The design and characteristic features of a new time-of-flight mass spectrometer with a spiral ion trajectory

Advances in high-resolution mass spectrometry techniques for analysis of high mass-to-charge ions

A major challenge in modern mass spectrometry (MS) is achieving high mass resolving power and accuracy for precision analyses in high mass-to-charge (m/z) regions. To advance the capability of MS for increasingly demanding applications, understanding limitations of state-of-the-art techniques and their status in applied sciences is essential. This review summarizes important instruments in high-resolution mass spectrometry (HRMS) and related advances to extend their working range to high m/z regions. It starts with an overview of HRMS techniques that provide adequate performance for macromolecular analysis, including Fourier-transform, time-of-flight (TOF), quadrupole-TOF, and related data-processing techniques. Methodologies and applications of HRMS for characterizing macromolecules in biochemistry and material sciences are summarized, such as top-down proteomics, native MS, drug discovery, structural virology, and polymer analyses.

A comparison of four liquid chromatography-mass spectrometry platforms for the analysis of zeranols in urine

Targeted biomonitoring studies quantifying the concentration of zeranols in biological matrices have focused on liquid chromatography interfaced to mass spectrometry (LC-MS). The MS platform for measurement, quadrupole, time-of-flight (ToF), ion trap, etc., is often chosen based on either sensitivity or selectivity. An instrument performance comparison of the benefits and limitations using matrix-matched standards containing 6 zeranols on 4 MS instruments, 2 low-resolution (linear ion traps), and 2 high-resolution (Orbitrap and ToF) was undertaken to identify the best measurement platform for multiple biomonitoring projects characterizing the endocrine disruptive properties of zeranols. Analytical figures of merit were calculated for each analyte to compare instrument performance across platforms. The calibration curves had correlation coefficients r = 0.989 ± 0.012 for all analytes and LODs and LOQs were ranked for sensitivity: Orbitrap > LTQ > LTQXL > G1 (V mode) > G1 (W mode). The Orbitrap had the smallest measured variation (lowest %CV), while the G1 had the highest. Instrumental selectivity was calculated using full width at half maximum (FWHM) and as expected, the low-resolution instruments had the broadest spectrometric peaks, concealing coeluting peaks under the same mass window as the analyte. Multiple peaks from concomitant ions, unresolved at low resolution (within a unit mass window), were present but did not match the exact mass predicted for the analyte. For example, the high-resolution platforms were able to differentiate between a concomitant peak at 319.1915 from the analyte at 319.1551, included in low-resolution quantitative analyses demonstrating the need to consider coeluting interfering ions in biomonitoring studies. Finally, a validated method using the Orbitrap was applied to human urine samples from a pilot cohort study.

High-performance miniature linear time-of-flight mass spectrometry as an advantageous tool in a high mass-to-charge range

A newly developed miniature MALDI-TOF mass spectrometer provides superior performance in a high m/z range.

Mass Spectrometry-Based Analytical Strategy for Comprehensive Molecular Characterization of Biodegradable Poly(lactic-co-glycolic Acid) Copolymers

An analytical methodology with mass spectrometry as the core technique was developed for precise characterization of end groups, size, and co-monomeric composition of poly(lactic-co-glycolic acid) (PLGA) copolymers, as a preliminary step to qualify their biodegradability. Four PLGA samples were studied, with GA molar content varying from 0 to 50% and M_w ranging from 18 to 75 kg mol^-1 according to the supplier. Size exclusion chromatography (SEC) and liquid state nuclear magnetic resonance (NMR) were used as either complementary or validation techniques. As confirmed by tandem mass spectrometry (MS/MS) experiments, macrocycles were most prominent in the low mass range. Nevertheless, elemental compositions derived from high resolution (HR) mass measurements of linear species were consistent with chain terminations revealed by NMR. Off-line coupling of SEC with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) permitted calibration curves to be built based on absolute molecular weights and, although slightly overestimated, so-obtained M_n and M_w values compared well with SEC and NMR results. Homogeneity of the co-monomeric content of all chains within each PLGA sample was demonstrated using surface-assisted laser desorption/ionization in a reactive mode (reactive-SALDI), a newly developed technique that takes advantage of residual acid on desorption ionization using through-hole alumina membrane (DIUTHAME) chips to induce dissociation of high-molecular-weight polymers containing cleavable C-O bonds. All HRMS data were best handled with Kendrick analysis, which helped reveal minor species and allowed automated computation of congested mass spectra.

Mass spectrometry as a tool to advance polymer science

In contrast to natural polymers, which have existed for billions of years, the first well-understood synthetic polymers date back to just over one century ago. Nevertheless, this relatively short period has seen vast progress in synthetic polymer chemistry, which can now afford diverse macromolecules with varying structural complexities. To keep pace with this synthetic progress, there have been commensurate developments in analytical chemistry, where mass spectrometry has emerged as the pre-eminent technique for polymer analysis. This Perspective describes present challenges associated with the mass-spectrometric analysis of synthetic polymers, in particular the desorption, ionization and structural interrogation of high-molar-mass macromolecules, as well as strategies to lower spectral complexity. We critically evaluate recent advances in technology in the context of these challenges and suggest how to push the field beyond its current limitations. In this context, the increasingly important role of high-resolution mass spectrometry is emphasized because of its unrivalled ability to describe unique species within polymer ensembles, rather than to report the average properties of the ensemble.

Time-of-flight mass spectrometers based on a wedge-shaped electrostatic mirror with a two-dimensional field

RATIONALE

For most of the last two decades, a considerable effort has been made towards improving time-of-flight mass spectrometry (TOF MS), which has become an irreplaceable instrumental platform for the purposes of performing analytical measurements in life sciences, such as molecular biology, proteomics, medicine, etc. This can primarily be attributed to the ability of TOF MS to rapidly detect and identify nearly any targeted chemical trace with both high precision and accuracy. However, multi-span TOF MS experiments are limited due to aberrations arising from multiple reflection; our proposed scheme will minimize these aberrations.

METHODS

The inhomogeneous accelerating field is generated without using meshes by changing the potentials on the electrodes of the mirror. The ions are extracted from the ion source by short impulse activation of the accelerating electric field. Since the ions are extracted from various points of the source, even ions with identical masses acquire different velocities during acceleration.

RESULTS

We have shown that the "rear" ions of the packet catch up with the "front" ions, and packets of ions with identical masses are compressed in the direction of their movement. It is concluded that, by placing the detector in a plane with the greatest compression of ion packets, an enhanced performance of a time-of-flight mass spectrometer is achieved.

CONCLUSIONS

We have shown that effective spatial-temporal focusing allows a small mass spectrometer to achieve high resolution and sensitivity. We also propose and numerically evaluate a new platform for designing multi-stage and multi-reflective time-of-flight analyzers with wedge-shaped mirrors. We applied the simulation results to the modernization of old equipment and showed that by simply replacing the electrostatic mirror with an optimized one, a significant increase in the analyzing power can be achieved.

The Kendrick analysis for polymer mass spectrometry

The mass spectrum of a polymer often displays repetitive patterns with peak series spaced by the repeating unit(s) of the polymeric backbones, sometimes complexified with different adducts, chain terminations, or charge states. Exploring the complex mass spectral data or filtering the unwanted signal is tedious whether performed manually or automatically. In contrast, the now 60-year-old Kendrick (mass defect) analysis, when adapted to polymer ions, produces visual two-dimensional maps with intuitive alignments of the repetitive patterns and favourable deconvolution of features overlaid in the one-dimensional mass spectrum. This special feature article reports on an up-to-date and theoretically sound use of Kendrick plots as a data processing tool. The approach requires no prior knowledge of the sample but offers promising dynamic capabilities for visualizing, filtering, and sometimes assigning congested mass spectra. Examples of applications of the approach to polymers are discussed throughout the text, but the same tools can be readily extended to other applications, including the analysis of polymers present as pollutants/contaminants, and to other analytes incorporating a repetitive moiety, for example, oils or lipids. In each of these instances, data processing can benefit from the application of an updated and interactive Kendrick analysis.

Molecular Characterization of High Molecular Weight Polyesters by Matrix-Assisted Laser Desorption/Ionization High-Resolution Time-of-Flight Mass Spectrometry Combined with On-plate Alkaline Degradation and Mass Defect Analysis

Matrix-assisted laser desorption ionization high-resolution time-of-flight mass spectrometry (MALDI HR TOF MS) is a powerful tool for the molecular characterization of industrial polymers. However, accurate mass determination and resolution of isobaric ions are possible for oligomer samples only typically below m/z 3000. To cut long polymer chains into oligomers suitable for high-resolution mass spectrometry, we propose a simple "on-plate" alkaline degradation of polyesters as a sample pretreatment technique prior to the MALDI TOF MS measurement. This pretreatment can be performed on a MALDI target using a small amount of sample (μg or less) and 1 μL of alkaline reagent by simple pipetting. Informative mass spectra in the oligomeric mass range are successfully recorded but complicated by the variation of end-groups and the copolymeric composition of the degradation products. Data processing is assisted by a series of advanced Kendrick mass defect (KMD) analyses recently proposed by the authors to plot visually understandable two-dimensional maps. On-plate degradation pretreatment, high-resolution MALDI TOF MS measurements, and advanced KMD analyses are innovatively combined for the compositional characterization of bacterial poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) and industrial poly(ethylene terephthalate) samples. Graphical Abstract ᅟ.

Improving the Resolution of Kendrick Mass Defect Analysis for Polymer Ions with Fractional Base Units

The concept of a fractional base unit for the Kendrick mass defect (KMD) analysis of polymer ions is introduced for the first time. A fraction of the ethylene oxide (EO) repeat unit (namely EO/8) has been used for the KMD analysis of a poly(ethylene oxide) and found to amplify the variations of KMD between monoisotopic and ¹³C isotopes, producing an isotopically resolved KMD plot at full scale when the KMD plot computed with EO is fuzzy. The expansion of the KMD dimension using a fractional base unit has then been successfully used to unequivocally discriminate all the distributions from a blend of poly(ethylene oxide)s in a high resolution KMD plot calculated with EO/3 as base unit. Extending the concept of fractional base units to other repeat units, the visualization of the co-oligomers from a poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymer has been dramatically improved using a fraction of the propylene oxide repeat unit (namely PO/3) in an oligomer and isotope resolved plot. High resolution KMD plots were eventually calculated from tandem mass spectra of poly(dimethylsiloxane) ions using a fraction of the dimethylsiloxane (DMS) unit (namely DMS/6) with clearer point alignments and a discrimination of all the product ion series, out of reach of the KMD analysis using DMS. Versatile and producing high resolution KMD plots, the introduction of fractional base units is believed to be a major step towards the implementation of the KMD analysis as a routine data mining tool for mass spectrometry in polymer chemistry.

Characterization of the cross-linking structures in UV- and EB-cured acrylic copolymer resins using high resolution MALDI-spiral-TOFMS combined with supercritical methanolysis

The cross-linking structures of ultraviolet (UV) and electron beam (EB)-cured acrylic copolymer resins prepared with pentaerithritol triacrylate and 1-vinyl-2-pyrrolidone (VP) mixtures were characterized using high resolution MALDI-TOFMS combined with supercritical methanolysis.

Multi-stage Mass Spectrometry of Poly(vinyl pyrrolidone) and Its Vinyl Succinimide Copolymer Formed upon Exposure to Sodium Hypochlorite

The degradation routes of poly(vinyl pyrrolidone) (PVP) exposed to sodium hypochlorite (bleach) have been previously investigated using chemical analyses such as infrared spectroscopy. So far, no reports have proposed mass spectrometry (MS) as an alternative tool despite its capability to provide molecular and structural information using its single stage electrospray (ESI) or matrix assisted laser desorption ionization (MALDI) and multi stage (MS ⁿ ) configurations, respectively. The present study thus reports on the characterization of PVP after its exposure to bleach by high resolution MALDI spiralTOF-MS and Kendrick mass defect analysis providing clues as to the formation of a vinyl pyrrolidone/vinyl succinimide copolymeric degradation product. A thorough investigation of the fragmentation pathways of PVP adducted with sodium and proton allows one main route to be described-namely the release of the pyrrolidone pendant group in a charge remote and charge driven mechanism, respectively. Extrapolating this fragmentation pathway, the oxidation of vinyl pyrrolidone into vinyl succinimide hypothesized from the single stage MS is validated by the detection of an alternative succinimide neutral loss in lieu of the pyrrolidone release in the ESI-MS ⁿ spectra of the aged PVP sample. It constitutes an example of application of multi-stage mass spectrometry for the characterization of the degradation of polymeric samples at a molecular level.

In pursuit of resolution in time-of-flight mass spectrometry: A historical perspective

Time-of-flight mass spectrometry is reviewed from its inception in the 1940s to the present day. The review is concerned with fundamentals of time-of-flight analyzers and of ion sources to the extent that sources influence analyzers. The patent literature has been covered, and efforts made to bring to light less well-known papers and studies © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 35:738-757, 2016.

MALDI SpiralTOF high-resolution mass spectrometry and Kendrick mass defect analysis applied to the characterization of poly(ethylene-co-vinyl acetate) copolymers

RATIONALE

Poly(ethylene-co-vinyl acetate) copolymers - usually referred to as EVA - are first class industrial polymers used for applications ranging from padding to photovoltaics as encapsulant for the silicon solar cells. Various techniques have been used for their characterization but the analysis of intact EVA chains using mass spectrometry (MS) has not been reported so far.

METHODS

Three copolymers containing 18, 25 and 40 wt% vinyl acetate (VA) have been characterized using an off-line coupling of size-exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization (MALDI) spiral-time-of-flight (TOF) high-resolution mass spectrometry (HRMS). The representativeness of those results for the entire samples has been checked using (13) C NMR spectroscopy. Lastly, Kendrick mass defect analysis has been proposed as an alternative and user-friendly data treatment method.

RESULTS

The shortest chains isolated by SEC fractionation and mass-analyzed by HRMS have been thoroughly described in terms of end-groups (found to be hydrogens) and co-monomeric composition. The VA content was successfully derived from the peak assignments in MS spectra for the EVA 40 wt% and 25 wt% while it tended to be overestimated for the latest EVA 18 wt% (increasing poly(ethylene) character). Similar results have been found using a faster data treatment method relying on the Kendrick mass defect analysis of the MS data.

CONCLUSIONS

EVA low molecular weight intact oligomers have been extensively characterized by MS for the first time and the structural features confidently extended to the full sample according to NMR data. The Kendrick mass analysis finally constituted an efficient method for a fast evaluation of their VA content with no need for manual assignment. © 2016 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.

High-resolution MALDI-TOF MS study on analysis of low-molecular-weight products from photo-oxidation of poly(3-hexylthiophene)

High-resolution matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS) was used for the analysis of the low-molecular-weight products from the photo-oxidation of poly(3-hexylthiophene) (P3HT) in solution and thin film. Eight new peak series were observed in the low-mass range of the mass spectra of the products degraded in solution, and the formulas of the eight components were determined from the accurate mass. From SEC/MALDI-TOF MS, two components were identified as the degraded products, and the other six components were derived from the fragmentation of the degraded products during the MALDI process. A mechanism for the formation of these components was proposed on the basis of the results of MALDI-TOF MS. For the thin film degradation, a part of products in the solution degradation were observed, which supports that the oxidation of P3HT in solution and thin film proceeded in the same mechanism. This study shows that high-resolution MALDI-TOF MS is effective for the analysis of the low-molecular-weight products from P3HT photo-oxidation and expected to be feasible for the degradation analyses of other polymers. Copyright © 2015 John Wiley & Sons, Ltd.

High-energy collision-induced dissociation by MALDI TOF/TOF causes charge-remote fragmentation of steroid sulfates

A method for structural elucidation of biomolecules dating to the 1980s utilized high-energy collisions (~10 keV, laboratory frame) that induced charge-remote fragmentations (CRF), a class of fragmentations particularly informative for lipids, steroids, surfactants, and peptides. Unfortunately, the capability for high-energy activation has largely disappeared with the demise of magnetic sector instruments. With the latest designs of tandem time-of-flight mass spectrometers (TOF/TOF), however, this capability is now being restored to coincide with the renewed interest in metabolites and lipids, including steroid-sulfates and other steroid metabolites. For these metabolites, structure determinations are required at concentration levels below that appropriate for NMR. To meet this need, we explored CRF with TOF/TOF mass spectrometry for two groups of steroid sulfates, 3-sulfates and 21-sulfates. We demonstrated that the current generation of MALDI TOF/TOF instruments can generate charge-remote fragmentations for these materials. The resulting collision-induced dissociation (CID) spectra are useful for positional isomer differentiation and very often allow the complete structure determination of the steroid. We also propose a new nomenclature that directly indicates the cleavage sites on the steroid ring with carbon numbers.

Separation of Isobaric Compounds Using a Spiral Orbit Type Time-of-Flight Mass Spectrometer, MALDI-SpiralTOF

The development of a MALDI-TOF mass spectrometer that utilizes spiral ion trajectory, SpiralTOF, is reported. The total flight path length was 17 m, which is five times longer than that in commonly used reflectron ion optical system. The SpiralTOF reduced the dependence of the mass resolving power on the mass of the analyte, while improving the accuracy of the mass measurements. Furthermore, SpiralTOF has two advantages that can be exploited for the separation of minor abundant isobaric components in mass spectra. One is the reduction in chemical background due to the post source decay (PSD), which is achieved through PSD ion elimination by electrostatic sectors contained within the SpiralTOF. The other is that the stabilities of peak positions are improved during mass spectrum accumulation. The peak drift caused by the fine structure of matrix crystals and the small irregularities on the sample surface can be reduced by extending the flight path. In this study, these advantages are demonstrated via the analysis of a block copolymer and mass spectrometry imaging (MSI) of lipids.

Structural analysis of triacylglycerols by using a MALDI-TOF/TOF system with monoisotopic precursor selection

A new MALDI-TOF/TOF system with monoisotopic precursor selection was applied to the analysis of triacylglycerols in an olive oil sample. Monoisotopic precursor selection made it possible to obtain product-ion mass spectra without interference from species that differed by a single double bond. Complete structure determination of all triacylglycerols, including structural isomers, was made possible by interpreting the charge-remote fragmentation resulting from high-energy collision-induced dissociation (CID) of the sodiated triacylglycerols.

Application of High-Resolution MALDI-TOFMS with a Spiral Ion Trajectory for the Structural Characterization of Free Radical Polymerized Methacrylate Ester Copolymers

The structural characterization of copolymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) remains a challenging task, since their random comonomer distribution creates very complicated mass spectra. In this study, a high-resolution TOF mass spectrometer with a spiral ion trajectory was applied to the structural and compositional characterization of free radical copolymerized poly(methyl methacrylate-co-tert-butyl methacrylate), poly(MMA-co-tBMA)s in ethyl lactate acting as a chain transfer agent. Virtually complete peak assignments of the isobaric components within the poly(MMA-co-tBMA)s served to identify the end-group combinations and copolymer compositions of individual copolymer components, allowing the distributions of comonomer compositions and six types of end-group combinations to be evaluated.

Detailed structural analysis of lipids directly on tissue specimens using a MALDI-SpiralTOF-Reflectron TOF mass spectrometer

Direct tissue analysis using a novel tandem time-of-flight (TOF-TOF) mass spectrometer is described. This system consists of a matrix-assisted laser desorption/ionization ion source, a spiral ion trajectory TOF mass spectrometer “SpiralTOF (STOF)”, a collision cell, and an offset parabolic reflectron (RTOF). The features of this system are high precursor ion selectivity due to a 17-m flight path length in STOF and elimination of post-source decay (PSD) ions. The acceleration energy is 20 keV, so that high-energy collision-induced dissociation (HE-CID) is possible. Elimination of PSD ions allows observation of the product ions inherent to the HE-CID process. By using this tandem TOF instrument, the product ion spectrum of lipids provided detailed structural information of fatty acid residues.

Rapid sequencing of a peptide containing a single disulfide bond using high-energy collision-induced dissociation

A peptide containing a single disulfide bond was sequenced using high-energy collision-induced dissociation (HE-CID) in conjunction with a high mass resolution time-of-flight tandem mass spectrometer equipped with a matrix-assisted laser desorption/ionization source. This mass spectrometer, which has spiral ion trajectory, allowed both high mass resolution and high precursor ion selectivity. It is difficult to obtain sufficient product ions from peptides containing disulfide bonds using HE-CID due to the single collision in the gas phase. To compensate for insufficient dissociation, the disulfide bond was cleaved via an in-source reduction process using 1,5-diaminonaphthalene, a reducing matrix. After applying the reduction in the ionization, subsequent sequencing using HE-CID provided the detailed structural information of the peptide containing the single disulfide bond.

Tandem time-of-flight mass spectrometer with high precursor ion selectivity employing spiral ion trajectory and improved offset parabolic reflectron

In this study, we have developed a tandem time-of-flight mass spectrometry (TOF/TOF) technique involving the use of a matrix-assisted laser desorption/ionization ion source that exhibits high precursor ion selectivity. An ion optical system with a 17 m spiral ion trajectory was used in the first time-of-flight mass spectrometer. High precursor ion selectivity was achieved by realizing a 15 m flight path, which is considerably longer than that of the conventional MALDI-TOF/TOF before the precursor ion selection by an ion gate; monoisotopic ions could be selected properly up to m/z 2500. Furthermore, the first time-of-flight mass spectrometer was composed of electrostatic sectors and could eliminate post-source decay (PSD) ions. Precursor ions with 20 keV kinetic energy were selected and injected into a collision cell, leading to the generation of fragment ions by high-energy collision-induced dissociation (HE-CID). The optimized second time-of-flight mass spectrometer included a post-acceleration region and an offset parabolic reflectron to record product ion spectra in the entire mass range. Our system could generate a simple HE-CID product ion spectrum because each fragment pathway could be observed as a single peak by the selection of monoisotopic ions of all precursor ions and HE-CID fragment pathways could be predominantly observed by the PSD ion elimination.

Development of multi-turn time-of-flight mass spectrometers and their applications

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.

Development of a new electron ionization/field ionization ion source for gas chromatography/time-of-flight mass spectrometry

We have developed a combined EI/FI source for gas chromatography/orthogonal acceleration time-of-flight mass spectrometry (GC/oaTOFMS). In general, EI (electron ionization) and FI (field ionization) mass spectra are complementary: the EI mass spectrum contains information about fragment ions, while the FI mass spectrum contains information about molecular ions. Thus, the comparative study of EI and FI mass spectra is useful for GC/MS analyses. Unlike the conventional ion sources for FI and EI measurements, the newly developed source can be used for both measurements without breaking the ion source vacuum or changing the ion source. Therefore, the combined EI/FI source is more preferable than the conventional EI or FI ion source from the viewpoint of the reliability of measurements and facility of operation. Using the combined EI/FI source, the complementarity between EI and FI mass spectra is demonstrated experimentally with n-hexadecane (100 pg): characteristic fragment ions for the n-alkane such as m/z 43, 57, 71, and 85 are obtained in the EI mass spectrum, while only the parent peak of m/z 226 (M+) without any fragment ions is observed in the FI mass spectrum. Moreover, the field desorption (FD) measurement is also demonstrated with poly(ethylene glycol)s M600 (10 ng) and M1000 (15 ng). Signals of [M+H]+, [M+Na]+ and [M+K]+ are clearly detected in the FD mass spectra.

High-resolution reflecting time-of-flight momentum and energy mapping system

A new system to map electron momentum and energy is proposed. A reflecting electrode is introduced into a time-of-flight (TOF) system whose decelerating electric field sends all the electrons back to a position-sensitive detector close to but behind the source of the electrons. The longer flying distance that results makes it possible to significantly improve the energy-resolved performance, especially in the higher energy region. The dependence of the new TOF system on its characteristic parameters is analyzed, along with its application to attosecond streak cameras. Experimental results verified a relative energy resolution better than 0.2 eV for 22 eV electrons and also revealed the availability of the improved relative energy resolution smaller than 1.0% for electron energy ranging from 30 to 40 eV.

Design of a new multi-turn ion optical system 'IRIS' for a time-of-flight mass spectrometer

A new multi-turn ion optical system 'IRIS' has been designed for use with a high-performance time-of-flight (TOF) mass spectrometer, which satisfies the new design concepts of time focusing and phase space stability. It has an elliptical flight path composed of four toroidal electric sectors, with a flight path length for one lap of 0.974 m. Dimensions and voltages of sector electrodes have been optimized to satisfy theoretical requirements by simulations using surface charge method. Generally, multi-turn instruments require an injection and ejection system to inject and eject ions. On the basis of this ion optical study, we have designed an injection and ejection ion optical system, which achieves time focusing for the total system. Furthermore, we have designed novel field-adjusting electrodes (FAEs) for the perforated sectors in the injection and ejection systems, which accurately correct the electric potential around the perforated sector's hole. We have also used simulations to evaluate mass resolving power and ion transmissions for various lap numbers or flight path lengths. Through these we have confirmed that mass resolving powers of over 100,000 can be achieved with reasonable ion transmissions for a given set of initial conditions. Usually a multi-turn TOF mass spectrometer with a closed optic axis has mass range limitations from overtaking ions. To solve this problem, a TOF segmentation method is proposed that identifies all peaks in a TOF spectrum, including those from overtaking ions.

Comparison of mass spectra of peptides in different matrices using matrix-assisted laser desorption/ionization and a multi-turn time-of-flight mass spectrometer, MULTUM-IMG

The mass spectra of peptides obtained with different matrices were compared using a matrix-assisted laser desorption/ionization (MALDI) ion source and a multi-turn time-of-flight (TOF) mass spectrometer, MULTUM-IMG, which has been developed at Osaka University. Two types of solid matrices, alpha-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB), and a liquid matrix made from a mixture of 3-aminoquinoline and CHCA were used. When measuring the peak signal intensity of human angiotensin II [M+H]+ from a fixed sample position, the liquid matrix produced a stable signal over 1000 laser shots, while the signal obtained with CHCA and DHB decayed after about 300 and 100 shots, respectively. Significant differences in the mass resolving power were not observed between the spectra obtained with the three matrices. Signal peak areas were measured as a function of the cycle number in a multi-turn ion trajectory, i.e., the total flight time over a millisecond time scale. For both [M+H]+ of human angiotensin II and bovine insulin, the decay of the signal peak area was the most significant with CHCA, while that measured with DHB was the smallest. The results of the mean initial ion velocity measurements suggested that the extent of metastable decomposition of the analyte ions increased in order of DHB, the liquid matrix, and CHCA, which is consistent with the difference in the decay of the signal peak area as the total flight time increased.

Development of a high-performance MALDI-TOF mass spectrometer utilizing a spiral ion trajectory

A novel MALDI-TOF mass spectrometer that utilizes a spiral ion trajectory was developed. In this mass spectrometer, the ions sequentially passed through four toroidal electrostatic sectors and revolved along a figure-eight-shaped orbit on a particular projection plane. Each toroidal electrostatic sector had eight stories, and during multiple revolutions, the ion trajectory shifted perpendicular to the projection plane in every cycle, thereby generating a spiral trajectory. The flight path length of one cycle was 2.1 m; therefore, when the ions completed eight cycles, the total flight path length was 17 m. By adopting an ion optical system that had a flight path length five times longer than that in the commonly used reflectron ion optical system, the mass dependence on the mass resolving power was reduced, while improving the mass accuracy of the mass measurements. The basic performance of the system was tested by using standard peptides or the tryptic digest of bovine serum albumin. A mass resolving power of 80,000 (full width at half maximum) was achieved at m/z = 2564 (ACTH18-39). An improved mass accuracy less than 2 ppm was realized over a wide m/z range of 500 to 3000 by correction using one or two internal standard substances.