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In AC Research contains brief introduciions to the research articles appearing in the October 1 issue of Analytical Chemistry plus a partial listing of articles tentatively scheduled for the October 15 issue. A free updated table of contents is available on the 1st and 15th of every month on the Web (http://pubs.acs.org/ac).
Accelerated Article Fairydust electrospray emitters Sheathless electrospray emitters are commonly coaled with a thin goldfilmto increase their conductivity; however, such designs arc physically unstable and typically have lifetimes of only a few hours. Karin E. Markides and coworkers at I Ippsala University (Sweden) describe a new approach called the "fairydust" technique, which produces highly stable, sheathless electrospray emitters with unlimited lifetimes. The technique, which essentially involves gluing 2-um gold particles to a thinfilmof polyimide. produces emitters that can be put directly on microcolumns without any coupling. ("A I lesign for Low-Flow Sheathless Electrospray Emitters"; 10.1021/ ac990252m;p4115)
Hexosamine monosaccharide diastereomers Julie A. Leary and Heather Desaire of the University of California-Berkeley report on a novel way to quantify oligosaccharide isomers without a separation step using multicomponent quantification. Three diastereomers of hexosamine monosaccharides are differentiated using electrospray ionization (ESI) quadrupole ion trap MS/MS, following derivatization of die hexosamines with [Co(DAP)2Cl2]Cl. This is the first method for quantifying diastereomeric mixtures and thefirstquantification of a threecomponent, isomeric mixture using ESI. ("Multicomponent Quantification of Diastereomeric Hexosamine Monosaccharides Using Ion Trap Tandem Mass Spectrometry"; 10..021/ ac990553w; p 4142) Refolding holomyoglobin Previous studies have shown that acid-induced denaturation of holomyoglobin induces substantial unfolding of the polypeptide chain and disruption of the heme-protein interactions. Lars Konermann and co-workers at the University of Western Ontario and the University of British Columbia (both in Canada) now investigate the reverse reaction—the reconstitution of acid-denatured holomyoglobin—bytime-resolvedelectrospray ionization MS. A continuous-flow setup with two sequential mixing steps is used to study the mechanism and the kinetics of the reaction. ("Reconstitution of Acid-Denatured Holomyoglobin Studied by Time-Resolved Electrospray Ionization Mass Spectrometry"; 10.1021/ac9904664; p 4154)
Fingerprinting arginine-containing peptides MALDI MS is a powerful tool for massffngerprintingpepttde mixtures obtained after enzymatic in-gel digestion of proteins separated by 2-D electrophoresis; however, several intrinsic properties of peptides influence their MALDI behavior. Peter R. Jungblut of Max Planck Institute for Infection Biology and coworkers at the Institute of Molecular Pharmacology and Jerini Bio Tools GmbH (all in Germany) examine the influence of arginine on the peak intensity of tryptic mass fingerprints. Peak intensities of arginine-containing peptides are shown to be significantly higher than those of lysine peptides for tryptic peptide maps from 100 proteins. ("The Dominance of ArginineContaining Peptides in MALDI-Derived Tryptic Mass Fingerprints of Proteins"; 10.1021/ac990298f; p 4160) Rapid screening of chiral selectors Tingyu Li and Yan Wang at Vannerbilt University report oo n method for developing chiral selectorsfromparallel combinatorial libraries mat does not require immobilizatton of the analyte. Potential chiral selectors are produced on pepttde synthesis resins snd rapidly screened using circular dichroism. The chiral resolution of (1-naphtliyl)-leucine ester using a 16-member library is studied to demonstrate the feasibility of me parallel screening procedure. ("Screening of a Parallel Combinatorial Library for Selectors for Chiral Chromatography"; 10.1021/ac9905017; p 4178) Immunoassay for okadaic acid Each year, thousands of people fall victim to poisoning from low molecular weight marine toxins. George G. Guilbault and colleagues at NUIC (Ireland) describe an immunoassay for one of these toxins, okadaic acid, with detection limits in the subfemtomole range. The ELISA system can be manipulated to quantitatively measure total diarrhetic shellfish poisoning content. Mussel samples are validated in percentage recovery tests. ("Development of an Ultrasensitive Immunoassay for Rapid Measurement of Okadaic Acid and Its Isomers"; 10.1021/ac9901642; p 4198) Disrupting bacterial spores Optimal detection of bacterial spores by PCR requires that the spores be disrupted to make the endogenous DNA available for amplification. Spore lysis, PCR, and detection can take several hours using conventional memods. Phillip Belgrader and colleagues at Lawrence Livermore National Laboratory and Cepheid describe a minisonicator that can disrupt spores in 30 s. Total time for disruption and detection using the minisonicator and a microchip PCR instrument is -dioxins and furans are discussed. ("In-Line Catalytic Derivatization Method for Selective Detection of Chlorinated Aromatics with a Hyphenated Gas Chromatography Laser Mass Spectrometry Technique: A Concept for Comprehensive Detection of Isomeric Ensembles"; 10.1021/ac990177f; p 4148) How electrospray shifts equilibria Because electrospray (ES) MS allows the simultaneous monitoring of multiple-solution species, it could be an important tool for studying kinetically labile species in complex samples. George R. Agnes and Hongjun Wang at Simon Fraser University (Canada) describe how the well-understood interactions between EDTA and the alkaline earth metals are used to probe the effect of ES. The researchers discuss how the equilibrium positions for the reactions are perturbed by passage through an ES source, and they consider the potential of utilizing ES-MS for kinetically labile equilibrium studies. ("Kinetically Labile Equilibrium Shifts Induced by the Electrospray Process"; 10.1021/ac981375u; p 4166) T w o new DEPs Jentaie Shiea and Chih-Pin Kuo at the National Sun Yat-Sen University (Taiwan) present two direct electrospray probes (DEPs) for generating an electrospray without using a capillary and/or syringe pump. One DEP consists of a copper coil connected to a high-voltage power supply. The sample solution is deposited on the coil, and the electrospray is generated at the tip of the coil. The other is constructed by inserting two parallel optical fibers through and beyond the end of a copper coil. Electrospray is generated at the tip of the fibers through the solution predeposited on the copper coil. ("Application of Direct Electrospray Probe To Analyze Biological Compounds and To Couple to Solid-Phase Microextraction To Detect Trace Surfactants in Aqueous Solutions"; 10.1021/ ac990049r; p 4413) • Denotes articles tentatively scheduled for the October 15 issue
Resolving amino acids Although condensed-phase techniques have been used to study enantioselective intermolecular interactions, gas-phase techniques are increasingly being used. R. Graham Cooks and colleagues at Purdue University report on the gas-phase enantiomeric distinction of D- and L-a-amino acids based on their copper(II) complexes. Amino acids with aromatic substituents display the largest chiral distinction, which correlates well with reported chromatographic results. ("Kinetic Resolution of D,L-Amino Acids Based on Gas-Phase Dissociation of Copper(II) Complexes"; 10.1021/ac990530h; p 4427) Counting fluorescent particles Microfabrication has focused on electrokinetically driven separations, such as CE, whereas manipulation of fluid flows on chips for counting and sorting particles or cells has received less attention. J. Michael Ramsey and coworkers at Oak Ridge National Laboratory use flow cytometry on a chip to detect and count fluorescently labeled and unlabeled 1- and 2-um latex particles with laser light scattering and fluorescence coincidence measurements. The particles are electrokinetically focused at a cross intersection, with detection occurring 50 um downstream of the intersection. The method could distinguish between the 1- and 2-um particles. A maximum throughput of 34 particles per second is achieved. ("Microchip Flow Cytometry Using Electrokinetic Focusing"; 10.1021/ac990372u; p 4173) Electrochemical detector for microchannels H. H. Girault and colleagues at Ecole Polytechnique Federale de Lausanne (Switzerland) use UV laser photoablation to fabricate and place carbon microband electrode detectors on the bottom or side walls of rectangular microchannels. Different electrochemical cell geometries are tested with ferrocenecarboxylic acid in 40- and 100-um-wide capillaries fabricated in planar polymer substrates. The limit of detection for a 1-electron redox species within a 120-pL volume is ~1 fmol with both cyclic voltammetry and chronoamperometry. ("Electrochemical Detection in Polymer Microchannels"; 10.1021/ ac981382i; p 4294) Microchip cross-correlation chromatography • Detection limits for samples in microfabricated electrophoresis columns and capillaries are often higher than desired because of the small injection volumes and detection zone pathlengths. J. Michael Ramsey and co-workers at Oak Ridge National Laboratory tackle this problem by demonstrating fluorescence detection combined with cross-correlation electrophoresis—in which multiple injections are performed in a continuous but random sequence. A mixture of 63-pM fluorescein and 70-pM dichlorofluorescein are separated on a microchip, yielding, respectively, estimated detection limits of 21 pM and 6.5 pM. ("Ultrasensitive Cross-Correlation Electrophoresis on Microchip Devices"; 10.1021/ac990853d) Analytical Chemistry News & Features, October 1, 1999 6 5 3 A
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Real-time imaging of CE Staffan Nilsson and co-workers at Lund University and Lund Institute of Tech nology (both in Sweden) present a real time detection system for CE. The sys tem uses an array of optical fibers to image the sample zones in motion through the capillary and deliver the information to a CCD camera. The researchers describe stud ies of dynamic events captured by the system and consider some observations of nonlinear migration. Compared with a camera lens system, the new system has a 10-fold improvement in S/N. The researchers also describe the use of signal-pro cessing algorithms to obtain further improvements. ("RealTime Imaging through Optical Fiber Array-Assisted Laser-In duced Fluorescence of Capillary Electrophoretic Enantiomer Separations"; 10.1021/ac9903981; p 4190) Simultaneous Cr(lll) and Cr(VI) determination Philip H. E. Gardiner of Sheffield Hallam University (U.K.) and co-workers at the Institute for Reference Materials and Measurements (Belgium) describe an optimized method for the simultaneous determination of Cr(III) and Cr(VI) in aque ous solutions using ion chromatography with chemiluminescence detection. Following separation on a continuously eluting, single-bed ion-exchange column, Cr(VI) is reduced to Cr(III) for the chromium-catalyzed reaction of luminol, with hydrogen peroxide to generate light. Detection limits are 0.002 ug/L for both species. ("Optimization of the Simulta neous Determination of Cr(III) and Cr(VI) by Ion Chroma tography with Chemiluminescence Detection"; 10.1021/ ac9902751; p 4203)
lites in Urine and Serum Samples"; 10.1021/ac990356x; p 4237) Aliphatic alcohols by reversed-phase LC Low molecular weight aliphatic alcohols are found in food, pharmaceuticals, and biological fluids. They are used as sol vents in industry, and they occur naturally in the environment. Xianliang Zhou and colleagues at the State University of New York-Albany and the New York State Department of Health describe precolumn derivatization of these compounds with 9-fluorenylmethyl chloroformate, separation by reversed-phase LC, and fluorescence detection. Detection limits are 4,40, 70, and 30 pmol for methanol, ethanol, propanol, and butanol, re spectively. ("Determination of Trace C ^ Q Aliphatic Alcohols in Aqueous Samples by 9-Fluorenylmethyl Chloroformate Deri vatization and Reversed-Phase High-Performance Liquid Chro matography"; 10.1021/ac990010m; p 4245) Second-order calibration Advances in GC/MS and other second-order instrumentation have increased interest in second-order calibration methodol ogies. Ru-Qin Yu and colleagues at Hunan University (Peo ple's Republic of China) describe a new chemometric proce dure, the coupled vectors resolution method, which yields direct solutions to various cases of second-order calibration. If multiple-calibration samples are available, the method deals with the calibration and prediction stages separately, allowing direct prediction when newly collected, unknown samples are used. The researchers discuss results from sim ulated and real experiments. ("Coupled Vectors Resolution Method for Chemometric Calibration with Three-Way Data"; 10.1021/ac990009n;p4254)
Packed column SFC/MS Results from a supercritical fluid chromatograph (SFC) inter faced with a mass spectrometer and using negative-mode atmos pheric-pressure chemical ionization (APCI) have already been reported. Following up on that work, Michael J. Greig and col leagues at Alanex Corp. describe the use of an SFC/MS with positive-ion APCI for analyzing compounds with a wide range of polarities. The researchers also discuss the advantages of SFC/MS compared with LC/MS for high-throughput analyses. ("Packed Column Supercritical Fluid Chromatography/Mass Spectrometry for High-Throughput Analysis. Part 2"; 10.1021/ ac9902906; p4223)
Electrically changing stationary phase Mobile-phase conditions can be changed on the fly, but altering stationary-phase conditions necessitates changing columns. Todd M. Przybycien and co-workers at Rensselaer Polytechnic Institute and Virginia Commonwealth University describe two novel sta tionary phases that change properties when an electrical potential is applied. Both media are based on gold-plated stainless steel beads coated with a self-assembled monolayer of 6-mercaptohexan-l-ol; however, one is functionalized with immobilized heme moieties. Ribonuclease A is the model protein, and iis retention is controlled on both stationary phases by applying a potentiall ("A Prototype Electrochemical Chromatographic Column for Use with Proteins"; 10.1021/ac981231f; p 4272)
β-blockers in biological fluids janusz Pawliszyn and colleagues at the University of Water loo (Canada) and Okayama University (Japan) evaluate auto mated in-tube solid-phase microextraction coupled with LC/ electrospray ionization MS for determining (3-blockers in urine and serum. Extraction parameters are optimized. The calibration curves are linear in the range 2-100 ng/mL, with correlation coefficients above 0.9982 and detection limits of 0.1-1.2 ng/mL. Recoveries of [3-blockers spiked into urine and serum are greater than 84% and 71%, respectively. ("Auto mated In-Tube Solid-Phase Microextraction Coupled with Liquid Chromatography/Electrospray Ionization Mass Spec trometry for the Determination of B-Blockers and Metabo-
Increased efficiency in membrane extraction In pulse introduction membrane extraction, when water contacts the membrane, a static boundary layer, which is a barrrer to per meation, is formed at the membrane's surface. Somenath Mitra and Xuemei Guo at the New Jersey Institute of Technology present methods for increasing extraction efficiency and decreas ing boundary layer effects with the goal of increased sensitivity and shorter analysis time. A stream of niirogen is introduced into the membrane after the sample is eluted to eliminate the aqueous boundary layer. ("Enhancement of Extraction Efficiency and Re duction of Boundary Layer Effects in Pulse Introduction Mem brane Extraction"; 10.1021/ac990352s; p 4407)
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Au nanotubule membranes • Charles R. Martin and co-workers at Colorado State University expand on their recent work exploring how pore size, charge, and chemistry affect the transport selectivity of gold nanotubule membranes. An electroless gold-deposition method is used to deposit the gold nanotubules within the pores of a polycarbonate template membrane. Thiols are chemisorbed inside the tubule walls, changing the transport properties. ("Effect of Thiol Chemisorption on the Transport Properties of Gold Nanotubule Membranes"; 10.1021/ac990615i)
Pulse introduction membrane extraction • Somenath Mitra and Xuemei Guo of the New Jersey Institute of Technology describe pulse introduction membrane extraction for the analysis of volatile organic compounds based on on-line GC with a sorbent trap as an interface. A mathematical model is developed, and parameters that affect sensitivity and time lag are examined. Larger sample volumes and lower flow rates enhance sensitivity but increase time lag. ("Theoretical Analysis of Non-Steady-State, Pulse Introduction Membrane Extraction with a Sorbent Trap Interface for Gas Chromatographic Detection"; 10.1021/ac981226b)
Fluorescence polarization for measuring affinity CE combined with molecular recognition often requires the formation of stable compounds between an analyte and a binding partner, such as a protein. Previous studies of the binding interactions using CE required timeconsuming multistep titration experiments. X. Chris Le and Qian-Hong Wan of the University of Alberta (Canada) introduce a simpler method using laser-inducedfluorescencepolarization, which allows on-line monitoring of affinity complex formation. The method is demonstrated with three binding systems that distinguish affinity complexes from unbound molecules. ("Fluorescence Polarization Studies of Affinity Interactions in Capillary Electrophoresis"; 10.1021/ ac9902796; p 4183)
Lead preconcentration with macrocycle sorbent The lead concentrations in many biological and environmental samples are below the detection limit of flame AA spectrometry. Xiu-Ping Yan and co-workers at Bodenseewerk Perkin Elmer (Germany) describe a method for trace analysis of lead, which combines flow injection on-line preconcentration and separation with flame AA spectrometry. The preconcentration column uses a macrocycle immobilized silica gel selective for Pb(II) as the packing material. With a sample loading rate of 3.9 mL/min and 30-s preconcentration, they obtain an enrichment factor of 52, a detection limit of 5-ug/L lead, and a sampling frequency of 63/h. ("Application of a Macrocycle Immobilized Silica Gel Sorbent to Flow Injection On-line Microcolumn Preconcentration and Separation Coupled with Flame Atomic Absorption Spectrometry for Interference-Free Determination of Trace Lead in Biological and Environmental Samples"; 10.1021/ac990341z; p 4216) • Denotes articles tentatively scheduled for the October 15 issue
Plasticized PVC membrane study Plasticized polyvinyl chloride) (PVC) membrane-based sensors are widely used in clinical, environmental, and industrial applications; but there have been few studies of their bulk properties. George Horvai and co-workers at the Technical University of Budapest and the Research Institute for Solid State Physics and Optics (both in Hungary) use small-angle neutron scattering to investigate the microstructure of plasticized PVC membranes in the dry state and during heavy water soaking. Inhomogeneities are found in the dry membrane, which could be particles of unplasticized PVC. ("Microstructure of Ion-Selective Plasticized PVC Membranes Studied by Small-Angle Neutron Scattering"; 10.1021/ac981416m; p 4313) Manipulating single microparticles Haeng-Boo Kim, Noboru Kitamura, and Osamu Kogi at Hokkaido University Qapan) describe a laser trapping microspectroscopy system combined with a fluid manifold for manipulating and analyzing single microparticles. After the microparticles are introduced into a flow cell and a single particle is trapped by a 1064-nm laser beam, the rest of the particles are removed by flowing water. The technique is applied to study a time course of dye adsorption processes. ("Single-Microparticle Measurements: Laser Trapping-Absorption Microspectroscopy Under Solution-Flow Conditions"; 10.1021/ac990450d; p 4338) CCD detector for CE David M. Goodall and co-workers at the University of York and UMIST (both in the U.K.) describe the development of a CCD camera that can be used for both single- and multiple-wavelength UV absorbance detection in CE. The use of a fiber-optic bundle enables more deuterium light flux to be used than is possible with a conventional single-point detector. Strategies, including on- and off-line data processing and signal referencing to compensate for fluctuations in illumination, are discussed. ("A Charge Coupled Device Array Detector for SingleWavelength and Multiwavelength Ultraviolet Absorbance in Capillary Electrophoresis"; 10.1021/ac9900351; p 4376) Quantitative SPR sensing Surface plasmon resonance (SPR) spectroscopy can determine very low levels of analyte wiihout labellng. However, ,i ts very sensitive to changes in the refractive index at the solid-solution interface. Rosina M. Georgiadis and James H. Grassi at Boston University discuss the use of critical-angle measurements in addition to SPR for cases in which the bulk refractive index varies during the experiment. In addition, the researchers explore the implications of incorrect accounting for the bulk solution when two-color (vs single-color) SPR sensing of ultrathin organic fiims is used. ('Temperature-Dependent Refractive Index Determination from Critical Angle Measurements: Implications for Quantitative SPR Sensing"; 10.1021/ac990125q; p 4392) Stretching DNA a bit Stretching and immobilizing biopolymers on a flat surface provides an excellent way to prepare samples for single-molecule detection by fluorescence and atomic force microscopies. Hiroki Yokota and colleagues at the University of Washington use a viscous drag created by a transient rotational flow to stretch randomly coiled DNA molecules and denatured proteins. Analytical Chemistry News & Features, October 1, 1999 6 5 5 A
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Stretching is achieved by dispensing a droplet of sample solution containing DNA onto a magnesium chloride-soaked mica surface. ("Spin-Stretching of DNA and Protein Molecules for Detection by Fluorescence and Atomic Force Microscopy"; 10.1021/ac9902695; p 4418) Pharmaceutical coatings • Staffan Folestad and co-workers at Lund University and AstraZeneca R&D Molndal (both in Sweden) report on the real-time analysis of film coating on pharmaceutical pellets during an industrial manufacturing process. Near-IR spectra are obtained using a diffuse reflectance fiber-optic probe positioned inside a fluidized bed process vessel. Data are modeled by partial leastsquares in a multivariate batch calibration. The method enables the coating thickness on pharmaceutical pellets to be estimated and the process endpoint to be determined with high precision. ("Quantitative Analysis of Film Coating in a Fluidized Bed Process by In-Line NIR Spectrometry and Multivariate Batch Calibration"; 10.1021/ac990256r) Extinction changes of gold particles • The extinction spectra of nanoscopic metal particles are sensitive to surface chemistry and the dielectric properties of their host matrix, but little work has focused on using these phenomena as the basis of detection and quantitation. Colby A Foss, Jr., and colleagues at Georgetown University use UV-vis spectroscopy to monitor changes to the surface plasmon resonance band of stable nanoscopic gold particle films as they come into contact with analytes of varying concentrations. As the host concentration surrounding the film increases, a characteristic red-shift and increase in intensity are observed. ("In Situ Monitoring of the Change in Extinction of Stabilized Nanoscopic Gold Particles in Contact with Aqueous Phenol Solutions"; 10.1021/ac990639p) Going deeper w i t h PAS • Photoacoustic spectroscopy has been used for the nondestructive study of inhomogenous samples, but for applications, such as biofilm analysis, the depth range is not sufficient. Reinhard Niessner and Christian Kopp of the Technical University of Munich (Germany) present a semiemperical method for the inversion of photoacoustic signals, which allows the depth-resolved determination of the absorption coefficient of nonscattering samples. The method is applied to layered hydrogel samples and a sample with continuously varying absorption properties. ("Depth-Resolved Determination of the Absorption Coefficient by Photoacoustic Spectroscopy within a Hydrogel"; 10.1021/ac990392w) Model-free XRF • Because adequate standards for analyzing thin-layered materials, such as metal on silicon wafers, rarely exist, so-called fundamental parameter methods are often used for these analyses. Lutgarde M. C. Buydens and co-workers at Katholieke Universiteit Nijmegen and Philips Research (both in The Netherlands) develop a two-step fundamental parameter method for model-free analysis of thin-layered materials by X-ray fluorescence spectrometry. A genetic algorithm is used to obtain the number of layers and an estimate of element concentrations and thickness; a gradient technique then refines this estimate. ("A Two-Step Approach toward Model-Free X-Ray Fluorescence Analysis of Layered Materials"; 10.1021/ac981053q) 656 A
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