in ac research
In AC Research contains brief introductions to the research articles appearing in the July 1 issue. A free updated table of contents is available on the Web (http://pubs.acs.org/ac).
ACCELERATED ARTICLE Complex protein mixtures. Neil L. Kelleher and colleagues at the University of Illinois at Urbana–Champaign use a two-dimensional approach to proteome fractionation that uses an acid-labile detergent instead of sodium dodecyl sulfate during continuous-elution gel electrophoresis. The detergent facilitates subsequent reversedphase LC, which transforms thousands of intact proteins into mixtures of 5–20 components (all within ~5 kDa of each other) that can be analyzed by FTMS. (“Processing Complex Mixtures of Intact Proteins for Direct Analysis by Mass Spectrometry”; 10.1021/ac020049i; p 2923)
BIOANALYTICAL
ogy (Germany) investigate the use of polymers to stabilize horseradish peroxidase in the presence of the substrate H2O2. They determine that polymer side chains protect the enzyme either by wrapping the protein structure and stabilizing protein solutions or by chemically protecting the enzyme from oxidative or radical attack. (“Mechanistic and Molecular Investigations on Stabilization of Horseradish Peroxidase C”; 10.1021/ac0108111; p 3037)
Imaging array for single cells. David R. Walt and Israel Biran at Tufts University fabricate a high-density, ordered array that contains thousands of microwells on an optical imaging fiber. Each individually addressable microwell is used to accommodate a single living cell. A charged-coupled device monitors cellular responses simultaneously using reporter genes or fluorescent indicators. Unique multiple responses of large populations of individual cells from different strains or cell lines can be monitored. (“Optical Imaging Fiber-Based Single Live Cell Arrays: A High-Density Cell Assay Platform”; 10.1021/ac020009e; p 3046)
Recreational drugs by SPME, FAIMS, and ESI MS. Microfluidic enzyme immunoassay. Jenny Emnéus and colleagues from Moscow State University (Russia) and Lund University (Sweden) evaluate different immobilization protocols for fabricating a microfluidic enzyme immunoassay on a silicon microchip with anti-atrazine antibodies. The best long-term stability is obtained with a linear polyethylenimine. (“Microfluidic Enzyme Immunoassay Using Silicon Microchip with Immobilized Antibodies and Chemiluminescence Detection”; 10.1021/ac015645b; p 2994)
Chip assays cardiac risk factors. John McDevitt and colleagues at the University of Texas–Austin develop a fluorescence assay based on macroscopic assays but that uses a manywelled microfluidic device that targets key markers of cardiac risk factors. Samples and reagents (up to 2.0 mL) are sequentially dosed across a chip that contains an array of pyramidal microwells, each 30 nL in volume and containing an antibody-coated 280-µm-diam spherical bead. A full position-specific assay is accomplished simultaneously at each bead, and the fluorescence assay, performed while the chip is in the flow cell, is completed in 90% agreement with the extraction-based method and are available in 5–20 min. (“Fast Quantification of Humic Substance and Organic Matter by Direct Analysis of Sediments Using DRIFT Spectroscopy”; 10.1021/ac011043g; p 2985)
PAHs on creosote-contaminated soil. J. H. Callahan and colleagues at the Naval Research Laboratory measure the distribution of polycyclic aromatic hydrocarbons (PAHs) on soil contaminated with creosote using scanning UV two-step laser desorption/laser ionization MS. The depth of field of the experiment allows surfaces with a roughness of up to 120 µm to be treated as a two-dimensional system and still achieve an accurate representation of the surface deposits. (“Scanning Ultraviolet Two-Step Laser Mass Spectroscopy of Polycyclic Aromatic Hydrocarbon Distributions on Creosote-Contaminated Soil Particles”; 10.1021/ac025510l; p 3019)
Leak detector has nose for hydrogen and helium isotopes. Manuel Grivet and colleagues at Université de Franche-Comte and Centre d’Etudes de Valduc (both in France) adapt a standard MS helium leak detector to measure 3 He and 4He at the parts-per-billion level and dimers and trimers composed of hydrogen, deuterium, and/or tritium down to the parts-per-million level with good precision. They show that the nondestructive determination of tritium in radioactive waste drums can replace bulky drum calorimeters with lower-cost, portable, MS helium leak detectors and commercially available software. (“Indirect Tritium Determination by an Original 3He Ingrowth Method Using a Standard Helium Leak Detector Mass Spectrometer”; 10.1021/ac010897y; p 3183)
MASS SPECTROMETRY Parallel HPLC/MS for high-throughput analyses.
ENVIRONMENTAL Determining tributyltin. Lu Yang and co-workers at the National Research Council–Canada describe a method for determining tributyltin in certified reference material that uses isotope dilution and HPLC/ICPMS. The 3 detection limit is 0.02 mg/kg based on a 0.5-g sample. (“Species-Specific Isotope Dilution-Based Calibration for Trace Element Speciation and Its Combined Uncertainty Evaluation: Determination of Tributyltin in Sediment by HPLC–ICPMS”; 10.1021/ac011280j; p 2968)
Humic acid determinations DRIFT away from extractions. Jean-Pierre Gagné and Luc Tremblay at Université du Québec à Rimouski (Canada) monitor absorbance at
To improve the quality of combinatorial libraries, Daniel Kassel and colleagues at Deltagen Research Labs, Micromass (United Kingdom), and Waters have developed a parallel HPLC/MS purification system in which an array of HPLC columns feeds into a single quadrupole mass spectrometer with a multiplexed ion source. The system collects up to four mass-directed fractions in parallel with no observable cross talk. (“High-Throughput Mass-Directed Parallel Purification Incorporating a Multiplexed Single Quadrupole Mass Spectrometer”; 10.1021/ac0255476; p 3055)
Automating nanoscale LC/MS/MS. Steven Gygi and colleagues at Harvard Medical School have risen to the challenge of fully automating nanoscale LC/MS/MS analyses. The researchers describe a method for interfacing 75-µm-i.d. capilJ U LY 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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in ac research
lary columns to a commercial autosampler using a vented column, which permits on-column enrichment and desalting at flow rates up to 5 µL/min. Test separations of peptide mixtures achieve 50-nL elution peak volumes and low- to subfemtomole detection limits. (“Automation of Nanoscale Microcapillary Liquid Chromatography–Tandem Mass Spectrometry with a Vented Column”; 10.1021/ac025529o; p 3076)
Establishing a new standard. Isotope ratio measurements are important to such fields as geology, climate research, and food authentication, but they depend heavily on standard materials that are no longer available. Instead, complex calculations are used. Katrin Russe and colleagues at the European Commission Joint Research Centre Institute for Reference Materials and Measurements (Belgium) have taken the first step toward an international comparison method based on conversion to a fluorinated product. (“Conversion of Carbon into CF4 for SI-Traceable Measurements of Absolute Carbon Isotope Amount Ratios: A Feasibility Study”; 10.1021/ac015700g; p 3199) Testing sonic spray ionization. André De Leenheer and colleagues at Universiteit Gent (Belgium) and Merck (Germany) compare sonic spray ionization—a novel atmospheric pressure ionization technique for LC/MS—with conventional ion spray. The effects of organic modifiers, volatile acids, and buffer systems are described, and the sonic spray interface is used for the simultaneous determination of opium alkaloids in heroin impurity profiling. (“Sonic Spray Ionization Technology: Performance Study and Application to a LC/MS Analysis on a Monolithic Silica Column for Heroin Impurity Profiling”; 10.1021/ac0112824; p 3206) Fluoride telomers by ESI-IT MS. J. C. Tabet and colleagues at Université Pierre et Marie Curie, Ecole Nationale Supérieure de chimie de Montpellier, and Atofina (all in France) report on the desorption and fragmentation of poly(vinylidene) fluoride telomers in an ion trap (IT) mass spectrometer coupled to an electrospray ionization (ESI) source. For lithiated telomers, the degree of polymerization can be determined from the product ion abundance in MS/MS. (“Collision-Induced Dissociation Studies of Poly(vinylidene) Fluoride Telomers in an Electrospray Ion Trap Mass Spectrometer”; 10.1021/ac0156464; p 3213) Better sensitivity for phosphopeptide mapping. To improve multidimensional electrospray MS for mapping protein phosphorylation events, Roland Annan, Steven Carr, and colleagues at GlaxoSmithKline and the University of Illinois at Urbana–Champaign add capillary chromatography and a microionspray source. The method detects phosphorylation levels of
