in ac research
In AC Research contains brief introductions to the research articles appearing in the April 1 issue. A free updated table of contents is available on the Web (http://pubs.acs.org/ac).
ACCELERATED ARTICLE
quiring multiple tandem MS. They suggest that IRMPD may be valuable for differentiating isomeric compounds. (“Infrared Multiphoton Dissociation of Alkali Metal-Coordinated Oligosaccharides”; 10.1021/ac026009w; p 1590)
A radical way to study protein–protein or protein–peptide interactions. Kevin Downard and
Improved detection of compounds associated with lung cancer in human breath. Conventional
colleagues at the University of Sydney (Australia) study the interaction of ribonuclease (RNase) S-protein and S-peptide using radicals generated by an electrical discharge within an electrospray ion source. Because the components are exposed to radicals for a short period of time, little or no damage is incurred. This method of producing radicals for protein interactions is comparable to the alternative method of exposing proteins to synchrotron light, and electrospray ion sources are more readily available than synchrotrons. (“Study of the Ribonuclease–S-Protein–Peptide Complex Using a Radical Probe and Electrospray Ionization Mass Spectrometry”; 10.1021/ac026400h; p 1557)
solid-phase microextraction (SPME) can detect nanomolar concentrations of volatile organic compounds (VOCs) in human breath, but Susan Olesik and Matthew Giardina at the Ohio State University use a modified SPME fiber to detect compounds present in picomolar concentrations, such as those correlated with lung cancer. They use low-temperature glassy carbon (LTGC)-SPME fibers that are four times longer than conventional SPME fibers. The researchers find that detection limits with the LTGC-SPME fibers are in the low- to sub-picomolar range. (“Application of Low-Temperature Glassy CarbonCoated Macrofibers for Solid-Phase Microextraction Analysis of Simulated Breath Volatiles”; 10.1021/ac025984k; p 1604)
BIOANALYTICAL Protein–protein interactions. S. S. Gambhir and R. Paulmurugan at the University of California–Los Angeles describe a protein-fragment-assisted complementation-based bioluminescence assay to quantitatively measure real-time protein–protein interactions in mammalian cells. They identify suitable sites to generate fragments on nitrogen and carbon portions of the protein that yield significant recovered activity through complementation. Complementation-based activation of split synthetic renilla luciferase protein driven by the interaction of two strongly interacting proteins is validated in five different cell lines using transient transfection studies. (“Monitoring Protein–Protein Interactions Using Split Synthetic Renilla Luciferase Protein-Fragment-Assisted Complementation”; 10.1021/ac020731c; p 1584)
Comparison of dissociation methods. Carlito Lebrilla and Yongming Xe at the University of California–Davis find that IR multiphoton dissociation (IRMPD) provides information that is complementary to data provided by collision-induced dissociation (CID). IRMPD yields results similar to CID when smaller metals are coordinated to oligosaccharides, and it allows determination of the reducing end of oligosaccharide alditols without re-
Detecting biomarkers of Bacillus species. Kent Voorhees and colleagues at the Colorado School of Mines and MassTech use atmospheric pressure MALDI and ion trap MS to detect biomarkers at each stage of Bacillus globigii growth. The biomarkers fengycin and surfactin are detected by pulsed UV laser irradiation of an intact cell. Definitive amino acid sequence information is obtained with tandem MS on the precursor ions of the biomarkers. (“Detection of Cyclic Lipopeptide Biomarkers from Bacillus Species Using Atmospheric Pressure Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry”; 10.1021/ac020506v; p 1628) An at-home male fertility test. Gary Smith, Shuichi Takayama, and colleagues at the University of Michigan develop a disposable microscale integrated system to sort motile sperm from nonmotile cells. The microscale integrated sperm sorter (MISS) features a novel gravity-driven pumping system that maintains a steady flow rate regardless of the reservoir fluid volume. Not only can the MISS be used in the clinic to select viable sperm for in vitro fertilization, but researchers also believe that an at-home male fertility test based on the MISS may soon be a reality. (“Passively Driven Integrated Microfluidic System for Separation of Motile Sperm”; 10.1021/ac020579e; p 1671) CEC meets FTMS. Milos Novotny, David Clemmer, and colleagues at Indiana University combine capillary electrochromatography (CEC) with FTMS to investigate complex mixtures A P R I L 1 , 2 0 0 3 / A N A LY T I C A L C H E M I S T R Y
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of glycoproteins. CEC offers a highly efficient way to separate isometric glycans, and FTMS allows the utmost m/z resolution and accuracy. This allows researchers to avoid performing the typical controlled degradation of glycoproteins to analyze their structures. (“Coupling Capillary Electrochromatography with Electrospray Fourier Transform Mass Spectrometry for Characterizing Complex Oligosaccharide Pools”; 10.1021/ac025985c; p 1684)
Enriching minor proteins with heparin columns. Catherine Fenselau and colleagues at the University of Maryland use an immobilized heparin column for simplifying complex protein mixtures and enriching minor proteins. The researchers use cytosol, which is separated into three fractions that are then characterized by protein analysis, two-dimensional gel electrophoresis, and MS. Some minor proteins are identified in the fractions that are not detectable in gel arrays of the total cytosol. (“Fractionation of Cytosolic Proteins on an Immobilized Heparin Column”; 10.1021/ac026153h; p 1691)
Monitoring crystallization with small volumes. Protein crystallization is a process still shrouded in mystery. Often, researchers do not know beforehand what conditions will cause their proteins of interest to form usable crystals for X-ray studies. To avoid wasting precious sample material, Eila Cedergren-Zeppezauer and colleagues at Lund University (Sweden) develop a method to monitor crystal nucleation using right-angle light scattering while acoustically levitating microliter drops of protein. (“Screening of Nucleation Conditions Using Levitated Drops for Protein Crystallization”; 10.1021/ac020496y; p 1733)
Characterization of histidine-phosphorylated peptides. Scott Napper and colleagues at the University of Saskatchewan and National Research Council (both in Canada) describe a method for the selective extraction of a phosphorylated histidine-containing peptide using immobilized copper(II) and disposable metal-chelating pipet tips. MALDI TOF MS with postsource decay confirms the identity phosphorylation state of the extracted peptide. Peptides containing unphosphorylated histidine residues or other phosphorylated amino acids are not retained. (“Selective Extraction and Characterization of a Histidine-Phosphorylated Peptide Using Immobilized Copper(II) Ion Affinity Chromatography and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry”; 10.1021/ac026340f; p 1741)
lower than those reported for amperometric detection using Bi–PbO2 electrodes and LC/MS are achieved. The researchers also analyze the concentration of the blood sample using a known enzymatic method, which yields similar results. (“Direct Electrochemical Oxidation of Disulfides at Anodically Pretreated Boron-Doped Diamond Electrodes”; 10.1021/ac020583q; p 1564)
New way to fabricate microthermocouples. Daniel Chiu and colleagues at the University of Washington–Seattle propose fabricating a nickel–silver microthermocouple (50–300 µm) by taking advantage of the spatially selective electroless and electrolytic deposition of metal. The researchers use scanning electron and atomic force microscopies to characterize the deposition and annealing process and test the performance of the microthermocouple. They report that the temperature–voltage curve is linear over the range 0–50 °C, with a slope of 61.9 °C mV –1 and a temperature measurement sensitivity of ~1 °C. (“Selective Electroless and Electrolytic Deposition of Metal for Applications in Microfluidics: Fabrication of a Microthermocouple”; 10.1021/ac020498I; p 1578) Understanding more about fluorescent copper labels. Roger Leblanc and colleagues at the University of Miami investigate the impact of the relative locations of ionophores and fluorophores in fluorescent organic chemosensors that detect divalent copper. The researchers investigate compounds that have the fluorophore group separated from the copper as well as compounds where the fluorophore can directly participate with the copper binding. Although both compounds detect copper, their mechanisms are different and cause differences in selectivity. (“Peptidyl Fluorescent Chemosensors for the Detection of Divalent Copper”; 10.1021/ac026285a; p 1706)
Vapor detectors. Nathan Lewis and colleagues at the California Institute of Technology tailor vapor detectors formed from conductor composites to increase their sensitivity to specific classes of analytes. The resulting detector arrays are sensitive to and display robust discrimination between various volatile organic acids. Measurements of the mass uptake, thickness change, and electrical conductivity of such composites indicate that the swelling is beyond what is expected and is caused by interactions between the polymer and the analytes. (“Enhanced Sensitivity to and Classification of Volatile Carboxylic Acids Using Arrays of Linear Poly(ethylenimine)–Carbon Black Composite Vapor Detectors”; 10.1021/ac020412l; p 1748)
ELECTROANALYTICAL ENVIRONMENTAL Disulfides at boron-doped diamond electrodes. A. Fujishima and co-workers at the University of Tokyo and Yokohama City University (both in Japan) use highly borondoped diamond electrodes to detect glutathione and glutathione disulfide in rat whole blood following LC. Detection limits much 136 A
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QCMs detect PAHs. C. J. Percival and colleagues at Nottingham Trent University and the University of Reading (both in the United Kingdom) use quartz crystal microbalances (QCMs) to develop a chemically coated piezoelectric sensor for
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determining polycyclic aromatic hydrocarbons (PAHs) in the environment. The researchers attach an organic monolayer containing the recognition element to the surface of a QCM gold electrode via a covalent thiol–gold bond. They can detect the target analyte at 2 ppb with a response range of 0–50 ppb. (“Detection of Polycyclic Aromatic Hydrocarbons Using Quartz Crystal Microbalances”; 10.1021/ac0257546; p 1573)
Detecting organophosphate esters in air. Anders Colmsjö and Magnus Ericsson at Stockholm University (Sweden) discuss a new on-line method for finding organophosphate esters in air samples collected on glass fiber filters. The sample is extracted from the filter by using dynamic microwave extraction coupled with solid-phase extraction. The sample is then sent to a large-volume injection GC. The extraction stage can recover >97% of the organophosphate esters. The detection limit is 61–186.2 pg/m3. (“Dynamic Microwave-Assisted Extraction Coupled On-Line with Solid-Phase Extraction and Large-Volume Injection Gas Chromatography: Determination of Organophosphate Esters in Air Samples”; 10.1021/ac026287v; p 1713)
Hydrostatically modified CE /AFS for mercury. Xiu-Ping Yan and colleagues at the Nankai University (China) demonstrate a new method using CE and atomic fluorescence spectrometry (AFS) to determine concentrations of mercury species, such as inorganic mercury, methylmercury, ethylmercury, and phenylmercury. To increase resolution, the electroosmotic flow (EOF) is modified by hydrostatic pressure in the opposite direction of the EOF. The separated fractions are then sent to the spectrometer by a newly developed interface. The technique is demonstrated on a dogfish muscle reference material. (“Speciation of Mercury by Hydrostatically Modified Electroosmotic Flow Capillary Electrophoresis Coupled with Volatile Species Generation Atomic Fluorescence Spectrometry”; 10.1021/ac026272x; p 1726)
MASS SPECTROMETRY
spray tip are integrated on a single piece of a fused-silica capillary. The researchers report the detection of femtomole levels of peptides with a CE/ESI MS configuration. (“A Sheathless Nanoflow Electrospray Interface for On-Line Capillary Electrophoresis Mass Spectrometry”; 10.1021/ac020661+; p 1615)
A glowing interface. Gary Glish and Christine Dalton at the University of North Carolina–Chapel Hill couple an electrospray (ES) source to an atmospheric sampling glow discharge ionization (ASGDI) source for the analysis of pollutants in drinking water. ES-ASGDI is used at ambient temperature, allowing analysis of volatile samples. This method also permits structural analysis of molecules with various functional groups. (“Electrospray-Atmospheric Sampling Glow Discharge Ionization Source for the Direct Analysis of Liquid Samples”; 10.1021/ac026087j; p 1620)
MALDI adducts. Richard B. Cole and colleagues at the University of New Orleans describe the formation and postsource decay of chloride adducts in negative-ion MALDI TOF MS. Highly acidic oligosaccharides do not form adducts with chloride, but mildly acidic saccharides form deprotonated molecules and chloride adducts; each may provide structural information concerning the oligosaccharides upon decomposition. (“Anionic Adducts of Oligosaccharides in Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry”; 10.1021/ac0205513; p 1638)
Orbitrap mass analyzer and electrospray ion source come together. Alexander Makarov and Mark Hardman at Thermo Masslab (United Kingdom) show that an orbitrap mass analyzer that uses the trapping of pulsed ion beams in an electrostatic quadro-logarithmic field could be coupled to a continuous electrospray ion source. The researchers construct a new external accumulation quadrupole when developing the orbitrap mass spectrometer, thus overcoming the problems of accumulation and ion injection. The instrument provides resolving power of up to 150,000 fwhm, with mass accuracies within a few parts per million and mass ranges of up to 2000 Da. (“Interfacing the Orbitrap Mass Analyzer to an Electrospray Ion Source”; 10.1021/ac0258047; p 1699)
A new way to sequence large charged proteins. Fred McLafferty and co-workers at Cornell University deduce the sequences of large multiply charged proteins by modifying electron capture dissociation (ECD) methods. The researchers use pulsed gas introduction to intersperse the reactants, which results in high ECD efficiency. They find that this method increases the number of cleavages over previously reported methods. (“Plasma Electron Capture Dissociation for the Characterization of Large Proteins by Top Down Mass Spectrometry”; 10.1021/ac020446t; p 1599)
Buckyball beam. John Vickerman and colleagues at UMIST and Ionoptika (both in the United Kingdom) develop a C60 ion beam for TOF secondary ion MS and use it to study a series of molecular solids and polymer systems in monolayers and thick films. At 10 keV, the beam can be focused to
