Modeling Surface Engineering: Use of Polymetallic Iron Cages and Computer Graphics To Understand the Mode of Action of a Corrosion Inhibitor

Simple organic molecules can have many functions. The active ingredient in the corrosion inhibitor 3-(4-methylbenzoyl)propionate works because it addresses the metal sites of a surface through carboxylate groups, forms hydrogen bonds with surface hydroxide groups (see picture), and provides excellent surface coverage through efficient packing of substituted aromatic groups.     

Ewald summations in systems with two-dimensional periodicity

This study presents formulas for the electrostatic energy of lattices with two-dimensional periodicity, based on Fourier representations and alternatively on the Ewald procedure for convergence acceleration. The work extends the contributions of previous investigators by taking full advantage of plane-group symmetry and by providing analytical formulas for all derivatives of the energy through second order. The derivatives considered include those with respect to the positions of all charges within the unit cell, those with respect to the lattice vectors (cell deformations), and those involving both types of variables. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 385–404, 1998     

Implementation of the chemical reaction interface mass spectrometry technique on a Hewlett-Packard mass-selective detector

A microwave-powered chemical reaction interface has been installed in a Hewlett-Packard gas chromatograph-mass spectrometer (GC-MS) system (5890 IT gas chromatograph-S971 mass-selective detector). The technical details and optimization strategies are discussed. The evaluation of this new setup is presented, showing detection limits of 1 ng of ¹³C-, ¹⁵N-, and Cl-containing compounds with signal-to-noise ratios greater than or egual to 3. Selective detection was evaluated with a urine sample from a dog dosed with ¹⁵N₃-midazolam that had been previously analyzed by using a differentially pumped research-level quadrupole mass spectrometer. The results show that the detection of ¹⁵N and Cl remains highly selective and the mass-selective detector gives comparable sensitivity to the larger instrument when the latter is operating over a conventional mass range. The capability for chemical reaction interface mass spectrometry can be easily accomplished with an inexpensive GC-MS system.     

How to measure the kinetic energy distribution of the precursor ion main beam in mass-analyzed ion kinetic energy spectrometry experiments

Scans of the electrostatic analyzer (ESA) across the precursor ion beam in reverse-geometry (BE) mass spectrometers that are operated under double-focusing conditions do not measure the “energy resolution of the main beam”: They only measure double-focusing resolution. The only way that ESA scans can measure the kinetic energy distribution of the main beam is to operate the instrument so that angular (directional) focusing is not achieved. Thus, the mass spectrometer is no longer double-focusing. Under double-focusing conditions, however, scans of the accelerating voltage while the magnetic field and ESA are held constant can be used to measure either the kinetic energy distribution of the main beam that enters the magnet or the energy-resolving power of the instrument. Scans at a constant ratio of B²/E can be used similarly. The energy-resolving power of any ESA is defined by its dispersion and the widths of the energy-resolving object and image slits that immediately precede and follow the ESA, respectively. The use of BE, EB, and triple-sector instruments to measure energy-resolving power and the kinetic energy distribution of the precursor ion main beam is compared and discussed.     

Ion formation processes in the afterpeak time regime of pulsed glow discharge plasmas

The formation of ions following the termination of power in a pulsed glow discharge ion source is investigated. The populations of ionized species containing sputtered atoms M⁺, M ₂ ¹ :, and MAr⁺ are observed to maximize after the termination of discharge power. Collisions involving sputtered atoms and metastable argon atoms, Penning and associative ionization, are considered to be responsible for the formation of ions in the discharge afterpeak time regime. The domination of these ion formation processes during the afterpeak time regime is supported by the results from investigations of discharge operating parameters, metastable argon atom quenching, and ion kinetic energy distributions.     

Improved fourier-transform ion-cyclotron-resonance mass spectrometry of large biomolecules

Initial results from a Fourier-transform mass spectrometer with a 6.2 Tesla magnet using electrospray ionization show substantial improvements in resolution, mass accuracy, mass range, signal/noise, and tandem mass spectromehy capabilities compared to our earlier 2.8 T instrument that demonstrated the first unit resolution mass spectra of molecules as large as myoglobin (17 kDa). The new instrument exhibits greater than 10⁶ and 10⁵ resolving power for 8.6 and 29 kDa, respectively, proteins. Using an internal standard, the mass measuring error for myoglobin is less than 1 ppm. Nozzle-skimmer dissociation during electrospray of carbonic anhydrase (29 kDa) has yielded 38 fragment ions for which both mass and charge are identifiable; of these, 21 have been assigned to expected oligopeptide fragments.     

Comparison of algorithms and databases for matching unknown mass spectra

The most used algorithms for the identification of electron-ionization mass spectra are INCOS and probability based matching (PBM). For unknown spectra of high purity, ～75% of rank 1 answers are correct for both algorithms, matched against the National Institute of Standards and Technology 62,235 spectrum database. With matching criteria that retrieve 50% of the possible correct answers from the Wiley 228,998 spectrum database, 54% of the PBM and 42% of the INCOS answers are correct; for 85% purity unknowns, 48% and 27% are correct. For an unknown spectrum of two compounds, neither was reported in the first three INCOS answers; eight of the first ten PBM answers identify both components.