Doubly-charged Ions Research Articles

Qualitative screening and quantitative determination of multiclass water-soluble synthetic dyes in foodstuffs by liquid chromatography coupled to quadrupole Orbitrap mass spectrometry

A LC-Q-Orbitrap HRMS analytical method for both qualitative screening and quantitative determination of 90 synthetic dyes including ten groups of isomers in foods has been established. An in-house synthetic dyes database and characteristic ions were also developed. Based on Q-Orbitrap HRMS, mass spectrum and fragmentation patterns of synthetic dyes were studied, which indicated that double charged ions were usually the main precursor ions. Matrix effects were successfully eliminated by the C18 d-SPE clean-up coupled with dilute and shoot approach with methanol–water (1:4, v/v) in 100-fold. For most of the compounds, mean recoveries were satisfactory between 70% and 120% with RSD < 20% at three spiked level in the range of 0.025–1.0 mg/kg. The screening detection limits ranged from 0.025 − 1.0 mg/kg. Method validation showed that the established method was efficient, rapid and high-throughput, which has been successfully applied to the monitoring of these water-soluble synthetic dyes in foods.

Generation of a Metal Ion Beam Using a Vacuum Magnetron Discharge

We have designed, fabricated and characterized an ion source based on a vacuum magnetron discharge. The magnetron discharge is initiated by a vacuum arc discharge, the plasma of which flows onto the magnetron sputtering target working surface. The vacuum arc material is usually the same as that of the magnetron target. The discharges operate at a residual pressure of 3 × 10−6 Torr without working gas feed. Pulses of vacuum arc (30 μs) and magnetron discharge (up to 300 μs) are applied simultaneously. After ignition by the vacuum arc, the magnetron discharge runs in a self-sustained mode. Cu–Cu, Ag–Ag, Zn–Zn, and Pb–Pb pairs of magnetron target material and vacuum arc cathode material were tested, as well as mixed pairs; for example, Cu vacuum arc cathode and Pb magnetron target. An ion beam was extracted from the discharge plasma by applying an accelerating voltage of up to 20 kV between the plasma expander and grounded electrodes. The ion beam collector current reached 80 mA. The ion beam composition, analyzed by a time-of-flight spectrometer, shows that the beam consists mainly of singly-charged (about 90%) and doubly-charged (about 10% current fraction) magnetron target material ions. The ion beam radial current density non-uniformity was as low as ±5% over a diameter of 6.6 cm, which is the diameter of the source output aperture.

Investigation of Resonance-Enhanced High-Order Harmonics by Two-Component Laser-Produced Plasmas

Resonance-enhanced harmonics from laser-produced plasma plumes are an interesting phenomenon, whose underlying mechanism is still under debate. In particular, it is unclear whether the macroscopic dispersion properties of the plasma are the key factors for the formation of the enhancement. To shed light on this problem, we perform experiments with two-component plasmas, in which one of the components (tin) is known to be able to generate enhanced harmonics and the other component (lead) is known for altering the overall dispersion properties of the plasma medium. We compare the harmonics spectra from the plasma of pure tin and the plasma of tin/lead alloy. Depending on the driving wavelength, we observe enhanced harmonics at around 47 or 44 nm in both types of plasmas. The two enhanced regions could be attributed to resonances in singly-charged and doubly-charged tin ions, respectively. Our results indicate that the co-existence of lead plasma does not destroy the presence of the enhanced harmonics of tin plasma, and it seems to suggest that the macroscopic properties of the plasma are not the origin of the resonance-enhanced harmonics in tin.

Development of a novel starch-based dietary fiber using glucanotransferase.

In this study, a glucanotransferase from prokaryotic Azotobacter chroococcum NCIMB 8003 was recombinantly expressed and its biochemical characteristics and bioconversion ability for starch were investigated. The purified enzyme has the optimum activity at 55 °C and pH 6.5-7.0, as well as a melting temperature of 62 °C. The double-charged ion Ca2+ stimulated the activity of the enzyme by approximately 2.4 times. The kinetic parameters and specificity analysis revealed that this glucanotransferase had a higher affinity for high-amylose starch. During the transglycosylation reaction, the starch molecule was converted into a relatively small polymer with a narrow size distribution. For the enzyme modification of high-amylose starch for 72 h, the amount of α-1,6 linkages increased from 1.9% to 22.7% and the content of resistant starch (RS) increased from 3.18% to 17.83%. In addition, the fine structure displayed the reuteran-like highly branched glucan linked by single linear α-1,6 linkages and α-1,4/6 branching points. These results revealed that a promising prebiotic dietary fiber was synthesized from starch with glucanotransferase modification.

Mathematical modelling of transport of single and double charged ions through layered ion exchange membranes

Monovalent selectivity of ion exchange membranes is important for such areas as hardness removal, stabilization of mining waters and fining of foods. The modern approach to the creation of monovalent selective ion exchange membranes is layer-by-layer adsorption of polyelectrolytes onto a membrane surface, which showed significant improvement in comparison with previously used approaches, most notably in comparison with the creation of a single thick layer of polyelectrolyte. Despite the practical importance, the mechanism of improvement in selectivity is unknown. Knowledge of the distribution of ions within the membrane and adjacent layers of solution would answer the question of the mechanism, but such information is unobtainable through the experiment. Hence we develop the 1D mathematical model based on Nernst-Planck-Poisson equations to describe the fluxes and the concentrations of single and double charged ions, as well as potential drop / current density through the ion exchange membrane. In this paper we formulate the problem and list experimentally determined parameters. Results of calculations will be compared with experimentally recorded I-V and V-t curves.

Modified planar sensors for determination of some cephalosporin antibiotics in biological and medicinal media

Pluripotential cephalosporin antibiotics of different generations active against Gram-negative bacteria are used when treating urinary tract infections, mild and moderate pyelonephritis, acute otitis in children, etc. Rapid determination of cephalosporin antibiotics in the biological fluids is important to evaluate physiological and biochemical processes resulting from their metabolism in a human organism. Planar potentiometric sensors of different types — unmodified and modified with polyaniline (0.3 – 1%), NiZnFeO nanoparticles, and their binary mixes — are developed on the basis of associates of tetradecylammonium (TDA) with complex compounds silver (I) — β -lactam [Ag (I) – ( β -lac) 2 ] which are sensitive to some cephalosporin antibiotics, i.e., cefazoline (Cef), cefuroksime (Cefur) and ceftriaksone (Ceftr). In the sensors of type I, electrode-active components (EAC) and modifiers were added to carbon-containing ink, whereas in type II sensors the polyvinylchloride plasticized unmodified and modified membranes based on [Ag 2 (Ceftr) 2 ] 2 · 2TDA were used. Electroanalytic and operational characteristics of unmodified and modified planar sensors in aqueous solutions of cefazoline, cefuroxime, ceftriaxone and against the background of oral fluid were estimated. It is shown that introduction of the modifiers into sensor membranes leads to stabilization of their potential, increases angular coefficients of electrode functions, decreases the antibiotic detection limit to 1.7 Ч 10 –5 M, reduces the response time and potential drift. Nanoparticles of NiZnFeO appeared to be the most effective modifier. For the sensors of type II linearity of electrode functions is observed in the range of ceftriaxone concentrations of 3.1 Ч 10 –5 – 0.1 Ч 10 –1 M. Depending on the content of the electrode active components in the membrane phase of the unmodified planar sensors, the values of the angular coefficients of the electrode functions vary within 25 – 27 mV/p C and correspond to the values of the non-static value for doubly-charged ions. The linearity intervals of sensor electrode functions are identical at all EAC concentrations under study; as Ceas increases, potential drift and response time decreases. The developed planar sensors were used for determination of cephalosporin antibiotics in model aqueous solutions, medicinal preparations and oral fluid.

Doubly-Charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals.

The fundamental mechanism underlying negative-ion catalysis involves bond-strength breaking in the transition state (TS). Doubly-charged atomic/molecular anions are proposed as novel dynamic tunable catalysts, as demonstrated in water oxidation into peroxide. Density Functional Theory TS calculations have found a tunable energy activation barrier reduction ranging from 0.030 eV to 2.070 eV, with Si2−, Pu2−, Pa2− and Sn2− being the best catalysts; the radioactive elements usher in new application opportunities. C602− significantly reduces the standard C60− TS energy barrier, while graphene increases it, behaving like cationic systems. According to their reaction barrier reduction efficiency, variation across charge states and systems, rank-ordered catalysts reveal their tunable and wide applications, ranging from water purification to biocompatible antiviral and antibacterial sanitation systems.

Biophysical mechanism for zinc as an anticancer agent

The experimental observation that an increase in calcium above micromolar concentrations results in a slowing or stopping of anaphase-A motion is evidence for an electrostatic mechanism for poleward mitotic chromosome motions. Specifically, higher concentrations of doubly-charged calcium ions screen negative charges at microtubule free “plus” ends at kinetochores and at centrosomes. These structures normally interact with positive charges at kinetochores and positively charged microtubule free ends vicinal to centrosomes to generate poleward force. As with calcium ions, doubly-charged zinc cations can also shield these negative charges, thereby interfering with force generation for anaphase-A chromosome motion, aborting mitosis. Experimental evidence reveals that dysregulation of free cytosolic zinc homeostasis contributes to cancerous transformation. Treatment of cancers by increasing zinc concentration has unknowingly been accomplished by utilizing zinc ionophores to facilitate zinc transport across the plasma membrane, revealing an inverse relationship between malaria incidence – and malaria treatment with zinc ionophores – and cancer mortality. Here we hypothesize a biophysical mechanism for cancer therapy employing zinc supplementation enhanced by zinc ionophores.

Experimental Study of Space Charge Structure and Expansion Dynamics of Laser Ablation Plasma

Using the method of spectrally selective photorecording in a nanosecond temporal resolution, the distribution of neutral atoms and single- and double-charged gallium ions in a plasma plume is investigated under the conditions of laser ablation of a gallium-indium target and so is the expansion dynamics of both components and the plume as a whole. The expansion velocity of a neutral atomic component of the plume is found. The expansion velocity of the glow boundary and the shift velocity of the glow intensity maximum are found to be close to 8.5∙103 and 6∙103 m/s, respectively. The kinetic energy range, corresponding to these values for the gallium atoms (13–26 eV) is quite consistent with the position of local maximum measured earlier from the energy distribution of single-charged gallium ions.

Electrochemical Deposition of NiFe Alloy at a Temperature of 70°C

The heating of chloride electrolyte to a temperature of 70°C excludes anomalous codeposition of NiFe alloy components as a result of a change of the nature of discharging iron ions from the single-charged (Fe2+Cl–)+ ions to the double-charged ions. Chloride electrolyte with a pH value corrected by hydrochloric acid provides the electrochemical deposition of permalloy at a concentration ratio cNi/cFe = 4.26. Conventional (not anomalous) codeposition of nickel and iron is observed also in the dilute solutions at room temperature due to their virtually complete dissociation.

THERMODYNAMIC CALCULATIONS OF ION-EXCHANGE SORBATION OF IRON IONS ON CLINOPTYLOLITE

Increased content of iron in water, impairs its quality and, in many cases, makes it impossible to use such water for home and industrial needs. Although iron is the basis of many biochemical processes in the human body, its excess content can have many negative effects. According to WHO standards, the permissible content of iron in drinking water is 0.3 mg/l. The high iron content is observed in the natural waters of many regions ofUkraineand other countries. This phenomenon is often not connected with anthropogenic influence but caused by the peculiarity of the geomorphological structure of the area. Therefore, the development of new and improvement of the existing methods of water desalination (iron removal) is a pressing issue.The methods of water desalination can be divided into four different categories: traditional techniques, biological methods, processes based on membrane technologies, and methods based on nanotechnologies. Among the traditional methods, one of the main approaches is ion-exchange.In this work, quantum-chemical calculations of iron ion exchange processes on clinoptilolite (structural type HEU) and its modified forms are carried out. The calculations used the software xTB. The semi-empirical GFN2-xTB method was chosen as the primary method, based on a modified density functional theory, namely the Density Functional based Tight Binding (DFTB) approach.Iron atoms were considered in oxidation states 2 and 3. Also, they considered the possible electronic states of each of the ions and sorption products (low spin state - multiplicity 1 and 2 in the case of Fe2+ and Fe3+, respectively, and high spin state - multiplicity 5 and 6 in the case of Fe2+ and Fe3+, respectively).Fe(H2O)6n+ + Zeo-X(H2O)a = X(H2O)6 + Zeo-Fe(H2O)b + y (H2O)6 (1) The thermodynamic calculations of the ion exchange (1) indicate the possibility of the forward reaction run (ΔG &lt;0). In the case of monovalent sodium exchange ions, ion exchange is possible both Fe2+ and Fe3+. In the case of double-charge calcium exchange ions, ion exchange is possible for Fe3+ ions. Ion exchange involving Fe3 + ions is much more energetically favorable than Fe2+ ions.

Identification of impurities in nafamostat mesylate using HPLC-IT-TOF/MS: A series of double-charged ions

Nafamostat mesylate is a serine protease inhibitor used in the treatment of acute pancreatitis. The impurities in nafamostat mesylate, the active pharmaceutical ingredient (API), were profiled via high performance liquid chromatography tandem ion trap coupled with time-of-flight mass spectrometer (HPLC-IT-TOF/MS). The chromatography was performed on an ACE-3 C18 column (200 mm × 4.6 mm, 3 μm) using methanol and 0.1% formic acid in purified water as mobile phase at a flow rate of 1.0 mL/min. The ions were detected by IT-TOF/MS with a full-scan mass analysis from m/z 100 to 800. In total, eleven impurities were detected in nafamostat mesylate API. The impurity profile was estimated based on the HPLC-IT-TOF/MS data, including accurate masses, MSn fingerprints of fragmentation pathways and a series of double-charged ions. Finally, seven impurities were identified and reported for the first time. The results will provide technical support for the quality control and clinical safety of nafamostat mesylate.

Modeling of vacuum arc plasmas in anode spot or anode plume mode taking into account multiple ion components

This work investigates the arc behaviors with CuCr25 electrodes considering anode vapor using a magneto-hydro-dynamic model. Different kinds of components are considered including ions (Cu and Cr) with different charge numbers, electrons, and atoms (Cu and Cr). The effect of the anode sheath is also considered. The density distributions of these components are analyzed and compared with the experiments during the anode spot mode and the anode plume mode. Simulation results show that the anode vapor can enter the arc column forming a cool and poorly conducting region (i.e., neutral atom vapor area, NAVA) under high anode temperature. Atoms and single-charged ions mainly gather near each electrode. The highest double-charged ion density can be seen in front of the NAVA. Triple-charged ion density is negligibly low and reaches its maximum where the electron temperature is high. Cr is more likely to be ionized to a higher ionization level compared with Cu. Our results agree with experimental measurements of density distributions of different components and plasma temperature.

In situ calcium isotopic ratio determination in calcium carbonate materials and calcium phosphate materials using laser ablation-multiple collector-inductively coupled plasma mass spectrometry

This study presents a highly precise and accurate Ca isotope analysis method using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) in calcium carbonates and calcium phosphates. High-sensitivity cones and nitrogen gas were used to improve the performance of the LA-MC-ICP-MS. The experiment results show that at the N2 mode, the signal intensity of 44Ca+ in the high-sensitivity cones (Jet + X cones) was 5-fold higher than that in the normal cones (S + H cones), while the polyatomic interferences of 40Ar1H1H+ and 40Ar16O+ in the high-sensitivity cones were suppressed by factors of 6.1 and 10.6, respectively, after the addition of 8 ml min−1 N2. The combination of high sensitivity cones and N2 addition did not increase the production of double charged ions. Additionally, the interference correction of doubly charged Sr ions was investigated in detail. The experiment results demonstrate that the concentration ratio of Sr to Ca (represented as I87Sr++/I44Ca+), the 87Sr/86Sr ratio and the mass fractionation factor of Sr (fSr) during the measurement process were key parameters for in situ Ca isotope ratios analysis. The threshold values of these key parameters were evaluated and are recommended to ensure an accurate correction of doubly charged Sr ions. Using the optimized instrumental conditions and correction strategies, an excellent within-run precision (<0.06‰, 2SE) and external reproducibility (<0.15‰, 2SD) for the microanalysis of δ44/42Ca915b were obtained in natural calcium carbonates and calcium phosphates. These precisions are better than the values previously reported in the literature regarding using LA-MC-ICP-MS. Matrix effects were observed during the in situ Ca isotope analysis among calcium carbonates, hydroxy calcium phosphates and igneous apatites. Using the matrix-matching standards, accurate δ44/42Ca915b values in natural materials with various matrices were achieved, confirming the availability of the proposed method to resolve the spatial variation of δ44/42Ca in natural materials.

Synthesis and characterization of organic-inorganic cross-linked membrane for the separation of mono-charged and double charged ions using UV irradiation

Currently, it is commonly observed that ion flux decreases as the separation performance of cation exchange membranes between mono- and double-charged ions improves. Therefore, cation exchange membranes with simultaneously excellent separation performance and high ionic flux must be developed. Herein, a series of pure and organic-inorganic cross-linked membranes were synthesized using UV irradiation. The synthetic membranes showed high ion-exchange capacity (IEC) and large ion flux. The organic-inorganic membranes achieved excellent mechanical properties, thermal stability, and separation properties owing to the addition of SiO2. When the silica content was 4 wt%, the three ionic perm-selectivity showed their highest separation performances of 1.70 ± 0.03(PKNa), 5.84 ± 0.04(PKMg), and 25.67 ± 0.04 (PKCa), representing an increase of 70% (PKNa), 279.22% (PKMg), and 1236.98% (PKCa) compared than those of pure membrane. In addition, the limiting current density of the prepared organic-inorganic membranes was all >8.74 mA/cm2, higher than that of commercial membrane. According to these excellent performances, the prepared membranes showed good prospects for separation performance of cation exchange membranes. The addition of a proper amount of inorganic particles can improve the ion perm-selectivity between mono- and double-charged ions.

Highly Ionized Arc He Plasma: Nonequilibrium, Nonideality, and Kinetics

Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for a plasma with an electron concentration above 1016 cm–3. This is found to be caused by transverse plasma nonuniformity and density effects. The plasma quasistatic microfield destroys the upper electron levels of He atoms, and the radial ambipolar diffusion flow transports the charged particles from the narrow (1–2 mm) plasma channel on the chamber wall. In the distribution of atoms and the ions over the excited levels, strong ionization nonequilibrium and a large gap of the ground state are observed; these factors cause substantial difficulties in the spectral diagnostics of the plasma parameters due to the inapplicability of the relations taking into account the equilibrium conditions. A method is proposed to measure the concentration of double-charged ions He++ (α particle), which is inaccessible by direct spectral registration, as well as a simple kinetic model of strongly ionized He plasma with the use of a modified diffusion approximation; the model adequately describes the plasma parameters.

Axisymmetric plasma plume characterization with 2D and 3D particle codes

The expansion of a rarefied axisymmetric plume emitted by a plasma thruster is analyzed and compared with a 3D Cartesian-type and a 2D cylindrical-type simulation code, both based on a particle-in-cell formulation for the heavy species and a simple Boltzmann-type model for the electrons. The first part of the paper discusses the 2D code numerical challenges in the moving of particles, their generation within the cells, and the weighting to the nodes, caused by the radial non-uniformity and the singular and boundary character of the symmetry axis. The second part benchmarks the 2D code against the 3D one for a high-energy, unmagnetized plume with three major species populations (injected neutrals, singly-charged and doubly-charged ions) and three minor species populations (constituted by particles coming from collisional processes, such as the charge-exchange reactions). The excellent agreement found in the results proves that both plume codes are capable of simulating, with a reasonable noise level, heavy particle populations differing by several orders of magnitude in number density. For simulations with a comparable level of accuracy, the 2D code presents a ten-fold gain in computational cost, although the symmetry axis remains its weakest point, due to particle depletion there and the related weighting noise.

Cationization and fragmentation of molecular ions sputtered from polyethylene glycol under gas cluster bombardment: An analysis by MS and MS/MS

In secondary ion mass spectrometry (SIMS), the detection of large organic molecules is accomplished using cluster ion bombardment. Ion formation often proceeds via cationization, through the attachment of (alkali) metal ions to the molecule. To study this process and its efficiency, the emission of secondary ions sputtered from polyethylene glycol (PEG 3000) mixed with Na trifluoroacetic acid (NaTFA) was investigated for 10 keV Ar2000+ cluster irradiation by MS and MS/MS. Apart from cationized molecular ions [Mn+Na]+ (with repeat units n of up to ∼80), fragment species were found corresponding to the loss of a water moiety or of two H atoms, respectively. In addition, an abundant flux of doubly-charged molecular ions, [Mn+2Na]2+ was observed in the mass spectra. Quite surprisingly, even triply-charged ions [Mn+3Na]3+ were detected. The ratio of [Mn+2Na]2+ to [Mn+Na]+ increases with increasing size of the molecules and reaches unit for n ∼70. The yield of [Mn+Na]+ ions around m/z 3000 depends strongly on the molecular composition ratio of NaTFA/PEG in the samples and can be enhanced by a factor of 50 by increasing the Na content. In MS/MS operation, [Mn+Na]+ and [Mn+2Na]2+ ions were subjected to collisions with Ar atoms; for sufficiently high collision energies, dissociation leads to characteristic fragment species. Collisions of [Mn+2Na]2+ assert the existence of doubly-charged ions in the sputtered flux. Collision cross sections were found to amount to ∼(0.5–1)×10−15 cm2 for center-of-mass collision energies of ∼3 eV.

A study of the aromaticity of heteroannelated cyclooctatetraene derivatives.

The aromaticity of the rings of thiophene, pyrrole, furan, and benzene annelated cyclooctatetraene (COT) derivatives and of their double charged ions was studied using the graph-theoretical theory of aromaticity. On the basis of topological resonance energy, it was found that the global aromaticity is dependent upon on the arrangement of heteroatoms in the given molecule. Relative stability of these molecules when in different charged states can been explained in terms of the topological charge stabilization rule. We expect that fusing the COT ring with an increasing number of aromatic rings will lead to an increase in the aromaticity of the molecule. According to the bond resonance energy (BRE) and circuit resonance energy (CRE) indices, local antiaromaticity of the COT ring is weakened as the number of fused rings increases, and these changes play a significant role in the global aromaticity of the molecule. For some compounds, our BRE and CRE indices do not predict the same order of magnitude of the local aromatic character of certain rings that the nucleus independent chemical shift (NICS(0) and (NICS(1)) methods predict. Finally, for the available compounds, correlations between the diatropic and paratropic chemical shifts of the protons and our ring current results were analyzed and good agreement was found.

Propidium ion enters viable cells with high membrane potential during live-dead staining

Live-dead staining with propidium iodide can give erroneous results for bacteria showing high membrane potentials. We observed uptake of propidium ions across intact cell membranes for Dinoroseobacter shibae and Bacillus subtilis. Apparently, a high membrane potential facilitates breakthrough of the double-charged propidium ion and can mark viable cells as dead.