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Brief introductions to the research articles appearing in the December 1 issue and tentatively scheduled to appear in the December 15 issue
Accelerated Articles Using a droplet as a sampler and optical cell The optical signal observed during the life of a drop can con tain considerable information. Purnendu K. Dasgupta and Hanghui Liu of Texas Tech University report on the analyti cal use of a dynamic droplet-based gas collection and anal ysis system that includes an LED photodiode. Chlorine gas is determined colorimetrically via its uptake by a droplet of dilute colorless solution of tetramethylbenzidine followed by a one-step rapid reaction with TMB at the droplet surface to form a yellow product. ("A Renewable Liquid Droplet as a Sampler and a Windowless Optical Cell. Automated Sen sor for Gaseous Chlorine"; AC9507350; p. 4221)
A holographic sensor for proteases Holograms, or more specifically, Bragg reflectors, have been used as sensors for physical parameters such as pressure and temperature. Roger B. Millington and colleagues at the University of Cambridge (U.K.) describe the use of a gela tin-based optical Bragg reflector as a quantitative sensor ele ment for measuring protease activity. Response is mea sured as the change in wavelength or brightness created when trypsin cleaves at peptide bonds adjacent to the arginine and lysine residues of gelatin and causes swelling of the hologram. ("A Holographic Sensor for Proteases"; AC950868L; p. 4229)
ΡΜΙΜ of redox gels • Phase measurement interferometric microscopy (PMIM) is a noncontacting laser interference microscopy that uses computerized phase measurements to determine the optical pathlength difference between the sample and an optical reference surface. Noboru Oyama and colleagues atToyko University of Agriculture and Technology Gapan) and the University of Utah describe the use of PMIM for in situ monitoring of volume changes of redox-active gel films as a function of temperature and electrode potential. The PMIM optical image can be directly converted to an image of the true physical dimensions of the redox gel film, provided that the refractive index of the redox gel is spatially uniform. ("In Situ Interferometric Microscopy of Temperature- and Potential-Dependent Volume Changes of a Redox Gel"; AC950782S)
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Single-cell analysis of glutathione
Glutathione, a low molecular weight thiol-containing species found in mam malian tissues, is involved in detoxifying functions of the cell as well as DNA and protein synthesis. Richard N. Zare and colleagues at Stanford University re port that 2,3-naphthalenedicarboxaldehyde reacts rapidly with glutathione and its precursor to form highly fluorescent deriva tives under physiological conditions. This selective labeling, combined with epiluminescent and confocal fluorescence mi croscopy, is used to quantitatively determine and histochemically localize glutathione in neurobiological samples. ("Use of 2,3-Naphthalenedicarboxaldehyde Derivatization for Single-Cell Analysis of Glutathione by Capillary Electrophoresis and Histochemical Localization by Fluorescence Microscopy"; AC950494W; p. 4261)
N-terminal amino acid sequencing using fluorescence Detection of thiazolinone (TZ) amino acids is often difficult be cause these cyclized derivatives tend to be unstable. Using a flu orescent Edman reagent that they recently developed, Kazuhiro Imai and colleagues at the University of Tokyo and Na gasaki University (Japan) report on a method for N-terminal amino acid sequencing of peptides that produces TZ amino ac ids that are sufficiently stable to be determined by LC fluores cence. The method is used to analyze sequences of Leu5enkephalin and angiotensin using samples of only 25-100 pmol. ("Development of an Efficient Amino Acid Sequencing Method Using Fluorescent Edman Reagent 7-[(JV,.N-Dimethylamino)sulfonyl]-2,l,3-benzoxadiazol-4-yl Isothiocyanate"; AC950328O; p. 4276)
Real-time detection of DNA hybridization probes Identification of nucleic acid systems with hybridization probes requires the use of labels such as radioactive isotopes or fluo rescent molecules for detection, a process that can take hours or days. Helen J. Watts and colleagues at the U.K. Laboratory of the Government Chemist and Fisons Applied Sensor Technol ogy (U.K.) describe a real-time optical biosensor, the resonant mirror, for direct detection of DNA-DNA hybridization. The au thors report that the lowest detectable concentration of target oligonucleotide (40 mer) was 9.2 nM. ("Real-Time Detection and Quantification of DNA Hybridization by an Optical Bio sensor"; AC950570V; p. 4283)
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An expression immunoassay for antigen quantitation Recent research in improving the sensitivity of immunoassays is geared primarily toward developing nonisotopic systems based on fluorescent, chemiluminescent, or enzyme labels. Theodore K. Christopoulos and Norman H.L. Chiu of the University of Windsor (Canada) describe the use of an expression immunoassay in which the label is a DNA fragment that encodes an enzyme. They find that as few as 3000 molecules of DNA label can be detected. ("Expression Immunoassay. Antigen Quantitation Using Antibodies Labeled with EnzymeCoding DNA Fragments"; AC950676Q; p. 4290)
Tryptic mapping with mass spectrometric probe tips With the advent of MAI J) I MS, direct mass spectrometric analysis of complex polypeptide mixtures has become routine, and the most useful information is obtained when MALDI is combined with conventional chemical and/or enzymatic treatments. Randall W. Nelson and colleagues at Arizona State University develop a method for accurate tryptic mapping of polypeptides using MALDI TOFMS and mass spectrometer probe tips activated through covalent immobilization of trypsin. They find that the new technique produces more characteristic proteolytic fragments and eliminates background signals caused by autolysis of trypsin. ("Rapid Tryptic Mapping Using Enzymatically Active Mass Spectrometer Probe Tips"; AC950577C; p. 4343)
Distribution of vitamin-related compounds in human serum The protective capabilities of vitamin-related micronutrients against cancer are being studied. In support of these studies, David L. Duewer and Katherine S. Sharpless of the National Institute of Standards and Technology analyze more than 1400 serum samples for 11 fat-soluble vitamin-related compounds collected in two studies of adult populations. They discuss between-study measurement scale bias and reproducibility for each analyte, univariate distributions of the analytes for the control and sample sera, bivariate correlations among analytes within the controls and across the two studies, and implications of the results. ("Population Distributions and Intralaboratory Reproducibility for Fat-Soluble Vitamin-Related Compounds in Human Serum"; AC950349I; p. 4416)
titated in the presence of a concurrent pH change. The sensor detects penicillin at 0.25-10.0 mM at pH 6.2-7.5. ("Improved Fiber-Optic Chemical Sensor for Penicillin"; AC9507451)
Direct bacterial counting • Rapid counts and estimates of viable bacterial cells is important for monitoring the movements and growth of these organ isms in drinking-water systems or in cooling towers. Tadashi Matsunaga and colleagues at the Tokyo University of Agricul ture and Technology (Japan) develop a two fluorescent dye method that directly counts viable and dead cells with only 1 min of incubation. The authors demonstrate the method with Vibrio alginolyticus cells. ("Direct Count of Bacteria Using Fluo rescent Dyes: Application to Assessment of Electrochemical Disinfection"; AC950141X)
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Selectivity of calixarenes
Although the length of the crown ether chain is the most important factor in se lectivity, structural features and bulky substituents also play a significant role. Giovanni Mori and colleagues at the Uni versité degli Studi (Italy) examine the detection limits, sensitivities, and selectivity constants of a series of calix crowns used as carriers in liquid-membrane electrodes. They correlate their results with the structural properties of the ligand and the polymeric membrane. ("Selectivity of Calix[4]arene-crown-6 for Cesium Ion in ISE: Effect of the Conformation"; AC950471H; p. 4234)
Measuring moisture in transformer oil Because of systematic biases in the measurement of moisture in transformer oil arising from the apparatus or solvent system used in the analysis, the American Society of Testing Materials requested studies to provide reference materials to evaluate these biases and define their sources. Sam A. Margolis of the National Institute of Standards and Technology describes the titration of moisture in oils using both coulometric and volumetric methods of Karl Fischer moisture titration. A variety of solvent systems and instruments are investigated. ("Amperometric Measurement of Moisture in Transformer Oil Using Karl Fischer Reagents"; AC950642I; p. 4239)
H202sensor Degradation of a potential antitumor drug The hexapeptide antagonist known as antagonist G inhibits the growth of small-cell lung cancer cells. Antagonist G is in phase I drug trials, and information on the degradation of the peptide in solution is required. J. Léon Ε. Reubsaet and colleagues at the Universiteit Utrecht (The Netherlands) report on the degradation products in acidic and alkaline solutions as studied by a variety of analytical methods. ("Structural Identification of the Degradation Products of the Antitumor Peptide Antagonist [Arg6, D-Trp7·9, MePhe8] Substance Ρ (6-11))"; AC950633+; p. 4431)
Measuring pH and penicillin simultaneously • The pH in fermentation broths changes dramatically through out the process and makes it difficult to measure pH and penicil lin concentration. David R. Walt and Brian G. Healey of Tufts University fabricate an array of penicillin- and pH-sensitive ma trices on the same optical fiber that allows penicillin to be quan692 A Analytical Chemistry, December 1, 1995
Although enhancing the thermostability of sensors by making them with enzymes isolated from thermophilic organisms has been considered, the enzymes either were not available in the needed quantity or did not have the appropriate activity. Adam Heller and colleagues at the University of Texas at Austin report on a thermostable wired enzyme electrode made with soybean peroxidase, which recently became commercially available. At 65 °C, the sensor's sensitivity decays at less than 2% per hour; at 25 °C, it maintains the sensitivity and dynamic range of earlier horseradish peroxidase-based sensors. ("A Thermostable Hydrogen Peroxide Sensor Based on 'Wiring' of Soybean Peroxidase"; AC950492B; p. 4247)
Getting a better SECM image • Surface roughness distorts the images obtained in scanning electrochemical microscopy, especially near the edges. Mark D. Pritzker and colleagues at the University of Waterloo (Canada) present a method for rigorously modeling the blurring process.
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They find that it may be possible to resolve features smaller than the tip by using a small sampling interval relative to the tip size. ("Modeling the Degradation of Scanning Electrochemical Microscope Images Due to Surface Roughness"; AC9503015)
Detecting histamine and 5-hydroxytryptamine in cells • Although histamine and 5-hydroxytryptamine (5-HT) have traditionally been measured by derivatization and chromatographic separation, these techniques have not been developed for use at the level of individual cells. R. Mark Wightman and colleagues at the University of North Carolina-Chapel Hill use carbon-fiber electrodes to measure histamine and 5-HT in individual mast cells separated by chromatography. The average quantity measured is 150 fmol histamine and 4 fmol 5-HT. ("Electrochemical Detection of Histamine and 5-Hydroxytryptamine at Isolated Mast Cells"; AC9506903)
Reproducible mercury films on glassy carbon • Studies of copper speciation in seawater often involve electrochemical analysis using glassy carbon-mercury film electrodes and acidification of the water sample. However, there are a number of problems with this analysis that lead to variable results. Alberto Zirino and colleagues at the Naval Control and Ocean Surveillance Center describe the process of mercury film formation and ways to optimize conditions to create reproducible films on glassy carbon in acidified seawater media. ("A 'Hybrid' Mercury Film Electrode for the Voltammetric Analysis of Copper and Lead in Acidified Seawater and Other Media"; AC950758E)
FT-IR of metal electrode surfaces • In situ IR spectroscopy has been used to examine a variety of interfacial processes, including electrochemical mechanisms, as well as the effects of the applied potential and surface microstructure on the spectral properties of adsorbed CO on metal electrodes. D. A. Scherson and colleagues at Case Western Reserve University use in situ ATR-FT-IR as a probe of molecular adsorption on metal electrode surfaces in aqueous electrolytes using 2,5-dihydroxybenzyl mercaptan adsorbed on gold as a model system. ("In Situ Fourier Transform Infrared Spectroscopy of Molecular Adsorbates at Electrode-Electrolyte Interfaces: A Comparison between Internal and External Reflection Modes"; AC9501046)
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Individual microparticle analysis
Measurements on individual microparticles can provide data on variations in composition or allow detection of an analyte of interest present in only a small fraction of the total particles. William B. Whitten and colleagues at Oak Ridge National Laboratory describe a laser desorption/ablation tandem MS method for detecting nonvolatile substances on particles. The new method analyzes microparticles by injecting them one by one into the center of the electrodes of an ion trap mass spectrometer, where they are sampled by laser desorption/ ablation. ("Laser Desorption Tandem Mass Spectrometry of Individual Microparticles in an Ion Trap Mass Spectrometer"; AC9506746; p. 4330)
Graphite SALDI MS of peptides and proteins Because the use of solid matrices makes it difficult to interface CE or HPLC to MALDI, the development of laser desorption of liquid solutions is of interest to biomedical mass spectrometrists who want to extend the range of desorption techniques. Jan Sunner and colleagues at Montana State University describe a new technique they term surface-assisted laser desorption/ionization TOFMS, or SALDI MS, in which relatively large graphite particles are used to couple the UV laser energy into the liquid solution. The signal intensity is as good as that in conventional MALDI and, under optimum conditions, few background peaks are observed even at low mass. ("Graphite Surface-Assisted Laser Desorption/ionization Time-of-Flight Mass Spectrometry of Peptides and Proteins from Liquid Solutions"; AC950263P; p. 4335)
Determining herbicide residues in lipid-rich tissue Detection of herbicide residues in aquatic biota typically requires around 10 g dry weight of tissue; for small invertebrates this may require the collection of thousands of individuals. John V. Headley and colleagues at Canada's National Hydrology Research Institute describe the application of tandem MS to the detection of picogram levels of herbicide analytes in tissue samples weighing < 1 mg. ('Tandem Mass Spectrometry of Herbicide Residues in Lipid-Rich Tissue"; AC950441E; p. 4349)
Separating the signal from the noise in CE/ESIMS Although the combination of CE with TOFMS using an electrospray interface has the potential to be a powerful technique for solving chemical and biochemical problems, background noise often prevents detection of peaks in the reconstructed electropherogram. Richard D. Smith and colleagues at Pacific Northwest Laboratory and GOOGLY Enterprises use sequential paired covariance to enhance the signal-to-noise ratio and allow immediate identification of the number of components in a mixture and their corresponding retention times. ("Application of Sequential Paired Covariance to Capillary Electrophoresis Electrospray Ionization Time-of-Flight Mass Spectrometry: Unraveling the Signal from the Noise in the Electropherogram"; AC950688B; p. 4371)
Improving TLC/MS imaging • Imaging problems in TLC/MS can be caused by analyte spreading. David M. Hercules and colleagues at the University of Pittsburgh and Vanderbilt University demonstrate an approach in which a matrix layer is generated on a substrate and then transferred to a plate. Successful direct imaging of silica gel TEC plates with a spatial resolution of 250-500 pm and high sensitivity are demonstrated for nanogram quantities of several compounds. ("Imaging of Thin-Layer Chromatograms Using Matrix-Assisted Laser Desorption/ionization Mass Spectrometry"; AC950472+)
Inertial spray extraction interface for VOCs • Although several methods exist for determining volatile organic compounds in aqueous samples, these approaches do not readily lend themselves to analyzing blood. Jane Montgomery and colleagues at Université de Montréal (Canada) and McGill University (Canada) describe the inertial spray extraction interface, which consists of a nozzle directed downward in a spray chamber that is coupled to an ion trap mass spectrometer
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through a helium jet separator. Detection limits are < 1 ppb for most compounds, and results for toluene and xylene in blood correlate well with conventional methods. ("Volatile Organic Compound Analysis by an Inertial Spray Extraction Interface Coupled to an Ion Trap Mass Spectrometer"; AC950450N)
Preserving tertiary peptide structure during analysis • MALDI MS is generally performed with samples dissolved in an acidic solution (pH < 2.0), a process that leads to denaturing of proteins and peptides. R. J. Cotter and colleagues at the Johns Hopkins School of Medicine describe new, less harsh solu tions using ammonium bicarbonate or ammonium citrate solu tions that allow the observation of MALDI mass spectra of noncovalently bound peptide-metal ion complexes and peptideenzyme complexes. ("Matrix-Assisted Laser Desorption/ Ionization of Noncovalently Bound Compounds"; AC9506488)
Identifying heteroaromatics in petroleum distillates • In the petroleum industry, knowledge of the composition of ar omatic hydrocarbons and heteroaromatics in distillates is im portant in refining crude oil and in the storage and use of re fined products. Alan G. Marshall, Stuart Scheppele, and col leagues at Florida State University and the University of IllinoisChicago use a dual-trap FT ion cyclotron resonance mass spectrometer to directly resolve ions in the low-voltage EI mass spectrum of the aromatic neutral fraction from a gas oil. They show that the FT-ICR system can differentiate hydrocarbons from heteroatom-containing compounds in petroleum distil lates and refinery streams. ("Resolution and Chemical Formula Identification of Aromatic Hydrocarbons and Aromatic Com pounds Containing Sulfur, Nitrogen, or Oxygen in Petroleum Distillates and Refinery Streams"; AC9507855)
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Leaching organotin compounds from sediments
Environmental analysis of toxic organo tin compounds in complex matrices of ten requires cumbersome sample prep aration steps. Olivier F. X. Donard and colleagues at the Université de Bordeaux (France) develop a rapid leaching method for butyl- and phenyltin derivatives from sediments using microwave-assisted digestion. This procedure, followed by capillary GC, offers detection limits of ~ 1 ng/g as tin and is validated using two certified reference materials. ("Microwave-Assisted Leaching of Organotin Compounds from Sediments for Speciation Analysis"; AC950029Z; p. 4250)
ITP/Raman spectroscopy Isotachophoresis, a technique that generally is not paired with other techniques, can concentrate an ion of interest to nearly the concentration of the leading electrolyte. Michael D. Morris and colleagues at the University of Michigan demonstrate isotachophoretic separation and on-line Raman spectroscopy of ATP, ADP, and AMP at concentrations of at least 5 χ 10"6 M. The analytes are concentrated to above 10~2 M at the detection window, al lowing measurement of the spectra with a 1-s integration time. ("On-Line Raman Spectroscopy of Ribonucleotides Preconcentrated by Capillary Isotachophoresis"; AC950776W; p. 4255) 694 A Analytical Chemistry, December 1, 1995
Near-IR for fluorescence lifetime determinations On-line fluorescence lifetime determinations during CE present new challenges not usually found in LC applications. Steven A. Soper and colleagues at Louisiana State University demonstrate a near-IR time-correlated single-photon counting instrument to measure fluorescence lifetimes of the dyes IR-125 and DTTCI on line. Their results agree favorably with static measure ments made at high concentrations. They also measure the life times of fluorescently tagged C-terminal fragments produced from the M13mpl8 template to demonstrate the instrument's capabilities against the high scattering background produced by the gel CE. ("On-Line Fluorescence Lifetime Determinations in Capillary Electrophoresis"; AC950597E; p. 4358)
Decoupling CE and EC Although electrochemical detection is well suited to the minia turization required for CE, the electrochemical cell must be well isolated from the current of the electrophoretic system. Craig E. Lunte and Sangryoul Park of the University of Kansas de scribe the fabrication of an end-column decoupler that provides the high current shunting ability of a long-cast Nation on-column decoupler as well as improved detection of cations and higher separation efficiencies. They demonstrate the char acteristics of the system by detecting catecholamines in Ringer's solution. ("A Perfluorosulfonated Ionomer EndColumn Electrical Decoupler for Capillary Electrophoresis/ Electrochemical Detection"; AC950610V; p. 4366)
A peroxyoxalate chemiluminescence detector for LC Although peroxyoxalate chemiluminescence detection often has 10-100 times the sensitivity of conventional fluorescence detec tion, the short half-life of the chemiluminescence reaction makes a low-dead-volume cell essential for efficient operation. Dolores Pérez-Bendito and colleagues at the University of Cordoba (Spain) describe a zero-dead-volume peroxyoxalate chemiluminescence detector for LC that can be assembled from commercially available parts. The detector is evaluated using polycyclic aromatic hydrocarbons. ("Zero-Dead-Volume Peroxyoxalate Chemiluminescence Detection in Liquid Chromatography"; AC950586L; p. 4376)
Water uptake onto solid adsorbents Water is a common interference in the analysis of volatile organic compounds in air samples. Detlev Helmig and Lee Vierling of the National Center for Atmospheric Research investigate the water-trapping capacity of a number of common solid absorbents used for collecting trace gas samples. Rather than measuring breakthrough volumes, the authors determine water uptake gravimetrically until saturation. ("Water Adsorption Capacity of the Solid Adsorbents Tenax TA, Tenax GR, Carbotrap, Carbotrap C, Carbosieve SIII, and Carboxen 569 and Water Management Techniques for the Atmospheric Sampling of Volatile Organic Trace Gases"; AC950581O; p. 4380)
Determining nitrosamines in water The U.S. Environmental Protection Agency's regulatory standard for yV-nitrosodimethylamine, a well-known carcinogen present in beverages and nitrite-cured meats, specifies that NDMA exist at levels lower than 0.7 ng/L in drinking water. Thus, sensitive methods for determining NDMA are needed to
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ensure regulatory compliance. Bruce A. Tomkins and col leagues at Oak Ridge National Laboratory describe a gas chro matographic method that uses a short-path thermal desorber to inject concentrated extraction residues onto the gas chromato graphic column followed by chemiluminescent detection to de tect NOMA at ng/L levels in drinking water and contaminated groundwater. ("Determination of iV-Nitrosodimethylamine at Part-per-Trillion Levels in Drinking Waters and Contaminated Groundwaters"; AC950532B; p. 4387)
Extract and derivatize at the same time Because of their polar nature, short-chain fatty acids are difficult to extract from aqueous samples. Janusz Pawliszyn and col leagues at the University of Waterloo (Canada) describe derivatization of polar analytes directly in the fiber coating of a solid-phase microextraction (SPME) device. They investigate SPME, with and without derivatization, as well as headspace SPME derivatization for determining these compounds in air. ("Determination of Fatty Acids Using Solid Phase Microextrac tion"; AC950506D; p. 4396)
A selective atrazine polymer receptor Detection of herbicides in environmental samples often requires preconcentration or purification by LC. Toshifumi Takeuchi and colleages at Hiroshima City University (Japan) describe an easily prepared, low-cost alternative in which molecularly im printed polymers are used to selectively bind atrazine, one of the most commonly used herbicides. At least two classes of bind ing sites exist in the imprinted polymer, and a dissociation con stant for the higher affinity site is estimated at 12 μΜ. Atrazine had the longest retention time among related 1,3,5-triazine com pounds. ("A Molecularly Imprinted Synthetic Polymer Recep tor Selective for Atrazine"; AC9506387; p. 4404)
Trace analysis of ethoxylated nonionic surfactants Because nonionic surfactants are used in a broad spectrum of household products and industrial applications, there is a need for analytical methods that can determine such surfactants at Ug/L levels in environmental samples. Anton T. Kiewiet and col leagues at the University of Amsterdam (The Netherlands) de scribe a routine analytical procedure involving sample cleanup techniques and reversed-phase HPLC with UV detection to determine ethoxylated nonionic surfactants at low concentra tions. ('Trace Analysis of Ethoxylated Nonionic Surfactants in Samples of Influent and Effluent of Sewage Treatment Plants by High-Performance Liquid Chromatography"; AC9505684; p. 4409)
Improving equations for predicting retention Earlier work that used dipole moment as a descriptor for regression models was not as complete as possible because di pole moments for all the solvents under study were not avail able. David Nurok and colleagues at Indiana UniversityPurdue University at Indianapolis and Tripos use computed di pole moment for first- and second-order models to predict separation of steroids and ^-nitrobenzyl esters of dansyl amino acids. They also compare forward and backward stepwise proce dures and find that the forward method is more reliable. ("Sol vent-Dependent Regression Equations for the Prediction of Re tention in Planar Chromatography"; AC950722M; p. 4423)
Blocking the cavity Although it is generally believed that chiral recognition by cyclodextrin requires formation of an inclusion complex, results using a phase with the cyclodextrin cavity blocked have not been re ported. Jerald S. Bradshaw and colleagues at Brigham Young Uni versity, the University of South Florida, Kangweon National Uni versity (Korea), and the University of Missouri-St. Louis prepare a cyclodextrin phase with a benzene-containing chain passing through the cavity that does not resolve chiral hydrocarbons but does resolve chiral polar compounds that interact with the ether groups on the cavity exterior. ("6A,61S-P-Cyclodextrin-Hexasiloxane Copolymers: Enantiomeric Separations by a β-CyclodextrinContaining Rotoxane Copolymer"; AC9506286; p. 4437)
Extracting PCBs using subcritical water • Supercritical water is an effective solvent for extracting organic compounds, but it is corrosive and the temperature needed to make supercritical water (374 ° C) is high enough to degrade some of the compounds being extracted. Steven B. Haw thorne and colleagues at the University of North Dakota demon strate the use of subcritical water at 50 atm and temperatures ranging from 50 to 300 ° C to extract PCBs from reference mate rials. Extraction at the higher temperatures is more complete and faster than at the lower temperatures. Their results com pare favorably with the values of the reference materials. ("Subcritical Water Extraction of Polychlorinated Biphenyls from Soil Sediment"; AC950665X)
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Delayed fluorescence optical thermometry
Remote fiber-optic sensors can be used to measure temperatures in the vicinity of electromagnetic fields and in hazard ous environments. Joel M. Harris and colleagues at the University of Utah de scribe an optical thermometer based on the temperature-dependent decay of the triplet state of an or ganic dye, acridine yellow, dissolved in a rigid mixed saccha ride glass composed of trehalose and glucose. High sensitivity to temperature change results in temperature uncertainties of < 1 °C over the range of-50 to 50 °C. ("Delayed Fluorescence Optical Thermometry"; AC9505435; p. 4269)
Using genetic algorithms to select variables Genetic algorithms have been proposed as a solution to the prob lem of selecting wavelengths to be retained in multivariate mod eling. Désiré-Luc Massart and colleagues at Vrije Universiteit Brussel (Belgium), Istituto di Analisi e Technologie Famaceutiche ed Alimenlari (Italy), and Koninklijke/Shell Laboratorium (The Netherlands) compare multiple linear regression using a genetic algorithm with partial least-squares regression using a near-IR spectroscopic data set. They conclude that the solutions are equivalent and that MLR can replace PLS in certain complex cases. ("Genetic Algorithms as a Tool for Wavelength Selection in Multivariate Calibration"; AC9505536; p. 4295)
Chemiluminescence using solid-phase detection A catalytic solid-phase detector is expected to have a long lifetime and simplify the development of luminescence detection systems. Knut Irgum and colleagues at the University of
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Analytical Chemistry, December 1, 1995 695 A
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696 A Analytical Chemistry, December 1, 1995
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Umeâ (Sweden) describe a catalytic SPD reactor for an immobilized chemiluminescence system. The authors investigate six amino polycyclic aromatic hydrocarbons immobilized on various supports for their suitability in solid-phase peroxyoxalate chemiluminescence detection. ("Immobilized Amino Aromatics for Solid-Phase Detection Using Imidazole-Mediated Bis(trichlorophenyl) Oxalate Chemiluminescence"; AC950667H; p. 4302) Analyzing multicomponent solid state NMR spectra When magic angle spinning NMR samples contain a mixture of chemically similiar components with nearly identical isotropic chemical shifts, analysis of the resultant spectrum's line shape is often complex. Jeff M. Koons of the University of South Carolina and Paul D. Ellis of Pacific Northwest Laboratory describe an abstract factor analysis target transformation technique that can be used to determine the number of constituents present and the component MAS NMR spectra. Compared with the conventional least-squares approach, the new technique demonstrates improved precision and accuracy. ("Applicability of Factor Analysis in Solid State NMR"; AC950499T; p. 4309) Raman chemical imaging Chemical imaging is an emerging area of study that provides rapid probing of material chemical heterogeneity at high spatial resolution and with molecular specificity. Patrick J. Treado and colleagues at the University of Pittsburgh and Bayer describe the application of Raman chemical imaging microscopy for visualizing polypropylene-polyurethane blends. The authors report that their Raman imaging is complementary to electron microscopy for polymer blend characterization but requires less extensive sample preparation. ("Raman Chemical Imaging: Noninvasive Visualization of Polymer Blend Architecture"; AC950767N; p. 4316) REMPI for methyl-substituted cyclohexanes Saturated six-membered rings are commonly found as structural components in biologically interesting systems. Tomas Baer and colleagues at the University of North Carolina evaluate 2+1 resonance-enhanced multiphoton ionization spectroscopy as a tool for stereochemically analyzing methyl-substituted cyclohexanes. They derive three additive shift parameters and use them to predict transition origins to within an average error of ± 58 cirf ' for 14 different methylcyclohexanes. They also find a correlation between the molecular ground-state steric properties and the 3s
