Efficient Ionization Research Articles

Characterization of Microwave Discharge Ion Source for high proton beam production

The production of high-current beams is a key point for different applications and the importance ofthis role is deemed to increase in the coming years, both for industrial applications and for research projects. High-current and high-brightness H+ beams can be provided by 2.45GHz MDIS --Microwave Discharge Ion Sources--, which presents many advantages in terms of compactness, high reliability, ability to operate in CW mode or in pulsed mode, reproducibility, and low maintenance. A detail characterization of two MDIS, VIS and SILHI is reported here: for each source the most important parameterwas measured and analyzed. Special attention was paid to improve the performance of the source, increasing the electron density for a more efficient ionization; as a consequence, studies to optimize the extracted current have been carried out. A series of measurements have been realized with the VIS source by inserting a thick Al2O3 tube inside the plasma chamber (passive technique) and an innovative mechanisms of plasma ignition based on electrostatic waves (ESW) was proved with a plasma reactor.

Attachment of Chloride Anion to Sugars: Mechanistic Investigation and Discovery of a New Dopant for Efficient Sugar Ionization/Detection in Mass Spectrometers

A new method for efficient ionization of sugars in the negative-ion mode of electrospray mass spectrometry is presented. Instead of using strongly hydrophobic dopants such as dichloromethane or chloroform, efficient ionization of sugars has been achieved by using aqueous HCl solution for the first time. This methodology makes it possible to use hydrophilic dopants, which are more appropriate for chromatographic separation techniques with efficient sugar ionization and detection in mass spectrometry. The interaction between chloride anions and monosaccharides (glucose and galactose) was studied by DFT in the gas phase and by implementing the polarizable continuum model (PCM) for calculations in solution at the high B3LYP/6-31+G(d,p)//B3LYP/6-311+G(2d,p) level of theory. In all optimized geometries of identified [M+Cl](-) anions, a non-covalent interaction exists. Differences were revealed between monodentate and bidentate complex anions, with the latter having noticeably higher binding energies. The calculated affinity of glucose and galactose toward the chloride anion in the gas phase and their chloride anion binding energies in solution are in excellent agreement with glucose and galactose [M+Cl](-) experimental intensity profiles that are represented as a function of the chloride ion concentration. Density functional calculations of gas-phase affinities toward chloride anion were also performed for the studied disaccharides sucrose and gentiobiose. All calculations are in excellent agreement with the experimental data. An example is introduced wherein HCl was used to effectively ionize sugars and form chlorinated adduct anions to detect sugars and glycosylated metabolites (anthocyanins) in real biological systems (Vitis vinifera grape extracts and wines), whereas they would not have been easily detectable under standard infusion electrospray mass spectrometry conditions as deprotonated species.

Efficient ionization of one-dimensional acetylene investigated by time-dependent Hartree-Fock calculations

The ionization of a model acetylene molecule (C${}_{2}$H${}_{2}$) by an intense laser pulse is studied by numerically solving the time-dependent Hartree-Fock equations. It is shown that when the C--H bond is stretched to twice the value of the equilibrium internuclear distance, the ionization probability is strongly enhanced. The physical mechanism is identified to be similar to the enhanced ionization found previously in H${}_{2}^{+}$, with the two HOMOs in acetylene playing the same role as the charge resonance states $1{\ensuremath{\sigma}}_{g}$ and $1{\ensuremath{\sigma}}_{u}$ in H${}_{2}^{+}$. Electrons are ejected in a two-step process. First, the electron density is transferred to one of the peripheral H atom sites, and then it is ejected from there by tunneling. The same process is effective also in C${}_{2}$H${}_{2}$${}^{2+}$. The mechanism is further clarified by employing both a simplified two-state model and the single-active-orbital approximation. In the enhancement of the ionization of C${}_{2}$H${}_{2}$, the elongation of the C--H distance plays a decisive role, while the variation of the C--C distance gives only a secondary contribution. In addition to the two highest occupied molecular orbitals, electrons in the third highest molecular orbital are also found to be ejected efficiently. The role of the third highest molecular orbital in the ionization dynamics is investigated by introducing projection operators.

Nonculture‐based identification of bacteria in milk by protein fingerprinting

Traditional methods for bacterial identification include Gram staining, culturing, and biochemical assays for phenotypic characterization of the causative organism. These methods can be time-consuming because they require in vitro cultivation of the microorganisms. Recently, however, it has become possible to obtain chemical profiles for lipids, peptides, and proteins that are present in an intact organism, particularly now that new developments have been made for the efficient ionization of biomolecules. MS has therefore become the state-of-the-art technology for microorganism identification in microbiological clinical diagnosis. Here, we introduce an innovative sample preparation method for nonculture-based identification of bacteria in milk. The technique detects characteristic profiles of intact proteins (mostly ribosomal) with the recently introduced MALDI Sepsityper(TM) Kit followed by MALDI-MS. In combination with a dedicated bioinformatics software tool for databank matching, the method allows for almost real-time and reliable genus and species identification. We demonstrate the sensitivity of this protocol by experimentally contaminating pasteurized and homogenized whole milk samples with bacterial loads of 10(3) -10(8) colony-forming units (cfu) of laboratory strains of Escherichia coli, Enterococcus faecalis, and Staphylococcus aureus. For milk samples contaminated with a lower bacterial load (10(4) cfu mL(-1) ), bacterial identification could be performed after initial incubation at 37°C for 4 h. The sensitivity of the method may be influenced by the bacterial species and count, and therefore, it must be optimized for the specific application. The proposed use of protein markers for nonculture-based bacterial identification allows for high-throughput detection of pathogens present in milk samples. This method could therefore be useful in the veterinary practice and in the dairy industry, such as for the diagnosis of subclinical mastitis and for the sanitary monitoring of raw and processed milk products.

Efficient photo-ionization for barium ion trapping using a dipole-allowed resonant two-photon transition

Two efficient and isotope-selective resonant two-photon ionization techniques for loading barium ions into radio-frequency (RF)-traps are demonstrated. The scheme of using a strong dipole-allowed transition at \lambda=553 nm as a first step towards ionization is compared to the established technique of using a weak intercombination line (\lambda=413 nm). An increase of two orders of magnitude in the ionization efficiency is found favoring the transition at 553 nm. This technique can be implemented using commercial all-solid-state laser systems and is expected to be advantageous compared to other narrowband photoionization schemes of barium in cases where highest efficiency and isotope-selectivity are required.

High-Pressure Gas Phase Femtosecond Laser Ionization Mass Spectrometry

We describe a novel ion source for analytical mass spectrometry based on femtosecond laser ionization at pressures at and above atmospheric and characterize its performance when coupled to a tandem quadrupole/time-of-flight mass spectrometer. We assess source saturation limits, ionization and sampling efficiencies, the effective ionization volume, and limits of detection. We demonstrate 100% efficient ionization for a set of organic compounds and show that the degree of ion fragmentation over a range of laser powers is favorable compared to electron impact ionization, especially in that a substantial parent ion signal is always observed. We show how collisional cooling plays a role in controlling fragmentation at high pressures and address how ion-molecule chemistry can be controlled or exploited. High-pressure femtosecond laser ionization will allow "universal" and efficient ionization, presenting a research direction that will broaden the options for gas phase analysis beyond the capabilities of electron impact ionization.

Study of plasma immersion ion implantation into silicon substrate using magnetic mirror geometry

The effect of magnetic field enhanced plasma immersion ion implantation (PIII) in silicon substrate has been investigated at low and high pulsed bias voltages. The magnetic field in magnetic bottle configuration was generated by two magnetic coils installed outside the vacuum chamber. The presence of both, electric and magnetic field in PIII creates a system of crossed E×B fields, promoting plasma rotation around the target. The magnetized electrons drifting in crossed E×B fields provide electron-neutral collision. Consequently, the efficient background gas ionization augments the plasma density around the target where a magnetic confinement is achieved. As a result, the ion current density increases, promoting changes in the samples surface properties, especially in the surface roughness and wettability and also an increase of implantation dose and depth.

Identification of multiply charged proteins and amino acid clusters by liquid nitrogen assisted spray ionization mass spectrometry

The development of liquid nitrogen assisted spray ionization mass spectrometry (LNASI MS) for the analysis of multiply charged proteins (insulin, ubiquitin, cytochrome c, α-lactalbumin, myoglobin and BSA), peptides (glutathione, HW6, angiotensin-II and valinomycin) and amino acid (arginine) clusters is described. The charged droplets are formed by liquid nitrogen assisted sample spray through a stainless steel nebulizer and transported into mass analyzer for the identification of multiply charged protein ions. The effects of acids and modifier volumes for the efficient ionization of the above analytes in LNASI MS were carefully investigated. Multiply charged proteins and amino acid clusters were effectively identified by LNASI MS. The present approach can effectively detect the multiply charged states of cytochrome c at 400nM. A comparison between LNASI and ESI, CSI, SSI and V-EASI methods on instrumental conditions, applied temperature and observed charge states for the multiply charged proteins, shows that the LNASI method produces the good quality spectra of amino acid clusters at ambient conditions without applied any electric field and heat. To date, we believe that the LNASI method is the most simple, low cost and provided an alternative paradigm for production of multiply charged ions by LNASI MS, just as ESI-like ions yet no need for applying any electrical field and it could be operated at low temperature for generation of highly charged protein/peptide ions.

Active capillary plasma source for ambient mass spectrometry

Imaging mass spectrometry with high spatial resolution has become a rapidly developing area of mass spectrometric research. Many scientific and industrial problems deal with mass spectrometric analysis at ambient pressures. This requires efficient transport and ionization of small amounts of substance. An active sampling capillary based on a dielectric barrier discharge was constructed for ambient mass spectrometry. The capillary serves as an ionization source as well as an atmospheric interface of the mass spectrometer. The analyzed samples are transported through the sampling capillary due to the pressure difference between the atmospheric environment and the vacuum in the mass spectrometer. Ionization of the transported samples is provided by a low-temperature dielectric barrier discharge. This active capillary was shown to work in a robust fashion for ionizing both gas-phase and laser-ablated solid-phase samples. The geometry of the electrodes was found to play a crucial role in ionization efficiency. The capillary was optimized in order to perform surface analysis of solid samples. Sensitivity tests were carried out to characterize different active capillary constructions. The sensitivity of the constructed active capillary was 0.1 ppb (relative concentration of a gaseous sample in ambient air). The active capillary was able to detect samples evaporated from a solid surface. With the active capillary source, it was possible to detect anthracene traces evaporated from a surface located 3 cm from the capillary inlet. A plasma-based active capillary ionization source was constructed. This concept of an active sample inlet should broaden the range of applications of ambient mass spectrometry.

Analysis of lipids with desorption atmospheric pressure photoionization‐mass spectrometry (DAPPI‐MS) and desorption electrospray ionization‐mass spectrometry (DESI‐MS)

In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat-soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization-MS (DESI-MS) and desorption atmospheric pressure photoionization-MS (DAPPI-MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M-H](+) ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods.

Confined direct analysis in real time ion source and its applications in analysis of volatile organic compounds of Citrus limon (lemon) and Allium cepa (onion)

The DART (direct analysis in real time) ion source is a novel atmospheric pressure ionization technique that enables efficient ionization of gases, liquids and solids with high throughput. A major limit to its wider application in the analysis of gases is its poor detection sensitivity caused by open-air sampling. In this study, a confined interface between the DART ion source outlet and mass spectrometer sampling orifice was developed, where the plasma generated by the atmospheric pressure glow discharge collides and ionizes gas-phase molecules in a Tee-shaped flow tube instead of in open air. It leads to significant increase of collision reaction probability between high energy metastable molecules and analytes. The experimental results show that the ionization efficiency was increased at least by two orders of magnitude. This technique was then applied in the real time analysis of volatile organic compounds (VOCs) of Citrus Limon (lemon) and wounded Allium Cepa (onion). The confined DART ion source was proved to be a powerful tool for the studies of plant metabolomics.

The search for the existence of 229mTh at IGISOL

An overview of preparatory work aiming at the identification of the low-lying 7.6 eV isomer in 229Th through a measurement of its hyperfine structure is presented. A 233U recoil gas cell has been developed and has undergone several iterations in order to improve the efficiency of extracting a low-energy beam of 229Th+ ions. Spectroscopic studies on stable 232Th have been carried out to establish an efficient laser ionization scheme. The latter will be applied in connection with the gas cell in order to improve the extraction efficiency by accessing the neutral atomic fraction. In addition to that of the 229Th ground state, the hyperfine structure of the isomer can then be determined either by collinear laser spectroscopy on the extracted and accelerated ions or by direct in-source/in-jet high-resolution Resonance Ionization Spectroscopy (RIS). The first experiments using high-resolution RIS have been performed and isotope shifts of 228Th, 229Th and 230Th relative to 232Th were measured on an atomic 7s 2 → 7s7p ground-state transition at 380.42 nm. A template of the ground-state hyperfine structure of 229Th has been established for a 261.24nm UV transition. This is an important step towards identification of the isomeric state

Evaluation of new mixed-mode UHPLC stationary phases and the importance of stationary phase choice when using low ionic-strength mobile phase additives

In this study, the selectivity, retention properties, peak shape and loading capacity for bases were practically evaluated using two UHPLC mixed-mode hybrid CSH stationary phases modified by C18 or Phenyl group. The data were compared with the data obtained on other UHPLC hybrid stationary phases (BEH C18, BEH C8, BEH Phenyl and BEH Shield RP18) at both basic and acidic conditions using conventional HPLC buffers (50mM ammonium formate/acetate) as well as low ionic-strength additives such as, e.g. 0.1–0.01% formic/acetic acid and 1mM solution of ammonium formate/acetate, which are widely used in LC–MS applications.Ten pharmaceutically important compounds encompassing acids, bases and neutral were included into the study. Due to properties of CSH sorbent (which possess positively charged surface besides RP group), much improved peak shapes and weaker retention was obtained for bases even at very low concentration of acidic additives. Such conditions are ideally suited for LC–MS analysis of bases, where typical RP chromatographic separation (retention and good selectivity at basic pH) and LS–MS conditions (efficient ionization at acidic pH) are not in agreement. On the other hand, acids were more strongly retained and for some compounds the peak shape was influenced negatively due to ion-exchange mechanism. Further, the behavior of acidic, basic and neutral solutes is discussed using various additives at both basic and acidic pH for all above stated columns. The robustness of retention times after pH change from basic to acidic was also evaluated. The new CSH stationary phases represent an interesting selectivity tool preferably for separation of basic compounds.

Characterization of the versatile ion source and possible applications as injector for future projects

The versatile ion source (VIS) is an off-resonance microwave discharge ion source which generates a slightly overdense plasma (n(e) ≈ 10(17) cm(-3)) operating at 2.45 GHz and producing more than 50 mA of proton beams. A detailed characterization of the source, by operating between 60 and 75 kV, in terms of emittance, current extracted and proton fraction is reported below. Moreover, passive techniques (alumina coating of the plasma chamber walls, BN disks at the injection and extraction endplates) have been used to improve the performance of the source, increasing the electron density for a more efficient ionization. The know-how achieved with the VIS source may be useful for the different project, particularly for the European spallation source.

A compact neutron generator using a field ionization source

Field ionization as a means to create ions for compact and rugged neutron sources is pursued. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 10(6) tips∕cm(2) and measure their performance characteristics using electron field emission. The critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties.

Comparison of Direct and Alternating Current Vacuum Ultraviolet Lamps in Atmospheric Pressure Photoionization

A direct current induced vacuum ultraviolet (dc-VUV) krypton discharge lamp and an alternating current, radio frequency (rf) induced VUV lamp that are essentially similar to lamps in commercial atmospheric pressure photoionization (APPI) ion sources were compared. The emission distributions along the diameter of the lamp exit window were measured, and they showed that the beam of the rf lamp is much wider than that of the dc lamp. Thus, the rf lamp has larger efficient ionization area, and it also emits more photons than the dc lamp. The ionization efficiencies of the lamps were compared using identical spray geometries with both lamps in microchip APPI mass spectrometry (μAPPI-MS) and desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS). A comprehensive view on the ionization was gained by studying six different μAPPI solvent compositions, five DAPPI spray solvents, and completely solvent-free DAPPI. The observed reactant ions for each solvent composition were very similar with both lamps except for toluene, which showed a higher amount of solvent originating oxidation products with the rf lamp than with the dc lamp in μAPPI. Moreover, the same analyte ions were detected with both lamps, and thus, the ionization mechanisms with both lamps are similar. The rf lamp showed a higher ionization efficiency than the dc lamp in all experiments. The difference between the lamp ionization efficiencies was greatest when high ionization energy (IE) solvent compositions (IEs above 10 eV), i.e., hexane, methanol, and methanol/water, (1:1 v:v) were used. The higher ionization efficiency of the rf lamp is likely due to the larger area of high intensity light emission, and the resulting larger efficient ionization area and higher amount of photons emitted. These result in higher solvent reactant ion production, which in turn enables more efficient analyte ion production.

Chemical Characterization of Crude Petroleum Using Nanospray Desorption Electrospray Ionization Coupled with High-Resolution Mass Spectrometry

Nanospray desorption electrospray ionization (nano-DESI) combined with high-resolution mass spectrometry was used for the first time for the analysis of the polar constituents of liquid petroleum crude oil samples. The analysis was performed in both positive and negative ionization modes using three solvents, one of which (acetonitrile/toluene mixture) is commonly used in petroleomics studies while two other polar solvents (acetonitrile/water and methanol/water mixtures) are generally not compatible with petroleum characterization using mass spectrometry. The results demonstrate that nano-DESI analysis efficiently ionizes petroleum constituents soluble in a particular solvent. When acetonitrile/toluene is used as a solvent, nano-DESI generates electrospray-like spectra. In contrast, strikingly different spectra were obtained using acetonitrile/water and methanol/water. Comparison with the literature data indicates that these solvents selectively extract water-soluble constituents of the crude oil. Water-soluble compounds are predominantly observed as sodium adducts in nano-DESI spectra indicating that addition of sodium to the solvent may be a viable approach for efficient ionization of water-soluble crude oil constituents. Nano-DESI enables rapid screening of different classes of compounds in crude oil samples based on their solubility in solvents that are rarely used for petroleum characterization providing better coverage of the crude oil composition as compared to electrospray ionization (ESI). It also enables rapid characterization of water-soluble components of petroleum samples that is difficult to perform using traditional approaches.

Paper spray: a simple and efficient means of analysis of different contaminants in foodstuffs

A simple and efficient ambient ionization method based on paper spray combined with tandem mass spectrometry allows rapid detection and quantitation of various contaminants (clenbuterol, melamine, plasticizer and sudan red) in various foodstuffs (e.g., meat, milk, sports drinks and chili powder).

Matrix-Assisted Laser Desorption/Ionization (MALDI) Imaging Mass Spectrometry (IMS): A Challenge for Reliable Quantitative Analyses.

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) is capable of determining the distribution of hundreds of molecules at once directly from tissue sections. Since tissues are analyzed intact without homogenization, spatial relationships of molecules are preserved. The technology is, therefore, undoubtedly powerful to investigate the molecular complexity of biological processes. However, several technical refinements are essential for full exploitation of MALDI-IMS to dictate dynamics alteration of biomolecules in situ; these include ways to collect tissues, target-specific tissue pretreatment, matrix choice for efficient ionization, and matrix deposition method to improve imaging resolution. Furthermore, for MALDI-IMS to reach its full potential, quantitative property in the IMS should be strengthened. We review the challenges and new approaches for optimal imaging of proteins, lipids and metabolites, highlighting a novel quantitative IMS of energy metabolites in the recent literature.

Evaluation of Matrix-Assisted Laser Desorption/Ionization Mass spectrometry for second-Generation Lignin Analysis

Matrix-Assisted Laser Desorption/Ionization time-of-flight (MALDI-TOF) mass spectrometry is evaluated as an elucidation tool for structural features and molecular weights estimation of some extracted herbaceous lignins. Optimization of analysis conditions, using a typical organic matrix, namely α-cyano-4-hydroxycinnamic acid (CHCA), in combination with α-cyclodextrin, allows efficient ionization of poorly soluble lignin materials and suppression of matrix-related ions background. Analysis of low-mass fragments ions (m/z 100–600) in the positive ion mode offers a “fingerprint” of starting lignins that could be a fine strategy to qualitatively identify principal inter-unit linkages between phenylpropanoid units. The molecular weights of lignins are estimated using size exclusion chromatography and compared to MALDI-TOF-MS profiles. Miscanthus (Miscanthus x giganteus) and Switchgrass (Panicum Virgatum L.) lignins, recovered after a formic acid/acetic acid/water process or aqueous ammonia soaking, are selected as benchmarks for this study.