoehrl, Jonathan H. Perkins, and Peter R. Griffiths*, Department of Chemistry and Idaho Center for Hazardous Waste Remediation Research, University of Idaho, Moscow, ID 83843 Mass Discrimination in Laser Desorption/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Cation-Attachment Spectra of Polymers Variations in velocity distribution of laser-desorbed polymers and salt adduct distributions result in mass selection in FTICR trapping of product ions. Calculations of polymer molecular weight distributions in resulting spect r a are affected. Jeremiah D. Hogan and David A. Laude, Jr.*, Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712-1167 Neutral-Ion Correlation Measurements: A Novel Tandem Mass Spectrometry Data Acquisition Mode for Magnetic Sector/Reflectron Time-of-Flight Instruments A magnetic sector/reflectron TOF instrument, which uses a data acquisition method based on t h e correlation of ions and neutrals to determine t h e mass-to-charge ratio of fragment ions, is described. F. H. Strobel, L. M. Preston, K. S. Washburn, and D. H. Russell*, Department of Chemistry, Texas A&M University, College Station, TX 77843 Capillary Zone Electrophoretic Detection of Biological Thiols and Their S-Nitrosated Derivatives CZE is used to separate and identify reduced thiol species, their S-nitrosated derivatives, and corresponding disulfides. This method allows rapid, reproducible, and unambiguous identification with minimal sample preparation. Joseph Loscalzo, Department of Medicine, Brigham and Wo men's Hospital, 75 Francis Street, Boston, MA 02115 Simultaneous Determination of Mixtures by Kinetic Analysis of General Order Reactions An error-compensating algorithm for kinetic determinations of dual-component mixtures without prior knowledge of reaction orders and rate constants is presented. The method is applicable over a wide range of parameters, and some restrictions (e.g., unity order) are described. Israel Schecter, Max-Planck-Institut fur Quantenoptik, D-8046 Garching, Germany
Preconcentration of Trace Rare Earth Elements in Seawater by Complexation with Bis(2-ethylhexyl) Hydrogen Phosphate and 2-Ethylhexyl Dihydrogen Phosphate Adsorbed on a C18 Cartridge and Determination by Inductively Coupled Plasma Mass Spectrometry Eight 1-L seawater samples can be preconcentrated in 1 h. Replicate analyses of 5-L seawater samples have an average precision for all REEs of 1.04%; t h e range is 0.51-2.11%. Mohammed B. Shabani*, Tasuku Akagi, and Akimasa Masuda, Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Tokyo 113, Japan Drug Release Profiles of Ophthalmic Formulations. 1. Instrumentation The in vitro method is carried out under conditions nearly representative of those observed in vivo. The analytical system is used to study drug release kinetics from controlled-release formulations such as gels and suspensions. Larry E. Stevens, Paul J. Missel, and John C. Lang*, Alcon Laboratories, Inc., 6201 South Freeway, Fort Worth, TX 76134 Combined Supercritical Fluid Extraction/Solid Phase Extraction with Octadecylsilane Cartridges as a Sample Preparation Technique for the Ultratrace Analysis of a Drug Metabolite in Plasma The selective isolation of ultratrace levels of a drug metabolite, mebeverine alcohol, from plasma is achieved by using SFE combined with octadecylsilane cartridges. The extraction method in conjunction with GC/MS analysis gives excellent accuracy and precision in t h e 10-250 ng/mL range. Hanjiu Liu, Linda M. Cooper, Douglas E. Raynie, J. David Pinkston, and Kenneth R. Wehmeyer*, The Procter & Gamble Company, Miami Valley Laboratories, P.O. Box 398707, Cincinnati, OH 45239-8707 Peptide Mapping of Complex Proteins at the Low-Picomole Level with Capillary Electrophoretic Separations Procedures for preparing disulfide-containing proteins for p e p t i d e - m a p p i n g separations a r e described. The quantity of protein required for peptide mapping is reduced to a few picomoles. Kelly A. Cobb and Milos V. Novotny*, Department of Chemistry, Indiana University, Bloomington, IN 47405 Pulsed Sample Introduction Interface for Combining Flow Injection Analysis with Multiphoton Ionization Time-of-Flight Mass Spectrometry Analytes in a liquid carrier are vaporized by passing through a heated capillary tube and then through the sample vaporizer of a high-temperature pulsed nozzle. Alan P. L. Wang and Liang Li*, Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
ANALYTICAL CHEMISTRY, VOL. 64, NO. 5, MARCH 1, 1992 • 307 A
