Direct Ionization Research Articles

Early detection of algal infection using direct real-time chemical ionization mass spectrometry

Early detection of algal infection using direct real-time chemical ionization mass spectrometry Robert S. Pomeroy, Teaching Professor at UC San Diego, guides us through the early detection of algal infections using direct real-time chemical ionization mass spectrometry. Petroleum, from the Latin “rock oil,” has transformed our lives. It has changed how we live, work, and play. Petroleum is, however, nothing more than ancient algae. The transformation of biomass to hydrocarbons results from being subjected to heat and pressure over millions of years. Algae accumulate oils that, when extracted, can be converted into renewable fuels such as gasoline, diesel, and jet fuel. In 1978, the U.S. Department of Energy launched the Aquatic Species Program to investigate energy production using algae. (1) The establishment of this program coincided with the rapidly rising fuel cost due to the Oil Embargo in 1973 and led to the creation of the U.S. Department of Energy.

Slug-Flow Microextraction Mass Spectrometry for Enhanced Detection of Analytes in Human Tear Fluids using Noninvasive Microsampling and Nanoelectrospray Ionization via a Capillary.

In vivo noninvasive sampling and sensitive analysis of human tear fluids at the microliter level is an important but challenging task in investigating eye health. In this work, capillary microsampling coupled with slug-flow microextraction mass spectrometry (SFME-MS) was developed for enhanced detection of analytes in human tear fluids. As low as 1.0 μL of human tear fluid could be directly sampled using a capillary, and extraction/spray solvent was then loaded into the capillary to perform slug-flow microextraction and direct nanoelectrospray ionization (nESI) of analytes. All analytical procedures, including tear microsampling, microextraction, and ionization of analytes, were performed using a capillary. Enhanced detection of therapeutic drugs and disease biomarkers in human tear fluids was successfully demonstrated. Acceptable analytical performances including sensitivity, reproducibility, and quantitation were obtained. It is found that the use of SFME could improve the nESI-MS detection of trace analytes over 100-fold that depends on the chemical properties of analytes. Overall, this study showed that SFME-nESI-MS is a highly effective method for enhanced detection of trace analytes in tear fluids and is expected to be a potentially powerful tool in significant biological and clinical applications.

Calculations of positron scattering from atomic oxygen

The single-center convergent close coupling (CCC) method has been applied to positron scattering from the oxygen atom. Cross sections have been calculated for total, elastic, momentum transfer, total ionization, inelastic, and excitation scattering processes from threshold to 5000 eV. Due to their relevance in transport studies, we also present stopping power and mean excitation energy results. Low-energy studies have been conducted to calculate scattering length, the hidden Ramsauer–Townsend minimum, and the energy of the positron virtual state. CCC-scaled complex optical potential calculations are utilized to calculate positronium-formation, direct ionization, and values between the positronium-formation and ionization thresholds. Good agreement is generally observed at high energies with past theory, electron-atomic oxygen experiment, and halved electron/positron O_2 experiment. Large discrepancies, however, have been found between current and previous calculations for positronium-formation cross section and for low-energy elastic scattering cross section.Graphic

Generation of Ultrafast Attosecond Magnetic Field from Ne Dimer in Circularly Polarized Laser Pulses

By numerically solving time-dependent Schrödinger equations, we investigate the generation of electron currents, ultrafast magnetic fields and photoelectron momentum distributions (PMD) when circularly polarized laser pulses interact with a Ne dimer in the charge migration (CM) process. By adjusting the laser wavelength, we consider two cases: (i) coherent resonance excitation (λ = 76 nm) and (ii) direct ionization (λ = 38 nm). The results show that the current and magnetic field generated by the Ne dimer under resonance excitation are stronger than under direct ionization. This phenomenon is due to the quantum interference between the initial state 2pσ g and the excited state 3sσ g under resonance excitation, so the CM efficiency of the dimer can be improved and the strength of the PMD under different ionization conditions is opposite to the strength of the electron current and induced magnetic field. In addition, we also find that both 2pπ g and 2pπ u have coherent resonance excitation with 3sσ g state and generate periodic oscillating currents for the Ne dimer. The study of the dynamics of the Ne dimer under different ionization conditions lays a foundation for research of ultrafast magnetism in complex molecular systems.

Plastic probe electrospray ionization mass spectrometry developed for rapid fingerprint profile of biological samples without pretreatment.

A triangular-shaped flat plastic substrate probe was prepared for direct electrospray ionization mass spectrometry (ESI-MS) for analysis of untreated chemical and biological samples including liquids (Met-Arg-Phe-Ala peptide, reserpine, and dodecyl aldehyde), solids (biological samples, traditional Chinese medicine), and powders (roasted coffee, rhizoma coptidis, lotus plumule, and Schisandra sphenanthera). Quantitative analysis of reserpine in water yielded a detection limit of 1ngmL-1, dynamic response range within 1-500ngmL-1, and linearity of signal response ˃0.9925. Compared to the conventional capillary ESI, this plastic probe ESI offers lower cost of analysis (US $0.0056 per probe), higher sensitivity, lower sample consumption, longer signal duration (>6min), better reproducibility, signal stability, and higher speed of analysis (<10s per sample, including sample loading). Overall, the results indicate the potential of ESI-MS based on flat plastic probes as a versatile method for simple, sensitive, and stable analysis of untreated biological sample analysis.

Effects of HZE-Particle Exposure Location and Energy on Brain Inflammation and Oxidative Stress in Rats.

Astronauts on exploratory missions will be exposed to particle radiation of high energy and charge (HZE particles), which have been shown to produce neurochemical and performance deficits in animal models. Exposure to HZE particles can produce both targeted effects, resulting from direct ionization of atoms along the particle track, and non-targeted effects (NTEs) in cells that are distant from the track, extending the range of potential damage beyond the site of irradiation. While recent work suggests that NTEs are primarily responsible for changes in cognitive function after HZE exposures, the relative contributions of targeted and non-targeted effects to neurochemical changes after HZE exposures are unclear. The present experiment was designed to further explore the role of targeted and non-targeted effects on HZE-induced neurochemical changes (inflammation and oxidative stress) by evaluating the effects of exposure location and particle energy/linear energy transfer (LET). Forty-six male Sprague-Dawley rats received head-only or body-only exposures to 56Fe particles [600 MeV/n (75 cGy) or 1,000 MeV/n (100 cGy)] or 48Ti particles [500 MeV/n (50 cGy) or 1,100 MeV/n (75 cGy)] or no irradiation (0 cGy). Twenty-four h after irradiation, rats were euthanized, and the brain was dissected for analysis of HZE-particle-induced neurochemical changes in the hippocampus and frontal cortex. Results showed that exposure to 56Fe and 48Ti ions produced changes in measurements of brain inflammation [glial fibrillary astrocyte protein (GFAP)], oxidative stress [NADPH-oxidoreductase-2 (NOX2)] and antioxidant enzymes [superoxide dismutase (SOD), glutathione S-transferase (GST), nuclear factor erythroid 2-related factor 2 (Nrf2)]. However, radiation effects varied depending upon the specific measurement, brain region, and exposure location. Although overall exposures of the head produced more detrimental changes in neuroinflammation and oxidative stress than exposures of the body, body-only exposures also produced changes relative to no irradiation, and the effect of particle energy/LET on neurochemical changes was minimal. Results indicate that both targeted and non-targeted effects are important contributors to neurochemical changes after head-only exposure. However, because there were no consistent neurochemical changes as a function of changes in track structure after head-only exposures, the role of direct effects on neuronal function is uncertain. Therefore, these findings, although in an animal model, suggest that NTEs should be considered in the estimation of risk to the central nervous system (CNS) and development of countermeasures.

Theoretical investigations of positron collisions with phosphorus-containing compounds

A theoretical investigation of positron scattering from phosphorus-containing compounds (viz., PH3, P2H4, PCl3, PF3, PBr3, POF3, POCl3, and H2PO4) is reported in this article. The quantum mechanical potential scattering approach is utilized to calculate integral elastic, excitation, momentum transfer, direct ionization, positronium formation, total ionization, inelastic, differential, and total cross sections on a fine energy grid from 1 to 5000 eV. The ionization contribution in the inelastic scattering is estimated using the complex scattering potential-ionization contribution technique. Prior research on positron collisions with these targets is scarce; as a result, the purpose of this study is to make up, at least in part, for this deficiency in cross-section data. In addition to being pertinent to positron transport analyses, such as Monte Carlo methods, the current results should be useful to benchmark the accuracy and validity of positron molecule collision computations and, more significantly, to compare these calculations with related electron scattering outcomes. Furthermore, the calculated cross sections of PH3 are compared with NH3 and other phosphorus-containing compounds. The analysis makes it abundantly evident that the atoms on the periphery of a molecule have a substantially larger impact on the scattering process than the central atom. To analyze the scattering dynamics of positrons and their anti-particle electrons, a comparative study of cross sections of H2PO4 and H2SO4 is also presented. For most of these targets, positron calculations are carried out for the first time.

Direct double ionization for molecules of H2 and N2 induced by electron-impact

The direct double ionization of H2 and N2 molecules induced by electron-impact are investigated theoretically. Our theoretical calculation combines the binary-encounter-Bethe theory employed for molecular electron-impact single ionization and knock-out mechanism derived from the many-body perturbation theory. The process of electron-impact direct double ionization for molecules in our consideration is treated as the coupling of primary single ionization and knock-out process. The knock-out process is constituted by all the possible secondary single ionization processes. There is a good agreement between our theoretical results and available experimental measurements both for the molecules of H2 and N2. Our approach can obtain the cross section of each ionization channel, which is helpful to understanding for ionization competition mechanism of small homo-nuclear diatomic molecules.

Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O.

We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path-OD+: a1Δ or b1Σ+ → A 3Π → X 3Σ- → B 3Σ--involving a combination of spin-orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels.

Electron-impact single ionization for the Fe2+ ion

Electron-impact ionization was analyzed for all 34 levels of the ground configuration of the Fe2+ ion. Both direct and indirect ionization processes are included in the study. For the direct process, the potential of the ionized ion was used to explain experimental data. For the indirect process, electron-impact excitation with subsequent autoionization was considered. The convergence of the cross sections of the indirect process was determined by considering the excitations up to shells with the principal quantum number n ⩽ 20. The main contribution to the indirect process was determined by the 3p → 3d excitations. The scaled distorted-wave approximation was applied to explain measurements for the Fe2+ ion. Scaling of the cross sections lowers values by ~35% at the peak for the ground level and ~50% for the highest level of the ground configuration of the Fe2+ ion. The experimental value for the single ionization threshold was used to provide better agreement with the measurements for the cross sections. This led to the cross sections for the levels of the ground configuration diminishing in size by 15–25%. The direct process contributes ~70% and ~50% to the total ionization from the lowest and highest levels of the ion, respectively.

Radiation damage by extensive local water ionization from two-step electron-transfer-mediated decay of solvated ions

Biomolecular radiation damage is largely mediated by radicals and low-energy electrons formed by water ionization rather than by direct ionization of biomolecules. It was speculated that such an extensive, localized water ionization can be caused by ultrafast processes following excitation by core-level ionization of hydrated metal ions. In this model, ions relax via a cascade of local Auger–Meitner and, importantly, non-local charge- and energy-transfer processes involving the water environment. Here, we experimentally and theoretically show that, for solvated paradigmatic intermediate-mass Al3+ ions, electronic relaxation involves two sequential solute–solvent electron transfer-mediated decay processes. The electron transfer-mediated decay steps correspond to sequential relaxation from Al5+ to Al3+ accompanied by formation of four ionized water molecules and two low-energy electrons. Such charge multiplication and the generated highly reactive species are expected to initiate cascades of radical reactions.

Hemoglobin Derivatives in Beef Irradiated with Accelerated Electrons.

The efficiency of food irradiation depends on the accuracy of the irradiation dose range that is sufficient for inhibiting microbiological growth without causing an irreversible change to the physical and chemical properties of foods. This study suggests that the concentration of hemoglobin derivatives can be used as a criterion for establishing the limit for chilled beef irradiation at which irradiation-induced oxidation becomes irreversible. The express spectrophotometry method for estimating the hemoglobin derivative concentration shows a nonlinear increase in methemoglobin concentration from 15% to 50% in beef irradiated by accelerated electrons with the doses ranging from 250 Gy to 10,000 Gy. The monitoring of the hemoglobin derivative concentration for three days after irradiation shows nonmonotonous dependencies of methemoglobin concentration in beef in the storage time since the oxidation of hemoglobin occur as a result of irradiation and biochemical processes in beef during storage. The proposed method based on the quantitative analysis of the hemoglobin derivative concentration can be used to estimate the oxidation level for irradiation of foods containing red blood cells. The study proposes a model that describes the change in hemoglobin derivative concentration in beef after irradiation considering that oxidation of hemoglobin can be triggered by the direct ionization caused by accelerated electrons, biochemical processes as a result of bacterial activity, and reactive oxygen species appearing during irradiation and storage. This research throws light on the mechanisms behind food irradiation during storage that should be taken into account for selecting the optimal parameters of irradiation.

Modified saddle-point method applied to direct ionization of noble gas atoms

When exposed to strong laser fields, atoms or molecules can absorb more photons from the laser field than is necessary for ionization. This process is called above-threshold ionization (ATI). In analyzing this process, the strong-field approximation (SFA) turns out to be a very useful theoretical tool. In the SFA the differential ionization rate, which is an observable quantity, can be expressed as an integral over the ionization time and can be calculated by numerical integration (NI) or using the saddle-point method (SPM). When we use the Slater orbitals to describe the ground-state wave function of the valence electron, the results obtained using the SPM and NI do not agree. We find the reasons for this disagreement and introduce a modified SPM that leads to excellent agreement between the SPM and NI results for various strong laser fields.

LMJSSP for analysis of prophylactic lubricants, spermicides and residues

DNA evidence in sexual assault cases have proven increasingly difficult to obtain and analyse due to increased condom use. With more interest in alternatives to DNA evidence, prophylactic lubricants, spermicides and residues may be interesting prospects. Current interest in the analysis of prophylactic residues focuses on the evaluation and identification of lubricants and constituents, primarily through gas chromatography or Fourier transform infrared spectroscopy. Though cost-effective methods, extensive sample preparation and destructive modes of analysis remain an area for improvement. As a result, the focus has since shifted to ambient ionization methods that offer adequate sensitivity and reduced sample preparation. The Liquid Microjunction Surface Sampling Probe (LMJSSP) is a versatile ambient ionization source that employs a probe that supports a continuously flushing droplet that extracts analytes when placed in contact with a surface. The analytes are aspirated into the mass spectrometer with a Venturi pressure. In this work we use the LMJSSP to analyse the trace transfer of condom lubricant to different types of fabric (cotton, cotton-spandex, and denim). Furthermore, we examine the sensitivity and storage conditions for the direct analysis method on different swab types (cotton, silicone, and foam). Additionally, Principal Component Analysis (PCA) and Maximally Collapsing Metric Learning (MCML) are utilized for visualization of differentiability of commercially available condom brands including Durex™ and Trojan™, and product subtypes. The results present an interesting multi-disciplinary approach of using a direct liquid extraction ambient ionization technique and machine learning to improve the overall workflow for the analysis of lubricants, swabs and fabrics. Machine learning algorithms were able to differentiate between inherent differences of Durex™ and Trojan™ condoms.

Investigation of the significance of excited species in wave-heated dense non-ideal microplasmas using particle-in-cell Monte Carlo-collision modeling

A computational model for the interaction of a high-pressure microplasma with an electromagnetic wave is presented. A one-dimensional particle-in-cell Monte Carlo collision model is used to investigate the plasma non-ideality effects in a second-stage laser-heated xenon plasma with a comprehensive chemistry mechanism, including excited species. A xenon microplasma at a temperature of 300 K and pressure of 10 bar becomes non-ideal after the laser heating stage with lower ionization and electronic excitation barriers, which makes the presence of excited species important to the plasma generation process. For these conditions, two-step ionization via excited species becomes a major contributor to plasma ionization. We find that full ionization of the plasma is obtained in ∼2 ps when excited species are included in the chemistry model, as opposed to ∼2.5 ps for a chemistry mechanism that does not consider their effect. With excited species, the ionization mode transitions from direct ionization via electron-neutral collisions to direct and stepwise ionization as the plasma generation progresses.

Electron scattering cross sections for the ground and excited states of tin

A comprehensive set of cross sections for electron scattering from the ground and first four excited states of tin has been calculated using the Relativistic Convergent Close-Coupling method. Elastic scattering, momentum transfer, total scattering, and total-inelastic scattering cross sections have been produced for the 5p23P0,1,2, 1D2 and 1S0 states of atomic tin over a projectile energy range of 0.1 eV to 1000 eV. Over the same projectile energy range, state-resolved cross sections for excitations to the 5p2, 5p6s, 5p5d and 5p6p manifolds from the ground and first four excited states of tin are presented. Total single-ionisation cross sections have been calculated which account for the direct ionisation of electrons in the valence 5p and closed 5s shells, as well as indirect contributions from excitation auto-ionisation. These ionisation cross sections are presented for projectile energies up to 1000 eV. Maxwellian rate coefficients have been calculated for all studied transitions over electron temperatures ranging from 0.5 eV to 200 eV and fitted with simple formulas. The fit coefficients are tabulated for use in modelling applications.

Molecular mechanisms of effects of ionizing radiation action. Irradiation effect on protein (literary review)

Target effects (direct and indirect effects of ionizing radiation). When exposed to ionizing radiation, it damages vital intracellular biomolecules which leads to multiple damage to cells and tissues as well as pathophysiological diseases such as inflammation, immunosuppression, etc. Such damage can be caused by direct ionization of biomolecules, but in almost 70% of cases due to indirect radiolysis of intracellular water with the formation of reactive oxygen species and free radicals, which ultimately causes oxidative stress.Non-target effects (abscopal effect, adaptive response, bystander effect, genomic instability). Over the past 25 years, many studies have explored the molecular mechanisms underlying in nontargeted effects (also known as effects not aimed at DNA). It is shown that these effects are the result of a huge dynamic and complex process induced in irradiated cells, transmitted to neighboring cells and, to some extent, to the whole body through activation of the immune system.The irradiation effect on protein. Under the direct action of ionizing radiation on a protein, an electron is knocked out of it, resulting in a defective site devoid of an electron, which migrates along the polypeptide chain due to the transfer of electrons until it reaches a site with increased electron-donor properties. At this point, free radicals arise in the side chains of amino acids. Under the indirect effect of ionizing radiation, the formation of free radicals occurs when protein molecules interact with the products of water radiolysis.

Sub-barrier recollisions and the three classes of tunneling time delays in strong-field ionization

Tunneling ionization is characterized by a negative time delay, observed asymptotically as a specific shift of the photoelectron momentum distribution, which is caused by the interference of the sub-barrier recolliding and direct ionization paths. In contrast, a \textit{Gedankenexperiment} following the peak of the wavefunction shows a positive tunneling time delay at the tunnel exit, considering only the direct ionization path. In this paper, we investigate the effects of sub-barrier recollisions on the time delay pattern at the tunnel exit. We conclude that the interference of the direct and recolliding trajectories decreases the tunneling time delay at the exit by the value equal to the asymptotic time delay maintaining, however, its sizeable positive value. Finally, we discuss the recent experiment [Light: Science \& Applications 11, 1 (2022)] addressing the tunneling time in a modified two-color attoclock setup. The analysis of the experimental findings with our theoretical model indicates the physical necessity to introduce a new time characteristic for tunneling ionization -- the time delay describing the initiation of the tunneling wave packet.

Direct mass spectrometric imaging of document handwriting with laser desorption ionization and post ultraviolet photodissociation

Handwriting represents personal education and physical or psychological states. This work describes a chemical imaging technique for document evaluation that combines laser desorption ionization with post ultraviolet photo-induced dissociation (LDI-UVPD) in mass spectrometry. Taken the advantages of chromophores in ink dyes, handwriting papers were subjected to direct laser desorption ionization without additional matrix materials. It is a surface-sensitive analytical method that uses a low intensity pulsed laser at 355 nm to remove chemical components from very outermost surfaces of overlapped handwritings. Meanwhile, the transfer of photoelectrons to those compounds leads to the ionization and the formation of radical anions. The gentle evaporation and ionization property enable the dissection of chronological orders. Paper documents maintain intact without extensive damages after laser irradiation. The evolving plume resulting from the irradiation of the 355 nm laser is fired by the second ultraviolet laser at 266 nm that is in parallel to the sample surface. In contrast to collision activated dissociation in tandem MS/MS, such post ultraviolet photodissociation generates much more different fragment ions through electron-directed specific cleavages of chemical bonds. LDI-UVPD can not only provide graphic representation of chemical components but also reveal hidden dynamic features such as alterations, pressures and aging.

Search for the interatomic Auger effect in Nitrous Oxide

The interatomic Auger effect following O 1s ionization in N2O has been experimentally investigated using multi-electron coincidence spectroscopy. The expected transition energies have been established by comparison to the measured N 1s−1v−1 core-valence double ionization energies. We describe a procedure to eliminate the background of two competing processes contributing spectroscopic signatures to the same energy range, namely double Auger decay of the O 1s vacancy and direct single-photon double ionization into the N 1s−1v−1 states. While the interatomic Auger transitions could not be successfully isolated, we provide an upper boundary of the transition probability of 0.07% with respect to the dominant single Auger decay after O 1s ionization.