High Ion Intensity Research Articles

Graphite Sheet-Assisted Laser Desorption Ionization-Mass Spectrometry for Small Organic Compound Analysis.

Carbon-based nanopowders have been used as ionization materials for laser desorption ionization-mass spectrometry (LDI-MS) and are very efficient at detection in low m/z regions. In this study, we aimed to develop a new sheet-type graphite material that possessed a randomly grooved nanostructured surface consisting of developed sp2-conjugated atomic carbon to facilitate the desorption/ionization of small compounds in LDI-MS. The graphite sheet exhibited higher UV absorption and provided higher ionization efficiency and survival yield in the LDI-MS detection of a thermometer ion, 4-chloro-benzopyridinium, than those of highly oriented graphite plates. These properties demonstrate that the present graphite sheet is suited for use as an LDI-MS material. Graphite sheet-assisted LDI-MS successfully detected various substances, including amino acids, peptides, and polyethylene glycol polymers, with higher ion intensities and less noise than those associated with conventional organic matrix-assisted LDI-MS (MALDI-MS). Furthermore, graphite sheet-assisted LDI-MS analysis provided more peaks (252 peaks) derived from soy sauce than those obtained by MALDI-MS (36 peaks) and required fewer preparation processes (dilution and air-dried) compared with previously established graphite carbon black-assisted LDI-MS (171 peaks) in the positive mode. This study demonstrates that graphite sheet-assisted LDI-MS has the potential for small organic compound analyses in the biomedical and food science fields.

Solvent effect on the detection of peptides and proteins by nanoelectrospray ionization mass spectrometry: Anomalous behavior of aqueous 2-propanol

To investigate the solvent effect on the detection of peptides and proteins, nanoelectrospray mass spectra were measured for mixtures of 1 % acetic acid and 5 × 10−6 M gramicidin S (G), ubiquitin (U), and cytochrome c (C) in water (W), methanol (MeOH), 1-propanol (1-PrOH), acetonitrile (AcN), and 2-propanol (2-PrOH). Although doubly protonated G (G2+) and multiply protonated U (Un+) and C (Cn+) were readily detected with a wide range of mixing ratios of W solutions for MeOH, 1-PrOH, and AcN, Cn+ was totally suppressed for the solutions with mixing ratios (v/v) of W/2-PrOH (50/50) and (70/30). However, denatured Cn+ started to be detected with W/2-PrOH (90/10) together with Gn+ (n = 1, 2) and native Un+ (n = 6–8). At the mixing ratio of W/2-PrOH (95/5), native Cn+ (n = 7–10) together with Gn+ (n = 1, 2) and native Un+ (n = 6–8) were detected with high ion intensities. The use of W/2-PrOH (95/5) is profitable because it enables the detection of native proteins with high detection sensitivities.

Optimization of Higher-Energy Collisional Dissociation Fragmentation Energy for Intact Protein-Level Tandem Mass Tag Labeling.

Isobaric chemical tag labeling (e.g., TMT) is a commonly used approach in quantitative proteomics, and quantification is enabled through detection of low-mass reporter ions generated after MS2 fragmentation. Recently, we have introduced and optimized an intact protein-level TMT labeling platform that demonstrated >90% labeling efficiency in complex samples with top-down proteomics. Higher-energy collisional dissociation (HCD) is commonly utilized for isobaric tag-labeled peptide fragmentation because it produces accurate reporter ion intensities and avoids loss of low mass ions. HCD energies have been optimized for isobaric tag labeled-peptides but have not been systematically evaluated for isobaric tag-labeled intact proteins. In this study, we report a systematic evaluation of normalized HCD fragmentation energies (NCEs) on TMT-labeled HeLa cell lysate using top-down proteomics. Our results suggested that reporter ions often result in higher ion intensities at higher NCEs. Optimal fragmentation of intact proteins for identification, however, required relatively lower NCE. We further demonstrated that a stepped NCE scheme with energies from 30% to 50% resulted in optimal quantification and identification of TMT-labeled HeLa proteins. These parameters resulted in an average reporter ion intensity of ∼4E4 and average proteoform spectrum matches (PrSMs) of >1000 per RPLC-MS/MS run with a 1% false discovery rate (FDR) cutoff.

Desorption Electrospray Ionization Mass Spectrometry Imaging Illustrates the Quality Characters of Isatidis Radix

For a long history, herbal medicines have made significant contributions to human health all around the world. However, the exploration of an effective approach to illustrate their inner quality remains a challenge. So, it is imperative to develop new methods and technologies to characterize and identify quality markers of herbal medicines. Taking Isatidis Radix, the dried root of Isatis indigotica as an example, desorption electrospray ionization (DESI), in combination with quadrupole-time-of-flight mass spectrometry (Q-TOF/MS), was applied in this work for the first time to reveal the comprehensive spatial distribution of metabolites and, further, to illustrate quality characters of this herbal medicine. After simple pretreatment, 102 metabolites including alkaloids, sulfur-containing compounds, phenylpropanoids, nucleosides, amino acids, organic acids, flavonoids, phenols, terpenes, saccharides, peptides, and sphingolipids were characterized, some of which were successfully localized and visualized in the transverse section of the root. Based on the ion images, samples with different quality characters were distinguished unambiguously by the pattern recognition method of orthogonal partial least squares discrimination analysis (OPLS-DA). Simultaneously, 11 major influencing components exerting higher ion intensities in superior samples were identified as the potential quality markers of Isatidis Radix. Desorption electrospray ionization (DESI) mass spectrometry imaging (MSI), together with chemometric analysis could not only improve the understanding of the plant biology of herbal medicines but also be beneficial in the identification of quality markers, so as to carry out better quality control of herbal medicines.

Directly transferring pepper constituents to triangular papers for pungency determination by paper spray ionization mass spectrometry.

A method named imprint paper spray ionization mass spectrometry (imprint-PSI-MS) has been developed and employed for the determination of pungency of peppers. A pepper fruit was cut into a triangular shape, deposited onto a triangular paper, and compressed by a homemade press tool aiming to imprint and transfer the pepper constituents onto the paper surface. Subsequently, the triangular paper was submitted to conventional PSI-MS analysis. Twelve peppers were analyzed, ranging from highly pungent to lowly pungent taste. Pepper pungency values from the Scoville scale (in Scoville heat units, SHU) were compared with the ion intensities of the capsaicin and dihydrocapsaicin compounds obtained from the imprint-PSI-MS analysis, and a correlation coefficient of 0.97 was achieved. In addition, the ion intensities of a sugar compound were monitored in all peppers, and the results were compared with the Scoville scale. Low sugar ion intensities were detected in pungent peppers, while high ion intensities were achieved in low-pungent peppers, suggesting that the pepper pungency may be determined by inversely relating pungency to sugar contents. This work demonstrates the utility of the imprint-PSI-MS method to perform rapid qualitative analyses of peppers and estimate the pungency by monitoring the pepper metabolites. Graphical abstract.

Flavonoid Biosynthesis Is Likely More Susceptible to Elevation and Tree Age Than Other Branch Pathways Involved in Phenylpropanoid Biosynthesis in Ginkgo Leaves.

Ginkgo leaves are always resources for flavonoids pharmaceutical industry. However, the effect of the elevation and tree age changes on flavonoid biosynthesis have not been detailly explored in Ginkgo leaves. In addition, whether these environmental pressures have similar effects on the biosynthesis of other non-flavonoids polyphenolics in phenylpropanoid biosynthesis is not known at present. In this research, de novo transcriptome sequencing of Ginkgo leaves was performed coupled with ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry analyses to obtain a comprehensive understanding of the influence of elevation and tree age on phenylpropanoid biosynthesis. A total of 557,659,530 clean reads were assembled into 188,155 unigenes, of which 135,102 (71.80%) were successfully annotated in seven public databases. The putative DFRs, LARs, and ANRs were significantly up-regulated with the increase of elevation in young Ginkgo tree leaves. The relative concentration of flavonoid derivatives with high parent ion intensity was likely to imply that the elevation increase promoted the biosynthesis of flavonoids. Complex gene variations involved in flavonoid biosynthesis were observed with the tree age increase. However, flavonoid derivatives analysis predicted that the rise of tree age was more likely to be detrimental to the flavonoids manufacture. Otherwise, multiple genes implicated in the synthesis of hydroxycinnamates, lignin, and lignan exhibited fluctuations with the elevation increase. Significantly up-regulated CADs and down-regulated PRDs potentially led to the accumulation of p-Coumaryl alcohol, one of the lignin monomers, and might inhibit further lignification. Overall, the putative DFRs seemed to show more considerable variability toward these stress, and appeared to be the main regulatory point in the flavonoid biosynthesis. Light enhancement caused by elevation increase may be the main reason for flavonoids accumulation. Flavonoid biosynthesis exhibited a greater degree of perturbation than that of hydroxycinnamates, lignins and lignans, potentially suggesting that flavonoid biosynthesis might be more susceptible than other branch pathways involved in phenylpropanoid biosynthesis. This research effectively expanded the functional genomic library and provide new insights into phenylpropanoid biosynthesis in Ginkgo.

Simultaneous determination of ten nonsteroidal anti-inflammatory drugs from drinking water, surface water and wastewater using micro UHPLC-MS/MS with on-line SPE system

A simple, accurate and sensitive micro UHPLC-MS/MS method was developed and validated for the simultaneous determination of 10 nonsteroidal anti-inflammatory drugs (NSAIDs) from different environmental matrices. The micro LC ‒ on-line SPE method described in this study allowed to determine the selected drugs at ultra-trace levels without the most commonly used complex off-line SPE sample preparation procedures. The presented method is capable of reaching satisfactory low LOQ values with analysing the sample directly after being diluted with water. In order to attain high sensitivity, mass spectrometry was carefully optimized for the analysis of the drugs. Fenoprofen, flurbiprofen and naproxen were found to produce CO2 loss during ionization, forming intense [M-H-CO2]- ions instead of [M-H]-. All the other compounds were analyzed through their [M+H]+ and [M-H]- ions. Effect of mobile phase pH on ionization was also studied. Lower pH resulted in higher ion intensities. For this reason, a reversed phase chromatographic separation was applied at pH 3.1 with formic acid at concentration of 0.01%. Matrix effects have been evaluated during validation and sample dilution was optimized focusing on the lowest achievable LOQ values. Analytes were determined from drinking water directly, from surface water and wastewater following dilution with purified water by 2 : 8 (v/v) and 1 : 9 (v/v), respectively. Finally, the method was applied to real sample analysis.

Integration of paper-based microarray and time-of-flight secondary ion mass spectrometry (ToF-SIMS) for parallel detection and quantification of molecules in multiple samples automatically

With its low-cost fabrication and ease of modification, paper-based analytical devices have developed rapidly in recent years. Microarrays allow automatic analysis of multiple samples or multiple reactions with minimal sample consumption. While cellulose paper is generally used, its high backgrounds in spectrometry outside of the visible range has limited its application to be mostly colorimetric analysis. In this work, glass-microfiber paper is used as the substrate for a microarray. The glass-microfiber is essentially chemically inert SiOx, and the lower background from this inorganic microfiber can avoid interference from organic analytes in various spectrometers. However, generally used wax printing fails to wet glass microfibers to form hydrophobic barriers. Therefore, to prepare the hydrophobic-hydrophilic pattern, the glass-microfiber paper was first modified with an octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) to make the paper hydrophobic. A hydrophilic microarray was then prepared using a CO2 laser scriber that selectively removed the OTS layer with a designed pattern. One microliter of aqueous drops of peptides at various concentrations were then dispensed inside the round patterns where OTS SAM was removed while the surrounding area with OTS layer served as a barrier to separate each drop. The resulting specimen of multiple spots was automatically analyzed with a time-of-flight secondary ion mass spectrometer (ToF-SIMS), and all of the secondary ions were collected. Among the various cluster ions that have developed over the past decade, pulsed C60+ was selected as the primary ion because of its high secondary ion intensity in the high mass region, its minimal alteration of the surface when operating within the static-limit and spatial resolution at the ∼μm level. In the resulting spectra, parent ions of various peptides (in the forms [M+H]+ and [M+Na]+) were readily identified for parallel detection of molecules in a mixture. By normalizing the ion intensity of peptides with respect to the glass-microfiber matrix ([SiOH]+), a linear calibration curve for each peptide was generated to quantify these components in a mixture.

Comparison of auxiliary cathode and conventional plasma nitriding of gamma-TiAl alloy

Effect of auxiliary cathode (ACN) and conventional plasma nitriding (CPN) processes on surface modification of gamma-TiAl has been investigated. Both processes were done at temperature of 800 °C under gas ratio of N2/H2 = 1. The process duration was selected to be 3, 6 and 9 h for ACN, while it was 10, 20 and 30 h for CPN. Characterizations of the microstructure, phases, elemental distribution and hardness were performed using FESEM, XRD, GDOES, RBS and microhardness tests. Ti2AlN and TiN phases were detected as the main nitride compounds in both processes. Passive oxide films disrupted diffusion of nitrogen atoms in CPN process; hence a narrow nitrided zone was formed due to this surface oxidation. Higher ion intensity and oxidation protection emphasized the ACN process. The thicker and more uniform compound layers with more surface hardness were achieved using the auxiliary cathode. About 70% of nitriding process time was saved by ACN, in comparison with the CPN process.

Dual-Channel Electrospray Microchip

A dual-channel electrospray microchip has been developed for electrospray ionization mass spectrometry (ESI-MS) where aqueous samples are mixed at the Taylor cone with an organic buffer. Due to the fast and effective mixing in the Taylor cone, the aqueous sample can be well ionized with a high ion intensity. The influence of geometric parameters such as the distance between the two microchannels at their junction at the tip of the emitter has been investigated together with chemical parameters such as the organic buffer composition.

A novel ToF-SIMS operation mode for improved accuracy and lateral resolution of oxygen isotope measurements on oxides

Oxygen isotope exchange with subsequent time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a highly valuable tool for determining oxygen diffusion coefficients in oxides. Since ToF-SIMS analysis enables an elemental and chemical mapping, it can also be used to visualize oxygen exchange-active zones by determining the local oxygen isotopic fraction. However, measuring accurate isotopic fractions can be a challenging analytical task owing to secondary ion interaction and signal saturation, particularly when dealing with high secondary ion intensities as commonly found when analyzing oxygen ions from oxides. It is shown that in many cases the calculated 18O− fraction erroneously shifts to higher values and can lead to systematic errors in the determination of diffusion coefficients. A novel ToF-SIMS operation mode, called “Collimated Burst Alignment” (CBA) mode, is therefore introduced to enable a more accurate determination of oxygen isotopic fractions with an optimized lateral resolution of sub-100 nm. Both improvements are rendered possible by a modified beam guidance in the primary ion gun. This modification reduces detector dead time effects and ion interactions to a minimum and secondary ion intensities can be obtained more accurately. The result of this optimization is demonstrated in measurements of the natural isotope abundance of several different oxides including SrTiO3 and Sr-doped LaCoO3.

Molecular dynamic‐secondary ion mass spectrometry (D‐SIMS) ionized by co‐sputtering with C60+ and Ar+

Dynamic secondary ion mass spectrometry (D-SIMS) analysis of poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA) was conducted using a quadrupole mass analyzer with various combinations of continuous C(60)(+) and Ar(+) ion sputtering. Individually, the Ar(+) beam failed to generate fragments above m/z 200, and the C(60)(+) beam generated molecular fragments of m/z ~1000. By combining the two beams, the auxiliary Ar(+) beam, which is proposed to suppress carbon deposition due to C(60)(+) bombardment and/or remove graphitized polymer, the sputtering range of the C(60)(+) beam is extended. Another advantage of this technique is that the high sputtering rate and associated high molecular ion intensity of the C(60)(+) beam generate adequate high-mass fragments that mask the damage from the Ar(+) beam. As a result, fragments at m/z ~900 can be clearly observed. As a depth-profiling tool, the single C(60)(+) beam cannot reach a steady state for either PET or PMMA at high ion fluence, and the intensity of the molecular fragments produced by the beam decreases with increasing C(60)(+) fluence. As a result, the single C(60)(+) beam is suitable for profiling surface layers with limited thickness. With C(60)(+)-Ar(+) co-sputtering, although the initial drop in intensity is more significant than with single C(60)(+) ionization because of the damage introduced by the auxiliary Ar(+), the intensity levels indicate that a more steady-state process can be achieved. In addition, the secondary ion intensity at high fluence is higher with co-sputtering. As a result, the sputtered depth is enhanced with co-sputtering and the technique is suitable for profiling thick layers. Furthermore, co-sputtering yields a smoother surface than single C(60)(+) sputtering.

Development of analytically capable time-of-flight mass spectrometer with continuous ion introduction

The present article describes the results and findings explored in the course of the development of the analytically capable prototype of continuous time-of-flight (CTOF) mass spectrometer. Currently marketed pulsed TOF (PTOF) instruments use ion introduction with a 10 ns or so pulse width, followed by a waiting period roughly 100 micros. Accordingly, the sample is under excitation in 10(-4) part of the total measuring time. This very low duty cycle severely limits the sensitivity of the PTOF method. A possible approach to deal with this problem is to use linear sinusoidal dual modulation technique (CTOF) as described in this article. This way the sensitivity of the method is increased, due to the 50% duty cycle of the excitation. All other types of TOF spectrometer use secondary electron multiplier (SEM) for detection, which unfortunately discriminates in amplification in favor of the lighter ions. This discrimination effect is especially undesirable in a mass spectrometric method, which targets high mass range. In CTOF method, SEM is replaced with Faraday cup detector, thus eliminating the mass discrimination effect. Omitting SEM is made possible by the high ion intensity and the very slow ion detection with some hundred hertz detection bandwidth. The electrometer electronics of the Faraday cup detector operates with amplification 10(10) V/A. The primary ion beam is highly monoenergetic due to the construction of the ion gun, which made possible to omit any electrostatic mirror configuration for bunching the ions. The measurement is controlled by a personal computer and the intelligent signal generator Type Tabor WW 2571, which uses the direct digital synthesis technique for making arbitrary wave forms. The data are collected by a Labjack interface board, and the fast Fourier transformation is performed by the software. Noble gas mixture has been used to test the analytical capabilities of the prototype setup. Measurement presented proves the results of the mathematical calculations as well as the future potentiality for use in chemical analysis of gaseous mixtures.

Imaging of nutrient elements in the leaves of Elsholtzia splendens by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for the quantitative imaging of nutrient elements (such as K, Mg, Mn, Cu, P, S and B) in the leaves of Elsholtzia splendens. The plant leaves were scanned directly with a focused Nd:YAG laser in the laser ablation chamber. The ablated material was transported with argon as carrier gas to a quadrupole-based ICP-MS (ICP-QMS), and the ion intensities of 39K +, 24Mg +, 55Mn +, 63Cu +, 31P +, 34S + and 11B + were measured by ICP-QMS to study the distribution of the elements of interest. The imaging technique using LA-ICP-MS on plant leaves does not require any sample preparation. Carbon ( 13C +) was used as an internal standard element to compensate for the difference in the amount of material ablated. Additional experiments were performed in order to study the influence of the water content of the analyzed leaves on the intensity signal of the analyte. For quantification purposes, standard reference material (NIST SRM 1515 Apple Leaves) was selected and doped with standard solutions of the analytes within the concentration range of 0.1–2000 mg L −1. The synthetic laboratory standards together with the samples were measured by LA-ICP-MS. The shape and structure of the leaves was clearly given by LA-ICP-MS imaging of all the elements measured. The elemental distribution varied according to the element, but with a high content in the veins for all the elements investigated. Specifically, Cu was located uniformly in the mesophyll with a slightly higher concentration in the main vein. High ion intensity was measured for S with a high amount of this element in the veins similar to the images of the metals, whereas most of the B was detected at the tip of the leaf. With synthetic laboratory standard calibration, the concentrations of elements in the leaves measured by LA-ICP-MS were between 20 μg g −1 for Cu and 14,000 μg g −1 for K.

Effect of Surface Oxide Films on Degradation of Titanium

Thermal desorption spectroscopy (TDS) was applied to measure the hydrogen in titanium (Ti). Because fracture by hydrogen embrittlement for medical/dental devices of Ti and Ti alloys was reported, dependence of surface oxidation film on hydrogen absorption and desorption behaviors of cp-Ti was carried out. To form the surface oxide film (rutile), the Ti wire samples were annealed in an ambient air at 800oC for 2 hours. Half of the specimens were immersed in a mixed solution of NaF and H3PO4 (APF). The part of the specimens were removed the surface films by abrasion after the heat and the immersion in the APF solution. TDS analysis was applied to detect released ions/molecules during heating from room temperature to 1200oC in a high vacuum vessel for the TiH2 powders, the Ti samples with and without the above treatments. High ion intensity was detected for hydrogen (m/z = 2), and ion intensities of the other ions/molecules were almost the background level in measurements. The concentration of hydrogen in the samples related with heat and chemical process was determined quantitatively, and was not significantly increased by the annealing and the immersion in APF solution if the sample had the tough surface film. However, the sample, which had been removed the surface films before the immersion in APF, showed typical chemical degradation after the immersion in APF for 7 days, that is, high ion intensities of hydrogen, fluoride, water and hydroxyl ions were detected. It was concluded that the control of the surface oxide film on the medical/dental Ti devices is important in determining its longevity.

Significant effect of water on surface reaction and related electrochemical properties of mixed conducting oxides

The interaction between water vapor and fluorite-type oxide ion conductors, and its effects on surface and electrochemical properties are investigated. High deuterium ion intensity was observed for rare-earth doped ceria annealed in D 2O-containing atmospheres. It indicates that a pretty amount of deuterium is absorbed in the ceria polycrystalline. The oxygen isotope exchange rate on YSZ surface increased with water vapor pressure, indicating that the interaction between water and oxygen vacancy in YSZ is significant. The interfacial conductivity at platinum/YSZ interface in air at T=968 K was drastically improved by addition of 1 kPa of water vapor pressure. This improvement was clearly observed for YSZ electrolyte, however, only a small effect was observed for Ce 0.8Gd 0.2O 1.9.

Accurate determination of sulfur in gasoline and related fuel samples using isotope dilution ICP-MS with direct sample injection and microwave-assisted digestion.

Inductively coupled plasma isotope-dilution mass spectrometry (ICP-IDMS) with direct injection of isotope-diluted samples into the plasma, using a direct injection high-efficiency nebulizer (DIHEN), was applied for accurate sulfur determinations in sulfur-free premium gasoline, gas oil, diesel fuel, and heating oil. For direct injection a micro-emulsion consisting of the corresponding organic sample and an aqueous 34S-enriched spike solution with additions of tetrahydronaphthalene and Triton X-100, was prepared. The ICP-MS parameters were optimized with respect to high sulfur ion intensities, low mass-bias values, and high precision of 32S/34S ratio measurements. For validation of the DIHEN-ICP-IDMS method two certified gas oil reference materials (BCR 107 and BCR 672) were analyzed. For comparison a wet-chemical ICP-IDMS method was applied with microwave-assisted digestion using decomposition of samples in a closed quartz vessel inserted into a normal microwave system. The results from both ICP-IDMS methods agree well with the certified values of the reference materials and also with each other for analyses of other samples. However, the standard deviation of DIHEN-ICP-IDMS was about a factor of two higher (5-6% RSD at concentration levels above 100 mircog g(-1)) compared with those of wet-chemical ICP-IDMS, mainly due to inhomogeneities of the micro-emulsion, which causes additional plasma instabilities. Detection limits of 4 and 18 microg g(-1) were obtained for ICP-IDMS in connection with microwave-assisted digestion and DIHEN-ICP-IDMS, respectively, with a sulfur background of the used Milli-Q water as the main limiting factor for both methods.

Oxide ion formation of long-lived radionuclides in double-focusing sector field inductively coupled plasma mass spectrometry and their analytical applications

The oxide ion formation of the long-lived radionuclides 226Ra, 230Th, 237Np, 238U, 239Pu, and 241Am was investigated in a mixed aqueous solution by double-focusing sector field inductively coupled plasma mass spectrometry (DF-ICP-MS) with a shielded torch under hot plasma conditions. The measurements of the relative oxide ion intensities by DF-ICP-MS were performed using different nebulizers [Meinhard nebulizer, microconcentric MicroMist nebulizer and a direct injection high-efficiency nebulizer (DIHEN)] for the solution introduction of aqueous standard solutions into the ICP. The highest oxide ion formation rate was observed for thorium in DF-ICP-MS under hot plasma conditions with a shielded torch (ThO +/Th + = 0.13, 0.26, and 0.41 for Meinhard nebulizer. MicroMist nebulizer and DIHEN, respectively). The application of the shielded torch in DF-ICP-MS yielded an increase in oxide ion formation for the Meinhard nebulizer by a factor of 2.7–7, for MicroMist nebulizer 1.6–13 and for DIHEN 1.7–2.8, compared to the original configuration without plasma shielding. The direct injection of sample solution by DIHEN-DF-ICP-MS results in a relatively high oxide ion formation rate (e.g. PuO +/Pu + of about 0.16 and 0.35 without and with a shielded torch, respectively). For the relative oxide ion intensities using the Meinhard and the microconcentric MicroMist nebulizers in DF-ICP-MS with shielded torch a decrease in the following sequence is observed: ThO +/Th + > UO +/U + > NpO +/Np + > PuO +/Pu + > AmO +/Am + ≫ RaO +/Ra +. The observed correlation of measured relative oxide ion intensities (ThO +/Th +, PuO +/Pu +, and UO +/U +) and bond energies of these oxides allows for the estimation of unknown bond energies for AmO and NpO (730 and 670 kJ/mol, respectively). High oxide ion intensity of long-lived radionuclides in DF-ICP-MS could be used in some cases for analytical purposes, e.g. the oxide ions are applied as analyte ions for interference-free isotope analysis and thus for checking the analytical results using the atomic ions of the analyte.

Surface treatment of HV electrodes for superconducting cyclotron beam extraction

At the Istituto Nazionale di Fisica Nucleare Laboratorio Nazionale del Sud of Catania, a K=800 superconducting cyclotron is in operation since 1994. The accelerator beam extraction is accomplished using electrostatic deflectors constituted by HV electrodes generating electric fields to 140 kV/cm in 6 to 8 mm gaps. The electrostatic performance is strongly dependent on the presence of high magnetic fields (up to 5 T) and of high ion energy and intensity of heavy ion beams. The behavior of these systems is mainly determined by the field electron emission effects on the cathode surface, by electron focalization processes due to the magnetic field and by heating effects due to the ion beams. A detailed study of these effects is under development starting with point, the characterization of the electrode surface vs. the material used (Ti, Cu, stainless steel, etc.) and of the best mechanical and chemical treatment available, Moreover, we are studying the electrostatic performance by using titanium surfaces and nitriding over a wide temperature range (300 to 800/spl deg/C). Preliminary results concerning the use of thermal processed polished surfaces are presented and discussed.

Properties of pulsed laser deposited optical coatings

Hafnia and yttria films for optical applications were prepared by pulsed laser ablation with oxygen ion bombardment of the growing films. The influence of the laser and ion beam parameters on the refractive index and microstructure of the films was investigated. The optical quality of the films with respect to absorption and laser damage was characterized at the Nd:YAG-laser wavelength by measuring the laterally resolved absorptivity and the laser damage thresholds. Both hafnia and yttria films prepared at low ion energy and intensity (150 eV, 50 μA/cm 2) were amorphous and had a high bulk-like refractive index and packing density. At high ion energy and intensity (700 eV, 400 μA/cm 2) the films became polycrystalline with high refractive index and packing density at relatively high growth rates above 10 to 20 nm/min or relatively low refractive index and packing density at low growth rates. Films with high laser damage threshold at 1.06 μm wavelength could only be prepared with strong oxygen bombardment. Highly reflective multilayer systems of only one material with alternately high and low refractive index were prepared by varying the parameters of oxygen ion bombardment during deposition. Their reflectivity and laser damage threshold at 1.06 μm as well as their microstructure were investigated.