in ac research
In AC Research contains brief introductions to the research articles appearing in the August 1 issue. A free updated table of contents is available on the Web (http://pubs.acs.org/ac).
BIOANALYTICAL QCM-based sensor for nonlabeling biomolecule detection. Hiroyuki Sota and colleagues from Amersham Biosciences and Tokyo Institute of Technology (both in Japan) introduce a new versatile planar sensor chip design, based on the quartz crystal microbalance (QCM), for a microliter-scale, on-line biosensor. By sealing the quartz resonator along its edges, uniform support is provided for the crystal face not exposed to the solvent. This greatly decreases deformation of the crystal resonator, which is under hydrostatic pressure. Direct handling is not needed when exchanging the delicate quartz crystal in the flow cell, thanks to the cassette design. (“Versatile Planar QCM-Based Sensor Design for Nonlabeling Biomolecule Detection”; 10.1021/ac025526b; p 3592)
Deuterium isotope effects. Fred E. Regnier and colleagues at Purdue University identify structural features responsible for resolving heavy isotope-coded peptides during reversed-phase chromatography using labeling coding agents that vary in structure, the number of deuterium atoms, the placement of deuterium in the coding agent, and the functional group targeted by the reagent. The single most dominant effect is the placement of deuterium atoms relative to hydrophilic functional groups in the coding agent. (“Controlling Deuterium Isotope Effects in Comparative Proteomics”; 10.1021/ac025614; p 3662)
Quantitation of oligonucleotides by MS, not UV. Gavin O’Connor and colleagues at LGC Limited (United Kingdom) describe a new method for the quantitation of oligonucleotides. Instead of using a sequence-specific standard or measuring UV absorbance, the researchers use isotope dilution MS to determine the concentrations of dAMP, dCMP, dGMP, and dTMP individually and add those values to get the final concentration of the oligonucleotide. (“Quantitation of Oligonucleotides by Phosphodiesterase Digestion Followed by Isotope Dilution Mass Spectrometry: Proof of Concept”; 10.1021/ac0255375; p 3670)
Cerebral H2O2. Lanqun Mao and colleagues at the Tokyo Institute of Technology, BioelectroAnalytical Science, and Graduate School of Integrated Science (all in Japan) demonstrate an amperometric method suitable for the continuous on-line measurement of cerebral H2O2 from a microdialysate using an enzyme-
modified ring–disk plastic carbon film electrode in a thin-layer radial flow cell. The procedure allows monitoring of trace levels of H2O2 without interference from physiological levels of vitamin C, uric acid, electroactive neurotransmitters, and their metabolites in a continuous-flow system. (“Continuous OnLine Measurement of Cerebral Hydrogen Peroxide Using Enzyme-Modified Ring–Disk Plastic Carbon Film Electrode”; 10.1021/ac011261+; p 3684)
CE and LIF help solve adduct binding stoichiometry. X. Chris Le, Michael Weinfeld, and co-workers at the University of Alberta (Canada) synthesize four oligonucleotides—each containing a single adduct of the carcinogenic benzo[a]pyrene diol epoxide—to study the binding stoichiometry between the DNA adduct and its antibody. The four oligonucleotides are fluorescently labeled and unlabeled 16- and 90-mers, and each free oligonucleotide and its complexes with mouse monoclonal antibody are separated using CE and detected with laser-induced fluorescence (LIF). The method provides direct information on antibody-binding stoichiometry and reveals ligand redistribution/exchange between the fluorescently labeled and unlabeled oligonucleotides in the antibody complexes. (“Binding Stoichiometry of DNA Adducts with Antibody Studied by Capillary Electrophoresis and LaserInduced Fluorescence”; 10.1021/ac0201979; p 3714)
Biotransformation of thalidomide. Gerhard Bringmann, Albrecht Mannschreck, Gottfried Blaschke, and colleagues at the Universities of Münster, Würzburg, and Regensburg (all in Germany) use circular dichroism spectroscopy to stereochemically characterize hydroxylated metabolites formed during the in vitro biotransformation of (R)- and (S)-thalidomide. (“In Vitro Biotransformation of (R)- and (S)-Thalidomide: Application of Circular Dichroism Spectroscopy to the Stereochemical Characterization of the Hydroxylated Metabolites”; 10.1021/ac0203138; p 3726) Analyzing carbonic anhydrase in blood. Although - and -hemoglobins are the most abundant proteins in human red blood cells, carbonic anhydrase deficiencies may indicate bone diseases or mental retardation. Detecting attomole levels of carbonic anhydrase in single cells is more challenging than detecting hemoglobin, where levels are apparent in standard MS work. Mehdi Moini and colleagues at the University of Texas–Austin have a CE/ESI-MS method that detects all of these proteins in one run without solvent extraction or ultrafiltration. (“Analysis of Carbonic Anhydrase in Human Red Blood A U G U S T 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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Cells Using Capillary Electrophoresis/Electrospray IonizationMass Spectrometry”; 10.1021/ac020022z; p 3772)
No horsing around. Human and equine sports would benefit from eliminating time-consuming sample preparation for analyses that root out a class of thiazide-based drugs, which can act as diuretics. Mario Thevis and colleagues at German Sport University Cologne and the University of Cologne (both in Germany) present an MS method that can characterize 21 thiazide fragments and derivatives. (“Mass Spectrometric Behavior of Thiazide-Based Diuretics after Electrospray Ionization and Collision-Induced Dissociation”; 10.1021/ac020020e; p 3802)
ELECTROANALYTICAL Nanoelectrode ensembles. Electrodes with microscopic dimensions are attractive tools for investigating redox processes that are too fast for conventional methods or doing experiments in highly resistive media. Erkang Wang and colleagues at the Chinese Academy of Sciences present a “bottom-up” approach to creating controlled ensembles using colloid nanoparticle self-assembly techniques. (“Colloid Chemical Approach to Nanoelectrode Ensembles with Highly Controllable Active Area Fraction”; 10.1021/ac025661o; p 3599)
FT-IR test for scrapie. Dieter Naumann and colleagues at the University of Trier and the Robert Koch-Institut (both in Germany) describe a new FT-IR spectroscopic approach for diagnosing scrapie infection. The researchers use artificial neural networks (ANNs) to detect differences between infected and uninfected blood and construct ANN models for analyzing unknown samples. They report that an optimized ANN correctly classified 77 out of 79 infected samples and all control samples. (“Identification of Scrapie Infection from Blood Serum by Fourier Transform Infrared Spectroscopy”; 10.1021/ac015688s; p 3865)
Test for the vasodilator prostacyclin. Sylvia Daunert and colleagues at the University of Kentucky and the Mount Sinai School of Medicine–New York describe the first assay to determine the levels of prostacyclin, a vasodilator used to treat primary pulmonary hypertension, in human plasma without extraction. Their immunoassay detects the surrogate marker 6-keto-prostaglandin F1, which is present at nanogram-permilliliter levels, by conjugating it to the bioluminescent protein aequorin. The researchers report a detection limit of 1 pg/ mL. (“Determination of Prostacyclin in Plasma through a Bioluminescent Immunoassay for 6-Keto-prostaglandin F1: Implication of Dosage in Patients with Primary Pulmonary Hypertension”; 10.1021/ac025518v; p 3892)
Concentrating through a hole. Wei Wei and Edward Yeung of Iowa State University/Ames Laboratory have developed a method for concentrating proteins and peptides using online capillary zone electrophoresis. In the presence of high voltage, proteins concentrate at the etched portion of a porous capillary, while the small buffer ions pass through the holes of the etched section. (“On-Line Concentration of Proteins and Peptides in Capillary Zone Electrophoresis with an Etched Porous Joint”; 10.1021/ac025612b; p 3899)
Fine-tuning MALDI-TOF MS peptide masses. Johan Gobom and colleagues at the Max-Planck-Institute for Molecular Genetics (Germany) report the development of a two-step calibration method that overcomes the limitations of using MALDI-TOF MS for measuring peptide molecular masses. (“A Calibration Method That Simplifies and Improves Accurate Determination of Peptide Molecular Masses by MALDI-TOF MS”; 10.1021/ac011203o; p 3915) 400 A
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Ascorbic acid plume tracker. Jirí Janata and colleagues at the Georgia Institute of Technology describe a sensing system for tracking turbulent plumes of ascorbic acid, which is a practical analyte found in the diet of marine animals. A platinum electrode coated with polyaniline is used in the system, and its behavior is studied with fluctuating concentrations of ascorbic acid in saline solution. (“Chemical Plume Tracking. 3. Ascorbic Acid: A Biologically Relevant Marker”; 10.1021/ac0202076; p. 3605) Mercury by microcantilever. Thomas G. Thundat, Hai-Feng Ji, and colleagues at Louisiana Tech University and Oak Ridge National Laboratory use a microcantilever coated with gold to detect Hg2+. The detection limit is 10–11 M. Other interfering cations have little effect on the deflection of the cantilever. (“Detection of Hg2+ Using Microcantilever Sensors”; 10.1021/ac0255781; p 3611) SECM and optical microscopy combined. Allen Bard and colleagues at the University of Texas–Austin combine scanning electrochemical microscopy (SECM) with scanning optical microscopy. In one paper, the researchers describe the fabrication of the necessary tips and report preliminary results. In a second paper, they obtain images of two relatively soft samples, a polycarbonate membrane and living diatoms. Both shear force and current feedback are used to regulate the tip–substrate distance. (“Fabrication and Characterization of Probes for Combined Scanning Electrochemical/Optical Microscopy Experiments”; 10.1021/ac015705d; p 3626; and “Combined Scanning Electrochemical/Optical Microscopy with Shear Force and Current Feedback”; 10.1021/ac015713u; p 3634) Better sensor for blood analysis. Blood-incompatible surface material is one obstacle to using accurate and reliable biosensors in vivo. In particular, poly(vinyl chloride) adsorbs proteins, which allows platelet adhesion that can adversely affect the patient. Leonidas Bachas and colleagues at the University of Kentucky have coated electrodes with a hydrogel that mimics the functionalities of phospholipids to improve biocompatibility and maintain sensor performance. (“Improving the Blood Compatibility of Ion-Selective Electrodes by Employing Poly(MPC-co-BMA), a Copolymer Containing Phosphorylcholine, as a Membrane Coating”; 10.1021/ac025604v; p 3644)
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Holographic sensors for metal ions. In the search for generic methods of producing inexpensive sensors, Christopher Lowe and colleagues at the University of Cambridge (United Kingdom) turn to holography, which furnishes an analyte-selective polymer matrix and an optical reporting system. The researchers report that holographic K+ sensors fabricated from crown ethers incorporated into polymeric hydrogels can quantitate K+ over the physiologically relevant range and are largely unaffected by changes in the background concentration of Na+. (“Metal Ion-Sensitive Holographic Sensors”; 10.1021/ac020131d; p 3649)
pling of Capillary Electrophoresis to Hydride Generation Atomic Fluorescence Spectrometry for Arsenic Speciation Analysis”; 10.1021/ac025735w; p 3720)
Tracking down herbicides in water. Robert Yokley
the University of Tokushima (Japan) demonstrate that the osmium(II)-dipyrido[3,2-a:2´3´-c]phenazine metal complex can detect DNA with good sensitivity and selectivity. (“DNA Sensor with a Dipyridophenazine Complex of Osmium(II) as an Electrochemical Probe”; 10.1021/ac011148j; p 3698)
and co-workers at Syngenta Crop Protection have come up with a Good Laboratory Practices (GLP) method to determine metolachlor, acetochlor, alachlor, dimethenamid, and their corresponding ethanesulfonic and oxanillic acid degradates in ground and surface water at a quantification limit of 0.10 ppb. Their method uses a C18 solid-phase extraction column and LC/electrospray ionization MS/MS. An analyst can prepare a set of 10 samples in ~3 h, and injection can be performed overnight. Their technique is the only reported GLP-validated analytical method applicable to the simultaneous analysis of all 12 analytes in water. (“Analytical Method for the Determination of Metolachlor, Acetochlor, Alachlor, Dimethenamid, and Their Corresponding Ethanesulfonic and Oxanillic Acid Degradates in Water Using SPE and LC/ESI-MS/MS”; 10.1021/ac020134q; p 3754)
Photocatalytic sensor determines COD. Isao Karube
X-rays and fluorescence for lead monitoring.
and co-workers at the University of Tokyo (Japan) develop a photocatalytic sensor to determine chemical oxygen demand (COD) using TiO2, a pair of oxygen electrodes, and flow injection analysis. They monitor oxygen consumption from the TiO2-catalyzed photochemical oxidation of organic compounds in samples with the working oxygen electrode. (“A Flow Method with Photocatalytic Oxidation of Dissolved Organic Matter Using a Solid-Phase (TiO2) Reactor Followed by Amperometric Detection of Consumed Oxygen”; 10.1021/ac015678r; p 3858)
Yasuo Izumi, Yoshimi Seida, and colleagues at the Tokyo Institute of Technology and the Institute of Research and Inno-
Osmium(II) complex acts as an electrochemical probe DNA sensor. Kenichi Maruyama and colleagues from
ENVIRONMENTAL Determining mass loss in coals and cokes. Jacqueline Mann and colleagues at the National Institute of Standards and Technology use a thermogravimetric analyzer to determine mass loss in Standard Reference Material (SRM) coals and cokes. They measure moisture loss as mass loss as a function of time at constant temperature in a dynamic, inert nitrogen atmosphere on 10 SRM coals (7 bituminous and 3 subbituminous) and 4 SRM cokes. Their goal is to minimize differences among laboratory results in moisture content and show that it is not always correct to assume that true constant mass (ideal behavior) can be obtained by drying. (“Observations of Anomalous Mass-Loss Behavior in SRM Coals and Cokes on Drying”; 10.1021/ac0157223; p 3585)
Novel arsenic speciation analysis. Xiu-Ping Yan and co-workers at Nankai University (China) couple CE to atomic fluorescence spectrometry for the speciation analysis of four environmentally toxic forms of arsenic. Detection limits are in the range 9–18 µg/L as arsenic, with recoveries of arsenic species in water and urine varying between 91 and 115%. (“On-Line CouA U G U S T 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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vation (both in Japan) determine the local structure of trace amounts of lead in an adsorbent matrix that contains a high concentration of iron and magnesium using X-ray absorption fine structure and fluorescence spectroscopies. (“X-ray Absorption Fine Structure Combined with Fluorescence Spectrometry for Monitoring Trace Amounts of Lead Adsorption in Environmental Conditions”; 10.1021/ac025550p; p 3819)
Plutonium in seawater. Cheol-Su Kim and colleagues at the Korea Institute of Nuclear Safety and the Korea Advanced Institute of Science and Technology describe an on-line sequential injection system combined with sector field inductively coupled plasma MS for determining ultratrace levels of 239Pu and 240 Pu in 5 L of surface seawater with an analysis time of 4 h. Detection limits are 0.64 fg/mL 239Pu and 0.19 fg/mL 240Pu. (“Determination of Pu Isotopes in Seawater by an On-Line Sequential Injection Technique with Sector Field Inductively Coupled Plasma Mass Spectrometry”; 10.1021/ac0255328; p 3824)
Nonylphenols detection method. Francesc Ventura and colleagues at AGBAR and the University of Barcelona (both in Spain) introduce an in-sample derivatization headspace solidphase microextraction method for the simultaneous determination in water of nonylphenol, its mono- and diethoxylates, and their acidic metabolites. Run-to-run precision had relative standard deviations of 8–18%; detection limits range from 20 to 1500 ng/L. (“Simultaneous Determination of Estrogenic Short Ethoxy Chain Nonylphenols and Their Acidic Metabolites in Water by an In-Sample Derivatization/Solid-Phase Microextraction Method”; 10.1021/ac020124p; p 3869)
MASS SPECTROMETRY
electrospray ionization FT-ion cycltron resonance MS/MS to study the influence of charge state on the product ion spectra of chondroitin sulfate oligosaccharides for determining the sulfate position on N-acetylgalactosamine residues. Ions in which the charge is less than the number of sulfates primarily dissociate to even-numbered ions, whereas ions with a charge equal to the sulfates yield odd-numbered fragment ions. (“Influence of Charge State on Product Ion Mass Spectra and the Determination of 4S/6S Sulfation Sequence of Chondroitin Sulfate Oligosaccharides”; 10.1021/ac025506+; p 3760)
Characterizing insoluble polymers. H. J. Räder and colleagues at the Max-Planck-Institute for Polymer Research (Germany) use solvent-free sample preparation for MALDItime-of-flight (TOF) MS to characterize an insoluble fraction of poly(9,9-diphenyl-2,7-fluorene) that was previously hindered by the lack of suitable methods. A specialized fragmentation study by postsource decay MALDI-TOF MS reveals a molecular-weightdependent change in the fragmentation mechanism—from an exclusive cleavage of side groups from long polymer chains to an additional cleavage of the polymer backbone of short polymer chains. (“Characterization of an Insoluble Poly(9,9-diphenyl2,7-fluorene) by Solvent-Free Sample Preparation for MALDITOF Mass Spectrometry”; 10.1021/ac0111863; p 3777) The MS way to determine enantiomeric purity. R. Graham Cooks and colleagues at Purdue University present the quotient ratio method to determine enantiomeric purity by MS. The technique requires only one sample of the analyte with known optical purity to allow construction of a calibration curve. This advantage is particularly useful for cases where only one sample of known enantiomeric excess is available for calibration. (“Quotient Ratio Method for Quantitative Enantiomeric Determination by Mass Spectrometry”; 10.1021/ac0201124; p 3783) Novel vacuum UV lamp. Fast on-line detection of organic
New affinity capture MALDI-TOF MS method. Andrew Kicman and colleagues at King’s College London and Queen Mary School of Medicine and Dentistry (both in the United Kingdom) have designed an affinity capture MALDI MS method by covalently immobilizing an Fc receptor (recombinant protein G) onto MALDI gold targets for the purpose of orientating an immunoglobulin G, with the Fab domains pointing away from the target surface. The researchers use the pregnancy and cancer marker, human chorionic gonadotropin core fragment (hCGcf), as their test sample and achieve a ~3-fold increase in MALDI signal after orientating the immunoglobulin. They also report that purified and enriched hCGcf can be obtained from a test solution containing contaminant peptides and proteins using on-target oriented immunoglobulins. (“Enhanced Affinity Capture MALDI-TOF MS: Orientation of an Immunoglobulin G Using Recombinant Protein G”; 10.1021/ ac025558z”; p 3677)
Charge state and sulfate positions. Joseph Zaia and co-workers at the Boston University School of Medicine use 402 A
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compounds in complex mixtures by MS requires a selective and fragment-free ionization technique, such as photoionization. R. Zimmermann and colleagues at GSF-Forschungszentrum, Gesellschaft für Schwerionenforschung, Technische Universität München, Universität Augsburg, and Bayerisches Institut für Angewandte Umweltforschung und Technik (all in Germany) introduce an excimer vacuum UV (VUV) light source, which is coupled to a compact and mobile time-of-flight mass spectrometer. The VUV lamp delivers light with good beam quality and high output, and allows different wavelengths and bandwidths to be used by changing the gas filling. (“Single Photon Ionization (SPI) via Incoherent VUV-Excimer Light: Robust and Compact Time-of-Flight Mass Spectrometer for On-Line, RealTime Process Gas Analysis”; 10.1021/ac0200825; p 3790)
No prep time. The methods commonly used to quantify methylmercury or inorganic mercury in biological samples generally require extraction or derivatization procedures that can lead to significant errors. R. Dams and colleagues at Ghent University (Belgium) have created an MS method that separates the two
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types of mercury in 75 s and requires no sample preparation. (“Direct Determination of Methylmercury and Inorganic Mercury in Biological Materials by Solid Sampling-Electrothermal Vaporization-Inductively Coupled Plasma-Isotope Dilution-Mass Spectrometry”; 10.1021/ac020060i; p 3833)
CHEF method isolates multiple ions. Marshall Siegel and co-workers at Bruker Daltonics show two new applications— stored, waveform-inverse FT and correlated harmonic excitation fields (CHEF)—for multiple ion isolations that are capable of notching out frequency (mass) regions to isolate the desired components. A technique called multi-CHEF is used, which was developed originally for the isolation of single ions in the cell of a FT-ion cyclotron resonance mass spectrometer equipped with an electrospray ionization source. Multi-CHEF’s tailored waveforms are used to “purify” closely spaced charged states in the gas phase of a mixture consisting of a covalently bound drug–protein complex and the native protein. (“Multiple Ion Isolation Applications in FT-ICR MS: Exact-Mass MSn Internal Calibration and Purification/Interrogation of Protein–Drug Complexes”; 10.1021/ ac020048q; p 3877)
Detecting a limit for IDMS. Lee Yu and colleagues at
On-chip EC detection. Richard P. Baldwin and co-workers at the University of Louisville develop and test microfabricated lab-on-a-chip devices that use a fully integrated electrochemical (EC) detection system. CE channels and all CE-EC electrodes are incorporated directly onto glass substrates via traditional microfabrication techniques, including photolithographic patterning, wet chemical etching, DC sputtering, and thermal wafer bonding. Unlike previously reported analogous CE-EC devices, no external electrodes are needed. (“Fully Integrated On-Chip Electrochemical Detection for Capillary Electrophoresis in a Microfabricated Device”; 10.1021/ ac011188n; p 3690) Electrokinetic microscale particle tracking. Shankar Devasenathipathy and colleagues at Stanford University and Kinki University (Japan) introduce micrometer-resolution particle image velocimetry (micro-PIV) and particle tracking velocimetry techniques to quantify and study flow phenomena in electrokinetic systems applicable to microfluidic bioanalytical devices. The researchers perform a series of seed particle calibration experiments to make the flow measurements quantitative. They also use PIV to measure velocities in a microchannel with variable potential and fabricated with molded poly(dimethyl siloxane)
the National Institute of Standards and Technology develop a formulation for the detection limit for isotope dilution MS (IDMS). The new formulation describes the detection limit as a function of the enrichment of the isotopic spike and the linear calibration detection limits measured at the masses for the isotope ratio measurement. (“Detection Limit of Isotope Dilution Mass Spectrometry”; 10.1021/ac011254L; p 3887)
Polymer characterization simplified. The properties of high-molecular-mass oligomers make analyzing them with many standard techniques complicated. That is why Josef Chmelík and colleagues at the Academy of Sciences of the Czech Republic built their own equipment. They find that creating a sample deposition device for the offline combination of SFC-MALDI helps to describe the mass distribution of silicone oils more accurately and is faster and more sensitive than the individual techniques. (“Sample Deposition Device for Off-Line Combination of Supercritical Fluid Chromatography and Matrix-Assisted Laser Desorption/Ionization Timeof-flight Mass Spectrometry”; 10.1021/ac020085h; p 3911)
MICROSCALE Chaotic stirring. Haim H. Bu and Shizhi Qian at the University of Pennsylvania investigate two-dimensional, time-dependent, and time-independent electroosmotic flows driven by a uniform electric field in a conduit with nonuniform potential distributions along its walls. Time-wise periodic alternations of the potentials can be used to induce chaotic advection for mixing. (“Chaotic Electroosmotic Stirrer”; 10.1021/ac025601i; p 3616) A U G U S T 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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methyl acrylate. (“Particle Tracking Techniques for Electrokinetic Microchannel Flows”; 10.1021/ac011243s; p 3704)
SEPARATIONS On-line focusing by dynamic pH junction. Philip Britz-McKibbin and colleagues at Himeji Institute of Technology and Kyoto University (both in Japan) introduce a preconcentration method for CE that uses dynamic pH junction and sweeping modes. Applying the approach to the separation of three flavins, they find a 1200-fold improvement in sensitivity over conventional methods, picomolar detection limits, a 4-fold improvement in bandwidth, and the ability to focus both hydrophobic and weakly acidic analytes. (“On-Line Focusing of Flavin Derivatives Using Dynamic pH Junction-Sweeping Capillary Electrophoresis with Laser-Induced Fluorescence Detection”; 10.1021/ac025701o; p 3736) Buffers that influence retention. Martí Rosés and colleagues at the Universitat de Barcelona (Spain) investigate the changes in buffer properties in acetonitrile and water mobile phases for the buffers acetate, phosphate, phthalate, citrate, and ammonia. Equations are proposed that relate the pH and capacity changes of the buffers to the initial aqueous pH value and to the volume fraction of acetonitrile. (“Retention of Ionizable Compounds on HPLC. 12. Properties of Liquid Chromatography Buffers in Acetonitrile–Water Mobile Phases That Influence HPLC Retention”; 10.1021/ac020012y; p 3809) Sulfur in oil. C. López García and colleagues at Institut Français du Pétrole and Service Central d’Analyse CNRS (both in France) describe the analysis of alkylbenzothiophenes and alkyldibenzothiophenes in light cycle oil and straight-run gas oils using GC with sulfur chemiluminescence detection and GC/ high-resolution MS. (“Analysis of Aromatic Sulfur Compounds in Gas Oils Using GC with Sulfur Chemiluminescence Detection and High-Resolution MS”; 10.1021/ac011190e; p 3849)
the analyte–micelle complex. Two authors of the original paper, James P. Landers and Dean S. Burgi of the University of Virginia, respond. (“‘Comment on’ and ‘Response to Comment on’ ‘Electrokinetic Stacking Injection of Neutral Analytes under Continuous Conductivity Conditions’”; 10.1021/ac025675u; p 3929; 10.1021/ac020355; p 3931)
SPECTROSCOPY Pigments on the Vinland map. Robin J. H. Clark and Katherine L. Brown at University College London (United Kingdom) use Raman microprobe spectroscopy to show that the black ink defining each feature on the Vinland map consists of carbon overlaying a yellow line containing anatase. Because anatase has not been found on other medieval artifacts, the map may have been produced after 1923. (“Analysis of Pigmentary Materials on the Vinland Map and Tartar Relation by Raman Microprobe”; 10.1021/ac025610r; p 3658)
Optimizing multielement analysis in ICPMS. When electrothermal vaporization is used to introduce samples in inductively coupled plasma (ICP) MS, the resulting transient signals can degrade the quality of multielement analyses. To address this problem, James Holcombe and colleagues at the University of Texas–Austin offer a mathematical solution and an experimental procedure for calculating the maximum number of transient signals that can be monitored by a scanning spectrometer. In experiments to validate the theory, the researchers report that a 10-ppb sample can be accurately quantified with a precision better than 9%. (“Optimizing the Multielement Analysis Capabilities of an ICP Quadrupole Mass Spectrometer Using Electrothermal Vaporization Sample Introduction”; 10.1021/ ac0110303; p 3744) On-line FT-IR detection for CE. Although FT-IR offers
Chun-hsien Chen and colleagues at National Sun Yat-Sen University and National Tsing Hua University (Taiwan) report the use of a fiber-optic electrochemical cell ideal for routine CE. (“Capillary–Electrode Alignment by an Optical-Fiber Connector for Amperometric Detection in Capillary Electrophoresis”; 10.1021/ac025679z; p 3906)
universal detection of analytes, it has not been used on-line with CE because fused-silica capillaries absorb in the IR region. To overcome that problem, Bernhard Lendl and colleagues at Stockholm University (Sweden) and the Vienna University of Technology (Austria) construct an IR-transparent flow cell from two CaF2 plates separated by a polymer coating and a titanium layer. The researchers report a detection limit of 800 pg for guanosine in an aqueous solution. (“On-Line Fourier Transform Infrared Detection in Capillary Electrophoresis”; 10.1021/ac025590t; p 3843)
Comments on electrokinetic stacking paper. In
Watching elements live. Diane Beauchemin and col-
response to a paper on the electrokinetic stacking of neutral analytes in micellar electrokinetic chromatography, Ring-Ling Chien of Caliper Technologies presents an alternative way to determine the maximum injectable length. Chien argues that the maximum injectable length depends on the ratio of the velocity of the electroosmotic flow to the velocity of the micelle, not the velocity of
leagues at Queen’s University (Canada) report that inductively coupled plasma MS can be used to monitor the concentration of metals in rocks during natural processes, such as leaching. (“Inductively Coupled Plasma Mass Spectrometry with OnLine Leaching: A Method to Assess the Mobility and Fractionation of Elements”; 10.1021/ac025671p; p 3924)
CE coupled with electrochemical detection.
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