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In AC Research contains brief introductions to the research articles appearing in the June 1 issue. A free updated table of contents is available on the Web (http://pubs.acs.org/ac).
Drug search gets a methanol boost. Stephen L. Morgan and colleagues at the South Carolina Law Enforcement Division and the University of South Carolina use CO2 modified with methanol (10%) to extract cocaine from human hair through supercritical fluid extraction (SFE). The procedure reportedly recovers cocaine from hair two times faster than GC/MS. The researchers also report that extraction times are shorter for SFE (70–80 min) than for existing classical techniques (24 h). (“Analysis of Cocaine, Benzoylecgonine, Codeine, and Morphine in Hair by Supercritical Fluid Extraction with Carbon Dioxide Modified with Methanol”; 10.1021/ac000871r; p 2371) Detecting in vivo formed DNA adducts. Paul Vouros and colleagues at Northeastern University and Nestle Research Centre (Switzerland) describe a capillary LC/microelectrospray MS method for detecting deoxyribonucleoside adducts of the food-derived mutagen 2-amino3-methylimidazo[4,5-f] quinoline from in vivo sources. Analyte detection is improved by nearly 2 orders of magnitude. (“Detection of In Vivo Formed DNA Adducts at the Partper-Billion Level by Capillary Liquid Chromatography/Microelectrospray Mass Spectrometry”; 10.1021/ac0100401; p 2397) TNT by antibodies in sol–gel. Miriam Altstein and colleagues at the Volcani Center and Israel National Police Headquarters (both in Israel) describe immunoaffinity purification and detection of trace amounts of TNT using antibodies in a ceramic sol–gel matrix. The trapped antibodies do not leach from the matrix, and the bound analytes could easily be eluted from the sol–gel matrix at high recoveries. (“Immunochemical Approaches for Purification and Detection of TNT Traces by Antibodies Entrapped in a Sol–Gel Matrix”; 10.1021/ ac001376y; p 2461) Fireflies shed light on protein interactions. Yoshio Umezawa and co-workers at the University of Tokyo (Japan) and the Japan Science and Technology Corp. propose a new method for detecting protein–protein interactions in intact mammalian cells using firefly luciferase fragments as optical probes. The approach, called the protein splicing-based split luciferase enzyme system, is based on protein splicing of a naturally split intein, or internal protein, of DnaE derived from the
cyanobacterium Synechocystis sp. PCC6803. The system can be used in high-throughput drug screening and quantitative analysis for a specific pathway in tyrosine phosphorylation of IRS-1 insulin signaling. (“Split Luciferase as an Optical Probe for Detecting Protein–Protein Interactions in Mammalian Cells Based on Protein Splicing”; 10.1021/ac0013296; p 2516)
Proteins identified directly from a mixture. David H. Russell and Zee-Yong Park from Texas A&M University achieve uniform trypsin digestion of proteins in solution after thermally denaturing the proteins. The proteolytic peptide solution is placed onto a MALDI plate and analyzed by high-resolution, high-mass-accuracy (average error ~5 ppm) MALDI time-of-flight mass spectrometry using protein database searches with search scoring systems. Their method is less complex and requires less time than similar results obtained with highresolution/high-throughput FT-MS. (“Identification of Individual Proteins in Complex Protein Mixtures by High-Resolution, High-Mass-Accuracy MALDI TOF-Mass Spectrometry Analysis of In-Solution Thermal Denaturation/Enzymatic Digestion”; 10.1021/ac001488p; p 2558) Iron release. Igor Kaltashov and Dmitry Gumerov at the University of Massachusetts–Amherst find a way to study transferrins, a class of metalloproteins that are important to the biological and healthcare fields because of their involvement in circulatory iron transport. The proteins are too large to be studied by NMR, but the researchers can use ESI MS to study the metal-ion binding and release and other dynamics of the transferrin system in vitro under conditions that are supposed to mimic the physiological environment. (“Dynamics of Iron Release from Transferrin N-Lobe Studied by Electrospray Ionization Mass Spectrometry”; 10.10.21/ac0015164; p 2565) Photometric screening for dimeric alkaloids. Dimeric naphthylisoquinoline alkaloids from plants are pharmacologically interesting because of their strong anti-HIV activity. After performing lead tetraacetate-initiated regioselective coupling on a crude plant extract, Gerhard Bringmann and colleagues at the University of Würzburg (Germany) determine the presence of the dimer from UV spectra. LC/electrospray ionization MS/MS verifies the screening result, and the constitution and relative configuration of the compound are determined online by LC/NMR and LC/circular dichroism. (“A Photometric Screening Method for Dimeric Naphthylisoquinoline Alkaloids and Complete On-Line Structural Elucidation of a Dimer in Crude Plant Extracts, by the LC–MS/LC–NMR/LC–CD
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Triad”; 10.1021/ac001503q; p 2571)
Tagging to isolate phosphopeptides. Richard D. Smith and colleagues at Pacific Northwest National Laboratory describe a method that utilizes phosphoprotein isotopecoded affinity tags and combines stable isotope and biotin labeling to enrich and quantitatively measure differences in the O-phosphorylation states of proteins. This approach is demonstrated using phosphoprotein -casein and yeast protein extract. (“Phosphoprotein Isotope-Coded Affinity Tag Approach for Isolating and Quantitating Phosphopeptides in Proteome-Wide Analyses”; 10.1021/ac010081x; p 2578)
Analyzing antisense oligonucleotides on-line. Ernst Bayer and colleagues at the University of Tübingen (Germany) couple capillary gel electrophoresis (CGE) and electrospray (ES) MS online to analyze antisense oligonucleotides. To avoid the usual incompatibility between CGE buffers and ESMS, the researchers use an entangled polymer solution for the separations. Single-nucleotide differences in length are detected among 12–20 mers, and failed products of oligonucleotide synthesis are separated and characterized. (“On-Line Coupling of Capillary Gel Electrophoresis with Electrospray Mass Spectrometry for Oligonucleotide Analysis”; 10.1021/ac0012290; p 2587)
Glycoform separation. Kazuaki Kakehi and colleagues at Kinki University (Japan) describe an easy method of separating glycoforms of ␣1-acid glycoprotein (AGP) from serum samples. Desalting, electrokinetic injection, and CE reveal multiple peaks. Molecular species of AGP are also separated by anion exchange chromatography, Con A affinity chromatography, and Cu(II)metal affinity chromatography. Glycoforms of these fractions are examined directly by CE. Glycoform and carbohydrate chains are needed to evaluate sialic acid-containing glycoprotein pharmaceuticals. (“Capillary Electrophoresis of Sialic Acid-Containing Glycoprotein. Effect of the Heterogeneity of Carbohydrate Chains on Glycoform Separation Using an ␣1-Acid Glycoprotein as a Model”; 10.1021/ac001382u; p 2640)
Organic solvents aid protein digestion. David Russell and colleagues at Texas A&M University demonstrate that trypsin digests proteins more rapidly and with better amino acid coverage in the presence of organic solvents than in plain aqueous solutions. The higher digestion yield increases the confidence level of subsequent database searches. (“Proteolysis in Mixed Organic–Aqueous Solvent Systems: Applications for Peptide Mass Mapping Using Mass Spectrometry”; 10.1021/ ac001332p; 2682)
Prussian Blue electrodes. Two new methods for making Prussian Blue-based carbon paste electrodes are described 296 A
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by D. Moscone and colleagues at Università di Tor Vergata (Italy) and the Faculté de Sciences et Techniques de Mohammadia (Morocco). The electrodes have long operational lifetimes, good stability over a wide pH range, high sensitivities, and fast response times. Coupling glucose oxidase and choline oxidase to the electrodes yields new biosensors that are optimized for working at alkaline pH. (“Construction and Analytical Characterization of Prussian Blue-Based Carbon Paste Electrodes and Their Assembly as Oxidase Enzyme Sensors”; 10.1021/ac001245x; p 2529)
Rotating electrochemical detectors for CE. John Luong and Abdelkader Hilmi at the National Research Council Canada confirm that, as principle suggests, a rotating disk electrode (RDE) outperforms the usual stationary electrode when detecting electroactive species separated by CE. For catechol, the RDE has a ~2.5-fold better detection limit than a stationary electrode. Because the RDE alleviates electrode passivation and electrical interference due to high separation potentials, it is particularly useful for phenolic and other compounds that rapidly foul the electrode surface. (“Development of Rotating Electrochemical Detectors for Capillary Electrophoresis”; 10.1021/ac001192j; p 2536) Cobalt(II) empowers CL detection for CE. Jicun Ren and Xiangyi Huang at Hunan Normal University (China) introduce indirect chemiluminescence (CL) detection for CE of cations using cobalt(II) as a probe ion in the running buffer. The cobalt(II) ion’s catalysis of the luminol–hydrogen peroxide reaction generates strong and stable background CL signal. The technique is based on migrating the sample ion to displace the probe ion, and it successfully detects noncatalytic metal ions. The method shows more universality and high throughput compared with direct CL detection for CE and conventional CL. (“Sensitive and Universal Indirect Chemiluminescence Detection for Capillary Electrophoresis of Cations Using Cobalt(II) as a Probe Ion”; 10.1021/ac001414d; p 2663)
The content of dirt. The need to understand biogeochemical soil processes has evoked recent interest in developing efficient and sensitive HPLC and GC methods for determining naturally occurring hydrophilic compounds and dissolved organic content in soil. Klaus Fischer et al. at the University of Trier (Germany) have developed a new, selective, and sensitive ion-pair method for simultaneous determination of carbohydrates, amino acids, and uronic acids in environmental soil solutions and landfill leachates. p-Aminobenzoic acid is applied as a precolumn derivatization agent to facilitate reductive amination of the analytes before analysis by RP-HPLC. (“Ion-Pair RP-HPLC Determination of Sugars, Amino Sugars, and Uronic Acids after Derivatization with p-Aminobenzoic Acid”;
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10.10.21/ac001402; p 2377)
Triazines in river water. Robert Koeber and collaborators at IIQAB-CSIC (Spain), University Hospital Grosshadern, and the University of Mainz (both in Germany) have described the first combination of restricted access material (RAM) with molecularly imprinted polymers for the analysis of environmental water samples. Simultaneous application of size-exclusion chromatography and reversed-phase chromatography in the RAM column is attractive because of the large differences in molecular size of the target analytes and the high molecular weight of the humic substances. (“Evaluation of a Multidimensional Solid-Phase Extraction Platform for Highly Selective OnLine Cleanup and High-Throughput LC–MS Analysis of Triazines in River Water Samples Using Molecularly Imprinted Polymers”; 10.10.21/ac001483s; p 2437)
Iron in seawater. Constant M. G. van den Berg and Hajime Obata at the University of Liverpool (U.K.) use adsorptive accumulation and cathodic stripping voltammetry (CSV) to measure iron in seawater. They achieve a detection limit of 13 pM, which can be lowered further by extending the adsorption time to 300 s. This system is ~5 times more sensitive than existing CSV methodologies. (“Determination of Picomolar Levels of Iron in Seawater Using Catalytic Cathodic Stripping Voltammetry”; 10.1021/ac001495d; p 2522)
Diffusion coefficients by microdispenser and microelectrodes. Marcus Mosbach and colleagues at Ruhr-Universität Bochum (Germany), Lund Institute of Technology, and Lund University (both in Sweden) describe two novel methods for determining diffusion coefficients based on locally applying tiny volumes of redox-active species with a dispenser nozzle at a defined distance from the surface of a microelectrode. In one method, the time needed to attain the maximum current and the distance between two dispensing points are used to determine the diffusion coefficient. In the other method, a second redox species is used for calibration. (“Determination of Diffusion Coefficients of Electroactive Species in Time-of-Flight Experiments Using a Microdispenser and Microelectrodes”; 10.1021/ac0012501; p 2468)
Unearthing ICPMS advantages in geology. Eizo Nakamura and Akio Makishima at Okayama University (Japan) propose a new technique to determine sulfur at microgram-pergram levels in milligram-sized silicate materials. The researchers use isotope dilution high-resolution inductively coupled plasma MS (ICPMS) equipped with a flow-injection system. Bromine quantitatively oxidizes the sulfur into sulfate, and isotope equilibrium is achieved between the sample and spike. Multi-element determinations from the same sample aliquot are possible. (“Determination of Total Sulfur at Microgram per Gram Levels
in Geological Materials by Oxidation of Sulfur into Sulfate with In Situ Generation of Bromine Using Isotope Dilution HighResolution ICPMS”; 10.1021/ac001550i; p 2547)
IMS usurps APIMS. Atmospheric pressure ionization (API) MS has limits of detection (LODs) appropriate for monitoring bulk, inert gases during the fabrication of semiconductors, but the technique’s cost and bulkiness prohibit routine monitoring. S. N. Ketkar and S. Dheandhanoo of Air Products and Chemicals use ion mobility spectrometry (IMS) to separate ions on the basis of their mobilities. The low-cost analyzer has fast response times and LODs lower than required, and it detects 55,000 in this reversed-phase system with greater efficiency than conventional granular packing materials. (“High-Performance Liquid Chromatography–Electrospray Ionization Mass Spectrometry Using Monolithic Capillary Columns for Proteomic Studies”; 10.1021/ac010046q; p 2390)
Vapor pressure for reluctant volatiles. Lars Rittfeldt of the Swedish Defence Research Agency fills the need for reliable vapor pressure data of low-volatility and toxic chemicals. A fused-silica column coated with a compound is placed in a gas chromatograph, and the vapor pressure at a given temperature is determined directly from the detector signal in the 10–3- to 103Pa range. The linear plot of P vs 1/T gives the enthalpy of vaporization (⌬Hvap) and vapor pressure at different temperatures for several compounds including 2,4-dinitrotoluene and two methylphosphono thiolates. (“Determination of Vapor Pressure of Low-Volatility Compounds Using a Method To Obtain Saturated Vapor with Coated Capillary Columns”; 10.1021/ ac010015v; p 2405) SPME gets crowned. Zhaorui Zeng et al at Wuhan University (China) have coated a hydroxy-terminated silicon oil solid-phase microextraction (SPME) fiber with hydroxydibenzo-14-crown-4 using sol–gel coating technology. Adding the crown ether increases the polarity of the coating; while the silicon oil lengthens the network and provides a more uniform surface. The new fiber is used to analyze five phenolic compounds, and it is also applied to the analysis of wastewater samples from a paper mill. (“Solid-Phase Microextraction
Using Fused-Silica Fibers Coated with Sol–Gel-Derived Hydroxy-Crown Ether”; 10.10.21/ac0012750; p 2429) Determining hafnium isotopes. Brieuc Le Fèvre and Christian Pin at the Université Blaise Pascal (France) develop a straightforward method to purify Zr + Hf by combining LiBO2 fusion and extraction by dipentyl pentyl phosphonate. The isotopes are measured by multiple collection inductively coupled plasma MS. Purification compares favorably with conventional ion-exchange methods and does not require large volumes of concentrated HF. (“An Extraction Chromatography Method for Hf Separation Prior to Isotopic Analysis Using Multiple Collection ICP-Mass Spectrometry”; 10.10.21/ac001237; p 2453)
Determining molybdenum isotopes. Nicolas Dauphas and colleagues at CNRS UPR 2300 and Ecole National Supérieure de Géologie (both in France) have a method to precisely determine molybdenum isotope abundances in natural samples. Samples are purified by solvent extraction using di(2-ethylhexyl)phosphate and separated from interfering species like zirconium and ruthenium by ion chromatography. Isotopic analyses are performed with multiple collector inductively coupled plasma hexapole MS. (“Solvent Extraction, Ion Chromatography, and Mass Spectrometry of Molybdenum Isotopes”; 10.10.21/ac000998g; p 2613) Determining enantiomeric compositions of peptides. A new micellar electrokinetic chromatography/laserinduced fluorescence method for determining the enantiomeric composition of peptides is described by Gunnar Thorsén and colleagues at Stockholm University, Göteborg University, Uppsala University, and AstraZeneca (all in Sweden). The method is tested on -amyloid peptides and senile plaques typical of Alzheimer’s disease. Separation efficiencies of ~1 million theoretical plates are achieved. (“Stereoselective Determination of Amino Acids in -Amyloid Peptides and Senile Plaques”; 10.1021/ac000861q; p 2625)
New model for ion interaction chromatography. T. Cecchi and colleagues at Università degli Studi di Camerino (Italy) present an extended thermodynamic approach to the modeling of ion interaction chromatography. The new theory of retention behavior is discussed with respect to experimental data and previous models. (“Extended Thermodynamic Approach to Ion Interaction Chromatography”; 10.1021/ ac001341y; p 2632)
Polarity at liquid–liquid interfaces. Using time-resolved total internal reflection fluorescence spectroscopy, Noboru Kitamura and colleagues at Hokkaido University (Japan) investigate interfacial polarity at a water–oil interface. The researchers find experimental evidence for a relationship between thickness/ J U N E 1 , 2 0 0 1 / A N A LY T I C A L C H E M I S T R Y
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roughness and polarity, though they add that a theoretical explanation of the results requires further study. (“Time-Resolved Total Internal Reflection Fluorometry Study on Polarity at a Liquid/Liquid Interface”; 10.1021/ac001124x; p 2421)
Water analysis gives clear performance. E. R. Th. Kerstel and co-workers at the University of Groningen and the Zoological Laboratory (both in The Netherlands) use laser spectrometry to analyze isotopically highly enriched water samples often used in the biomedical doubly labeled water method to quantify energy metabolism. The researchers report that the measurements on highly enriched, small samples (10 µL liquid water) show better accuracy for 2H/1H. The precision with laser spectrometry is also better for 2H/1H and 18 O/16O, with the same level of accuracy for 18O/16O as obtained with conventional isotope ratio (IR) MS. The biggest advantage of the new system is its conceptual simplicity and the absence of chemical sample pretreatments, which are necessary with traditional IRMS. (“Stable Isotope Ratio Measurements on Highly Enriched Water Samples by Means of Laser Spectrometry”; 10.1021/ac001428j; p 2445)
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Odor discrimination. David R. Walt, Tim C. Pearce, and colleagues at Tufts University and the University of Leicester (U.K.) use a fiber-optic bead-based sensor array platform to discriminate between six different odors and air carrier gas. Six different bead sensor types, with more than 250 replicates of each, are monitored before, during, and after odor exposure to produce time-dependent fluorescence response patterns, which are unique for each sensor–analyte combination. At low-odor concentrations, the multibead array system exhibits classification rates that are >85%. (“Optical Multibead Arrays for Simple and Complex Odor Discrimination”; 10.1021/ac001137a; p 2501) Improving multiplex sample NMR analysis. Daniel Raftery and colleagues at Purdue University show two improved methods for analyzing multiple samples using multiplex sample NMR. In the first method, the scientists applied frequency-selective 90° radio frequency pulses and large pulsed-field gradients to excite and detect multiple samples in rapid succession. The second approach uses chemical shift imaging to acquire spectral and spatial information of multiple samples at the same time. (“Analysis of Multiple Samples Using Multiplex
