In AC
Research
In AC Research contains brief introductions to the research articles appearing in the November 1 issue of Analytical Chemistry plus a partial listing of articles tentatively scheduled for the November 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 Articles GPC/MS of polymers Gel permeation chromatography (GPC) fractions are usually collected off line, before MS characterization, which adds time to the analysis. William J. Simonsick, Jr., and co-workers at DuPont Marshall R&D Laboratory and the University of Florida report on a more efficient approach—the on-line coupling of GPC to FTMS using a modified electrospray ionization interface. The system is used to characterize a narrow molecular weight distribution (MWD) poly(methyl methacrylate) polymer and a broad-MWD glycidyl methacrylate/butyl methacrylate copolymer. ("Gel Permeation Chromatography Coupled to Fourier Transform Mass Spectrometry for Polymer Characterization"; 10.1021/ac990722c; p 4793)
Parallel protein digestion Sequential methods of protein digestion, such as in-gel digestion, create a bottleneck in protein identification. To increase throughput for protein characterization, Jean-Charles Sanchez and co-workers at Geneva University Hospital, University Medical Center, and the Swiss Institute of Bioinformatics (all in Switzerland) investigate three methods for performing protein digestion in parallel. All methods produce a collection of digested protein fragments on a poly(vinylidene difluoride) membrane after a transblotting process. ("Toward a Clinical Molecular Scanner for Proteome Research: Parallel Protein Chemical Processing before and during Western Blot"; 10.1021/ac990448m; p 4800)
Perspective Article Shape selectivity in reversed-phase LC In reversed-phase LC, die separation of compound mixtures of similar polarity can present a significant challenge. Compounds with rigid, well-defined molecular shapes are best separated using a column with enhanced shape-selectivity characteristics. Lane Sander and colleagues at the National Institute of Standards and Technology present an overview of column properties that influence shape selectivity for constrained solutes. Retention models of shape discrimination are presented that are consistent with observed retention behavior. ("Shape Selectivity for Constrained Solutes in Reversed-Phase Liquid Chromatography"; 10.1021/ac9908187; p 4821)
Raman waveguide LC detector The application of Raman spectroscopy as a detector for HPLC has been limited by its inherent lack of sensitivity. Lloyd W. Burgess and co-workers at the University of Washington describe a new real-time liquid-core Raman waveguide HPLC detector, which provides enhanced selectivity over typical HPLC detectors and greatly improves the sensitivity of a typical Raman measurement without resorting to surface enhancement or resonance approaches. Detection limit improvements of over 1000-fold are achieved for the measurement of alcohols in the aqueous phase using the liquid-core waveguide technology. ("A Raman Waveguide Detector for Liquid Chromatography"; 10.1021/ac9907336; p 4808)
Solenoid microcoil probes for NMR A. G. Webb and colleagues at the University of IIllnois aa Urbana-Champaign present two designs for incorporating multiple solenoidal microcoils into a single probe head to increase throughput in high-resolution NMR. By combining rr switches and low-noise amplifiers, multiple NMR spectra can be acquired in the same time as a single spectrum from a conventional probe consisting of one coil. A 4-coii system is used for proton NMR at 250 MHz using a wide-bore magnet with an observe volume of 28 nL for each microcoil. A more compact 2-coil configuration for operation at 500 MHz is also presented with observe volumes of 5 and 31 nL. .(Multiple Sollnoidal Microcoil Probes for High-Sensitivity, High-Throughput Nuclear Magnetic Resonance Spectroscopy"; 10.1021/ ac990855y; p 4815)
High-throughput hybridization Efforts are under way to make technologies for monitoring gene expression patterns more suitable for high-throughput analysis. Z. Hugh Fan and co-workers at Sarnoff Corporation and Orchid Biocomputer present a dynamic DNA hybridization approach for performing gene expression analysis that involves coupling microfluidics with paramagnetic beads. The approach reduces DNA hybridization time from hours to seconds and enables the simultaneous analysis of multiple samples on a single chip. Specific hybridization reactions in an array format are demonstrated using four synthesized DNA targets and five probes. ("Dynamic DNA Hybridization on a Chip Using Paramagnetic Beads"; 10.1021/ac9902190; p 4851)
ACS and other publishers have adopted the Digital Object Identifier (DOI) as a unique identifier for articles in print and on the Web. For Analytical Chemistry, the DOI consists of 10.1021/ followed by the manuscript number. DOIs can be found on the first page of publlshed articles and with In AC Research citations. More information on the DOI is available at http://www.doi.org. Please use the DOI when orderrng documents. Analytical Chemistry News & Features, November 1, 1999 717 A
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Thermodynamics between polypeptides and hydrophobic ligands Milton T. W. Hearn and Guollng Zhao of Monash University (Australia) address the experimental requirements for determining linear-free energy relationships, the derivation of partition coefficients, and other extradynamic parameters for polypeptides and hydrophobic ligands in the presence of waterorganic solvent mixtures. Their results confirm that entropyenthalpy compensation effects participate in the interaction of polypeptides with hydrophobic ligands. Their investigation also confirms that using solvent-water mixtures of defined composition is essential to deriving thermodynamically consistent values for binding affinities and partition coefficients. ("Investigations into the Thermodynamics of Polypeptide Interaction with Non-Polar Ligands"; 10.1021/ac990028x; p 4874)
Automating proteomic research To increase the throughput of protein identification, PierreAlain Binz and co-workers at the University Medical Center and Geneva University Hospital (both in Switzerland) present a highly automated method that generates a fully annotated twodimensional (2-D) map starting from a 2-D electrophoresis map. The method uses a powerful proteomic visualization tool, called a molecular scanner, which combines parallel methods for protein digestion and electrotransfers with peptide mass fingerprinting approaches. Proteins of a 2-D electrophoresis map are simultaneously digested and electrotransferred onto a poly(vinylidene difluoride) membrane, which is directly scanned by MALDI-TOF MS. ("A Molecular Scanner To Automate Proteomic Research and To Display Proteome Images"; 10.1021/ac990449e, p 4981)
Lactulose in heated milk The goal of thermally treating milk is to destroy microorganisms that could cause spoilage. The extent of sterilization can be assessed by measuring the loss of thermolabile constituents such as lactulose. Tommaso R. I. Cataldi and colleagues at the Universita della Basilicata (Italy) describe an anion-exchange chromatographic method for separating and determining lactulose and other milk carbohydrates in heat-treated milks. The mean value of lactulose in skim, partially skim, and whole milk treated by ultra-high temperature is 10-90 mg/100 mL; in botdesterilized whole milk, lactulose is >140 mg/100 mL ("Mettiod Development for the Quantitative Determination of Lactulose in Heat-Treated Milks by HPAEC with Pulsed Amperometric Detection"; 10.1021/ac990493u; p 4919)
Separating DNA by MUSGE Tsuguo Sawada and colleagues at the University of Tokyo and the Kanagawa Academy of Science and Technology (both in Japan) develop a miniaturized vertical ultra-thin slab gel electrophoresis (MUSGE) apparatus for separating DNA fragments. A 25-mm long and 80-um thick resolving gel is used to separate a 100-bp ladder DNA within 10 min. Bandwidth is reduced to 100-200 um, thus improving the number of theoretical plates to 22,000. Satisfactory lane-to-lane reproducibility and gel-to-gel reproducibility are obtained. ("Miniaturized Ultrathin Slab Gel Electrophoresis with Thermal Lens Microscope Detection and Its Application to Fast Genetic Diagnosis"; 10.1021/ac990408i; p 5003)
Stabilizing sialyl residues Charged glycans cause numerous problems during MALDIMS measurements, including loss of sialyl residues. Milos V. Novotny and co-workers at Indiana University report on a way to stabilize sialyl residues during the desorption/ionization process by perbenzoylation. The approach allows for the analysis of subpicomole levels of charged sialoglycans and benzoylated neutral glycans by MALDI-MS in the positive-ion mode. ("Mass Spectrometric Analysis of Benzoylated Sialooligosaccharides and Differentiation of Terminal a2->3 and a2->6 Sialogalactosylated Linkages at Subpicomole Levels"; 10.1021/ac990674w; p 4969)
Benzo[a]pyrene-DNA adducts • Robert J. Hurtubise and co-workers at the University of Wyoming, XenoBiotic Laboratories, and NIOSH/CDC/HELD/ TMBB demonstrate that linear relationships can be obtained between the solid-matrix phosphorescence (SMP) and the percentage modification of benzo[a]pyrene-7,8-dihydrodiol-9,10epoxide (BPDE)-DNA adducts. Changes in SMP intensities are investigated as a function of the amount of BPDE and sample size. Good reproducibility of the SMP signals is obtained with varying percentages of modified DNA, and the limit of detection for the BPDE-DNA adducts is 2 adducts in 107 bases. ("Determination of Benzo [a]pyrene-DNA Adducts by SolidMatrix Phosphorescence"; 10.1021/ac9905726)
MS for H/D exchange The H/D exchange rate of backbone amide hydrogens can be used to study the secondary and tertiary structures of proteins. Satoko Akashi and co-workers at the Institute of Physical and Chemical Research Qapan) show that capillary-skimmer dissociation with electrospray ionization Fourier transform ion cyclotron resonance MS can be used to characterize the H/D exchange of the protein ubiquitin. The deuterium content of each fragment ion is investigated at different times. The data are consistent with structural features obtained by X-ray and NMR analyses, although some labeling information may be lost by the scrambling of amide protons during capillary-skimmer dissociation. ("Observation of Hydrogen-Deuterium Exchange of Ubiquitin by Direct Analysis of Electrospray Capiilary-Skimmer Dissociation with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry"; 10.1021/ac990444h, p 4974)
Separating and elucidating biological constituents • Part of the drug discovery process is isolating and elucidating unknown compounds in biological materials, but these steps can be tedious and time-consuming. Steen Honore Hansen and co-workers at the Royal Danish School of Pharmacy (Denmark) and Zeneca Pharmaceuticals (U.K.) describe the on-line separation and structure elucidation of constituents of an extract from Hypericum perforatum L. using HPLC coupled with UV-vis, NMR, and MS. All the major known constituents are identified, and two substances never reported before are discovered and their structures elucidated. ("High-Performance Liquid Chromatography On-Line Coupled to High-Field NMR and Mass Spectrometry for Structure Elucidation of Constituents oi Hypericum perforatum L."; 10.1021/ac990598x)
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Gold 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; p 4913) Microelectrodes in flow systems Electrochemical detection in flow systems with microelectrodes is an analytical application that is becoming increasingly popular and, thus, there is a need to study the effects of combined diffusional and convective mass transport to the electrodes. Zbigniew Stojek and colleagues at the University of Warsaw (Poland) and Uppsala University (Sweden) examine the current response of a 10-um wall-tube microelectrode to several redox systems under conditions of low ionic strength in a flow injection system. The current is found to decrease with increasing flow rate, although a local current minimum could be seen when the microelectrode was centeraligned with the capillary tip. Under certain conditions, results similar to the excess supporting electrolyte case could be obtained. ("Influence of Mixed Diffusional, Migrational, and Convective Mass Transport on the Response of a WallTube Microelectrode in a Flow Injection System"; 10.1021/ ac990430b;p 4926) Potential stability of ISEs Using chronopotentiometry and electrochemical impedance spectroscopy, Johan Bobacka of Abo Akademi University (Finland) evaluates the relationship between the stability of the electrode potential of all-solid-state ion-selective electrodes (ISEs) and the capacitance of the solid contact where ion-toelectron transduction takes place. Because of its excellent environmental stability, the conducting polymer poly(3,4-ethylenedioxythiophene) is used as a model compound for the solid contact material. Polymer layers of different thicknesses are investigated as solid contacts with potassium ISEs. ("Potential Stability of All-Solid-State Ion-Selective Electrodes Using Conducting Polymers as Ion-to-Electron Transducers"; 10.1021/ ac990497z; p 4932)
Imaging microelectrodes Central to using electrogenerated chemiluminescence in imaging is selecting a chemical system that provides high light intensity. R Mark Wightman and colleagues at the University of North Carolina-Chapel Hill use the DPA'+/benzonitrile"" system to image microelectrodes in the micrometer range. Spatially nonuniform light at disk- and band-shaped microelectrodes is observed under certain conditions, with the highest intensity occurring at tire region of highest curvature. ("Imaging of Nonuniform Current Density at Microelectrodes by Electrogenerated Chemiluminescence"; 10.1021/ac9905827; p 4944) Myoglobin-containing electrodes for biosensing Joseph Wang and colleagues at New Mexico State University demonstrate the use of myoglobin as an alternative to fluorocarbon pasting liquids for designing oxygen-rich composite biomaterials. Doping the mineral oil paste binder wiih diiferent loadings of myoglobin dramatically improves the oxygen storage capacity of carbon-paste microelectrodes. The doped microelectrodes display a highly stable glucose response over 6- to 7-h operattons in oxygen-free solutions, indicating no depletion of the internal oxygen supply. ("Myoglobin-Containing Carbon-Paste Enzyme Microelectrodes for the Biosensing of Glucose under Oxygen-Deficit Conditions"; 10.1021/ac990170y; p 5009) Analyzing PCAs Because of tighter regulations on shortchained polychlorinated M-alkanes (PCAs), the use of medium-chain (C14C17) PCAs OwPCAs) is likely to increase; however, a recent study suggests that these medium-chain compounds could bioaccumulate in die environment more than the short-chain PCAs. Gregg T. Tomy and Gary A Stern of the Department of Fisheries and Oceans (Canada) present a memod for quantifying mPCAs in environmental matrixes using accelerated solvent extraction-high-resolution GC/electron capture negative ion high-resolution MS in the selected ionmonitoring mode. Detection limits are 13 ng/g for fish and 1.4 ng/uLfor sediment. ("Analysis of C14-C17 Polychloro-»alkanes in Environmental Matrixes by Accelerated Solvent Extraction-High-Resolution Gas Chromatography/Electron Capture Negative Ion High-Resolution Mass Spectrometry"; 10.1021/ac990458n; p 4860)
Strontium membrane electrodes Mojtaba Shamsipur and co-workers at Bou-Ali Sina University and Shiraz University (both in Iran) investigate the use of eight different benzo-substituted macrocyclic diamides as strontium ion carriers in PVC membrane electrodes. The sensors exhibit significantly high selectivity to Sr2+ over alkali, alkaline, and several transition-metal ions. For one electrode, a Nernstian response for Sr2+ ions over the range 10"1 to 10"5 M is sbtained, with hetection limits in the parts-per-million range. ("Strontium-Selective Membrane Electrodes Based on Some Recently Synthesized BenzoSubstituted Macrocyclic Diamides"; 10.1021/ac990167e; p 4938)
TMAO in w a t e r and biological media Trimethylamine-Af-oxide (TMAO) is a nitrogenous osmolyte, which is widely distributed in marine organisms; the reduction of TMAO to trimethylamine (TMA) is characteristic of spoiled fish. TMAO also plays a role in the biogeochemical cycle of nitrogen and the regulation of atmospheric pH. Angela D. Hatton and Stuart W. Gibb of the University of East Anglia and Plymouth Marine Laboratory (both in the U.K.) present a method in which TMAO is reduced to TMA and measured using flow injection gas-diffusion ion chromatography. The detection limit is 1.35 nmol/dm3 TMAO, and the precision is 3% for standards in the range 40-600 nmol/dm3. ("Technique for the Determination of Trimethylamine-Af-oxide in Natural Waters and Biological Media"; 10.1021/ac990366y; p 4886)
• Denotes articles tentatively scheduled for the November 15 issue
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Detecting organophosphorus neurotoxins Current approaches for detecting neurotoxins are limited in their specificity because the cholinesterases used can react with everythingfromheavy metals to chemical warfare agents. Michael Pishko and colleagues at Texas A&M University describe preparing poly(ethylene glycol) hydrogels with encapsulated seminapthofluorescein-organophosphorus hydrolase enzyme conjugates. Using spectrofluorometry, concentrations of paraoxon as low as 8 x 10"7 M could be determined. On the basis of S/N, a detection limit of 16 nM is determined. ("Polyethylene glycol) Hydrogel-Encapsulated Fluorophore-Enzyme Conjugates for Direct Detection of Organophosphorus Neurotoxins"; 10.1021/ac990901u; p 4909)
ble biological effects. In a companion paper, they describe five pH-sensitive and three calcium-selective PEBBLE sensors, each of which combine an ion-selective fluorescence indicator and an ion-insensitive internal standard entrapped within an acrylamide polymeric matrix. Calibrations, leaching of the dye from the matrix, photobleaching, reversibility of the measurements, and interferences from other ions are discussed for each sensor. ("Optical Nanosensors for Chemical Analysis Inside Single Living Cells. 1. Fabrication, Characterization, and Methods for Intracellular Delivery of PEBBLE Sensors"; 10.1021/ac990629o; p 4831; and "2. Sensors for pH and Calcium and the Intracellular Application of PEBBLE Sensors"; 10.1021/ ac990630n; p 4837)
Oxygen isotopes Conventional off-line techniques of extracting 0 2 from air, soil, or water and its conversion to C0 2 for isotopic analysis are time-consuming, potentially fractionating, and require large sample volumes. Leonard I. Wassenaar and Geoff Koehler of Environment Canada report on a simple, inexpensive analytical method for rapidly measuring 8180 and 8170 values in air, soil gas, and water samples using continuous-flow isotope-ratio MS. The technique does not require cryogenic preconcentration of 0 2 or conversion to C02, and thus significantly reduces the possibilities of isotopic fractionation. ("An On-line Technique for the Determination of the 5180 and 8170 of Gaseous and Dissolved Oxygen"; 10.1021/ac9903961; p 4965)
Diffusional manipulation of droplets Diffusional microburets (DMBs) are valuable tools for manipulating droplets in microscopic titrations, adjusting the chemical composition of cell cytoplasm, and a host of other studies on microdomains. Miklos Gratz and co-workers at Case Western Reserve University describe a novel procedure for subtracting substances, such as Lucifer Yellow CH fluorescent dye, from droplets using DMBs. The substance is diffused out of a droplet, exhibiting exponential decay, which can be quantitatively adjusted. ("Fine Chemical Manipulations of Microscopic Liquid Samples. 2. Consuming and Nonconsuming Schemes"; 10.1021/ac9813989; p 4896)
Understanding laser ablation ICPMS • Unlike most sampling methods, laser ablation requires little or no sample preparation; it also consumes very little material. R. E. Russo and co-workers at Lawrence Berkeley National Laboratory investigate the relationship between laser-generated particlesfromthe single-pulse laser ablation of glass samples and inductively coupled plasma MS signal intensity. They find that new surfaces yield a lower signal intensity than preablated surfaces, the laser beam diameter is a more important factor than power density for particle generation, and the carrier gas flow rate affects particle loss during transport from the ablation chamber to the mass spectrometer. ("Effects of Particle Size Distribution on Inductively Coupled Plasma Mass Spectrometry Signal Intensity during Laser Ablation of Glass Samples"; 10.1021/ac990455a) PEBBLEs for intracellular analysis PEBBLEs (probes encapsulated by biologically localized embedding) are 20- to 200-nm diameter spherical optical nanosensors that contain a fluorescent indicator and are small enough to analyze intracellular environments. Raoul Kopelman and colleagues at the University of Michigan present a generalized polymerization procedure for producing PEBBLEs containing any hydrophilic dye or combination of dyes in a polyacrylamide matrix. Cell viability and cell status assays indicate that the PEBBLEs are biocompatible and have negligi720 A
Analytical Chemistry News & Features, November 1, 1999
Acetylcholinesterase inhibitor assay • J. Michael Ramsey and colleagues at Oak Ridge National Laboratory describe a microfabricated device for flow injection analysis and the electrophoretic separation of acetylcholinesterase (AChE) inhibitors. The system is based on the AChE-catalyzed hydrolysis of acetylthiocholine to thiocholine, which is converted to a thioether and detected by laser-induced fluorescence; inhibitors reduce the signal, providing a negative peak diagnostic for the type of inhibition. The microfabricated device was shown to separate and detect a mixture of 4 cationic inhibitors within 70 s. ("Microfluidic Assays of Acetylcholinesterase Inhibitors"; 10.1021/ac990591f) Untangling spectra J. L Martinez Vidal and colleagues at the University of Almeria (Spain) investigate how well the cross-section approach combined with partial least squares resolves 12 overlapping components, which are the result of analyzing a complex pesticide mixture by HPLC with diode array detection. Ten of the pesticides are well-resolved; the remaining two could not be determined, probably because of their low analytical signal. The combined approach is used to predict concentrations of independent test set samples and determine these pesticides in groundwater. ("Use of the Cross-Section Technique Linked with Multivariate Calibration Methods To Resolve Complex Pesticide Mixtures"; 10.1021/ac990024s; p 4844) Aqua-impregnated resins Dmitri Muraviev, Manuel Valiente, and Maria Oleinikova of Universitat Autonoma de Barcelona (Spain) have previously demonstrated the applicability of combining ion exchange and solvent
extraction in one process using aqua-impregnated resins to separate metal ions under batch conditions. Now they report on separating polyvalent metal ions on iminodiacetic and carboxylic resins using heptane solutions of bis(2-ethylhexyl) phosphoric and bis(2-ethylhexyl) dithiophosphoric acids as organic eluents. The technique is the first successful application of combined ion-exchange-solvent extraction for the separation of metal ions on columns in water-immiscible organic media. ("AquaImpregnated Resins. 2. Separation of Polyvalent Metal Ions on Iminodiacetic and Polyacrylic Resins Using Bis(2-ethylhexyl) Phosphoric and Bis(2-ethylhexyl) Dithiophosphoric Acids as Organic Eluents"; 10.1021/ac9902345; p 4866) Ultratrace U(VI) determination Because uranium exists in low concentrations in natural waters, any method for determining the uranyl ion must include a separation and preconcentration step. Mojtaba Shamsipur and coworkers at Razi University and Tarbiat Modarres University (both in Iran) present a rapid extraction and determination procedure for uranium in natural waters, which uses octadecylbonded silica membrane disks modified with tri-»-octylphosphine oxide followed by spectrophotometric determination with dibenzoylmethane as a chromogenic reagent. The detection limit is 100 ng/1000 mL. ("Solid-Phase Extraction of Ultratrace Uranium (VI) in Natural Waters Using Octadecyl Silica Membrane Disks Modified by Tri-M-octylphosphine Oxide and Its Spectrophotometric Determination with Dibenzoylmethane"; 10.1021/ac981229o; p 4892) Absorption detection for CE CE is an increasingly popular way to achieve high-throughput separations of biological molecules. Edward S. Yeung and Xiaoyi Gong at Ames Laboratory-USDOE and Iowa State University describe a multiplexed capillary zone electrophoresis (CZE) system that uses a linear photodiode array for absorbance detection. The system is tested on a 96-capillary array, and CZE and micellar electrokinetic chromatography are performed. A detection limit of —1.8 x 10~8 M for rach capillary is achieved for rhodamine 6G. ("An Absorption Detection Approach for Multiplexed Capillary Electrophoresis Using a Linear Photodiode Array"; 10.1021/ac9900634; p 4989) Optimizing for fluorescence detection Separation conditions in CE with native fluorescence detection often represent a compromise in terms of the separation and detection figures of merit. J. V. Sweedler and colleagues at the University of Illinois at Urbana-Champaign use a sheath-flow cell for independent optimization of separation and detection conditions to greatly increase sensitivity for detecting catecholamines. More than 1 order of magnitude improvement in the detection limit for dopamine and epinephrine is achieved. ("Independent Optimization of Capillary Electrophoresis Separation and Nattve Fllorescence Detection Conditions for Indolamine and Catecholamine Measurements"; 10.1021/ac990659r; p 4997)
tion of a copolymer of chloromethylstyrene and diethoxymethylvinylsilane onto zirconia. The new stationary phase is stable over the pH range 1-13 and at temperatures up to 160 °C, and it exhibits different selectivity from polybutadiene-coated zirconia. ("Synthesis and Evaluation of an Aromatic Polymer-Coated Zirconia for Reversed-Phase Liquid Chromatography"; 10.1021/ac9900477) Polyelectrolyte-coated capillaries • Joseph B. Schlenoff and Timothy W. Graul of Florida State University describe fused-silica capillaries modified with polyelectrolyte multilayers for CE. The columns are easy to construct, exhibit reproducible control of electroosmotic flow, achieve stable flow rates immediately upon exposure of the column to running buffer, and allow for reversed flow. In addition, the columns are stable at extreme pH and ionic strength and to dehydration and rehydration, making them well suited for protein separations. ("Capillaries Modified by Polyelectrolyte Multilayers for Electrophoretic Separations"; 10.1021/ac9902771) SERS meets immunoassay Many immunoassays require the concomitant determination of several analytes. Marc D. Porter and colleagues at Ames Laboratory-USDOE and Iowa State University describe a new immunoassay readout method based on surface-enhanced Raman scattering, in which detection antibodies are conjugated with gold colloids that are labeled with different Raman reporter molecules. Using labels with little spectral overlap, two different antigenic species can be detected simultaneously. ("Immunoassay Readout Method Using Extrinsic Raman Labels Adsorbed on Immunogold Colloids"; 10.1021/ac990616a; p 4903) Arsenic in dilute serum J. B. Simeonsson and D. J. Swart of the University of Iowa report on an electrothermal atomization laser-excited atomic fluorescence spectrometry (ETA-LEAFS) procedure for directly measuring arsenic at trace levels (
