Showing papers on "Ion published in 2008"

Ion mobility-mass spectrometry.

Abstract: This review article compares and contrasts various types of ion mobility-mass spectrometers available today and describes their advantages for application to a wide range of analytes. Ion mobility spectrometry (IMS), when coupled with mass spectrometry, offers value-added data not possible from mass spectra alone. Separation of isomers, isobars, and conformers; reduction of chemical noise; and measurement of ion size are possible with the addition of ion mobility cells to mass spectrometers. In addition, structurally similar ions and ions of the same charge state can be separated into families of ions which appear along a unique mass-mobility correlation line. This review describes the four methods of ion mobility separation currently used with mass spectrometry. They are (1) drift-time ion mobility spectrometry (DTIMS), (2) aspiration ion mobility spectrometry (AIMS), (3) differential-mobility spectrometry (DMS) which is also called field-asymmetric waveform ion mobility spectrometry (FAIMS) and (4) traveling-wave ion mobility spectrometry (TWIMS). DTIMS provides the highest IMS resolving power and is the only IMS method which can directly measure collision cross-sections. AIMS is a low resolution mobility separation method but can monitor ions in a continuous manner. DMS and FAIMS offer continuous-ion monitoring capability as well as orthogonal ion mobility separation in which high-separation selectivity can be achieved. TWIMS is a novel method of IMS with a low resolving power but has good sensitivity and is well intergrated into a commercial mass spectrometer. One hundred and sixty references on ion mobility-mass spectrometry (IMMS) are provided.

An excess of cosmic ray electrons at energies of 300-800 GeV

Abstract: Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants. All components of the cosmic rays show an intensity that decreases as a power law with increasing energy (for example as E(-2.7)). Electrons in particular lose energy rapidly through synchrotron and inverse Compton processes, resulting in a relatively short lifetime (about 10(5) years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away). Here we report an excess of galactic cosmic-ray electrons at energies of approximately 300-800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar or micro-quasar) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza-Klein particle with a mass of about 620 GeV).

Low-temperature plasma probe for ambient desorption ionization.

Abstract: A low-temperature plasma (LTP) probe has been developed for ambient desorption ionization. An ac electric field is used to induce a dielectric barrier discharge through use of a specially designed electrode configuration. The low-temperature plasma is extracted from the probe where it interacts directly with the sample being analyzed, desorbing and ionizing surface molecules in the ambient environment. This allows experiments to be performed without damage to the sample or underlying substrate and, in the case of biological analysis on skin surfaces, without electrical shock or perceptible heating. Positive or negative ions are produced from a wide range of chemical compounds in the pure state and as mixtures in the gaseous, solution, or condensed phases, using He, Ar, N2, or ambient air as the discharge gas. Limited fragmentation occurs, although it is greater in the cases of the molecular than the atomic discharge gases. The effectiveness of the LTP probe has been demonstrated by recording characteristi...

Laser-Induced Electron Tunneling and Diffraction

Abstract: Molecular structure is usually determined by measuring the diffraction pattern the molecule impresses on x-rays or electrons. We used a laser field to extract electrons from the molecule itself, accelerate them, and in some cases force them to recollide with and diffract from the parent ion, all within a fraction of a laser period. Here, we show that the momentum distribution of the extracted electron carries the fingerprint of the highest occupied molecular orbital, whereas the elastically scattered electrons reveal the position of the nuclear components of the molecule. Thus, in one comprehensive technology, the photoelectrons give detailed information about the electronic orbital and the position of the nuclei.

Desolvation of ions in subnanometer pores and its effect on capacitance and double-layer theory.

Abstract: The study of charged solid–liquid interfaces, manifested as “double layers”, represents a problem of both practical and scientific importance. Double layers are present in all electrolyte solutions and have been traditionally studied using planar noble-metal electrodes and mercury drops. However, in the ionic channels in cells or the small-diameter pores of electrochemical double-layer capacitors (EDLCs),ions are in a very confined situation, which is different from that of a planar solid/electrolyte interface. By using nanoporous carbon with pores smaller than the size of an ion and a single associated solvent molecule, we show that the implicit assumption that double layers are governed only by ion/ electrode charge separation may be short-sighted. Other factor may play a more dominant role than previously thought, for example, increasing the confinement of the ions leads to an increase in the capacitance. Including the effect of partially desolvating ions in the current double-layer theory could lead to a better understanding of the behavior of ions in confined environments.

Signal enhancement in laser ablation ICP-MS by addition of nitrogen in the central channel gas

Abstract: The effects of adding nitrogen to the central gas flow (Ar + He) of an Ar plasma in laser ablation inductively coupled plasma mass spectrometry are presented. The optimum central gas flow rate was found to be negatively correlated with the N2 gas flow rate. The addition of 5–10 ml min−1nitrogen to the central channel gas in LA-ICP-MS increases the sensitivity for most of the 65 investigated elements by a factor of 2–3. The degree of enhancement depends, to some extent, on the 1st ionization energy. Another important advantage of N2 mixed gas plasma for LA-ICP-MS is that the oxide ratios (ThO+/Th+) are significantly reduced (one order of magnitude). The hydride ratio (ArH+/Ar+) is also reduced up to a factor of 3, whereas the doubly charged ion ratio (Ca2+/Ca+) is increased. The background signals at masses 29, 31, 42, 51, 52 and 55 are significantly increased due to the nitrogen based polyatomic interferences. Compared to the spatial profiles of the ion distributions in the normal mode (without nitrogen), the addition of 5 ml min−1nitrogen leads to significant wider axial profiles and more uniform distribution of ions with different physical and chemical properties. Our results also show that the makeup gas flow (central channel gas) rate has a significant effect on the ion distribution of elements with different physical and chemical properties. A very consistent increase of argon signal by the addition of nitrogen (5 ml min−1) corroborates better energy transfer effect of nitrogen in the plasma.

The Plasma and Suprathermal Ion Composition (PLASTIC) Investigation on the STEREO Observatories

Abstract: The Plasma and Suprathermal Ion Composition (PLASTIC) investigation provides the in situ solar wind and low energy heliospheric ion measurements for the NASA Solar Terrestrial Relations Observatory Mission, which consists of two spacecraft (STEREO-A, STEREO-B). PLASTIC-A and PLASTIC-B are identical. Each PLASTIC is a time-of-flight/energy mass spectrometer designed to determine the elemental composition, ionic charge states, and bulk flow parameters of major solar wind ions in the mass range from hydrogen to iron. PLASTIC has nearly complete angular coverage in the ecliptic plane and an energy range from ∼0.3 to 80 keV/e, from which the distribution functions of suprathermal ions, including those ions created in pick-up and local shock acceleration processes, are also provided.

Ionic liquid near a charged wall: structure and capacitance of electrical double layer.

Abstract: We study the effects of ion size asymmetry and short-range correlations on the electrical double layer in ionic liquids: we perform molecular dynamics simulations of a model ionic liquid between two “electrodes” and calculate the differential capacitance of each as a function of the electrode potential. The capacitance curve has an asymmetric “bell-shape” character, in qualitative agreement with recent experiments and the mean-field theory (MFT) which takes into account the limitation on the maximal local density of ions. The short-range ionic correlations, not included in the MFT, lead to an overscreening effect which changes radically the structure of the double layer at small and moderate charging. With the radius of cations taken to be twice as large as anions, the position of the main capacitance maximum is shifted positively from the potential of zero charge (PZC), as predicted by MFT. An extension of the theory (EMFT), however, reproduces the simulated capacitance curve almost quantitatively. Capac...

Ionic Selectivity of Single Nanochannels

Abstract: There has been an increasing interest in single nanochannel ionic devices, such as ionic filters that control the type of transported ions and ionic diodes that rectify the ionic flow. In this article, we theoretically investigate the importance of the dimensions, surface charge, electrolyte concentration, and applied bias on nanopore performance. We compare numerical solutions of the Poisson, Nernst−Planck (PNP), and Navier−Stokes (NS) equations with their one-dimensional, analytical approximations. We show that by decreasing the length of the nanopore, the ionic current and ionic selectivity become affected by processes outside the nanochannel. The contribution of electroosmosis is noticeable, especially for highly charged nanochannels, but is insignificant, justifying the use of the simple one-dimensional approximation in many cases. Estimates for the critical electric field at which the nanopore selectivity decreases and the ion current starts to saturate are provided.

On the Structure of Relativistic Collisionless Shocks in Electron-Ion Plasmas

Abstract: Relativistic collisionless shocks in electron-ion plasmas are thought to occur in the afterglow phase of gamma-ray bursts (GRBs) and in other environments where relativistic flows interact with the interstellar medium. A particular regime of shocks in an unmagnetized plasma has generated much interest for GRB applications. In this Letter, we present ab initio particle-in-cell simulations of unmagnetized relativistic electron-ion shocks. Using long-term 2.5-dimensional simulations with ion-electron mass ratios from 16 to 1000, we resolve the shock formation and reach a steady state shock structure beyond the initial transient. We find that even at high ion-electron mass ratios initially unmagnetized shocks can be effectively mediated by the ion Weibel instability with a typical shock thickness of ~20 ion skin depths. Upstream of the shock, the interaction with merging ion current filaments heats the electron component, so that the postshock flow achieves near-equipartition between the ions and electrons, with the electron temperature reaching 50% of the ion temperature. This energy exchange helps to explain the large electron energy fraction inferred from GRB afterglow observations.

Ion current rectification at nanopores in glass membranes.

Abstract: The origin of ion current rectification observed at conical-shaped nanopores in glass membranes immersed in KCl solutions has been investigated using finite-element simulations. The ion concentrations and fluxes (due to diffusion, migration, and electroosmotic convection) were determined by the simultaneous solution of the Nernst-Planck, Poisson, and Navier-Stokes equations for the two-ion (K+ and Cl-) system. Fixed surface charge on both the internal and external glass surfaces that define the pore structure was included to account for electric fields and nonuniform ion conductivity within the nanopores and electric fields in the external solution near the pore mouth. We demonstrate that previous observations of ion current rectification in conical-shaped glass nanopores are a consequence of the voltage-dependent solution conductivity in the vicinity of the pore mouth, both inside and outside of the pore. The simulations also demonstrate that current rectification is maximized at intermediate bulk ion concentrations, a combination of (i) the electrical screening of surface charge at high concentrations and (ii) a fixed number of charge-carrying ions in the pore at lower concentration, which are physical conditions where the voltage dependence of the conductivity disappears. In addition, we have quantitatively shown that electroosmotic flow gives rise to a significant but small contribution to current rectification.

Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas

Abstract: This Letter presents the first ab initio, fully electromagnetic, kinetic simulations of magnetized turbulence in a homogeneous, weakly collisional plasma at the scale of the ion Larmor radius (ion gyroscale). Magnetic- and electric-field energy spectra show a break at the ion gyroscale; the spectral slopes are consistent with scaling predictions for critically balanced turbulence of Alfven waves above the ion gyroscale (spectral index -5/3) and of kinetic Alfven waves below the ion gyroscale (spectral indices of -7/3 for magnetic and -1/3 for electric fluctuations). This behavior is also qualitatively consistent with in situ measurements of turbulence in the solar wind. Our findings support the hypothesis that the frequencies of turbulent fluctuations in the solar wind remain well below the ion cyclotron frequency both above and below the ion gyroscale.

New Relativistic Atomic Natural Orbital Basis Sets for Lanthanide Atoms with Applications to the Ce Diatom and LuF3

Abstract: New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are inluded as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.

Dust acoustic solitons in plasmas with kappa-distributed electrons and/or ions

Abstract: An investigation into both small and large amplitude dust acoustic solitary waves in dusty plasmas with cold negative dust grains and kappa-distributed ions and/or electrons is discussed. Existence conditions for the arbitrary amplitude case are found in an appropriate parameter space, viz., an effective Mach number of the structure speed and the fraction of the charge density that resides with the free electrons, expressed in terms of the ion density. Results indicate that the kappa distribution has only a quantitative, not a qualitative effect on the existence domains and only negative potential solitons exist regardless of whether the electrons or the ions, or both, have a kappa distribution. Despite a wide-ranging search, we have not found double layers in such a plasma. In the case of positive dust, an equivalent set of results holds.

Precipitation of radiation belt electrons by EMIC waves, observed from ground and space

Abstract: We show evidence that left-hand polarised electromagnetic ion cyclotron (EMIC) plasma waves can cause the loss of relativistic electrons into the atmosphere. Our unique set of ground and satellite observations shows coincident precipitation of ions with energies of tens of keY and of relativistic electrons into an isolated proton aurora. The coincident precipitation was produced by wave-particle interactions with EMIC waves near the plasmapause. The estimation of pitch angle diffusion coefficients supports that the observed EMIC waves caused coincident precipitation ofboth ions and relativistic electrons. This study clarifies that ions with energies of tens of ke V affect the evolution of relativistic electrons in the radiation belts via cyclotron resonance with EMIC waves, an effect that was first theoretically predicted in the early 1970's.

Ionic Liquids in Chemical Analysis

Abstract: Room-temperature ionic liquids are salts with a melting point close to or below room temperature. They form liquids composed in the majority of ions. This gives these materials the potential to behave very differently when they are used as solvents compared to conventional molecular liquids. The search for their application is growing in every area of analytical chemistry—electrochemistry, chromatography, electrophoresis, and even mass spectrometry. The literature on ionic liquids is growing almost exponentially. The basis for this activity is the easy preparation of salts with different ion constituents. This ability might best be described as the “chemical tunability” of ionic liquids, a class of solvents with members possessing similar physical properties but having different chemical behavior. Their good solvating properties, together with large spectral transparency, make ionic liquids suitable solvents for spectroscopic measurements. It has been demonstrated that task-specific ionic liquids have adv...

Monoenergetic ion beams from ultrathin foils irradiated by ultrahigh-contrast circularly polarized laser pulses

Abstract: Acceleration of ions from ultrathin foils irradiated by intense circularly polarized laser pulses is investigated using one- and two-dimensional particle simulations. A circularly polarized laser wave heats the electrons much less efficiently than the wave of linear polarization and the ion acceleration process takes place on the front side of the foil. The ballistic evolution of the foil becomes important after all ions contained in the foil have been accelerated. In the ongoing acceleration process, the whole foil is accelerated as a dense compact bunch of quasineutral plasma implying that the energy spectrum of ions is quasimonoenergetic. Because of the ballistic evolution, the velocity spread of an accelerated ion beam is conserved while the average velocity of ions may be further increased. This offers the possibility to control the parameters of the accelerated ion beam. The ion acceleration process is described by the momentum transfer from the laser beam to the foil and it might be fairly efficient in terms of the energy transferred to the heavy ions even if the foil contains a comparable number of light ions or some surface contaminants. Two-dimensional simulations confirm the formation of the quasimonoenergetic spectrum of ions and relatively good collimation of the ion bunch, however the spatial distribution of the laser intensity poses constraints on the maximum velocity of the ion beam. The present ion acceleration mechanism might be suitable for obtaining a dense high energy beam of quasimonoenergetic heavy ions which can be subsequently applied in nuclear physics experiments. Our simulations are complemented by a simple theoretical model which provides the insights on how to control the energy, number, and energy spread of accelerated ions.

Ions at aqueous interfaces: from water surface to hydrated proteins.

Abstract: The surfaces of aqueous solutions are traditionally viewed as devoid of inorganic ions. Molecular simulations and surface-selective spectroscopic techniques show, however, that large polarizable anions and hydronium cations can be found (and even enhanced) at the surface and are involved in chemistry at the air/water interface. Here, we review recent studies of ions at the air/water interface and compare from this perspective water with other polar solvents. For water, we focus in particular on the surface behavior of its ionic product (i.e., hydronium and hydroxide ions). We also investigate the feasibility of dielectric models for the description of the protein/water interface, in analogy to the air/water interface. Little correlation is found between these two interfaces in terms of ion segregation. Therefore, we suggest a local model of pairing of ions from the solution with charged and polar groups at the protein surface. We also describe corresponding results of experimental studies on aqueous model systems.

Development of a low-temperature photoelectron spectroscopy instrument using an electrospray ion source and a cryogenically controlled ion trap.

Abstract: The ability to control ion temperatures is critical for gas phase spectroscopy and has been a challenge in chemical physics. A low-temperature photoelectron spectroscopy instrument has been developed for the investigation of complex anions in the gas phase, including multiply charged anions, solvated species, and biological molecules. The new apparatus consists of an electrospray ionization source, a three dimensional (3D) Paul trap for ion accumulation and cooling, a time-of-flight mass spectrometer, and a magnetic-bottle photoelectron analyzer. A key feature of the new instrument is the capability to cool and tune ion temperatures from 10to350K in the 3D Paul trap, which is attached to the cold head of a closed cycle helium refrigerator. Ion cooling is accomplished in the Paul trap via collisions with a background gas and has been demonstrated by observation of complete elimination of vibrational hot bands in photoelectron spectra of various anions ranging from small molecules to complex species. Further evidence of ion cooling is shown by the observation of H2-physisorbed anions at low temperatures. Cold anions result in better resolved photoelectron spectra due to the elimination of vibrational hot bands and yield more accurate energetic and spectroscopic information. Temperature-dependent studies are made possible for weakly bonded molecular and solvated clusters, allowing thermodynamic information to be obtained.

Core−Shell Li3V2(PO4)3@C Composites as Cathode Materials for Lithium-Ion Batteries

Abstract: Core−shell Li3V2(PO4)3@C nanostructured composites were prepared via a sol−gel route followed by hydrothermal treatment. XRD patterns showed that Li3V2(PO4)3 has a monoclinic structure with space group P21/n. TEM images exhibited that Li3V2(PO4)3 particles are encapsulated with a carbon shell ∼10 nm in thickness. Compared with pure Li3V2(PO4)3, core−shell Li3V2(PO4)3@C composites presented enhanced electrochemical Li ion intercalation performances. Cyclic voltammetry and electrochemical impedance spectroscopy disclosed that carbon shells improved Li ion diffusion and electrical conductance significantly and also retarded formation of solid electrolyte interphase film of Li3V2(PO4)3 cathode materials.

Dissociative Recombination of Molecular Ions

Abstract: 1 Introduction 2 Experimental methods 3 Theoretical methods 4 The H2+molecule 5 Diatomic hydride ions 6 Diatomic ions 7 The H3+ molecule 8 Polyatomic ions 9 Related processes 10 Applications

A coumarin-derived fluorescence probe selective for magnesium.

Abstract: Two different coumarin derivatives have been connected via an imine linkage to obtain a new fluorescence signaling system This compound itself does not show any emission due to rapid isomerization around the C═N bond However, in the presence of a Mg(II) ion, this isomerization is stopped because of bonding to the metal ion resulting in high-intensity (∼550-fold) emission Other metal ions like Li(I), Ca(II), and Zn(II) show very little emission, while biologically relevant transition-metal ions do not show any emission In this way, the Mg(II) ion can be detected in the presence of these ions

Fine Structure in Swift Heavy Ion Tracks in Amorphous SiO2

Abstract: We report on the observation of a fine structure in ion tracks in amorphous SiO2 using small angle x-ray scattering measurements. Tracks were generated by high energy ion irradiation with Au and Xe between 27 MeV and 1.43 GeV. In agreement with molecular dynamics simulations, the tracks consist of a core characterized by a significant density deficit compared to unirradiated material, surrounded by a high density shell. The structure is consistent with a frozen-in pressure wave originating from the center of the ion track as a result of a thermal spike.

On the possibility of making a geometrically symmetric RF-CCP discharge electrically asymmetric

Abstract: A fundamental problem in technological plasmas has been how to control the ion energy and the ion flux (plasma density) independently of one another. A simple, but previously overlooked asymmetry effect is reported that should allow a high degree of control of the ion energy. The idea is that when a temporally symmetric, multi-frequency voltage waveform containing one or more even harmonics is applied to a discharge, even a geometrically symmetric one, the two sheaths are necessarily asymmetric. To balance the charged particle fluxes, a dc self-bias develops. Optimally, this is achieved with a dual frequency discharge that uses the phase locked fundamental and its second harmonic. The resulting dc self-bias and hence the ion energy are a nearly linear function of the phase angle between the two applied RF voltages. This works even for geometrically symmetric discharges, and the roles of the two electrodes can be reversed using the phase. This means that the technique can be used to increase or decrease the ion energy striking a substrate while leaving the applied RF voltage and frequency and thereby the discharge parameters effectively unchanged.

Comment on "free energy simulations of single and double ion occupancy in gramicidin A"

Abstract: In a recent article published by Bastug and Kuyucak [J. Chem. Phys.126, 105103 (2007)] investigated the microscopic factors affecting double ion occupancy in the gramicidin channel. The analysis relied largely on the one-dimensional potential of mean force of ions along the axis of the channel (the so-called free energy profile of the ion along the channel axis), as well as on the calculation of the equilibrium association constant of the ions in the channel binding sites. It is the purpose of this communication to clarify this issue.

Cold Reactive Collisions between laser-cooled ions and velocity-selected neutral molecules.

Abstract: We report a new experimental method to study reactive ion-molecule collisions at very low temperatures. A source of laser-cooled ions in a linear Paul trap has been combined with a quadrupole-guide velocity selector to investigate the reaction of Ca{sup +} with CH{sub 3}F at collision energies E{sub coll}/k{sub B}{>=}1 K with single-particle sensitivity. The technique represents a general approach to study reactive collisions between ions and polar molecules over a wide temperature range down to the cold regime.

Ion-driven deuterium retention in tungsten

Abstract: The ion-driven retention of deuterium in polycrystalline tungsten (PCW) is studied experimentally and theoretically as a function of temperature, incident ion energy, and ion fluence. Deuterium retention was investigated by thermodesorption spectroscopy and ion beam analysis. The peculiarities of deuterium behavior in PCW such as (i) ion-induced defect formation at low-energy implantation and (ii) higher D retention of low-energy ions (60–200eV) compared to high-energy ions (3keV) at high fluences are considered. The effect of intrinsic defects (dislocations, vacancies, grain boundaries) and ion-induced defects (vacancies, dislocations, deuterium clusters) is discussed for polycrystalline tungsten.

Nanocomposite ion gels based on silica nanoparticles and an ionic liquid: ionic transport, viscoelastic properties, and microstructure.

Abstract: The dispersion of silica nanoparticles made an ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]), gelled even by the addition of 2−3 wt %, due to the formation of interconnected particulate silica networks in [C2mim][NTf2]. The ionic transport and viscoelastic properties of these nanocomposite ion gels were investigated in relation to the microstructure. Despite their solid-like behavior, the nanocomposite ion gels exhibited a high ionic conductivity of approximately 10−2 S cm−1 at 30 °C, which is comparable to that of neat [C2mim][NTf2]. Intriguing viscoelastic responses, such as shear-thinning and shear-induced sol−gel transitions, were found in all of the nanocomposite ion gels. By adjusting the silica concentration, the elastic modulus (G′) could be precisely controlled in a range of more than 3 orders of magnitude and reached approximately 106 Pa without a considerable decrease in the ionic conductivity; the characteristic viscoelastic response was also mai...

Atmospheric pressure chemical ionization source. 2. Desorption-ionization for the direct analysis of solid compounds.

Abstract: The flowing afterglow-atmospheric pressure glow discharge (APGD) ionization source described in part 1 of this study (in this issue) is applied to the direct analysis of condensed-phase samples. When either liquids or solids are exposed to the ionizing beam of the APGD, strong signals for the molecular ions of substances present on their surfaces can be detected without compromising the integrity of the solid sample structure or sample substrate. As was observed for gas-phase compounds in part 1 of this study, both polar and nonpolar substances can be ionized and detected by mass spectrometry. The parent molecular ion (or its protonated counterpart) is usually the main spectral feature, with little or no fragmentation in evidence. Preliminary quantitative results show that this approach offers very good sensitivity (detection limits in the picogram regime are reported for several test compounds in part 1 of this study) and linear response to the analyte concentration. Examples of the application of this s...