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Analytical and Bioanalytical Chemistry (v.373, #7)
No Title by Bryan G. Splawn; Fred E. Lytle (pp. 519-525).
Square hollow waveguides are used to integrate measurement of absorption with chip-based electrophoresis. The 50×50 µm liquid channel and 50×50 µm waveguide are etched as a negative pattern into a silicon master and replicated as a positive in poly-dimethylsiloxane (PDMS). The uniform refractive index of the chip prevents guiding by total internal reflection. Instead, light at 488 nm is guided by reflection at the air-PDMS interface. The waveguide has a 60% efficiency over a distance of 3.2 cm. Separation of fluorescein and the dye BODIPY is demonstrated. A detection limit (S/N=3) of 200 µM fluorescein is obtained using a 50 µm pathlength and a simple photocell detector.
Keywords: Waveguides Absorption detection Capillary electrophoresis Poly-dimethylsiloxane Chip
No Title by Joo-Woon Lee; Joseph A. Gardella (pp. 526-537).
Impressive advances in biotechnology, bioengineering, and biomaterials with unique properties have led to increased interest in polymers and other novel materials in biological and biomedical research and development over the past two decades. Although biomaterials have already made an enormous impact in biomedical research and clinical practice, there is a need for better understanding of the surface and interfacial chemistry between tissue (or cells) and biomedical materials. This is because the detailed physicochemical events related to the biological response to the surface of materials still often remain obscure, even though surface properties are important determinants of biomedical material function. In this regard, data available in the literature show the complexity of the interactions (surface reorganization, non-specific/specific protein adsorption, and chemical reactions such as acid–base, ion pairing, ion exchange, hydrogen bonding, divalent-ion bridging) and the interrelationship between biological environments, interfacial properties, and surface functional groups responsible for the biological responses. Because of the multidisciplinary nature of surface and interfacial phenomena at the surface of biomedical polymers, this review focuses on several aspects of current work published on poly(α-hydroxy acid)s and their associated copolymers:surface structure–biomedical function relationships;physicochemical strategies for surface modification; and, finally,synthetic strategies to increase biocompatibility for specific in-vivo and/or in-vitro biomedical applications.
Keywords: Biocompatibility Biodegradable polymers Surface analysis
No Title by Jason W. Flora; Allison P. Null; David C. Muddiman (pp. 538-546).
A universal dual-electrospray (ESI) source is demonstrated on a quadrupole orthogonal-accelerated time-of-flight mass spectrometer (Q-ToF-MS) for both genomic and proteomic applications. This facile source modification enables internal calibration for consistent mass measurements by a mainstream MS platform and requires no mixing of analyte and calibrant prior to ion formation. In this report, the dual-sprayer is demonstrated in the negative-ion mode for internal calibration of polymerase chain reaction (PCR) amplicons generated from synthetic and genomic templates as well as a proteolytic digest of a naturally phosphorylated protein. For all PCR amplicons, experimentally determined average mass measurements are well within the instrument specifications of better than 0.01%. For the proteolytic fragments of the phosphoprotein, average mass errors of the isotopically resolved peptides are better than 10 ppm.
Keywords: Electrospray Time-of-flight Mass spectrometry Internal calibration Accurate mass
No Title by Nithya Vaidyanathan; David M. Hercules; Marwan Houalla (pp. 547-554).
A series of WO3/ZrO2 catalysts with tungsten (W) loadings ranging from 0.5 to 11.4 wt% was prepared by incipient wetness impregnation on a preformed ZrO2 support. The oxidic catalysts were characterized using XRD, Raman spectroscopy, XPS, ISS, and IR spectroscopy. XRD and Raman results showed that the ZrO2 support was predominantly present in the monoclinic form. XPS and Raman measurements indicated the formation of increasing amounts of W interaction species for catalysts with W loadings up to 8.8 wt% WO3. In addition to the W interaction species, bulk WO3 was also observed for catalysts with W loadings ≥ 3.0 wt% WO3. Comparison of the XPS results with coverage measurements by ISS and CO adsorption suggests that the W surface phase is in the form of two-dimensional polymeric patches for catalysts with W loadings 3.0 ≤ wt% WO3 ≤ 4.5. For catalysts with W loadings >4.5 wt% WO3, the results indicated an additional build-up of a bilayer (or multilayer) polymeric W species. Analysis of the hydroxyl region of ZrO2 by IR spectroscopy showed that initial additions of W occur on the high frequency hydroxyl group. A schematic for the structure of the catalysts has been proposed based on the above observations.
Keywords: Tungsten oxide Zirconia WO3/ZrO2 ISS XPS Raman IR
No Title by Lee Zhang; Rudolf W. Seitz (pp. 555-559).
We have demonstrated the feasibility of a new type of pH sensor by combining a bead of porous lightly crosslinked diethanolamine derivatized poly(vinylbenzyl chloride) with a strain gauge, i.e. a pressure sensitive resistor. The polymer bead is toughened with Kraton G1652, a styrene-ethylene,butylene-styrene triblock copolymer. The sensor is constructed so that the shrunken form of the bead is held in contact with the strain gauge with a small force. Increases in the hydrogen ion concentration protonate the diethanolamine introducing a positive charge onto the polymer backbone. This results in an electrostatic swelling force that causes the polymer to swell. This is detected as a change in strain gauge resistance that is readout via a Wheatstone bridge. When the pH of 0.10 M buffers is changed from 10 to 4, the response time is 390 s for a bead that is 0.25 mm in diameter in the shrunken state. The response varies with the square of the bead radius. The magnitude of the response is highly correlated with the penetration modulus, a measure of the extent to which the bead resists deformation when subjected to an external force. The response to pH appears to be shifted by the application of pressure in the sensor. This instrumentally simple approach to sensing has the potential to be stable and long-lived if the polymer bead can undergo a large number of swelling/shrinking cycles without changing mechanical properties.
No Title by T. Dang; T. Frisk; M. Grossman (pp. 560-570).
Several surface analytical techniques, including electron spectroscopy for chemical analysis (ESCA)(X-ray photoelectron spectroscopy) and sputtered neutral mass spectrometry (SNMS), were used to study the interaction between Hg and other components of fluorescent lamps, a very critical issue in lighting industries. Active sites, responsible for Hg interaction/deposition, can be successfully identified by comparing the x-y distribution (obtained by ESCA mapping) and depth distribution (available through SNMS) of respective lamp components with that of Hg. A correlation in both depth and x-y distribution is strong evidence of site preference for Hg interaction/deposition. A burial mechanism is, however, proposed when only depth distribution, not x-y, is correlated. Other modes of ESCA (high resolution, angle-resolved, etc.) were also helpful. Information about the valence states of the interacted Hg species would help to define the nature of the interaction.
Keywords: Electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy) Sputtered neutral mass spectrometry Fluorescent lamps Mercury interaction Mercury-rare gas discharge
Small molecule analysis by MALDI mass spectrometry by Lucinda H. Cohen; Arkady I. Gusev (pp. 571-586).
This review focuses on the application of matrix assisted laser desorption/ionization (MALDI) mass spectrometry to the characterization of molecules in the low mass range (<1500 Da). Despite its reputation to the contrary, MALDI is a powerful technique to provide both qualitative and quantitative determination of low molecular weight compounds. Several approaches to minimize interference via sample preparation and matrix selection are discussed, as well as coupling of MALDI to liquid and planar chromatographic techniques to extend its range of applicability.
Keywords: MALDI MS Mass spectrometry Low molecular weight compounds
No Title by Adam P. Schellinger; Yun Mao; Peter W. Carr (pp. 587-594).
One of the most important aspects of method development in reversed-phase high-performance liquid chromatography (RPLC) is the accurate prediction of the resolution as one or more experimental variables (usually the mobile-phase composition) are changed. By use of commercially available computer simulation programs, e.g. Drylab 2000, data from a few initial experimental runs are used to predict how the separation will vary with composition so that a computer program can then rapidly locate the optimum conditions. Assumption of a linear relationship between log k′ (retention factor) and φ (volume fraction of organic modifier in the element) minimizes the number of initial runs required for a separation and is usually adequate when the range of φ is not large. In this work the linearity of plots of log k′ against φ for octadecylsilane-coated silica (ODS) and carbon-coated zirconia (C-ZrO2) columns were compared and the plots were used to determine whether prediction of the separation of triazine herbicides was adequate. Analysis of the slopes and intercepts of such plots are presented for both types of columns.
Keywords: Drylab Carbon-coated zirconia Triazine herbicides
No Title by Yeonhee Lee; Seunghee Han; Hyuneui Lim; Youngwoo Kim; Haidong Kim (pp. 595-600).
Inert-gas (Ar, Xe) and reactive-gas (O2, N2) plasma-source ion-implantation (PSII) treatment of PI, PET, PS–BD, and MPPO surfaces was performed at an ion energy of 30 keV to improve the electrical properties of the polymers. The effect of ion energy, treatment time, rf frequency, and power on the surface resistivity of polymer was investigated. Depending on ion energy, dose, and ion species, the surface resistivity of the film was reduced by several orders of magnitude. XPS, TOF–SIMS, and SEM were used to characterize MPPO surfaces treated by Ar-PSII and Xe-PSII. From these measurements it was found that the improvement in surface resistivity after PSII treatment was related to graphite carbon or cross-linked carbon-double-bond species formed on the surface.
Keywords: Surface analysis Polymer modification Plasma-source ion-implantation XPS TOF–SIMS
No Title by W. Temesghen; P. Sherwood (pp. 601-608).
The valence band and core-level X-ray photoelectron spectroscopy (XPS) of iron and its oxides are reported, and the valence band spectra interpreted by various calculation models. The paper focuses upon the valence band region, which shows significant differences between the metal and the following oxidized iron species: FeO, Fe3O4, α-Fe2O3, γ-Fe2O3, α-FeOOH and γ-FeOOH. The core region is of little analytical value as a means of distinguishing between these species, but the valence band region shows significant differences. These differences are consistent with spectra predicted by cluster and band structure calculations. Cluster calculations are valuable as a means for interpreting the spectra of iron oxides with multiple iron sites and defect characteristics.
Keywords: X-ray photoelectron spectroscopy Valence band Iron oxides Cluster calculations Band structure calculations
No Title by Stanislav V. Verkhoturov; Emile A. Schweikert (pp. 609-611).
A novel approach is proposed for extracting a maximum of information from secondary ions ejected when surfaces are bombarded with keV mono or polyatomic ions. It is known that the event-by-event bombardment-detection mode allows identification of spatiotemporal relationships among individual secondary ions which in turn reveal surface composition within nanometric dimensions. We have devised a procedure for identifying spatiotemporal relationships among individual secondary ions without the requirement of pulsed sample interrogation (one single projectile at a time). The consequence of "mass separated time-of-flight mass spectrometry" is a much improved measurement duty cycle.
Keywords: Secondary ions Mass spectrometry ToF Coincidence Wien filter
No Title by John M. Koomen; Brandon T. Ruotolo; Kent J. Gillig; John A. McLean; David H. Russell; Mijeong Kang; Kim R. Dunbar; Katrin Fuhrer; Marc Gonin; Albert J. Schultz (pp. 612-617).
Matrix-assisted laser-desorption ionization followed by ion-mobility separation and time-of-flight mass analysis (MALDI–IM–TOFMS) has been used to characterize native and chemically modified DNA oligonucleotides up to eight bases in length. Mobility resolution between 20 and 30 can be used to separate oligonucleotides of different length, but not to differentiate between isomers or even different compositions of the same length. MALDI–IM–TOFMS does, however, have additional utility in the analysis of mixtures of DNA oligonucleotides and peptides, because these classes of molecules can be distinguished on the basis of differences in their mobility. Oligonucleotide sequencing is also possible by MALDI–IM–TOFMS. Ion signals corresponding to nucleobase losses, w-type, and y-type fragments were identified by use of differences in ion mobility. MALDI–IM–TOFMS was also used to resolve DNA-platinum adducts from the corresponding unmodified oligonucleotides.
Keywords: Ion mobility Oligonucleotides Sequencing DNA modifications Cisplatin
No Title by Lianming Wu; Andy W. Tao; R. Cooks (pp. 618-627).
Chiral recognition of α-hydroxy acids has been achieved, and mixtures of enantiomers have been quantified in the gas phase, by using the kinetics of competitive unimolecular dissociation of singly-charged transition metal ion-bound trimeric complexes, [MII(A)(ref*)2–H]+ (MII=divalent transition metal ion; A=α-hydroxy acid; ref*=chiral reference ligand), to form the dimeric complexes [MII(A)(ref*)–H]+ and [MII(ref*)2–H]+. Chiral selectivity, the ratio of these two fragment ion abundances for the complex containing the analyte in one enantiomeric form expressed relative to that for the fragments of the corresponding complex containing the other enantiomer, ranges from 0.65 to 7.32. Chiral differentiation is highly dependent on the choice of chiral reference compound and central metal ion. The different coordination geometry of complexes resulting from the different d-orbital electronic configurations of these transition metal ions plays a role in chiral discrimination . Of all the transition metal ions examined chiral recognition is lowest for CuII, because of large distortion of the coordination complexes, and hence weak metal–ligand interactions and small stereochemical effects. It seems that two independent π-cation interactions occur when N-acetyl-substituted aromatic amino acids used as the reference ligands and this accounts for improved chiral discrimination. If both metal–ligand and ligand–ligand interactions are optimized, large chiral selectivity is achieved. The sensitive nature of the methodology and the linear relationship between the logarithm of the fragment ion abundance ratio and the optical purity, which are intrinsic to the kinetic method, enable mixtures to be analyzed for small enantiomeric excess (ee) by simply recording the ratios of fragment ion abundances in a tandem mass spectrum.
Keywords: α-Hydroxy acids Chiral analysis Kinetic method Tandem mass spectrometry Electrospray ionization Transition metal-bound complexes
No Title by Tania Magoon; Keiko Ota; Jennifer Jakubowski; Michelle Nerozzi; T. Werner (pp. 628-631).
A simple, efficient, and rapid method is described for separation of the enantiomers of propoxyphene by capillary electrophoresis with neutral cyclodextrins as chiral separators. This method has several advantages over the crystallization method employed by some forensic laboratories, including unambiguous results, ease of use, and smaller sample-size requirement. The method enables baseline separation of the propoxyphene enantiomers in approximately six minutes, which is less than one-third of the time required for a previously published method.
Keywords: Propoxyphene Cyclodextrins Capillary electrophoresis Enantiomers
No Title by Sanford A. Asher; Serban F. Peteu; Chad E. Reese; Ming Lin; David Finegold (pp. 632-638).
We have developed intelligent polymerized crystalline colloidal array (IPCCA) chemical-sensing materials for detection of Pb2+ in high ionic-strength environments such as body fluids with a detection limit of <500 nmol L–1 Pb2+ (100 ppb). This IPCCA lead sensor consists of a mesoscopically periodic array of colloidal particles polymerized into an acrylamide hydrogel. The array Bragg-diffracts light in the visible spectral region because of the periodic spacing of the colloidal particles. This material also contains a crown ether chelating agent for Pb2+. Chelation of Pb2+ by the IPCCA in low-ionic-strength solutions results in a Donnan potential that swells the gel, which red-shifts the diffracted light in proportion to the Pb2+ concentration. At high ionic strength the Donnan potential is, unfortunately, swamped and no static response occurs for these sensors. We demonstrate, however, that we can determine Pb2+ at high ionic strength by incubating these IPCCA in a sample solution and then measuring their transient response on exposure to pure water. The non-complexed ions diffuse from the IPCCA faster than the bound Pb2+. The resulting transient IPCCA diffraction red-shift is proportional to the concentration of Pb2+ in the sample. These IPCCA sensors can thus be used as sensing materials in optrodes to determine Pb2+ in high-ionic-strength solutions such as body fluids.
Keywords: Intelligent polymerized crystalline colloidal array (IPCCA) Pb2+ body fluid sensor Photonic crystal Bragg diffraction Hydrogel chemical sensors
No Title by R. Kurte; C. Beyer; H. Heise; D. Klockow (pp. 639-646).
Sulfur hexafluoride is a chemically inert gas which is used in gas insulated substations (GIS) and other high-voltage equipment, leading to a significant enhancement of apparatus lifetime and reductions in installation size and maintenance requirements compared to conventional air insulated substations. However, component failures due to aging of the gas through electrical discharges may occur, and on-site monitoring for risk assessment is needed. Infrared spectroscopy was used for the analysis of gaseous by-products generated from electrical discharges in sulfur hexafluoride gas. An infrared monitoring system was developed using a micro-cell coupled to an FTIR spectrometer by silver halide fibers. Partial least-squares calibration was applied by using a limited number of optimally selected spectral variables. Emphasis was placed on the determination of main decomposition products, such as SOF2, SOF4, and SO2F2. Besides the different electrical conditions, the material of the plane counter electrode of the discharge chamber was also varied between silver, aluminum, copper, tungsten, or tungsten/copper alloy. For the spark experiments the point electrode was the same material as chosen for the plane electrode, whereas for partial discharges a stainless steel needle was employed. Complementary investigations on the chemical composition within the solid counter electrode material by secondary neutral mass spectrometry (SNMS) were also carried out. Under sparking conditions, the electrode material plays an important role in the decomposition rates of the gas-phase, but no relevant material dependence could be observed under partial discharge conditions.
Keywords: Fourier transform infrared spectroscopy Trace gas analysis Sulfur hexafluoride decomposition By-product monitoring Partial least-squares calibration
No Title by Siqing Song; Ronald D. Macfarlane (pp. 647-655).
A plasma desorption mass spectrometry study was made on the properties of glucose and glucose/glucuronic acid thin films as matrices for amino acids, small and large peptides and insulin. Amino acids and small peptides are distributed throughout the film as it is formed from aqueous solutions and the mass spectra are similar to what is observed for nitrocellulose matrices. AngiotensinII (angII), insulin, and reduced insulin containing the separated A- and B-chains concentrate at the surface of the film due to the hydrophobic interaction. Extensive positive and negative fragmentation patterns are observed for angII using the glucose glass film. The fragment ions appear to be formed from layers just below the surface of the film. The co-matrix of glucuronic acid/glucose produces a higher molecular ion yield. The spectrum of insulin in glucuronic acid/glucose consists mainly of positive ions with a fragmentation pattern from the B-chain. The spectrum of reduced insulin using a nitrocellulose matrix gives B-chain ions but glucose/glucuronic acid gives A-chain ions in both the positive and negative ion spectra. The fragmentation patterns of the A-chain and B-chain ions are sensitive to the nature of the matrix. An extensive negative ion A-chain fragmentation pattern was observed with glutamate ions serving as the charge centers. The reasons for the behavior of the A- and B-chain fragmentation patterns in these matrices is not clear.
Keywords: Plasma desorption mass spectrometry Glucose glass Fragmentation patterns Insulin Angiotensin
No Title by Kenneth R. Marcus; Alwyn B. Anfone; Wandee Luesaiwong; Teresa A. Hill; Dvora Perahia; Kenichi Shimizu (pp. 656-663).
While the array of analytical methods routinely applied for depth profile analysis was fairly static over the decades of the 1980s and 1990s, there appears to be an emerging technique that has a number of very positive and complementary attributes, and warrants serious consideration by the thin film community. Radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is a technique that provides depth-resolved elemental composition information on a wide variety of sample types. In a manner very much like most depth profiling methods, the rf-GD plasma utilizes an ion sputtering step to ablate sample material in a layer-by-layer fashion. Different from the more commonly applied methods, the device operates at elevated pressures [2–10 Torr Ar (266–1,330 Pa)] and has the inherent capability of sputtering electrically insulating materials directly, without any auxiliary means of charge compensation. In addition, sputtering rates on the order of 1 µm/min provide rapid analysis, with depth resolving powers that are comparable to high-vacuum sputtering methods. Three examples of the use of the rf-GD-OES method are presented as examples of its analytical potential: (1) boron-implanted silicon wafer, (2) a barrier-type alumina film, and (3) a porous-type alumina film. It is believed that the method holds a great deal of promise as part of the arsenal of weapons in the thin films laboratory.
Keywords: Radio frequency glow discharge Optical emission spectroscopy Depth profiling Aluminium oxide
No Title by Jason A. Day; María Montes-Bayón; Anne P. Vonderheide; Joseph A. Caruso (pp. 664-668).
Regulating arsenic species in drinking waters is a reasonable objective, since the various species have different toxicological impacts. However, developing robust and sensitive speciation methods is mandatory prior to any such regulations. Numerous arsenic speciation publications exist, but the question of robustness or ruggedness for a regulatory method has not been fully explored. The present work illustrates the use of anion exchange chromatography coupled to ICP-MS with a commercially available "speciation kit" option. The mobile phase containing 2 mM NaH2PO4 and 0.2 mM EDTA at pH 6 allowed adequate separation of four As species (As(III), As(V), MMAA, DMAA) in less than 10 min. The analytical performance characteristics studied, including method detection limits (lower than 100 ng L–1 for all the species evaluated), proved the suitability of the method to fulfill the current regulation. Other parameters evaluated such as laboratory fortified blanks, spiked recoveries, and reproducibility over a certain period of time produced adequate results. The samples analyzed were taken from water utilities in different areas of the United States and were provided by the U.S. EPA. The data suggests the speciation setup performs to U.S. EPA specifications but sample treatment and chemistry are also important factors for achieving good recoveries for samples spiked with As(III) as arsenite and As(V) as arsenate.
Keywords: As speciation Drinking water Anion-exchange chromatography ICP-MS