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Brief introductions to the research articles appearing in the September issues of Analytical Chemistry ACS and several other publishers have adopted a publisher item identifier (Pll) composed of 17 alphanumeric characters as a unique means of cataloging documents published since January 1, 1996. These identifiers are included in the following citations and can be used to obtain articles from the Chemical Abstracts Document Detective Service. The Pll is also found at the bottom of the first page of published articles. More information on the Pll is available at http://pubs.acs.org/ journals/pubiden.html.
Accelerated Articles
Glow discharge of amino acids
Microfabricated devices are used for a variety of sample preparation and separation techniques. J. Michael Ramsey and co-workers at Oak Ridge National Laboratory describe a microfabricated device in which the dilution and mixing of reagents in an enzyme assay are controlled by electrokinetic flow. The enzyme p-galactosidase is assayed using resorufin P-D-galactopyranoside as the substrate. An enzyme assay can be performed on the microchip within 20 min, using only 120 pg of enzyme and 7.5 ng of substrate. ("Microchip Device for Performing Enzyme Assays"; S0003-2700(97)00192-3; p. 3407)
Glow discharge methods have been widely used for inorganic analyses but not for organic analyses. R. Kenneth Marcus and co-workers at Clemson University describe a particle beam/hollow cathode glow discharge atomic emission spectroscopy system for the analysis of hydrogen and carbon in amino acids. The analytical response curves for the hydrogen and carbon in amino acids are obtained with 200-uL injections, showing less than 10% RSD over rhe range 10-250 ppm, with detection limits of 3 and 1 ppm, ,espectively, for C and H emission. .(Analysis of Organic Compounds by Particle Beam/Hollow Cathode Atomic Emission Spectroscopy: Determinations of Carbon and Hydrogen in Amino Acids"; S0003-2700(97) 00417-4; p. .3419
Combinatorial approaches to sensor diversity
Capacitive immunosensor measurements •
Combinatorial chemistry is most frequently considered a drug discovery technique, but it can also be used to synthesize a variety of polymers, which can be incorporated into chemical sensors. David R. Walt and colleagues at Tufts University and Tufts School of Medicine use two approaches to combinatorial methods to synthesize diverse sensors: discrete combinations of two monomers and photopolymerization to form a continuous gradient. The responses of the array and gradient sensors to benzene, methanol, and hexane are discussed. ("Generating Sensor Diversity through Combinatorial Polymer Synthesis"; S00032700(97)00501-5; p. 3413)
In capacitive immunosensors, the recognition layer should provide electrical insulation to prevent interference from the solution but be as thin as possible to achieve high sensitivity. Gillis Johansson and Christine Berggren of the University of Lund (Sweden) use antibodies toward human chorionic gonadotropin, interleukin-2, and human serum albumin as model substances. The antibody layers and their interactions with antigens in solution are investigated with capacitance measurements and cyclic voltammetry. Detection limits are in the pg/mL range. ("Capacitance Measurements of Antibody-Antigen Interactions in a Flow System"; S00032700(97)00203-5)
Enzyme assays on a chip
Sensitive detection for neurotransmitters With the exception of catecholamines and indolamines, neurotransmitters lack features that enable their sensitive detection by conventional techniques. Richard N. Zare and co-workers at Stanford University and Goteborg University (Sweden) describe a CE-patch clamp analysis that allows the identification of receptor ligands based on the characteristic receptor responses they evoke and their differential electrophoretic migration rates. CE-patch clamp is used to separate and detect the natural receptor agonists ^aminobutyrate and L-glutamate and the synthetic glutamate receptor agonists ./V-methyl-D-aspartate and kainic acid. ("Patch Clamp Detection in Capillary Electrophoresis"; S0003-2700(97)00158-3; p. 3427) • Denotes articles tentatively scheduled for the September 15 issue
Measuring a plant neurotoxin Although the seeds from Lathyrus sattvus srovide e aourishing diet of protein and carbohydrates during times of famine in underdeveloped countries, the seeds contain a neurotoxin; eating them for longer than three months can cause health problems. Research into developing zero or low-toxin varieties of the seeds involves processing a large number of samples, thereby requiring a fast and selective method for monitoring the neurotoxin. Lo Gorton and colleagues at Addis Ababa University (Ethiopia), the Institute of Biochemistry (Lithuania), and the University of Lund (Sweden) describe a system based on an anion exchange column and a modified graphite rod electrode that can measure as low as 4-um neurotoxin; real samples are found to contain 3.3-5.2 g/kg. ("LCBiosensor System for the Determination of the Neurotoxin S-./V-Oxalyl-L-oe,B-diaminopropionic Acid"; S0003-2700(96) 01098-0; p 3471) Analytical Chemistry News & Features, September 1, 1197 5 1 1 A
detection by mercuryfilmmicroelectrode arrays, indium (III) is a good internal standard for these blood analyses. Square-wave anodic stripping voltammetry shows that the ratio of the anodic stripping peak currents for lead and indium varies linearly with the concentration of lead in blood, yielding an average intraassay precision (RSD) of 6.7% ("Indium as Internal Standard in Square Wave Anodic Stripping Analysis of Lead in Blood with Microelectrode Arrays"; S0003-2700(96)01248-6; p. 3539)
electrode. The noncentrosymmetric ZPfilmsuse the nonlinear optical chromophores HAPA and PY-AZO. For a 6.7-nm ZP HAPAfilm,a change in electrode potential of 50 mV corresponds to a change in electric field strength of 1.4 x 104 V/cm. ("Electric Fields and Interference Effects Inside Noncentrosymmetric Multilayer Films at Electrode Surfaces from Electrochemically Modulated Surface Plasmon Resonance Experiments"; S0003-2700(97)00208-4)
Electrochemical detection of nucleotides Werner G. Kuhr and Pankaj Singhal of the University of California at Riverside use sinusoidal voltammetry to detect purineand pyrimidine-based nucleic acids. Detection limits for the purine-containing nucleotides are —70-200 nM; submicromolar limits are also observed for the pyrimidine-based compounds. The detector is not fouled by the nucleotides and can be used for the detection of analytes eluting continuously in a flowing stream. ("Direct Electrochemical Detection of Purine- and Pyrimidine-Based Nucleotides with Sinusoidal Voltammetry"; S0003-2700(97)00333-8; p. 3552)
Rotating sample system • Electrochemical techniques using a rotating electrode provide useful data, but the approach is limited to relatively large samples and requires complicated and expensive equipment. Miklos Gratzl and Andrea Cserey of Case Western Reserve University describe a simpler and less costly system that instead rotates the sample with a mild jet of nitrogen, creating the equivalent of a rotating electrode. Voltammetric experiments carried out with 20-uL samples and gold ring electrodes microfabricated on a Pyrex substrate are described. ("Rotating Sample System: An Equivalent of a Rotating Electrode for Microliter Samples"; S0003-2700(97)00315-6)
Miniature ion-selective electrode • In spite of the analytical and commercial success of polymeric membrane ion-selective electrodes, the in vivo acute and chronic medical application of such devices remains a serious challenge. Albrecht Uhlig and colleagues at the Fraunhofer Institut fur Siliziumtechnologie (Germany) and the Technical University of Budapest (Hungary) report on the fabrication and optimization of miniaturized potentiometric cells with multilayer, planar ion-selective sensors designed for use in aqueous electrolyte solutions, human serum, urine, and whole blood. The sensors are evaluated based on their ion sensitivity, longterm stability, and reproducibility. ("Miniaturized Ion-Selective Chip Electrode for Sensor Application"; S0003-2700 (96) 00957-2) Detecting sugar • The interest in detecting sugars in complex matrices has focused attention on group-selective sugar-oxidizing enzymes, such as oligosaccharide dehydrogenase (ODH). Immobilizing enzymes and redox-active mediator functionalities in redox hydrogels offers the possibility of forming a chemically stable reaction layer. Lo Gorton and colleagues at Addis Ababa University (Ethiopia), the Institute of Biochemistry (Lithuania), the University of Texas at Austin, and the University of Lund (Sweden) describe a sensor based on cross-linking ODH with an osmium-based redox polymer for detecting sugars in a flowinjection mode. Calibration curves for glucose are llnear over the range 30-500 uM with a sensitivity of 23.0 ± 1.4 4A mM_1cm"2 and an apparent Michaelis-Menten constant of 4.26 ± 0.95 mM. ("Oligosaccharide Dehydrogenase-Modified Graphite Electrodes for the Amperometric Determination of Sugars in a Flow Injection System"; S0003-2700 (97) 00127-3)
Anodic stripping voltammetry and ICPMS In ASV/ICPMS, analytes can be selectively accumulated at the working electrode and electrolytically released into a solvent system for detection by ICPMS. Gary J. Van Berkel and colleagues at Oak Ridge National Laboratory discuss a setup that uses a thin-layer flow-cell system and microconcentric nebulization for signal enhancement. They obtain high analyte deposition efficiencies, substantial signal enhancement, excellent linearity, and good precision. ("Anodic Stripping Voltammetry Coupled On-Line with Inductively Coupled Plasma Mass Spectrometry: Optimization of a Thin-Layer Flow Cell System for Analyte Signal Enhancement"; S0003-2700 (97) 00360-0; p. .544) Probing ionophores with liquid beam MS Within the past few years, various attempts have been made to quantitatively determine stability constants for ion-ionophore complexes in solution by MS techniques. Bernhard Brutschy and colleagues at J.W. Goethe-Universitat (Germany) introduce a novel method for these measurements using laser-induced liquid beam ionization/desorption combined with a reflectron time-of-flight mass analyzer. With this approach they examined selective ion binding with valinomycin, monensin, and crown ether carriers. No fragment ions are detected, and the observed ion selectivity is in good qualitative agreement with published stability constants. ("Cation Selectivity of Natural and Synthetic Ionophores Probed with Laser-Induced Liquid Beam Mass Spectrometry"; S0003-2700(96)01099-2; p. 3587)
Electrochemically modulated SPR of ZP multilayers • A limited number of studies have measured field strengths within monolayer films at electrode surfaces and variations in the electric fields as a function of position in ultrathinfilm.Robert M. Corn and Dennis G. Hanken at the University of Wisconsin-Madison use electrochemically modulated surface plasmon resonance to measure the electricfieldprofile within selfassembled zirconium phosphonate (ZP) multilayers at a gold
Ultrahigh mass accuracy FT-ICR Fourier transform ion cyclotron resonance (FT-ICR) MS is a powerful tool for molecular mass determination, but tandem MS is required for structural characterization. Albert J. R. Heck and Peter J. Derrick of the University of Warwick (U.K.) combine FT-ICR MS, sustained off-resonance irradiation collisional activated decomposition, and correlated sweep excitation to analyze the single isotopomer of doubly protonated bradykinin.
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The approach allows the unambiguous assignment of all detected fragment ions, the measured values of which are within 1 ppm of the expected m/z. ("Ultrahigh Mass Accuracy in Isotope-Selective Collision-Induced Dissociation Using Correlated Sweep Excitation and Sustained Off-Resonance Irradiation: A Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Case Study on the [M + 2H]2+ Ion of Bradykinin"; S00032700(97)00254-0; p. 3603) MALDI-TOFMS with frozen solution matrixes Because of their relatively fragile structure, DNA oligomers are difficult to volatilize intact; thus the detection efficiency for these molecules at high masses by MALDI techniques is currently much lower than that for proteins. Joanna M. Hunter and colleagues at GeneTrace Systems describe MALDI-time-of-flight MS of single-stranded DNA oligomers embedded in thin films of frozen solutions containing photoabsorbing substituted phenols. Sensitivity and mass resolution approaching that obtained using the most effective roomtemperature crystalline matrix are consistently and reproducibly obtained. ("Cryogenic Frozen Solution Matrixes for Analysis of DNA by Time-of-Flight Mass Spectrometry"; S0003-2700 (97) 00376-4; p. 3608) Laminar flow nebulizer with MALDI Aerosol MALDI is a direct liquid introduction method for MALDI MS, in which a solution of matrix and analyte is delivered directly into the mass spectrometer. Kermit K. Murray and Lin He of Emory University report results from a laminar flow pneumatic nebulizer that was coupled to an aerosol MALDI reflectrontime-of-flightmass spectrometer and tested with bradykinin, angiotensin II, vitamin B12, and bovine insulin. The mass spectrum of bovine insulin is reported with a mass resolution of 100. ("A Laminar Flow Nebulizer for Aerosol MALDI"; S0003-2700(97)00019-X; p. 3613)
crostructure of Acrylonitrile-Butadiene Copolymers by Pyrolysis-Photoionization Mass Spectrometry"; S00032700(97)00147-9) TOF for volatiles • Using the ion trap as a pulsed extraction source for TOFMS is attractive because the storage parameters can be set to exclude abundant air matrix species and to enhance others through accumulation. David M. Chambers and colleagues at Lawrence Livermore National Laboratory report modifications to the ion trap that improve the overall performance of ion store/ TOFMS for air monitoring. Detection limits are typically in the low ppb range. The hardware and electronics configuration necessary to obtain optimum resolution (2000 m/Am, fwhm), mass accuracy, and sensitivity are described. ("Development of an Ion Store/Time-of-Flight Mass Spectrometer for the Analysis of Volatile Compounds in Air"; S0003-2700 (97)00102-9) 3D SIMS analysis • Renaat Gijbels and colleagues at the University of Antwerp (Belgium) and Agfa-Gevaert N. V. (Belgium) introduce a procedure to characterize silver halide microcrystals in photographic emulsions using secondary ion MS (SIMS). A digital imaging processing system connected to the instrument permits the acquisition of spatially resolved mass-selected data as well as the 3D reconstruction of the chemical composition of the microcrystals. Two examples are presented to illustrate the methodology. ('Three-Dimensional Chemical Characterization of Complex Silver Halide Microcrystals by Scanning Ion Microprobe Mass Analysis"; S0003-2700 (97) 00010-3)
Free radical ionization energies Recently, interest in thermochemical determinations has included the use of the kinetic method of tandem MS. R. Graham Cooks and colleagues at Purdue University apply the kinetic method to the electron ionization mass spectra of substituted 1,2-diphenylethanes to estimate the ionization energies of substituted benzyl free radicals. A correlation is observed between the Hammett c constant of the substituents and the kinetic method parameter \n(kx/kH); weakly bound cluster ions also show a good correlation. ("Estimation of Free Radical Ionization Energies by the Kinetic Method and the Relationship between the Kinetic Method and the Hammett Equation"; S0003-2700(97)00470-8; p. 3641)
Suppressing EOF with surfactants Although capillary zone electrophoresis is a powerful tool for separations, the inability to control the electroosmotic flow (EOF) and the adsorption of solutes onto the capillary walls create problems. Charles A. Lucy and Ken K.-C. Yeung at The University of Calgary (Canada) use low concentrations of zwitterionic surfactants to suppress EOF and prevent adsorption of cationic proteins. Coco (amidopropyl)hydroxyldimethylsulfobetaine suppresses EOF by 50-90% at pH 3-12 and prevents adsorption of lysozyme, a-chymotrypsinogen A, cytochrome c, and ribonuclease A. ("Suppression of Electroosmotic Flow and Prevention of Wall Adsorption in Capillary Zone Electrophoresis Using Zwitterionic Surfactants"; S0003-2700(96)01231-0; p. 3435)
Analyzing copolymer structure • Qualitative analysis of copolymer microstructure is routinely performed by MS, but quantitative analysis is still difficult. Murray V. Johnston and David L. Zoller of the University of Delaware use pyrolysis-photoionization MS to determine the composition and microstructure of acrylonitrile-butadiene copolymers ranging from 19 to 51 weight percent acrylonitrile. Bernoullian and Markovian models are used to interpret the mass spectral data. The models agree quantitatively with the reported compositions, but the Markovian model gives more precise fits to the mass spectra. ("Composition and Mi-
Understanding ThFFF The application of thermalfield-flowfractionation (ThFFF) to colloids and particles is a recent development. Martin E. Schimpf and colleagues at Boise State University investigate factors that influence the ThFFF retention of chemically modified polystyrene and silica colloids in aqueous carrier liquids. The authors report on the effects of several additives in the carrier, surface polarity and surface charge, electrostatic interactions, and pH. ("Compositional Effects in the Retention of Colloids by Thermal Field-Flow Fractionation"; S00032700(96)01304-2; p. 3442)
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In search of alternate materials The shortcomings of glass devices as substrates for integrated CE on chips inspired Carlo S. Effenhauser and colleagues at Novartis Pharma AG (Switzerland) to look for alternate materials. A poly (dimethylsiloxane) silicone elastomer is molded against a microfabricated master, resulting in a network of sealed microchannels and thus eliminating die problems associated with elaborate bonding procedures. Detection limits for DNA restriction fragments are on the order of a few zeptomoles. ("Integrated Capillary Electrophoresis on Flexible Silicone Microdevices: Analysis of DNA Restriction Fragments and Detection of Single DNA Molecules on Microchips"; S00032700(97)00391-0; p. 3451)
Surface tension for surfactant detection The surface tension of a surfactant solution can change greatly with the surfactant concentration. Robert E. Synovec and colleagues at the University of Washington and Seattle University describe a multidimensional dynamic surface tension detector (DSTD) that provides information on dynamic surface tension at the air-liquid interface and adhesion at the solid-liquid interface for each drop in a surfactant solution. The DSTD is applied to LC, and the multidimensional data are shown to be useful in identifying and characterizing poly (ethylene glycols) separated from 2-propanol. ("Dynamic Surface Tension and Adhesion Detection for the Rapid Analysis of Surfactants in Flowing Aqueous Liquids"; S0003-2700(96)01195-X; p. 3496)
FID for WRPLC To take advantage of their sensitivity and selectivity, researchers have been adapting GC-type detectors for LC. Robert E. Synovec and colleagues at the University of Washington report on the coupling of a water-only RPLC column to a flame ionization detector using an interface comprising a small-volume dynamic headspace sampler based on eluent drop formation. For analytes in water, the system is linear over more than 5 orders of 1-butanol concentration and can detect sub-ppb amounts of o-xylene and other aromatics. ("Simultaneous Flame Ionization and Absorbance Detection of Volatile and Nonvolatile Compounds by Reversed-Phase Liquid Chromatography with a Water Mobile Phase"; S0003-2700(97)00114-5; p. 3465)
Extraction by HVIFE In heterogenous samples, the extractable substances of interest may be dispersed as colloidal droplets or adsorbed onto particles and may be difficult to separate by liquid-liquid extraction. Johan Roeraade and colleagues at the Royal Institute of Technology (Sweden) and Abo Akademi University (Finland) demonstrate high-velocity injection flow extraction (HVIFE) on a water sample containing colloidal wood resin from paper pulp. The dissolved components extracted well with HVIFE and classical flow extraction, but HVIFE provides an extraction enhancement of up to nine times for colloidal triglycerides. ("Continuous-Flow Extraction of Colloidal Components in Aqueous Samples"; S0003-2700 (96) 01232-2; p. 3565)
Watching out for pitfalls By analyzing a commercially available reference material and showing that the results agree with certified values, a laboratory can demonstrate that its analytical procedure, which may differ considerably from the procedures used in the standard's certification process, can obtain accurate data. However, even with well-known analytes for which reference materials are available, a thorough investigation of the sample and an extensive knowledge of the analytical pitfalls are needed to obtain accurate results. Jan T. Andersson and Bernhard Schmid at the University of Ulm (Germany) use GC-AED to examine three NIST standard reference materials and determine the concentration of polycyclic aromatic sulfur heterocycles. Coelution problems are common, and it is suggested that noncertified NIST values for several compounds be reexamined. ("Critical Examination of the Quantification of Aromatic Compounds in Three Standard Reference Materials"; S0003-2700 (97) 00194-7; p. 3476)
N e w reagent for determining aldehydes Although hydrazines are used to derivatize aldehydes, the reagents react with ozone and nitrogen dioxide, and the products may interfere with the chromatographic measurement of aldeyhdes. Uwe Karst and Andrea Biiidt at Westfallsche WiihelmsUniversitat Miinster (Germany) describe the use of 1-methyl-l(2,4-dinitrophenyl)hydrazine (MDNPH) for the HPLC determination of aldehydes and ketones. In contrast to otiier hydrazines, MDNPH is oxidized by both ozone and nitrogen dioxide to a compound that can be separated from the hydrazones of the lower aldehydes. ("l-Methyl-l-(2,4-dinitrophenyl)hydrazine as a New Reagent for die HPLC Determination of Aldehydes"; S00032700(97)00146-7; p. 3617)
Artificial molecular receptors for selective extraction Using highly selective artificial molecular receptors greatly reduces the amount of solvent necessary for extracting organic compounds. Stephen G. Weber and co-workers at the University of Pittsburgh examine poly (vinyl chloride) plasticizers as molecular receptors for phenobarbital and explore the effects of various solvents on hydrogen bond-directed molecular recognition. Linear free energies associated with receptor solubility, partitioning of phenobarbital and the complex, and complex stability are derived from solvatochromic measurements. ("Solvatochromic Study of Polyvinyl chloride) Plasticizers and Their Solutions in Chloroform: Application to Phenobarbital Partitioning and Molecular Recognition of Phenobarbital"; S0003-2700(96)01279-6; p. 3490)
Peroxides by LC Peroxyacetic acid (PAA) and H202 are increasingly used in industry for disinfection and bleaching because of their ecological properties. Although GC and LC methods work well lor measuring these compounds in most samples, strongly acidic solutions with very high H202 concentrations have storage and sample preparation problems. Uwe Karst and colleagues at Westfalische Wilhelms-Universitat Miinster (Germany) describe a quasi-simultaneous method in which PAA reacts with methyl ^-tolyl sulfide and H 2 0 2 reacts with triphenylphosphine, yielding products that can be separated by RPLC. Samples can be stored for several days after derivatization. ("Simultaneous HPLC Determination of Peroxyacetic Acid and Hydrogen Peroxide"; S0003-2700(97) 00175-3; p. 3623) Iodide in seawater Iodine is an essential micronutrient for many organisms, and the distribution of iodide and iodate can provide information about the marine environment. Kazuaki Ito of Hiroshima University (Japan) describes using a high-capacity anion-exchange Analytical Chemistry News & Features, September 1, 1997 5 1 5 A
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resin with a polystyrene-divinylbenzene matrix and UV detection for measuring iodide in seawater. The detection limit for iodide is 0.2 ug/L in 6 mL of artificial seawater; chloride and sulfate ions did not interfere. ("Determination of Iodide in Seawater by Ion Chromatography"; S0003-2700 (97) 00078-4)) p. 3628) High-efficiency molded capillaries for CEC Capillary electrochromatography is a method in which uncharged molecules are separated in a fused-silica capillary packed as in reversed-phase HPLC, but the mobile phase is forced through the column by an electroosmotic flow. Jean M. J. Frechet and co-workers at the University of CallforniaBerkeley prepare, in a single step, rigid monolithic capillary columns for reversed-phase CEC in untreated fused-silica capillary by the copolymerization of ethylene dimethacrylate, butyl methacrylate, and 2-acrylamido-2-methyl-l-propanesulfonic acid in the presence of a porogenic solvent. Capillaries with an efficiency higher than 120,000 plates/m are obtained. ("Molded Rigid Polymer Monoliths as Separation Media for Capillary Electrochromatography"; S0003-2700 (97) 00377-6; p. 3646) Predicting chiral separations • No reliable way exists to predict which of the many commercially available chiral stationary phases should be applied to a particular enantiomeric separation. Irving W. Wainer and colleagues at McGill University (Canada) apply multivariate regression analysis, combined with multilayer feed-forward neural networks trained with error back-propagation, to model the enantioselective chromatographic retention behavior of 29 aromatic acids and amides. Combinations of charge transfer, electrostatic, lipophilic, and dipole interactions are found to describe retention and enantioselectivity. ("Prediction of Chiral Chromatographic Separations Using Combined Multivariate Regression and Neural Networks"; S00032700(97)00215-1) A model for dealing with non-Gaussian peaks • The simplest chromatographic models predict Gaussian elution profiles, but when peaks deviate significantly from a Gaussian distribution, large errors can be introduced with such an assumption. M. C. Garcia-Alvarez-Coque and co-workers at Universitat de Valencia (Spain) propose a family of models for the description of skewed chromatographic peaks, based on the modification of the standard deviation of a pure Gaussian peak. The model is used to accurately predict the profile of asymmetrical peaks, using the values of efficiency and asymmetry factors measured experimentally. ("A Model for the Description, Simulation, and Deconvolution of Skewed Chromatographic Peaks"; S0003-2700 (97) 00223-0)
Total fluorescence emission detection Most fluorescence detection for HPLC is limited to the excitation and emission wavelengths. Michael A. Dvorak and colleagues at North Dakota State University describe on-the-fly determination of the entire fluorescence decay profile during isocratic reversed-phase HPLC elution, which adds an additional dimension to determining an analyte. A pulsed Nd:YAG laser system with photomultiplier tube and digital storage oscilloscope is used to detect polycyclic aromatic hydrocarbons at low ppb levels. The determination of fluorescence lifetimes under coelution conditions is also discussed. ("On-the-Fly Fluorescence lifetime Determination with Total Emission Detection in HPLC"; S0003-2700(96)01095-5; p. 3358) Multistep fast reaction rates by PAF-PRO Pulsed-accelerated-flow (PAF) methods with integrated observation can be used to monitor the kinetics of rapid reactions; however, the technique is limited to single-step reactions. Dale Margerum and co-workers at Purdue University use a pulsedaccelerated-flow system with position-resolved observation (PRO) to monitor several rapid multistep reactions. A CCD array detector, positioned perpendicular to the solution flow, allows for detection at multiple points along the cell. ("PulsedAccelerated-Flow Spectrometer with Position-Resolved Observation"; S0003-2700(97)00598-2; p. 3513) CI and Br by dual-microplasma AES There is no low-cost method for measuring extractable organic chlorine and bromine, which are indicative of the quantity of halogenated organics in the environment. Tone Normann Asp and colleagues at the Norwegian College of Veterinary Medicine and the University of Oslo (Norway) describe a system that consists of two plasmas in the same stream of helium and a probe for applying the sample in the interplasma region. The first plasma vaporizes the sample, and the second is where atomic emission is measured. For chlorine and bromine, 120 pg detection limits are obtained and responses are linear over 3 orders of magnitude. ("Determination of Extractable Organic Chlorine and Bromine by Probe Injection Dual-Microplasma Atomic Emission Spectrometry"; S0003-2700(96)01219-X; p. 3558) Thermospray in the microwave The thermospray nebulizer generates a hot and very fine primary aerosol that causes a high percentage of the analyte to reach the atomization cell in ICP-AES, but it is not well suited to working with acidic solutions. Antonio Canals and colleagues at Universidad de Alicante (Spain) present a thermospray nebulizer based on the absorption of microwave radiation by aqueous solutions of strong acids. For solutions 0.75 M in strong acid, the new nebulizer improves sensitivity, detection limits, and background equivalent concentration. ("A Microwave-Powered Thermospray Nebulizer for Liquid Sample Introduction in Inductively Coupled Plasma Atomic Emission Spectrometry"; S0003-2700(96)01247-4; p. 3578)
Zone migration theory • The mass balance equation forms the basis of both electrophoretic and chromatographic theory for the migration rate of an elute zone. Jan Stahlberg of Stockholm University (Sweden) presents a solution of the mass balance equation for finite concentration differences for electrochromatography. Numerical examples are shown to illustrate the physical consequences of the solution. ("The Theory for Zone Migration in Electrochromatography"; S0003-2700 (96) 00984-5)
A detector for trace-level nitrogen The detection of impurities in argon is particularly important in high-technology industries, but commercially available analyz-
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ers cannot detect ppb levels of nitrogen in argon. Hiroshi Ogino and Tetsuya Seki of the Taiyo Toyo Sanso Co. (Japan) describe a nitrogen detector that uses a low-pressure, capillary glow discharge. The detector is linear over the range 0.1 ppb to 100 ppm. ("Development of a Detector for Ultratrace Nitrogen in Argon Using Low-Pressure, Capillary Glow Discharge Molecular Emission Spectrophotometry"; S0003-2700(96)01197-3; p. 3636) Fiber-optic sensor for MECC • Michael J. Sepaniak and colleagues at the University of Tennessee evaluate a separation-based fiber-optic sensor for the measurement of neutral analytes separated by micellar electrokinetic capillary chromatography (MECC). Relative standard deviations of
