in ac research
In AC Research contains brief introductions to the research articles appearing in the January 1 issue. A free updated table of contents is available on the Web (http://pubs.acs.org/ac).
try Techniques in the Drug Discovery Process”; 10.1021/ac010569y; p 1)
Affinity-based MS for drug discovery. Biomolecular MS (bio-MS) is providing a novel and direct means to study molecular properties and interactions. Affinitybased techniques use a variety of methods to select, purify, probe, or enrich analytes of interest. These techniques are often used to create an alternative strategy when classical MS methods are insufficient. Michele Kelly and colleagues of Pfizer Global R&D demonstrate how a combination of bio-MS and these affinity-based biochemical techniques has the potential to promote new directions in drug discovery. (“Strategic Use of Affinity-Based Mass Spectrome-
Sample evaporation in hot GC injectors. To elucidate the vaporization process during split and splitless sample injection for capillary GC, Koni Grob and Maurus Biedermann of the Official Food Authority of the Canton of Zurich (Switzerland) study the critical factor of solvent evaporation. Differences between the two principal approaches of thermospray injection and injection with band formation are discussed, and optimized experimental conditions and injector designs are offered. (“Two Options for Sample Evaporation in Hot GC Injectors: Thermospray and Band Formation. Optimization of Conditions and Injector Design”; 10.1021/ac0107554; p 10)
“Sandwich” immunoassay with ICPMS detection. In an effort to find nonisotopic detection methods, Xin-
HPLC/MS characterization of an isomeric peptide library. David Clemmer and colleagues at Indiana University and Beyond Genomics combine reversed-phase LC with ion mobility/time-of-flight MS to characterize a combinatorial library of ~4000 peptides. The library of 3- to 6residue-long peptides contains structural and sequence isomers, with as many as 20–30 isomers present at a given m/z. The researchers estimate that they resolve ~82% of the library components. (“Resolving Isomeric Peptide Mixtures: A Combined HPLC/Ion Mobility-TOFMS Analysis of a 4000-Component Combinatorial Library”; 10.1021/ac0108562; p 26)
An immunoassay with public health potential. Diane A. Blake and Ibrahim A. Darwish at the Tulane University Health Sciences Center and the Tulane–Xavier Center for Bioenvironmental Research report on an immunoassay for analyzing heavy metals in biological fluids—in this case, Cd(II) in humans. The researchers have developed a one-step, platebound antibody immunoassay for the determination of Cd(II) in human serum at concentrations as low as 0.24 µg/L. The assay uses a monoclonal antibody that recognizes Cd(II)–EDTA complexes—not metal-free EDTA—and uses a peroxidase conjugate of Cd(II)–EDTA as an enzyme label. (“Development and Validation of a One-Step Immunoassay for Determination of Cadmium in Human Serum”; 10.1021/ac010510r; p 52)
rong Zhang and colleagues at Tsinghua University (People’s Republic of China) develop a “sandwich” immunoassay that uses inductively coupled plasma (ICP) MS. The analyte—in this case, a rabbit antibody directed against human immunoglobulin (IgG)—is trapped between an immobilized human IgG and a second antibody, which is labeled with colloidal gold nanoparticles. ICPMS detects the gold nanoparticles, and a linear relationship between the signal intensity and the analyte concentration is obtained in the range 0.8–50 ng/mL. (“Application of the Biological Conjugate between Antibody and Colloid Au Nanoparticles as Analyte to Inductively Coupled Plasma Mass Spectrometry”; 10.1021/ac0103468; p 96)
Membrane redox activity. Michael Mirkin and colleagues at Queens College and the University of Connecticut previously reported methods using scanning electrochemical microscopy (SECM) to study the redox activity of mammalian cell membranes. In this work, the researchers compare SECM responses from individual purple bacteria with the mammalian results and explore the differences in charge-transfer mechanisms. (“Scanning Electrochemical Microscopy of Living Cells. 3. Rhodobacter sphaeroides”; 10.1021/ac010945e; p 114) Sandwich test for RNA and DNA. Adam Heller and colleagues at the University of Texas–Austin describe a one-step, enzyme-amplified, amperometric sandwich hybridization test for RNA and DNA based on a carbon electrode modified with a J A N U A R Y 1 , 2 0 0 2 / A N A LY T I C A L C H E M I S T R Y
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film of co-electrodeposited avidin and redox polymer, which wires the horseradish peroxidase reaction centers upon contact. High concentrations of irrelevant DNA and diluted serum did not interfere with the assay. When the electrodes are rotated to accelerate the solution-phase mass transfer, the test is completed in 30 min. (“Enzyme-Amplified Amperometric Sandwich Test for RNA and DNA”; 10.1021/ac015602V; p 158)
Voltammetry and catalysis with Mycobacterium tuberculosis catalase–peroxidase. James F. Rusling and colleagues at the University of Connecticut and the City University of New York attempt to obtain insight into the catalytic electrochemical responses to hydrogen peroxide common to iron heme enzymes and to address the analytical possibilities of peroxidases in lipid films. Relative apparent turnover rates at pH 6 based on steady-state currents at 0 V versus SCE in the presence of hydrogen peroxide are in the order horseradish peroxidase > cytochrome c peroxidase > soybean peroxidase > myoglobin > KatG > catalase. (“Direct Voltammetry and Catalysis with Mycobacterium tuberculosis Catalase–Peroxidase, Peroxidases, and Catalase in Lipid Films”; 10.1021/ac010701u; p 163)
Mitochondrial diversity. Edgar Arriaga and co-workers at the University of Minnesota believe the mobility distributions of mitochondria isolated from NS1 and CHO cells are evidence of intrinsic mitochondrial diversity as well as diversity caused by preparation procedures. Postcolumn laser-induced fluorescence on samples labeled with 10-nonyl acridine orange reveals mobility distributions and detects individual mitochondria. The researchers project that the method can be applied to other organelles or artificial nanoparticles. (“Determination of Electrophoretic Mobility Distributions through the Analysis of Individual Mitochondrial Events by Capillary Electrophoresis with Laser-Induced Fluorescence Detection”; 10.1021/ ac010939i; p 171) Truncated oligos. Ulf Landegren and co-workers at the Karolinska Institute and Rudbeck Laboratory (both in Sweden) propose that oligonucleotide quality can improve, at optimal temperatures, the performance of oligonucleotide hybridization microarrays. They investigate the effect that truncated oligonucleotides generated by DNA microarray manufactured via photolithographic synthesis might have on a researcher’s ability to distinguish target sequence variants that differ in a single nucleotide. They monitor the extent of hybridization over a range of temperatures via the fluorescence of a doublestrand-specific dye. (“Effect of Oligonucleotide Truncation on Single-Nucleotide Distinction by Solid-Phase Hybridization”; 10.1021/ac010555s; p 199) A fitting sequence. A computer algorithm verifies DNA sequences and detects insertions, deletions, and point mutations in 5- to 51-mer oligodeoxynucleotides. Christian Huber and associates at Leopold-Franzens University (Austria) compare experimental and predicted m/z fragment ion spectra from collision-induced dissociation following electrospray ionization. 8 A
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They define properties for the “fitness” of matching spectra such that small values correspond to a closer match. The group plans to extend their method up to a 100-mer sequence and fully automate their software program. (“Comparative Sequencing of Nucleic Acids by Liquid Chromatography–Tandem Mass Spectrometry”; 10.1021/ac015595a; p 211)
HPLC of ecdysteroids in plants. Ian D. Wilson and colleagues at AstraZeneca Pharmaceuticals, the Laboratory of the Government Chemist (both in the United Kingdom), and CNRS (France) use superheated D2O as the mobile phase in HPLC and various spectroscopic methods to analyze plant extracts containing 20-hydroxyecdysones and ecdysteroids. Using UV, FT-IR, 1H NMR, and MS allows for the on-flow collection of data. (“HPLC Analysis of Ecdysteroids in Plant Extracts Using Superheated Deuterium Oxide with Multiple On-Line Spectroscopic Analysis (UV, IR, 1H NMR, and MS)”; 10.1021/ac0107397; p 288) Uracil in human DNA. Jicun Ren and colleagues from the University of Bergen (Norway) and Shanghai Jiaotong University (People’s Republic of China) have developed an HPLC/tandem MS method for determining uracil in human DNA. Contamination from RNA is avoided by excising with uracil DNA glycosylase. Human DNA uracil isolated from peripheral white blood cells did not differ between subjects with folate deficiencies and subjects with normal red cell folate levels. (“Uracil in Human DNA from Subjects with Normal and Impaired Folate Status as Determined by High-Performance Liquid Chromatography– Tandem Mass Spectrometry”; 10.1021/ac010556k; p 295)
Circuit measures properties of polymer films. William D. Hinsberg and colleagues at the IBM Almaden Research Center and Stanford University show that the simultaneous measurement of resonant frequency and motional resistance (R), which can be carried out at high data acquisition rates, provides information so researchers can better understand the viscoelastic properties of polymer films. The researchers combine the quartz crystal microbalance and the compound resonator as a Butterworth–Van Dyke equivalent circuit, from which they isolate resistance values with the help of a compensated phase-locked oscillator. They report that the behavior of R as a function of film thickness or corresponding frequency shift not only quantitatively determines the shear viscosity and elastic modulus of films but also qualitatively compares various systems. (“Determination of the Viscoelastic Properties of Polymer Films Using a Compensated Phase-Locked Oscillator Circuit”; 10.1021/ac0108358; p 125)
Biosensors for glycolic acid in real samples. Miltiades Karayannis and colleagues at the University of Ioannina
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(Greece) describe the first enzyme-based biosensors for detecting glycolic acid in urine, instant coffee, cosmetics, and other complex matrixes. A membrane bearing either glycolate oxidase or a glycolate oxidase–catalase mixture is sandwiched between a polycarbonate membrane, which rejects large molecules, and a cellulose acetate membrane, which rejects smaller interfering agents. This assembly is mounted on an amperometric flow cell. (“Development of Amperometric Biosensors for the Determination of Glycolic Acid in Real Samples”; 10.1021/ac0106896; p 132)
Amperometric biosensor for TNT. H. D. Abruña and colleagues at Cornell University describe an amperometric biosensor to detect 2,4,6-trinitrotoluene (TNT) and other nitroaromatic compounds. Particular attention is paid to the interaction of the enzyme—a maltose binding protein–nitroreductase fusion protein—with the electroactive N-(3-pyrrol-1-ylpropyl)4,4´ bipyridine film on which the enzyme is immobilized. Detection limits are estimated at 2 µM for TNT and 2,4-dinitrotoluene in solution. (“Amperometric TNT Biosensor Based on the Oriented Immobilization of a Nitroreductase Maltose Binding Protein Fusion”; 10.1021/ac010596o; p 140) Chronoamperometric technique measures up.
Dissolving DDT. John Dean and Lisa Fitzpatrick of the University of Northumbria–Newcastle (United Kingdom) develop a method to predict a suitable solvent for obtaining samples of DDT and similar compounds from soil for later determination of contaminants. Their model, based on the Hildebrand solubility parameter, describes the solvent in relation to its hydrogen-bonding, dispersion, and polarity contributions. Extraction of DDT and similar analytes corresponds well with this model, and the researchers believe the method can be applied to other environmental contaminants. (“Extraction Solvent Selection in Environmental Analysis”; 10.1021/ac001336u; p 74) Fungal spores in aerosols. Thoughts of Austrian mountains in winter may evoke the sensation of cool, clean, mountain air, but Anne Kasper-Giebl and colleagues at the Vienna University of Technology, the University of Agricultural Sciences, and the University of Vienna (all in Austria) are more interested in finding the contribution of fungal spores to atmospheric carbon aerosols. Tests on spores of four airborne genera show that fungal carbon accounts for 2.9–5.4% of the organic carbon in the coarse, 2.5- to 10-µm size range of soot. The carbon-per-volume ratio is 0.38 pg C/µm3. (“Determination of the Carbon Content of Airborne Fungal Spores”; 10.1021/ac010331+; p 91)
Wojciech Hyk, Zbigniew Stojek, and Anna Nowicka at Warsaw University (Poland) present a new method for determining the diffusion coefficients of a substrate and the product of an electrode process. The method is based on a numerical model of migrational chronoamperometry, the radius of the microelectrode prior to the experiment, and linear regression analysis. They show that double-potential step chronoamperometry may provide complete information on the transport properties of a studied redox couple, regardless of the level of ionic support present in the system. (“Direct Determination of Diffusion Coefficients of Substrate and Product by Chronoamperometric Techniques at Microelectrodes for Any Level of Ionic Support”; 10.1021/ac0109117; p 149)
REEs from a single rock digest. Ilka C. Kleinhanns and colleagues at the Universität Bern (Switzerland), Universität Loeben (Austria), University of Bristol (United Kingdom), and the University of Queensland (Australia), present a method to simultaneously determine lutetium, hafnium, samarium, neodymium, and other rare earth elements (REEs) from a single aliquot of rock sample. The sample is sintered with sodium peroxide and separated and purified by ion-exchange chromatography. Isotopic distributions are determined by multicollectorICPMS. Poor reproducibility of the Lu/Hf ratio is caused by sample heterogeneity. (“Combined Chemical Separation of Lu, Hf, Sm, Nd, and REEs from a Single Rock Digest: Precise and Accurate Isotope Determinations of Lu–Hf and Sm–Nd Using Multicollector-ICPMS”; 10.1021/ac010705z; p 67) J A N U A R Y 1 , 2 0 0 2 / A N A LY T I C A L C H E M I S T R Y
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Selenium in mustard leaves. Because various Brassica species accumulate selenium, they may be candidates for phytoremediation. Joseph A. Caruso and colleagues at the University of Cincinnati describe the uptake, distribution, and speciation of selenium found in Brassica juncea (Indian Mustard plants grown in a selenite-spiked medium). Proteinase K provides the best extraction at 75%. Some of the species produced by the plant are identified by reversed-phase LC/ICPMS at parts-per-billion levels. (“Initial Studies of Selenium Speciation in Brassica juncea by LC with ICPMS and ES-MS Detection: An Approach for Phytoremediation Studies”; 10.1021/ac0106804; p 107) Impure nerve agents. Detecting and analyzing military nerve agents requires certified, standard, pure, analytical reference materials. With no sample preparation, Terry Henderson of Battelle Memorial Institute Edgewood Operations uses stem coaxial inserts to introduce reference material for the quantitative purity determination of sarin, soman, and VX by 31 P NMR. There is no reaction with the nerve agent to cause impurities, and the ~0.5% precision and ~1% accuracy rival chromatographic methods for certification of analytical standards. (“Quantitative NMR Spectroscopy Using Coaxial Inserts Containing a Reference Standard: Purity Determinations for Military Nerve Agents”; 10.1021/ac010809+; p 191) Free amines by HPLC. Yukui Zhang and co-workers at the Chinese Academy of Sciences and the Qufu Normal University (China) report on a method for HPLC analysis of wastewater amines that uses precolumn derivatization and fluorescence detection. The LC separation of the derivatized amines shows good reproducibility (RSD of
