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Development of a mass spectrometry imaging system utilizing t-SPESI and its application to lipid imaging of tissue sections. The effects of solvent properties on the extraction-ionization process and the spatial resolution of ion images are discussed.

The application of proton transfer ionization reaction mass spectrometry (PTR MS) combined with microscale supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC) aiming to quantitate single-cell fatty acid analysis levels was investigated. Using a microscale extraction vessel, the obtained low limits of quantitation (LLOQs) of arachidonic acid and arachidic acid were 1.2 and 2.7 fmol, respectively, by using less than 1 µL of sample on stainless steel frit. A series of phthalate, vitamin K

Proton-transfer-reaction (PTR) mass spectrometry (MS) is capable of detecting trace-level volatile organic compounds (VOCs) in gaseous samples in real time. Therefore, PTR-MS has become a popular method in many different study areas. Most of the currently reported PTR-MS applications are designed to determine volatile compounds. However, the method might be applicable for nonvolatile organic compound detection. Supercritical fluid chromatography (SFC) has been studied in the last 5 decades. This approach has high separation efficiency and predictable retention behavior, making separation optimization easy. Atmospheric ionization techniques, such as atmospheric chemical ionization (APCI) and electrospray ionization (ESI), are the most studied SFC-MS interfaces. These processes require the addition of makeup solvents to prevent precipitation or crystallization of the solute while depressurizing the mobile phase. In contrast, the PTR process is carried out in a vacuum; supercritical carbon dioxide may release solute into the PTR flow tube without a phase transition as long as it is maintained above a critical temperature. Therefore, this might constitute yet another use for the SFC-MS interface. Caffeine and a few other nonpolar compounds in supercritical carbon dioxide were successfully detected with time-of-flight MS without adding solvent by using preliminarily assembled supercritical flow injection and supercritical fluid extraction (SFE)-PTR interfaces.

Simultaneous ion counting and waveform averaging implemented on a field-programmable gate array compiled with a high-speed digitizer was applied to ultraperformance liquid chromatography-time-of-flight mass spectrometric analysis of sulfa drugs. Ion counting was carried out by a "Peak Detection" (PKD) function that works together with signal averaging (AVG). Sulfadimidine (SDD) and sulfadimethoxine (SDMX) were measured in human serum (HS) model sample matrix. By using simultaneous PKD and AVG acquisition, we observed a unified calibration curve for more than 3 orders of magnitude of sample amounts (0.010-100.0 pmol). The ion count rate for the "practical" sample amounts, such as less than 1 pmol, was below 30%, which is suitable for PKD-based ion counting for quantitative accuracy and excellent peak identification performance. Samples containing 200 fmol or less could not be identified from the AVG waveform. Adding HS treated with acetonitrile severely suppressed the SDMX ion to less than one-half (58.1%). However, a linear response was observed for chromatographic peak area for analytes calculated from PKD waveforms. Also, the mass-resolving power calculated from the peak on the PKD waveform was 24% better than the corresponding AVG waveform, which also improves performance for analyte identification.

Organic aerosols (OA) are major components of fine particulate matter, yet their formation mechanism remains unclear, especially in polluted environments. In this study, we investigated the diurnal chemical compositions and formation processes of OA in carbonaceous particles during winter in Beijing using aerosol time-of-flight mass spectrometry. We found that 84.5% of the measured carbonaceous particles underwent aging processes, characterized by larger diameter and more secondary species compared to fresh carbonaceous particles, and presented different chemical compositions of OA in the daytime and nighttime. During the day, under high O

We developed a novel imaging mass spectrometer based on our accumulating technology for projection-type imaging mass spectrometry, the simulation of an accurate ion trajectory, and the theory for ion optics. The newly developed apparatus yields high spatial resolution with a substantially shorter image-acquisition time compared with conventional scanning-type imaging mass spectrometers. In order to maintain a high mass resolution, a multi-turn time-of-flight mass spectrometer is combined with post-extraction differential acceleration methods. Consequently, a mass resolution of m/Δm ∼ 10 000 and a spatial resolution of 1 μm were achieved simultaneously in this study. Application of our newly established apparatus to biological samples accomplished successful imaging mass spectrometry by exhibiting an organ-specific distribution of endogenous ions as well as a localized distribution of exogenously applied ions with an ultra-high spatial resolution image in the size of 18.5 megapixels.

International audience; The OKEANOS mission utilizing the Solar Power Sail is one of the candidates of the strategic middle-class space exploration to the outer Solar System lead by the JAXA. The mission is planning to be launched in 2030's, and rendezvous for spectral observations and landing for in-situ measurements of light isotopes and organic molecules to a D or P type Jupitar Trojan asteroid in 2040's. The flagship instrument on board is a high-resolution mass spectrometry (HRMS) system together with suits of remote-sensing instruments. Through in-depth scientific observations, the OKEANOS mission will provide critical input to the key questions of (1) constraining planet formation/migration theories, and (2) inventory and distribution of volatiles in the Solar System. We have conducted experimental tests of a sample canister sealing by a metal seal knife-edge, sample canister-MULTUM test, gas chromatograph-MULTUM coupling test for organics, and H and N isotopic measurements in the atmospheric air. Current performances are (1) high mass resolution was 30,000 at m/z = 20, (2) sample canister system with a knife-edge metal seal kept 90 % of a released gas in 1 hour for Cu or Au gaskets with/without regolith, (3) error meets the required precision and accuracy for nitrogen isotopic measurement but for hydrogen. These experiment tests need to continue for our scientific proposes on the asteroids.

Organic aerosols (OA) are major components of fine particulate matter, yet their formation mechanism remains unclear, especially in polluted environments. Laboratory studies have shown that the OA formation processes may be different under irradiated and dark conditions, but few studies have explored this aspect in ambient air. Here we investigate the diurnal chemical composition and formation processes of OA in carbonaceous particles during winter in Beijing using aerosol time-of-flight mass spectrometry. Our results show that 84.5% of carbonaceous particles undergo aging processes, characterized with larger size and more secondary species compared to fresh carbonaceous particles, and present different chemical compositions of OA in the daytime and nighttime. During the day, organosulfates and oligomers exist in the aged carbonaceous particles, which are mixed with a higher abundance of nitrate compared with sulfate. At night, distinct spectral signatures of hydroxymethanesulfonate and organic nitrogen compounds, and a minor abundance of other hydroxyalkylsulfonates and high molecular weight organic compounds are present in the aged carbonaceous particles, which are mixed with a higher abundance of sulfate compared with nitrate. Our results indicate that photochemistry dominates the formation of OA under high oxidant concentrations in the daytime, while aqueous chemistry plays an important role in the formation of OA under high relative humidity in the nighttime. The findings can help improve the performance of air quality and climate models on OA simulation.

Using a multi-turn time-of-flight (TOF) mass spectrometer, we have extracted a single xenon isotope ion, 129Xe+, from its orbit at given a lap number without disturbing the rest of isotopes. After detecting the 129Xe+ at 20 laps, the rest of the xenon isotope spectrum was obtained at 30 laps, which generated a TOF spectrum where the TOF difference between 129Xe+ and 130Xe+ was 87.4 μs while 130Xe+ and 131Xe+ were 1.03 μs. The time distance between 129Xe+ and other isotopes can be set by any lap difference that is a factor of 8.7 μs, which depends on the acceleration voltage and the mass of the ion. Method accuracy was verified by comparing the isotopic abundance ratio of the xenon sample after withdrawing one of the ions from the isotope cluster to the abundance ratio obtained from the conventional method. The TOF stability was also evaluated at various lap numbers between 10 to 230.

We developed a mass spectrometric soil-gas flux measurement system using a portable high-resolution multi-turn time-of-flight mass spectrometer, called MULTUM, combined with an automated soil-gas flux chamber for continuous field measurement of multiple gas concentrations. The developed system continuously measures concentrations of four different atmospheric gases (i.e., N2O, CH4, CO2, and O2), of which the concentrations range over six orders of magnitude at a time within a single gas sample. The measurements were performed every 2.5 min with analytical precisions (two standard deviations) of ±34 ppbv for N2O, ±170 ppbv for CH4, ±16 ppmv for CO2, and ±0.60 vol% for O2 at their atmospheric concentrations. The developed system was used for continuous field soil–atmosphere flux measurements of greenhouse gases (GHGs: N2O, CH4, and CO2) and O2 with 1 h resolution. The minimum quantitative fluxes (two standard deviations) were estimated through simulation as 70.2 µg N m−2 h−1 for N2O, 139 µg C m−2 h−1 for CH4, 11.7 mg C m−2 h−1 for CO2, and 9.8 g O2 m−2 h−1 (negative) for O2, whereas the estimated minimum detectable fluxes (two standard deviations) were 17.2 μg N m−2 h −1 for N2O, 35.4 μg C m−2 h−1 for CH4, 2.6 mg C m−2 h−1 for CO2, and 2.9 g O2 m−2 h−1 for O2. The developed system was deployed in the University Farm of the Ehime University (Matsuyama, Ehime, Japan) for a field observation over five days. Interestingly, an abrupt increase in N2O flux from 70 to 682 µg N m−2 h−1 was observed a few hours after the first rainfall, whereas no obvious increase in the CO2 flux was observed, although the temporal responses were different from those observed in a laboratory experiment. No abrupt N2O flux change was observed in succeeding rainfalls. Continuous multiple-gas flux and concentration measurements can be a powerful tool for tracking and understanding of underlying biological and physicochemical processes in the soil through measuring more tracer gases, such as volatile organic carbon gases, reactive-nitrogen gases, and noble gases by taking advantage of the broad versatility of mass spectrometry in detecting broad range of gas species.

An ion trap/time-of-flight mass spectrometer equipped with a metastable atom bombardment (MAB) ionization source was constructed in order to observe ion-molecule reactions controlled by the internal energy of ions. In the MAB source, the internal energy of the generated ions was controlled by using different rare gases. Moreover, the constructed device was used to analyze ion-molecule reactions of the p-xylene cation and its dissociation ions with p-xylene. It was found that the reaction afforded a single product without any structural isomers, which could then be easily analyzed. An abundant amount of [M]+ (m/z 106, C8H10+ ) and trace levels of dissociation products were observed in the Kr MAB ionization, while in the Ar MAB ionization, [M−CH3]+, [M−H]+ (m/z 105, C8H9+), and [M+CH]+ (m/z 119, C9H11+) ions were generated in addition to the molecular ion. Moreover, investigating the production routes to [M−H]+ and [M+CH]+ ions using a resonance ejection method in the ion trap indicating that generation of these ions was related to the hydride transfer reaction of C7H7+ with p-xylene. Results from the calculations of the reaction profile of this transfer using the density functional theory (DFT) method supported the experimental results.

Two different types of data acquisition methods, "averaging mode" and "ion-counting mode", have been used in a time-of-flight (TOF) mass spectrometry. The most common method is an averaging mode that sums waveform signals obtained from each flight cycle. While it is possible to process many ions arriving at the same TOF in one flight cycle, low-abundance ions are difficult to measure because ion signals are overwhelmed by noises from the detection system. An ion-counting mode is suitable for the detection of such low-concentration ions, but counting loss occurs when two or more ions arrive at the detector within the dead time of the acquisition system. In this study, we introduce a technique that combines two methods to measure target ions with a high concentration difference, i.e., averaging mode and ion-counting mode are used simultaneously for high abundant and trace ions, respectively. By processing waveforms concurrently during data acquisition, one can choose to analyze either or both types of data to achieve a highly quantitative mass spectrum over a wide range of sample concentrations. The result of the argon isotope analysis shows that this method provides a more accurate determination of the isotope ratio compared to averaging mode alone at one-twentieth of the analysis time required by ion-counting alone. Graphical Abstract ᅟ.

A time-of-flight mass spectrometer that uses a closed-orbit flight path can achieve a high mass resolving power and a high mass accuracy with a small instrument footprint. It has long been known that a drawback to a closed flight path is an obtained spectrum may contain peaks by ions at a different number of laps. A lower m/z ion may overtake higher m/z ions, resulting in the peak being superimposed on an acquired mass spectrum; therefore, such a mass bandwidth of the analyzer is limited to a narrow range given the current situation. However, recent research has documented a solution to the problem based on careful study of the equation of motion of an ion in a closed-path analyzer. All of the ions in the analyzer remain in motion in orbit by the nature of the closed flight path, thus resulting in a superimposed spectrum with the width of the orbital period of the highest mass in the sample matrix, which contains several different lap numbers. When target ions for the sample are known in advance, the time-of-flight for a given m/z can be determined regardless of the lap number under given analyzer conditions, and peak assignment can be self-validated by comparison to a mass spectrum acquired at a different lap condition. Furthermore, the m/z value for an unknown ion can also be determined by comparing time-of-flight values on spectra acquired at different lap conditions.

Previously, we reviewed several mass spectrometers designed for field analysis, also known as harsh mass spectrometers. The majority of these instruments are focused on the instrument footprint size and weight, which compromise the performance, for instance, in terms of mass-resolving power. Our recent work employed a shoebox-size (mini-tower personal computer size) high-resolving-power mass analyzer equipped with a robust gas chromatograph in the firm field, which successfully monitored the soil-gas compositional changes on-the-fly in real time. We evaluated the system performance for mass accuracy, self-validation testing for analyte peaks, and quantitative precision through long-term continuous data acquisitions of 1429 replicates of model gas samples for 48 h. The observed mass drift was 4 mDa, which was compensated within 0.45 mDa using a novel algorithm without the addition of mass reference materials. In addition, the optimized algorithm for high-resolution ion chromatogram extraction for this application was evaluated. Results indicated that the proposed method limited the chromatographic peak area variance. The coefficient of variance (CV) for determining CO2 amounts for the 1429 sample runs was 8.6%. Furthermore, the CO2 average retention time was 48.06 ± 0.29 s (CV = 0.61%), average number of theoretical plates was 3500, and asymmetry factor was 1.09.

Detector gain saturation is a well-known issue with the chevron microchannel plate (MCP) detector configured with two MCPs, which is widely used in the time-of-flight (TOF) mass spectrometer. In these detectors, high-intensity signals saturate the gain stages, thus reducing the magnitude of subsequent signals. To solve this issue, we developed a new detector that combines an MCP with an avalanche diode. Gain saturation was evaluated by measuring the percent of signal intensity loss of the second significant ion peak on the TOF spectrum using xenon isotopes, and then verified by argon spiked with nitrogen as a model sample. The signal intensity ratio of 132Xe/129Xe on the chevron MCP and the new detector named ‘MIGHTION’ was 0.31 and 0.94 using the ion counting result as the reference, which corresponds to 69 % signal suppression for the chevron MCP, but only an 8% difference for MIGHTION. By using trace-level argon spiked with nitrogen, the argon intensity change was monitored by alternately switching the nitrogen sample on and off with the ion gate. The intense nitrogen peak did not suppress the argon intensity peak, which appears 1 . 17 μ s later. The nitrogen peak intensity was about 240 times larger compared to argon, and the peak voltage was 3.25 V with a 50- Ω load.

Rapid acquisition of time-of-flight (TOF) spectra from fewer acquisitions on average was investigated using the newly introduced 12-bit digitizer, Keysight model U5303A. This is expected to achieve a spectrum acquisition 32 times faster than the commonly used 8-bit digitizer for an equal signal-to-noise (S/N) ratio. Averaging fewer pulses improves the detection speed and chromatographic separation performance. However, increasing the analog-to-digital converter bit resolution for a high-frequency signal, such as a TOF spectrum, increases the system noise and requires the timing jitter (aperture error) to be minimized. We studied the relationship between the S/N ratio and the average number of acquisitions using U5303A and compared this with an 8-bit digitizer. The results show that the noise, measured as root-mean-square, decreases linearly to the square root of the average number of acquisitions without background subtraction, which means that almost no systematic noise existed in our signal bandwidth of interest (a few hundreds megahertz). In comparison, 8-bit digitizers that are commonly used in the market require 32 times more pulses with background subtraction.

A simple, effective accurate mass assignment procedure for a time-of-flight mass spectrometer is desirable. External mass calibration using a mass calibration standard together with an internal mass reference (lock mass) is a common technique for mass assignment, however, using polynomial fitting can result in mass-dependent errors. By using the multi-turn time-of-flight mass spectrometer infiTOF-UHV, we were able to obtain multiple time-of-flight data from an ion monitored under several different numbers of laps that was then used to calculate a mass calibration equation. We have developed a data acquisition system that simultaneously monitors spectra at several different lap conditions with on-the-fly centroid determination and scan law estimation, which is a function of acceleration voltage, flight path, and instrumental time delay. Less than 0.9 mDa mass errors were observed for assigned mass to charge ratios ( m/z) ranging between 4 and 134 using only 40Ar+ as a reference. It was also observed that estimating the scan law on-the-fly provides excellent mass drift compensation.

We report time-of-flight mass spectrometry under the irradiation of the terahertz free electron laser pulses with different excitation frequencies to clarify the novel desorption caused by the strong excitation resonance with the THz modes in hydrogen-bonded solids.

Helium isotope determination may be useful in measuring volcanic activity and issuing earlier warnings of possible eruptions. A method is presented for measuring the 3He/4He ratio in a gas sample using a multiturn time-of-flight mass spectrometer “infiTOF”. In contrast to conventional waveform averaging, peaks are determined by counting ion pulses from each time-of-flight trigger. Samples were also measured by conventional magnetic-sector mass spectrometry for comparison. Magnetic sector results were used to designate a standard for infiTOF measurement and to calculate a ratio for each sample measured by infiTOF. Mass assignment error for ultrapure 3He+ standard was 4.30 × 10–5 Da. Mass assignment error of 4He2+ and 3He+ for sample cylinders was 3.00 × 10–8 Da and 2.25 × 10–4 Da, respectively. Abundance ratios determined by infiTOF were found to be within 2% of the abundance ratios determined by magnetic-sector mass spectrometry. Mass drift was

Many miniaturized mass spectrometers used for on-site analysis have been designed and developed recently utilizing a broad range of analyzer platforms. These instruments are expected to have widespread applications covering many fields of interest. In our laboratory, a miniaturized multi-turn time-of-flight (TOF) mass spectrometer "MULTUM-S II" was designed and constructed. The size and weight of the developed "MULTUM-S II" are 45 cm × 23 cm × 64 cm and 36 kg. Irrespective of this small platform, it still boasts a high mass resolution capability of more than 30,000. In this study, we attempted to carry out real-time monitoring of gaseous compounds such as N2, O2, CO2, N2O and CH4. Using conventional miniaturized mass spectrometers, CO2 and N2O cannot be detected simultaneously due to the low mass resolution inherent to these established analyzer designs. Using a new method, "GC/high resolution mass spectrometry" described in this paper, real time monitoring of gases emitted from soils can be achieved. In a soil incubation experiment, CO2 and N2O started to increase just after water supplement and these gases varied similarly during the experiment, thus showing that this improved gas analyzing system could monitor the short time response of gaseous production in soil.

The quantitative accuracy and throughput performance for the newly developed hardware-based simultaneous ion counting and waveform averaging (AVG) in a time-of-flight (TOF) mass spectrometer was studied. The peak detection (PKD) algorithm was used for ion counting instead of voltage threshold detection method that is widely used in ion counting techniques. The silicon isotope abundance ratios were determined by the ion counting with ± 4 % uncertainties relative to the known isotope ratios. The measurements were carried out at relatively higher count rate condition (40 % which means that 0.4 ions arrived at the detector for each TOF trigger), but no systematic errors observed, which indicates the PKD algorithm was able to resolve two or more ions detected simultaneously compared to a simple voltage threshold detection algorithm. An excellent linear response was observed between PKD-based ion counts and the peak area determined by AVG waveform for 2 orders of magnitude. By using peak area based on AVG waveform for higher abundance ions and ion counting based on PKD for lower abundance ions, the silicon isotope abundance ratios were determined with the same analytical precision at one-tenth of the analysis time required for the ion counting alone.

We investigated the soft desorption mechanism of organic molecules under irradiation of intense THz free electron laser pulses resonant for intermolecular motions in the solids by time-of-flight mass spectrometry and time-resolved luminescence measurements.

High molecular weight organic compounds (HMW-OCs), formed as secondary organic aerosols (SOA), have been reported in many laboratory studies. However, little evidence of HMW-OCs formation, in particular during winter season in the real atmosphere, has been reported. In January 2013, Beijing faced historically severe haze pollution, in which the hourly PM2.5 concentration reached as high as 974 μg m-3. Four typical haze events (HE1 to HE4) were identified, and HE2 (Jan. 9-16) was the most serious of these. Based on the hourly observed chemical composition of PM2.5 and the daily organic composition analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), we found that abundant ion peaks in m/z 200-850 appeared on heavy haze days, whereas these were negligible on a clear day, indicating the existence of HMW-OCs in the wintertime haze. A negative nonlinear correlation between HMW-OCs and O3 suggested that gas oxidation was not likely to be the dominant mechanism for HMW-OCs formation. During the heavy haze events, the relative humidity and mass ratio of H2O/PM2.5 reached as high as 80% and 0.2, respectively. The high water content and its good positive correlation with HMW-OCs indicated that an aqueous-phase process may be a significant pathway in wintertime. The evidence that acidity was much higher during HE2 (0.37 μg m-3) than on other days, as well as its strong correlation with HMW-OCs, indicated that acid-catalyzed reactions likely resulted in HMW-OCs formation during the heavy winter haze in Beijing.

Periodontitis is one of the most prevalent threats to oral health as the most common cause of tooth loss. In order to perform effective treatment, a clinical test that detect sites where disease activity is high and predicts periodontal tissue destruction is strongly desired, however, it is still difficult to prognose the periodontal tissue breakdown on the basis of conventional methods. The aim of this study is to examine the usefulness of gas chromatography/mass spectrometry (GC/MS), which could eventually be used for on-site analysis of metabolites in gingival crevicular fluid (GCF) in order to objectively diagnose periodontitis at a molecular level. GCF samples were collected from two diseased sites (one site with a moderate pocket and another site with a deep pocket) from each patient and from clinically healthy sites of volunteers. Nineteen metabolites were identified using GC/MS. Total ion current chromatograms showed broad differences in metabolite peak patterns between GCF samples obtained from healthy sites, moderate-pocket sites, and deep-pocket sites. The intensity difference of some metabolites was significant at sites with deep pockets compared to healthy sites. Additionally, metabolite intensities at moderate-pocket sites showed an intermediate profile between the severely diseased sites and healthy sites, which suggested that periodontitis progression could be observed with a changing metabolite profile. Principal component analysis confirmed these observations by clearly delineating healthy sites and sites with deep pockets. These results suggest that metabolomic analysis of GCF could be useful for prediction and diagnosis of periodontal disease in a single visit from a patient and provides the groundwork for establishing a new, on-site diagnostic method for periodontitis.

A new tandem time-of-flight mass spectrometer with an electrospray ionization ion source 'ESI-TOF/quadTOF' was designed and constructed to achieve the desired aim of structural elucidation via high-energy collision-induced dissociation (CID), and the simultaneous detection of all fragment ions. The instrument consists of an orthogonal acceleration-type ESI ion source, a linear TOF mass spectrometer, a collision cell, a quadratic-field ion mirror and a microchannel plate detector. High-energy CID spectra of doubly protonated angiotensin II and bradykinin were obtained. Several fragment ions such as a-, d-, v- and w-type ions, characteristic of high-energy CID, were clearly observed in these spectra. These high-energy CID fragment ions enabled confirmation of the complete sequence, including leucine-isoleucine determinations. It was demonstrated that high-energy CID of multiply protonated peptides could be achieved in the ESI-TOF/quadTOF.

A tandem time-of-flight (TOF) mass spectrometer with an electrospray ionization (ESI) ion source (ESI-TOF/quadTOF) was enhanced to perform high-energy electron transfer dissociation (ETD) experiments. Specifically, the collision cell for rare gas targets of ESI-TOF/quadTOF was replaced with one for alkali metal targets. High-energy ETD spectra were obtained of doubly protonated polypeptides and a phosphopeptide using a Cs target. Peaks due to several c- and z-type fragment ions formed by the high-energy ETD process were clearly observed in all cases. These results demonstrate that high-energy ETD can be performed using ESI-TOF/quadTOF.

The mass resolution of a time-of-flight (ToF) mass spectrometer is directly proportional to its total flight path length. We have developed multi-turn ToF mass spectrometers, where ions are stored in a fixed orbit within electrostatic sectors and allowed to propagate the said orbit numerous times. With each successive orbit, the flight path is correspondingly increasing. The first multi-turn ToF mass spectrometer, the MULTUM Linear plus, was developed for cometary exploration. The spectrometer consists of four cylindrical electrostatic sectors and 28 electrostatic quadrupole lenses. The size of the analyzer is 40 cm square. Mass resolution is demonstrated to increase according to the number of ion cycles. A mass resolution of greater than 350,000 was achieved after 501.5 cycles. Another multi-turn ToF mass spectrometer, the MULTUM II, which consists of only four toroidal electrostatic sectors, was also developed in an effort to reduce the number of quadrupole lenses. We are developing various types of mass spectrometer based on the MULTUM II technology, a ToF/ToF mass spectrometer “MULTUM-TOF/TOF”, a stigmatic imaging mass spectrometer “MULTUM-IMG” and miniature mass spectrometers of high mass resolving power, the “MULTUM-S” series.

Relative intensities of singly-charged mono-bromide silver clusters Ag xBr+ formed from sputtering of a pressed pellet of silver bromide were measured by mass spectrometry. The obtained results suggest that the Ag xBr+ clusters have a structural formula of the form Ag x–1+(AgBr). The relative stability of Ag x–1+(AgBr) was determined by the intrinsic stability of the remaining metallic portion of the cluster (Ag x–1+) as predicted by the spherical jellium model (SJM). Unimolecular and high-energy collision-induced dissociation (CID) spectra of Ag xBr+ ( x = 2, 4, 6, 8, 10) clusters were also measured. In all of the spectra, the most intense fragment peaks were assigned to the Ag x–1+ ions accompanying the loss of AgBr. The difference in the relative intensities of the Ag x–1+ peaks between unimolecular dissociation and CID spectra led us to conclude that the weakest bond in the excited cluster Ag xBr+* is the Ag x–1+–AgBr bond and the structure of Ag xBr+ is a metallic Ag x–1+ ion cluster adduct with AgBr. The primary fragments observed in the CID spectra were also explained by the stabilities of the generated ion products and neutral fragments, both having even delocalized valence electrons. The present results were consistently explained by SJM. The dissociation behavior of Ag2Br+ can be explained on the basis of the calculated thermochemical data.