Multiply Charged Ions Research Articles

Photochemistry of diethyl ether clusters at 1012 W/cm2: A mass spectrometry and charge density study

Photochemistry of diethyl ether clusters has been studied at discrete laser wavelengths spanning from UV to IR region at intensity ~1012 W/cm2 using time-of-flight mass spectrometry. At 266 nm, singly charged fragments, protonated cluster ions were observed due to multiphoton ionisation of clusters. Further, intra cluster ion–molecule reactions lead to generation of H2+, H3+ ions. In addition, C2+ ions were observed at this wavelength. With increase in laser wavelength to 355, 532 and 1064 nm, systematic increase in charge state of multiply charged atomic ions of oxygen, carbon was observed. Highest observed charge states were O6+, C4+ at 1064 nm. Mass spectrometric study was complemented by charge density measurement, which shows an increasing trend with wavelength supporting efficient ionisation of clusters at longer wavelength. Studies reveal that ionisation is initiated via multiphoton ionisation followed by electron ionisation. The multiple ionisation of diethyl ether clusters predominantly depends on the rate of energisation of electrons in the laser field and Coulomb stability of the cluster has insignificant contribution to the final ionic outcome.

X-ray production and charged-particle acceleration in the irradiation of micro- and nanorod arrays by high-power femtosecond laser pulses

The effect of the size of the rods at the structured silicon target surface on the parameters of the plasma produced when the target is exposed to a high-contrast femtosecond laser pulse with an intensity of 2 × 1018 W cm−2 is investigated. It is shown that irradiation of a target with subwavelength rods (∼ 100 nm in diameter) provides a significant (up to 250 keV) increase in the temperature of hot plasma electrons and their number in comparison with those obtained in the case of a plane target. It was found that in this case the yield of hard X-ray radiation increases several-fold. The observed effect can be attributed to increased absorption and particle motion in a complex field near plasma nonuniformities. It is shown that the presence of rods with a characteristic size of ∼ 1 μm promotes an increase in the production efficiency of multiply charged silicon ions. The result obtained is apparently associated with the radiation penetration between the rods and with collisional ionisation of particles as they fly into vacuum from deeper target layers.

Label-free microRNA detection through analyzing the length distribution pattern of the residual fragments of probe DNA produced during exonuclease III assisted signal amplification by mass spectrometry

Biosensors based on various spectroscopic techniques discriminate the target microRNA (miRNA) from non-target ones with single nucleotide polymorphisms (SNPs) according to the differences in signal intensities which can be caused by other factors besides SNPs. As a result, they are liable to produce false positive results. Herein, we report an attempt to develop a false-positive resistance, sensitive and reliable mass spectrometric platform for miRNA detection. In the proposed platform, the qualitative and quantitative information of the target miRNA was obtained through analyzing mass spectral responses of the multiply charged ions of the residual fragments of the probe DNA produced during exonuclease III assisted signal amplification reaction using an advanced data analysis method. The proposed platform could achieve sensitive and accurate quantitative results for the target miRNA (e.g., miRNA-141) in complex medium with a detection limit of about 1 pM, and unambiguously identify non-target miRNAs with SNPs based on the length distribution patterns of residual fragments of probe DNA. The findings obtained in this study might open an avenue for the design of new miRNA detection methods based on mass spectrometry in combination with various nuclease assisted signal amplification strategies.

Over‐Darkening of Pulsating Aurora

AbstractRecent analyses of high‐time resolution ground‐based optical observations of pulsating aurora (PsA) have reported that the brightness of PsA sometimes decreases below the diffuse background level immediately after the ON phase of the main pulsation finishes. To date, however, the generation mechanism of such an “over‐darkening PsA” is still unclarified. In this study, we investigated the characteristics of the over‐darkening PsA by using simultaneous observations of PsA with an electron multiplying charge coupled device all‐sky camera in Sodankylä, Finland and the Arase satellite. During one of the conjunction events in Scandinavia on March 29, 2017, almost all the PsA pulses showed clear over‐darkening characteristics. By analyzing the 2D all‐sky images at the times of over‐darkening we discovered that over‐darkening areas appeared in the trailing edge of PsA patches and moved in tandem with the poleward propagating patches. It was also found that similar over‐decreasing characteristics were not seen in the chorus data from the wave instruments onboard Arase located at the magnetospheric counterpart of PsA. These results indicate that the over‐darkening PsA is not caused by a temporal variation of chorus at a fixed point, but is produced by a propagation of over‐darkening area with PsA patches. That is, the over‐darkening PsA is a result of compounding effects of spatial structure and recurrent propagation of PsA. The mechanism creating the dark area is still unknown, but the existence of over‐darkening PsA suggests that the temporal variation of PsA is not always a perfect copy of the modulation of lower‐band chorus waves in the magnetosphere.

A Fock space coupled cluster based probing of the single- and double-ionization profiles for the poly-cyclic aromatic hydrocarbons and conjugated polyenes.

Sequential formation of a poly-cyclic aromatic hydrocarbon (PAH) dication in the H I regions of the interstellar medium (ISM) is proposed to be a function of internal energy of the doubly ionized PAHs, which, in turn, is dependent on the single- and double-ionization potentials of the system. This sets a limit on the single- and double-ionization energies of the system(s) that can further undergo sequential absorption of two photons, leading to a dication (PAH+2). Here, we report the single-ionization (I+1) and double-ionization (I+2) energies and the I+2/I+1 ratio for some selected PAHs and conjugated polyenes obtained using the Fock space coupled cluster technique, enabling simultaneous consideration of several electronic states of different characters. The I+2 to I+1 ratio bears a constant ratio, giving allowance to determine I+2 from the knowledge of single-ionization (I+1) and vice versa. Our observations are in good agreement with the established literature findings, confirming the reliability of our estimates. The measured single- and double-ionization energies further demonstrate that the sequential formation and fragmentation of a PAH dication in the H I regions of the ISM for systems such as benzene and conjugated polyenes such as ethylene and butadiene are quite unlikely because I+2-I+1 for such system(s) is higher than the available photon energy in the H I regions of the ISM. Present findings may be useful to understand the formation and underlying decay mechanisms of multiply charged ions from PAHs and related compounds that may accentuate the exploration of the phenomenon of high-temperature superconductivity.

On the Sputtering of Copper Phthalocyanine Molecules on a GaAs Substrate under Bombardment with Multiply Charged Ions

On the Sputtering of Copper Phthalocyanine Molecules on a GaAs Substrate under Bombardment with Multiply Charged Ions

Time-of-flight mass spectrometry of aluminium plasma: investigation of multiply charged ions and clusters

Ionic species in laser-produced plasma plume are generally analyzed by the time-of-flight method using a charge collector placed near to the target surface. One of the shortcomings of these methods is sacrifice of the important information for large mass cluster ions and the different charge states of atomic ions. In the present manuscript, design, development, and optimization procedure of a modified Wiley–McLaren type time-of-flight mass spectrometer (TOFMS) for the diagnostics of ions and cluster distribution in laser produced plasma (LPP) plume is presented. Second harmonic (532 nm) from a pulsed Nd:YAG laser is used to ablate aluminium disk in a vacuum chamber evacuated to base pressure of 7 × 10−8 mbar. The mass spectrometric results of aluminium (Al) plasma are presented and discussed in detail. To minimize the degradation in detection and mass resolution of spectrometer due to the wide angular and energy spared of the ions in the plasma plume, optimization of the TOF spectrometer in different configurations, single as well as a double field, is also discussed. Cluster ions as large as and multiply charged ions (MCI) up to Al11+ are observed in the mass spectra. The possible pathways for the production of MCI and cluster ions are discussed on the basis of the Coulomb explosion mechanism. The dependence of ion distribution on the laser fluence is also discussed.

An Improved Calibration Approach for Traveling Wave Ion Mobility Spectrometry: Robust, High-Precision Collision Cross Sections.

The combination of ion-mobility (IM) separation with mass spectrometry (MS) has impacted global measurement efforts in areas ranging from food analysis to drug discovery. Reasons for the broad adoption of IM-MS include its significantly increased peak capacity, duty-cycle, and ability to reconstruct fragmentation data in parallel, all of which greatly enable the analyses of complex mixtures. More fundamentally, however, measurements of ion-gas molecule collision cross sections (CCSs) are used to support compound identification and quantitation efforts as well as study the structures of large biomolecules. As the first commercialized form of IM-MS, Traveling Wave Ion Mobility (TWIM) devices are operated at low pressures (∼3 mbar) and voltages, are relatively short (∼25 cm), and separate ions on a timescale of tens of milliseconds. These qualities make TWIM ideally suited for hybridization with MS. Owing to the complicated motion of ions in TWIM devices, however, IM transit times must be calibrated to enable CCS measurements. Applicability of these calibrations has hitherto been restricted to primarily singly charged small molecules and some classes of large, multiply charged ions under a significantly narrower range of instrument conditions. Here, we introduce and extensively characterize a dramatically improved TWIM calibration methodology. Using over 2500 experimental TWIM data sets, covering ions that span over 3.5 orders of magnitude of molecular mass, we demonstrate robust calibrations for a significantly expanded range of instrument conditions, thereby opening up new analytical application areas and enabling the expansion of high-precision CCS measurements for both existing and next-generation TWIM instrumentation.

Generation of multiply charged ions from homogeneous MALDI microcrystals

The homogeneity of matrix assisted laser desorption/ionization (MALDI) microcrystals, laser fluence, and the proton affinity (PA) of matrices determine the generation of multiply charged ions. Here we adopt three structurally similar matrices, i.e. α-cyano-4-hydroxycinnamic acid (CHCA), 4-chloro-α-cyanocinnamic acid (Cl-CCA), and (E)-propyl α-cyano-4-hydroxyl cinnamylate (CHCA-C3) to examine the homogeneity of microcrystals by measuring the relative standard deviation (RSD) values of the matrices with the homogeneous sample preparation method, e.g. forced dried droplet (FDD). The average RSD values of CHCA, Cl-CCA, and CHCA-C3 matrices are ∼15%, ∼10%, and ∼20%, respectively. With the same CHCA matrix, we found the charge state of myoglobin ions can obtain more charges (+6) with the FDD method as compared to +5 charges obtained by the inhomogeneous sample preparation method, i.e. dried droplet (DD). The laser fluence also affects the generation of multiply charged ions. For instance, the maximum charge states of myoglobin and cytochrome c ions are +6 with CHCA and +4 with CHCA-C3 at threshold laser fluence and decreases at elevated laser fluence. The charge state of myoglobin ions with Cl-CCA matrix is +3 at threshold laser fluence and increases to the maximum charge state of +6 and eventually reduces to +5 with elevated laser fluence. Moreover, we found low PA value of matrix results in high charge state of analyte ions and vice versa. The matrix PA modulates the proton transfer reaction, leading to the formation of multiply charged ions. The homogeneous samples help control the charge states of ions and generate the multiply charged protein ions which can be used as potential mass calibration standards to search suitable protein samples at high m/z ratios with a MALDI time-of-flight mass spectrometer.

Infrared Laser Desorption and Electrospray Ionisation of Non‐Covalent Protein Complexes: Generation of Intact, Multiply Charged Species

AbstractWe present a novel method enabling the infrared laser desorption and electrospray ionisation (ESI) of protein complexes in their native state. Using this method, we demonstrate the surprising generation of intact, multiply charged ions of myoglobin, non‐covalent haemoglobin complex, and intact immunoglobulin G antibody in their native states. The observation of a surviving population of intact non‐covalent complexes is characteristic of the low internal energy build‐up experienced during both laser desorption from solution and subsequent ionisation. Compared to conventional nano‐ESI, this approach yielded slightly lower average charge states suggesting additional maintenance of tertiary structure during desorption and ionisation, and is more tolerant to salts enabling simpler sample purification procedures. This approach may enable the development of high‐throughput native‐MS methods capable of analysing the composition and sequence of multiple macromolecular samples per minute.

Techniques and Applications of Protein Mass Spectrometry

Protein mass spectrometry demands that proteins in solution or solid form be ionised in the gas phase before being injected and accelerated in an electric or magnetic field for analysis. Electrospray Ionisation (ESI) and matrix-assisted laser desorption/ionization are the two most used techniques for ionising proteins. Electrospray allows delicate molecules to be ionised whole, sometimes retaining non-covalent connections, since the ions are generated from proteins in solution. In MALDI, proteins are placed in a matrix that is typically solid, and ions are generated by laser light pulses. Electrospray generates more multiply-charged ions than MALDI, allowing for higher mass protein measurement and better fragmentation for identification, whereas MALDI is faster and less susceptible to contamination, buffers, and additives.

A Compact Ion Accelerator for Ion-Beam Technologies

We propose approaches to the development and construction of an easy-to-make compact accelerator of positive multiply charged metal ions in different charge states in the energy range of 1–500 keV. Such accelerator can be used in research and applied works in the field of advanced ion-beam technologies. Computer simulation of ion beam trajectories in the accelerator using the SIMON 8.0 code confirmed the effectiveness of the proposed approach.

The fully relativistic multi-configuration Dirac–Hartree–Fock method for atomic structure calculations for multiply charged ions: the example of Ca XV

In this work, fully relativistic multi-configuration Dirac–Hartree–Fock approach for calculating atomic structure parameters has been presented and compared to other approaches such as Hartree–Fock pseudo-Relativistic (HFR) method. As an example of application, results of fully relativistic calculations for the ion Ca XV have been obtained and compared to Hartree–Fock pseudo-relativistic calculations and to NIST database values.This example is important for plasma diagnostic and astrophysical studies because Ca XV atomic data of high accuracy are still very scarce.

Cover Feature: Infrared Laser Desorption and Electrospray Ionisation of Non‐Covalent Protein Complexes: Generation of Intact, Multiply Charged Species (Analysis & Sensing 1/2021)

Cover Feature: Infrared Laser Desorption and Electrospray Ionisation of Non‐Covalent Protein Complexes: Generation of Intact, Multiply Charged Species (Analysis & Sensing 1/2021)

Mass Analysis of Macro-molecular Analytes via Multiply-Charged Ion Attachment.

A novel gas-phase charge and mass manipulation approach is demonstrated to facilitate the mass measurement of high mass complexes within the context of native mass spectrometry. Electrospray ionization applied to solutions generated under native or near-native conditions has been demonstrated to be capable of preserving biologically relevant complexes into the gas phase as multiply charged ions suitable for mass spectrometric analysis. However, charge state distributions tend to be narrow and extensive salt adduction, heterogeneity, and so on tend to lead to significantly broadened peaks. These issues can compromise mass measurement of high mass bio-complexes, particularly when charge states are not clearly resolved. In this work, we show that the attachment of high mass ions of known mass and charge to populations of ions of interest can lead to well-separated signals that can yield confident charge state and mass assignments from otherwise poorly resolved signals.

Generation of Multiply Charged Argon Ions in Nanosecond Laser Field Ionization of Argon Clusters.

Zhang and co-workers ( J. Phys. Chem. Lett. 2020, 11, 1100-1105) have recently reported results of experiments involving irradiation of argon clusters doped with bromofluorene chromophores by nanosecond-long pulses of 532 nm laser light. Multiply charged ions of atomic argon (Arn+, 1 ≤ n ≤ 7) and carbon (Cn+, 1 ≤ n ≤ 4) are observed, which are sought to be rationalized using an evaporation model. The distinguishing facet of exploding clusters being progenitors of energetic ions and electrons constitutes the key driver for contemporary research in laser-cluster interactions; it is, therefore, important to point out inconsistencies that are intrinsic to the model of Zhang and co-workers. In light of similar reports already in the literature, we show that their model is of limited utility in describing the dynamics that govern how fast, multiply charged atomic ions result from laser irradiation of gas-phase clusters. We posit that it is plasma behavior that underpins cluster heating and cluster explosion dynamics.

Production of Multiply Charged Argon Ions in Moderate Nanosecond Laser Fields: An Open Question or a Forgone Conclusion?

We reply to the Viewpoint by Vatsa and Mathur on our publication reporting the observation of multiply charged atomic ions from argon clusters doped with aromatic chromophores in a moderate nanosecond laser field. Vatsa and Mathur raised three concerns about the proposed explanation and offered additional ideas for the reported process. We agree with some of their concerns and welcome the addition of information, and we also clarify a few misunderstandings of our intention, perhaps caused by our implicit assumption of contextual relations. While the experimental results are indisputable, the interpretation is still a topic of debate, subject to further experimental investigations and theoretical modeling.

Water Splitting and Transport of Ions in Electromembrane System with Bilayer Ion-Exchange Membrane.

Bilayer ion-exchange membranes are mainly used for separating single and multiply charged ions. It is well known that in membranes in which the layers have different charges of the ionogenic groups of the matrix, the limiting current decreases, and the water splitting reaction accelerates in comparison with monolayer (isotropic) ion-exchange membranes. We study samples of bilayer ion-exchange membranes with very thin cation-exchange layers deposited on an anion-exchange membrane-substrate in this work. It was revealed that in bilayer membranes, the limiting current’s value is determined by the properties of a thin surface film (modifying layer). A linear regularity of the dependence of the non-equilibrium effective rate constant of the water-splitting reaction on the resistance of the bipolar region, which is valid for both bilayer and bipolar membranes, has been revealed. It is shown that the introduction of the catalyst significantly reduces the water-splitting voltage, but reduces the selectivity of the membrane. It is possible to regulate the fluxes of salt ions and water splitting products (hydrogen and hydroxyl ions) by changing the current density. Such an ability makes it possible to conduct a controlled process of desalting electrolytes with simultaneous pH adjustment.

Utility of Ion-Mobility Spectrometry for Deducing Branching of Multiply Charged Glycans and Glycopeptides in a High-Throughput Positive ion LC-FLR-IMS-MS Workflow

High-throughput glycan analysis has become an important part of biopharmaceutical production and quality control. However, it is still a significant challenge in the field of glycomics to easily deduce isomeric glycan structures, especially in a high-throughput manner. Ion mobility spectrometry (IMS) is an excellent tool for differentiating isomeric glycan structures. However, demonstrations of the utility of IMS in high-throughput workflows such as liquid chromatography-fluorescence-mass spectrometry (LC-FLR-MS) workflows have been limited with only a small amount of collision cross section (CCS) data available. In particular, IMS data of glycan fragments obtained in positive ion mode are limited in comparison to those obtained in negative ion mode despite positive ion mode being widely used for glycomics. Here, we describe IMS TWCCSN2 data obtained from a high-throughput LC-FLR-IMS-MS workflow in positive ion mode. We obtained IMS data from a selection of RapiFluor-MS (RFMS) labeled N-glycans and also glycopeptides. We describe how IMS is able to distinguish isomeric N-glycans and glycopeptides using both intact IMS and fragment-based IMS glycan sequencing experiments in positive ion mode, without significantly altering the high-throughput nature of the analysis. For the first time, we were able to successfully use IMS in positive ion mode to determine the branching of isomeric glycopeptides and RFMS labeled glycans. Further, we highlight that IMS glycan sequencing of fragments obtained from RFMS labeled glycans was similar to that of glycopeptides. Finally, we show that the IMS glycan sequencing approach can highlight shared structural features of nonisomeric glycans in a high-throughput LC-FLR-IMS-MS workflow.

High-speed Analysis of Large Sample Sets – How Can This Key Aspect of the Omics Be Achieved?

High-speed analysis of large (prote)omics sample sets at the rate of thousands or millions of samples per day on a single platform has been a challenge since the beginning of proteomics. For many years, ESI-based MS methods have dominated proteomics because of their high sensitivity and great depth in analyzing complex proteomes. However, despite improvements in speed, ESI-based MS methods are fundamentally limited by their sample introduction, which excludes off-line sample preparation/fractionation because of the time required to switch between individual samples/sample fractions, and therefore being dependent on the speed of on-line sample preparation methods such as liquid chromatography. Laser-based ionization methods have the advantage of moving from one sample to the next without these limitations, being mainly restricted by the speed of modern sample stages, i.e. 10 ms or less between samples. This speed matches the data acquisition speed of modern high-performing mass spectrometers whereas the pulse repetition rate of the lasers (>1 kHz) provides a sufficient number of desorption/ionization events for successful ion signal detection from each sample at the above speed of the sample stages. Other advantages of laser-based ionization methods include the generally higher tolerance to sample additives and contamination compared with ESI MS, and the contact-less and pulsed nature of the laser used for desorption, reducing the risk of cross-contamination. Furthermore, new developments in MALDI have expanded its analytical capabilities, now being able to fully exploit high-performing hybrid mass analyzers and their strengths in sensitivity and MS/MS analysis by generating an ESI-like stable yield of multiply charged analyte ions. Thus, these new developments and the intrinsically high speed of laser-based methods now provide a good basis for tackling extreme sample analysis speed in the omics.