Total Number Of Ions Research Articles

Utilizing Artificial Neural Networks in MATLAB to Achieve Parts-Per-Billion Mass Measurement Accuracy with a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

Fourier transform ion cyclotron resonance mass spectrometry has the ability to realize exceptional mass measurement accuracy (MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped in the ICR cell for a particular measurement, as well as relative ion abundance of a given species. Artificial neural network calibration in conjunction with automatic gain control (AGC) is utilized in these experiments to formally account for the differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. In addition, artificial neural network calibration is used to account for both differences in total ion population in the ICR cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion level.

Electrosorption selectivity of ions from mixtures of electrolytes inside nanopores

Grand canonical Monte Carlo (GCMC) simulations are employed to study the selective electrosorption of ions from a mixture of symmetric and asymmetric electrolytes confined in pores and results are compared to experimental observations obtained via cyclic voltammetry and batch electrosorption equilibrium experiments. GCMC simulations have the advantage over other Monte Carlo methods to unambiguously quantify the total number of ions in the pore solution. The exclusion parameter and selectivity factor are used to evaluate the selective capacity of pores toward different ionic species under various conditions. The number of coions inside the pore solution is determined by the proportion of different counterions present in the double-layer region. Because of the competitive effects resulting from asymmetries in charge and size associated with different ions, the electrosorption selectivity of small monovalent over large divalent counterions first decreases with increasing surface charge, passes through a minimum, and then increases with further increase in surface charge. At low and moderate surface charge densities, the fact that large divalent counterions preferentially screen the surface charge has a strong effect on pore occupancy; whereas at a very high surface charge density, size-exclusion effects dominate and determine the accessibility of different ions into the pores. Therefore, electrosorption selectivity of ions from a mixture of electrolytes could, in principle, be achieved via tuning the electrical double-layer formation inside the pores through the regulation of surface charge tailored for different ion characteristics. The findings of this work provide important information relevant to ion selectivity during separation processes and energy storage in supercapacitors.

Examining the fragmentation of 158 A GeV lead ions on copper target: Charge-changing cross sections

A stack of plastic CR-39 Track Detectors were exposed to 158 A GeV 207Pb ions at the CERN-SPS beam facility. The exposure of stack was performed at normal incidence with a fluence of about 1500 ions / cm 2 . The total number of lead ions in each spill was about 7.8 × 10 4 with eight spills on each stack. For the stack with the Cu target, the lengths of etched cones on one face of the CR-39 detectors (before and after the target) were measured. Using these measurements and charge identification methodology in CR-39 track detectors, total and partial charge changing cross sections of 158 A GeV Pb 82 + ions on Cu and CR-39 targets are determined in the charge region 63 ⩽ Z ⩽ 82 . The possibilities of presence and absence of odd–even effect in measured partial charge changing cross sections of 158 A GeV Pb ions for Cu and CR-39 targets are described. The charge resolution ( σ Z ) achieved in the present experiment is ∼ 0.18 e –0.21e. The analysis of discrepancies between our experimental results and other published results for the identical reaction is also presented.

Enhancement of Protein Sensitivity for MALDI Imaging Mass Spectrometry After Chemical Treatment of Tissue Sections

MALDI imaging mass spectrometry (IMS) has become a valuable tool for the investigation of the content and distribution of molecular species in tissue specimens. Numerous methodological improvements have been made to optimize tissue section preparation and matrix deposition protocols, as well as MS data acquisition and processing. In particular for proteomic analyses, washing the tissue sections before matrix deposition has proven useful to improve spectral qualities by increasing ion yields and the number of signals observed. We systematically explore here the effects of several solvent combinations for washing tissue sections. To minimize experimental variability, all of the measurements were performed on serial sections cut from a single mouse liver tissue block. Several other key steps of the process such as matrix deposition and MS data acquisition and processing have also been automated or standardized. To assess efficacy, after each washing procedure the total ion current and number of peaks were counted from the resulting protein profiles. These results were correlated to on-tissue measurements obtained for lipids. Using similar approaches, several selected washing procedures were also tested for their ability to extend the lifetime as well as revive previously cut tissue sections. The effects of these washes on automated matrix deposition and crystallization behavior as well as their ability to preserve tissue histology were also studied. Finally, in a full-scale IMS study, these washing procedures were tested on a human renal cell carcinoma biopsy.

Application of the statistical test of equivalent pathways (STEP) method to the triple quadrupole mass spectrometer

Recently, we demonstrated a new method, STEP (Statistical Test of Equivalent Pathways) analysis, which differentiates first-generation product ions (primary product ions) from second-generation product ions (secondary product ions) obtained in tandem mass spectrometric (MS/MS) experiments on a quadrupole ion trap mass spectrometer. The study presented here defines how to adapt the STEP method to a more routinely used mass analyzer, the triple quadrupole. New ion activation conditions were developed to adapt the STEP method to the triple quadrupole mass spectrometer using peptides and carbohydrates. The application of this method to the triple quadrupole is useful because it provides an efficient approach to differentiate primary and secondary ions on this instrument. Out of the total number of ions that were subjected to the STEP analysis, this method correctly identified 96% of ions as primary or secondary, indicating that this analysis is effective for carbohydrates and peptides undergoing collision-induced dissociation (CID) on a triple quadrupole mass spectrometer.

The crystal structure of meurigite

The crystal structure of meurigite, ideally [K(H 2 O) 2.5 ][Fe 8 3+ (PO 4 ) 6 (OH) 7 (H 2 O) 4 ], monoclinic, C2/c, a = 29.018(5), b = 5.1892(6), c = 19.695(3) Å, β = 106.987(1)°, Z = 4, from the Santa Rita mine, New Mexico, has been solved and refined to R 1 = 4.69%, wR 2 = 12.6% using 3325 unique [Fo > 4σ(F o )] reflections collected using a Bruker 6000 SMART CCD diffractometer and synchrotron radiation of wavelength 0.41328 Å. The structure of meurigite is a framework consisting of face-sharing octahedral Fe 2 3+ O 9 dimers, which are linked by sharing corners with corner-sharing dimers and isolated Fe 3+ O 6 octahedra to form thick slabs of octahedra parallel to the a-c plane. PO 4 tetrahedra further link octahedra within the slabs and also link slabs to one another perpendicular to the a-c plane. Relatively large channels through the framework along the b axis contain disordered K atoms and H 2 O molecules, which take part in two overlapping arrays. Partial vacancies in the Fe and P sites may account for discrepancies between the empirical and ideal chemical formulas. Packing considerations suggest that the empirical formula should be based on the total number of large ions (K + Na + O = 38.5 per formula unit), which for the chemical analysis provided in the original description yields [(K 0.91 Na 0.03 ) Σ0.94 (H 2 O) 2.56 ] Σ3.50 [(Fe 3+ 7.52 Al 0.17 Cu 0.03 ) Σ7.72 (PO 4 ) 5.48 (CO 3 ) 0.21 (OH) 7.20 (H 2 O) 5.23 ]. The meurigite structure is related to those of other fibrous ferric phosphates with 5 Å fiber axes and shows a particularly close relationship with the structure of dufrénite. Crystal chemical evidence suggests that, even if meurigite and phosphofibrite are isostructural, phosphofibrite may qualify as a distinct species based upon its low K content (<0.5 apfu based on a recalculation of the original chemical analysis).

Rapid He ii→He i recombination and radiation arising from this process

Abstract Recombination of the primordial helium plasma (He ii → He i, z≃ 1500–3000) is considered. This process has an effect on the cosmic microwave background radiation (CMBR) anisotropy and CMBR spectrum distortion. In this work the influence of neutral hydrogen on the kinetics of He ii → He i recombination is investigated in the framework of the standard cosmological model. It is shown that a small amount of neutral hydrogen (a fraction 10−5–10−2 of the total number of hydrogen ions and atoms) leads to the acceleration of He ii → He i recombination at z≲ 2000, and at z≲ 1600 quasi-equilibrium He ii → He i recombination (according to the Saha formula) becomes valid.

Parts-per-billion mass measurement accuracy achieved through the combination of multiple linear regression and automatic gain control in a Fourier transform ion cyclotron resonance mass spectrometer.

Fourier transform ion cyclotron resonance mass spectrometry has the ability to achieve unprecedented mass measurement accuracy (MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped in the ion cyclotron resonance (ICR) cell for a particular measurement. Even through the use of automatic gain control (AGC), the total ion population is not constant between spectra. Multiple linear regression calibration in conjunction with AGC is utilized in these experiments to formally account for the differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. This ability allows for the extension of dynamic range of the instrument and for the mean MMA values to remain less than 1 part-per-million (ppm). In addition, multiple linear regression calibration is used to account for both differences in total ion population in the ICR cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion (ppb) level.

Relative information content and top-down proteomics by mass spectrometry: utility of ion/ion proton-transfer reactions in electrospray-based approaches.

Computer simulations of electrospray ionization (ESI) and collision-induced dissociation (CID) experiments were employed to examine the informing power associated with "top-down" proteomics implemented with some commonly used mass analyzers, i.e., the quadrupole ion trap (QIT), the Fourier transform-ion cyclotron resonance mass spectrometer (FT-ICRMS), and the time-of-flight (TOF) mass spectrometer. Using a ratio of the separated (or resolved) peaks to the total number of predicted peaks as a measure of informing power, the ESI-MS simulation of a mixture of proteins showed that the FT-ICRMS exhibited the highest informing power among the three instruments being studied, with the QIT giving the lowest informing power, which was expected from the analysis of the "component capacity" of the three approaches. Also as expected on the basis of resolving elements per component, a dramatic increase in the informing power of the approach was obtained when ion/ion proton-transfer reactions were used to reduce the number of peaks and to minimize overlap between ions of different mass and charge but similar mass-to-charge ratio. With the assumptions made in this study, the informing power of the TOF + ion/ion approach rivaled or even exceeded that of the FT-ICRMS approach, despite significantly lower mass resolution. This result stemmed from both a reduction in the number of peaks and their dispersion over a much wider range of mass-to-charge ratios. Similar results were obtained from the CID simulation, where the informing power of different approaches was evaluated on the basis of the ratio of the number of ions for which a mass could be determined unambiguously to the total number of ions in the spectra.

Measurement of storage time, estimation of ion number and study of absorption line profile in a Paul trap

Europium (Eu+) ions were confined in a Paul trap and detected by non-destructive method. Storage time of Eu+ ions achieved in vacuum was improved by orders of magnitude employing buffer gas cooling. The experimentally detected signal was fitted to the ion response signal and the total number of ions trapped was estimated. It is found that the peak signal amplitude as well as the product of FWHM and the peak signal amplitude is proportional to the total number of trapped ions. The trapped ion secular frequency was swept at different rates and its effect on the absorption line profile was studied both experimentally and theoretically.

Single Molecule Force Spectroscopy of Salt-dependent Bacteriophage T7 Gene 2.5 Protein Binding to Single-stranded DNA

The gene 2.5 protein (gp2.5) encoded by bacteriophage T7 binds preferentially to single-stranded DNA. This property is essential for its role in DNA replication and recombination in the phage-infected cell. gp2.5 lowers the phage lambda DNA melting force as measured by single molecule force spectroscopy. T7 gp2.5-Delta26C, lacking 26 acidic C-terminal residues, also reduces the melting force but at considerably lower concentrations. The equilibrium binding constants of these proteins to single-stranded DNA (ssDNA) as a function of salt concentration have been determined, and we found for example that gp2.5 binds with an affinity of (3.5 +/- 0.6) x 10(5) m(-1) in a 50 mm Na(+) solution, whereas the truncated protein binds to ssDNA with a much higher affinity of (7.8 +/- 0.9) x 10(7) m(-1) under the same solution conditions. T7 gp2.5-Delta26C binding to single-stranded DNA also exhibits a stronger salt dependence than the full-length protein. The data are consistent with a model in which a dimeric gp2.5 must dissociate prior to binding to ssDNA, a dissociation that consists of a weak non-electrostatic and a strong electrostatic component.

Role of the static pressure in experiments on flow control by means of surface capacitor discharges

The effect of the static pressure on the reaction force exerted on a plate above whose surface a gas flow has been induced by exciting a capacitor (barrier) discharge is investigated. In the experiments the discharge was restructured so that the reaction force and the corresponding momentum entrained by the neutral flow increased when the pressure was reduced from atmospheric pressure to 200 Torr, the power supplied to the discharge being fixed. The charge exchange effect is of importance for the formation of the resulting gas flow. It is shown that under the experimental conditions the effect of an increase in the force with decrease in pressure is associated with an increase in the plasma volume ahead of the electrodes and the total number of ions in this volume.

57Fe Mössbauer spectroscopy studies of Sr2Fe1−x Cr x Mo1−x W x O6 double perovskite compounds

Polycrystalline double perovskites Sr2Fe1−x Cr x Mo1−x W x O6 with x=0, 0.05, 0.10, 0.15, 0.20, and 0.30 have been prepared by sold state reactions. A continuous decrease of the tetragonal unit cell parameters α and c with increasing x values is observed. The highest Curie temperature T c =426 K is recorded for the x=0.10 compound. 57Fe Mossbauer spectroscopy measurements indicate a non-integral electronic configuration of ≈3d5.3 for the Fe ions at the ordered double perovskite structure for x≤0.20, which reaches ≈3d5.4 for x=0.30. Fe-Mo/W anti-site and anti-phase boundary defects are observed in all samples in equal concentrations of around 3% of the total number of Fe ions in their structure.

Energy balance in laser ablation of metal targets

Laser-generated plasma was induced on metallic targets glued to a piezoelectric microphone and placed between the plates of a planar charged capacitor. The plasma generates a temporal redistribution of electric charge on the plates that can easily be measured by a resistor connected to the ground plate; this signal is proportional to the total number of ions removed by breakdown. Both the absorbed and scattered energies were simultaneously monitored by the photoacoustic signal and an energy meter. From these signals it was possible to determine the energy involved in each of the processes. Just above the ablation threshold most of the delivered energy is absorbed and the acoustic signal prevails compared to other contributions. Above this region, the electric signal, which is proportional to the energy involved in the ablation process, becomes dominant.

Do intermolecular interactions reflect in sound velocity?

A new attempt in acoustical investigations of interactions between components of liquid solution is presented and tested. It was shown, basing on very simple assumptions and relatively simple experiment, that changes in the concentration dependences of the adiabatic compressibility (calculated from sound velocity and density data) are influenced by intermolecular interactions occurring in solutions. However, it was also shown that these changes are not very strong and the strongest are caused by processes, where the total number ofions and/or their charge density are changing. We also suggest that for some weak association-like processes the compressibility can remain almost undisturbed and, consequently, not sensitive for them.

Aspirated capacitor measurements of air conductivity and ion mobility spectra

Measurements of ions in atmospheric air are used to investigate atmospheric electricity and particulate pollution. Commonly studied ion parameters are (1) air conductivity, related to the total ion number concentration, and (2) the ion mobility spectrum, which varies with atmospheric composition. The physical principles of air ion instrumentation are long established. A recent development is the computerized aspirated capacitor, which measures ions from (a) the current of charged particles at a sensing electrode, and (b) the rate of charge exchange with an electrode at a known initial potential, relaxing to a lower potential. As the voltage decays, only ions of higher and higher mobility are collected by the central electrode and contribute to the further decay of the voltage. This enables extension of the classical theory to calculate ion mobility spectra by inverting voltage decay time series. In indoor air, ion mobility spectra determined from both the voltage decay inversion, and an established voltage switching technique, were compared and shown to be of similar shape. Air conductivities calculated by integration were: 5.3±2.5 and 2.7±1.1fSm−1, respectively, with conductivity determined to be 3fSm−1 by direct measurement at a constant voltage. Applications of the relaxation potential inversion method include air ion mobility spectrum retrieval from historical data, and computation of ion mobility spectra in planetary atmospheres.

Effect of the Solvent Flow Rate on the Ionization Efficiency in Atmospheric Pressure Photoionization-Mass Spectrometry

In the novel atmospheric pressure photoionization-mass spectrometry the ionization efficiency has been observed to decrease when the solvent flow rate is increased. The effect of the flow rate on the ionization efficiency was studied by comparing the behavior of two analytes, one of which is ionized through charge exchange, the other through proton transfer. Additional information about the ion loss mechanisms was obtained by comparing results obtained with two different APPI ion sources: a Sciex prototype and the Agilent/Syagen APPI source. In addition to the measurements done by using the mass analyzer, the total ion current in the ion source was obtained by measuring the currents of the ions arriving at curtain/end plate and orifice/capillary of the two mass spectrometers. The total ion current measurements showed a significant decrease at high solvent flow rates. Loss of dopant radical cations was thought to be the reason for the signal decrease of the analytes formed through charge exchange. Analytes formed through proton transfer were not as seriously ected by the high solvent flow rates, but some saturation of their signal was nevertheless observed. Loss of photons through absorption by solvent vapor is another mechanism that can be held responsible for a reduction of the total number of ions produced by the APPI source.

Catalytically active species in new metathesis systems [W n+ (Mo n+ )–ionic liquid–olefin]: A quantitative ESR study

For the first time, a quantitative approach is successfully used in the ESR study of new catalysts for olefin metathesis prepared by dissolution of WCl 6 and MoCl 5 in ionic liquids (hmimBF 4, hpyrBF 4, etc.). ESR monitoring of frozen probes taken upon interaction between the phases of an ionic liquid and hex-1-ene permits one to elucidate the key role of isolated paramagnetic complexes of W 5+ and Mo 5+ ions in catalysis. The use of MoCl 5 as a starting reagent opens a way for a quantitative observation of paramagnetic active species in two liquid phases. It is shown that the reaction in the biphasic system proceeds as a heterogeneous catalytic process: virtually all the isolated W 5+ or Mo 5+ species are located in the ionic liquid. The kinetics of formation/accumulation of the isolated paramagnetic W 5+ species at the initial slow step of W 6+ reduction by an olefin agrees closely with the kinetics of metathesis leading to the formation of a C 8 product. No induction period is observed in the case of Mo 5+ ions. The number of the ESR-visible isolated paramagnetic Mo 5+ complexes reaches ∼90% of the total number of molybdenum ions in the sample. Thus, the Mo(V) state of the active sites localized in ionic liquids is responsible for the further catalytic process. The same seems to be true for the W(V) species accumulated in the ionic liquid at the end of the first step of the reaction.

Peak Height Precision in Hadamard Transform Time-of-Flight Mass Spectra

Hadamard transform (HT) time-of-flight mass spectrometry (TOFMS) is a multiplexing technique that offers high duty cycle for the mass analysis of continuous ion sources. The multiplexing advantage is maximized when spectral noise is independent of signal intensity. For conditions in which shot noise predominates, the variance in each peak is a function of the population of all measured species. We develop expressions for the performance of a HT-TOF mass spectrometer based on Poissonian statistics for the arrival times of ions at the detector. These expressions and complementary probabilistic simulations are used to estimate the magnitude of the baseline noise as a function of mass spectral features and acquisition conditions. Experiment validates the predictions that noise depends on the total number of ions in the acquired spectrum, and the achieved signal-to-noise ratio for a given species depends on its relative population. We find that for HT-TOFMS experiments encoded with an n-order binary off-on sequence that contains N=2n−1 elements, the peak height precision, which is the peak intensity divided by its standard deviation, is greater than that of an equivalent conventional TOF experiment by a factor of √N/2 times the square root of the fractional abundance of the peak of interest. Thus, HT-TOFMS is superior to conventional TOF for all species whose fractional abundance Fi exceeds 2/N, which for a typical N value of 2047 corresponds to Fi > 0.001. HT-TOF mass spectra collected at 2500 per second demonstrates the method’s capability of monitoring transient processes not possible by conventional means.

Compression of a cylindrical hydrogen sample driven by an intense co-axial heavy ion beam

The compression of a cryogenic hydrogen cylindrical sample contained in a hollow gold target driven by an intense co-axial uranium beam has been studied. The ion distribution is assumed to be Gaussian in space and parabolic in time. The hydrodynamics of the target is analyzed by means of one- and two-dimensional numerical simulations. A parametric study is performed to achieve the maximum average hydrogen density and temperature as a function of the sample radius, total number of ions and spread of the spatial ion distribution. A window in the beam-target parameters for which hydrogen compression is higher than a factor of 10 and temperature is below 0.2 eV has been found by considering a single bunch that contains 2 × 1011 uranium ions delivered in 100 ns. In this range of high densities and low temperatures, it is expected that hydrogen may become metallic.