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Development of low radioactivity photomultiplier tubes for the XMASS-I detector
摘要： XMASS-I is a single-phase liquid xenon detector whose purpose is direct detection of dark matter. To achieve the low background requirements necessary in the detector, a new model of photomultiplier tubes (PMTs), R10789, with a hexagonal window was developed based on the R8778 PMT used in the XMASS prototype detector. We screened the numerous component materials for their radioactivity. During development, the largest contributions to the reduction of radioactivity came from the stem and the dynode support. The glass stem was exchanged to the Kovar alloy one and the ceramic support were changed to the quartz one. R10789 is the first model of Hamamatsu Photonics K. K. that adopted these materials for low background purposes and provided a groundbreaking step for further reductions of radioactivity in PMTs. Measurements with germanium detectors showed 1.2 ± 0.3 mBq/PMT of 226Ra, less than 0.78 mBq/PMT of 228Ra, 9.1 ± 2.2 mBq/PMT of 40K, and 2.8 ± 0.2 mBq/PMT of 60Co. In this paper, the radioactive details of the developed R10789 are described together with our screening methods and the components of the PMT.
关键词： Mass spectrometry,PMT,Radioactivity,HPGe
更新于2025-09-19 17:15:36
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Chiral differentiation of <scp>d</scp> - and <scp>l</scp> -isoleucine using permethylated β-cyclodextrin: infrared multiple photon dissociation spectroscopy, ion-mobility mass spectrometry, and DFT calculations
摘要： Chiral di?erentiation of protonated isoleucine (Ile) using permethylated b-cyclodextrin (perCD) in the gas-phase was studied using infrared multiple photon dissociation (IRMPD) spectroscopy, ion-mobility, and density functional theory (DFT) calculations. The gaseous protonated non-covalent complexes of perCD and D-Ile or L-Ile produced by electrospray ionization were interrogated by laser pulses in the wavenumber region of 2650 to 3800 cm?1. The IRMPD spectra showed remarkably di?erent IR spectral features for the D-Ile or L-Ile and perCD non-covalent complexes. However, drift-tube ion-mobility experiments provided only a small di?erence in their collision cross-sections, and thus a limited separation of the D- and L-Ile complexes. DFT calculations revealed that the chiral distinction of the D- and L-complexes by IRMPD spectroscopy resulted from local interactions of the protonated Ile with perCD. Furthermore, the theoretical results showed that the IR absorption spectra of higher energy conformers (by B13.7 kcal mol?1) matched best with the experimentally observed IRMPD spectra. These conformers are speculated to be formed from kinetic-trapping of the solution-phase conformers. This study demonstrated that IRMPD spectroscopy provides an excellent platform for di?erentiating the subtle chiral di?erence of a small amino acid in a cyclodextrin-complexation environment; however, drift-tube ion-mobility did not have su?cient resolution to distinguish the chiral di?erence.
关键词： chiral differentiation,ion-mobility mass spectrometry,permethylated β-cyclodextrin,IRMPD spectroscopy,DFT calculations,isoleucine
更新于2025-09-19 17:15:36
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How the methyl group position influences the ultrafast deactivation in aromatic radicals
摘要： Excited xylyl (methyl–benzyl) radical isomers have been studied by femtosecond time-resolved photoelectron spectroscopy and mass spectrometry. Depending on the substitution we find different deactivation channels after excitation into the D3(2A00) state (310 nm, 4 eV). While the ortho and para isomer exhibit deactivation rates similar to the benzyl radical, meta-xylyl sticks out and depletes twice as fast into the vibrationally hot ground state. We found that a ring deformation mode rather than the methyl pseudorotation enables access to a conical intersection, which is responsible for the faster deactivation. Transitions in the photoelectron spectrum can be assigned to several Rydberg series with mostly d angular momentum components. Absorption of two 4 eV photons triggers hydrogen loss reactions on a femtosecond timescale.
关键词： photoelectron spectroscopy,mass spectrometry,conical intersection,Rydberg states,femtosecond spectroscopy,ultrafast deactivation,xylyl radicals
更新于2025-09-19 17:15:36
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Quantifying and improving the optical performance of the Laser Ablation Aerosol Particle Time of Flight Mass Spectrometer (LAAPToF) instrument
摘要： Single particle mass spectrometer (SPMS) instruments have been used for in-situ chemical characterization of atmospheric aerosols, both in the field and laboratory, for over two decades. SPMSs typically combine precise optical particle sizing with laser desorption and ionization followed by time of flight mass spectrometry. Among the advantages of SPMSs over other aerosol chemistry measurement techniques are their single particle resolution and high sensitivity counting efficiency in the size range 500-2000 nm vacuum aerodynamic diameter. We also present mass spectral performance for characterizing atmospherically-relevant particles in a comparison to a current SPMS design, the Particle Analysis by Laser Mass Spectrometry. The AeroMegt Laser Ablation Aerosol Particle Time of Flight Mass Spectrometer (LAAPToF) is a commercially available member of this instrument class, aiming for a compact size and simplicity for the end user. This paper quantifies the performance of LAAPToF with an emphasis on optical counting efficiency. Recommendations for improving detection compared to the base LAAPToF hardware are described. Our results show that changes to the optical detection scheme can lead to over two orders of magnitude improvement in optical counting efficiency.
关键词： aerosol chemistry,LAAPToF,Single particle mass spectrometer,optical counting efficiency,time of flight mass spectrometry
更新于2025-09-19 17:13:59
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Phospholipid imaging of zebrafish exposed to fipronil using atmospheric pressure matrix-assisted laser desorption ionization mass spectrometry
摘要： Mass spectrometry imaging can effectively detect and reflect the information of molecular spatial distribution, and has been widely used for in situ analysis of endogenous or exogenous molecules in organisms. The present work applied the atmospheric pressure matrix-assisted laser desorption ionization mass spectrometry (AP-MALDI-MS) in the imaging of whole zebrafish slices exposed to fipronil. The chemical fingerprints in the range of m/z 600-950 showed significant differences in phospholipids between the fipronil exposed and untreated zebrafish groups. The major perturbed phospholipids were identified as PC(34:2), PC(34:1), PC(34:2)+Na, PC(36:4), PC(38:6), and PS(18:0/22:6), PI(18:0/20:4), PI(18:1/20:4) etc. Our results indicated that the exposure of fipronil obviously affected the phospholipid metabolism of zebrafish, especially of the fish eye region. Our work provides a new method or possibility for toxicological study and related metabolic analysis of pesticides in animals.
关键词： Fipronil,In vivo Phospholipids,Mass spectrometry imaging,MALDI,Zebra fish
更新于2025-09-19 17:13:59
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Identification of Proteins Using Four Methods of Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry
摘要： An upper-division undergraduate- or graduate-level laboratory experiment, challenging students to identify bovine serum albumin, equine myoglobin, bovine calmodulin, and bovine cytochrome c, uses four methods of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS): linear positive, in-source decay, peptide mass fingerprint, and postsource decay. Individual hands-on experience with each method is provided in a three week experiment. The importance of sequencing proteins/peptides when identifying proteomic targets using MALDI-TOF MS is emphasized.
关键词： Mass Spectrometry,Hands-On Learning/Manipulatives,Upper-Division Undergraduate,Laboratory Instruction,Graduate Education/Research,Bioanalytical Chemistry,Biotechnology,Analytical Chemistry,Biochemistry
更新于2025-09-19 17:13:59
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Off-colony screening of biosynthetic libraries by rapid laser-enabled mass spectrometry
摘要： Leveraging advances in DNA synthesis and molecular cloning techniques, synthetic biology increasingly makes use of large construct libraries to explore large design spaces. For biosynthetic pathway engineering the ability to screen these libraries for a variety of metabolites of interest is essential. If the metabolite of interest or the metabolic phenotype is not easily measurable, screening soon becomes a major bottleneck involving time-consuming culturing, sample preparation, and extraction. To address this, we demonstrate the use of automated Laser-Assisted Rapid Evaporative Ionisation Mass Spectrometry (LA-REIMS) – a form of ambient laser desorption ionisation mass spectrometry – to perform rapid mass spectrometry analysis direct from agar plate yeast colonies without sample preparation or extraction. We use LA-REIMS to assess production levels of violacein and betulinic acid directly from yeast colonies at a rate of 6 colonies per minute. We then demonstrate the throughput enabled by LA-REIMS by screening over 450 yeast colonies in under 4 hours, while simultaneously generating recoverable glycerol stocks of each colony in real-time. This showcases LA-REIMS as a pre-screening tool to complement downstream quantification methods such as LCMS. Through pre-screening several hundred colonies with LA-REIMS, we successfully isolate and verify a strain with a 2.5-fold improvement in betulinic acid production. Finally, we show that LA-REIMS can detect 20 out of a panel of 27 diverse biological molecules, demonstrating the broad applicability of LA-REIMS to metabolite detection. The rapid and automated nature of LA-REIMS makes this a valuable new technology to complement existing screening technologies currently employed in academic and industrial workflows.
关键词： synthetic biology,metabolic engineering,REIMS,ambient mass spectrometry,high throughput screening
更新于2025-09-19 17:13:59
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Development of a novel sheathless CE-ESI-MS interface via a CO2 laser ablated opening
摘要： A new and easy to construct sheathless capillary electrophoresis electro spray ionization mass spectrometry (CE-ESI-MS) interface was developed that offers several advantages compared to traditional liquid junction interfaces. The fabrication of the device only requires a CO2 laser engraver that most groups working with microfluids have access to. It only takes a few seconds to create a CO2 laser ablated opening in the bare-fused silica capillaries and the opening can be placed as close as a few mm from the spray tip. The capillary is punctured through a silicone tube such that the opening is directly placed inside this tube, which also serves as a liquid reservoir for the make-up liquid. Electrical contact required for both CE separation and ESI is established via the liquid in this reservoir which is in contact with the electrode of an external high voltage power supply. The developed CE-ESI-MS interface is capable of analysing both small molecules and biomolecules such as peptides in physisorbed PEG polymer brush coated capillaries. Proof-of-principle of the interface was demonstrated by analysing a tryptic digest of BSA. Further, a range of drugs of abuse were also investigated. The examined small molecules (pethidine, nortriptyline, methadone, haloperidol and loperamide) have a quantification limit (LOQ) of 150 ng/mL and a detection limit (LOD) of 40 ng/mL (except for loperamide: LOD = 80 ng/mL). Finally, we used our novel CE-MS interface for the analysis of the Aβ40 peptide. This is a member of the beta-Amyloid peptide family, involved in the development of Alzheimer's disease. A LOQ of 9 μg/mL was obtained for Aβ40, corresponding to 23 fmoles in a sample volume of 11 nL.
关键词： Mass spectrometry,Aβ40,CO2 laser,Sheathless interface,Capillary electrophoresis
更新于2025-09-19 17:13:59
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Epitaxial n++-InGaAs ultra-shallow junctions for highly scaled n-MOS devices
摘要： High electron mobility III-V semiconductors like InGaAs are excellent candidates for sub-10 nm n-metal-oxide-semiconductor (nMOS) devices. One of the critical challenges in downscaling III-V devices is achieving low-resistance contacts by forming low-defect, ultra-shallow junctions < 9 nm in depth, with n-type dopant concentrations above 1019 cm?3. In the current study, we combine time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis, atomic force microscopy (AFM) imaging, and high-resolution transmission electron microscopy (HR-TEM) to determine the optimal doping strategy for growing Si-doped n++-In0.25Ga0.75As ultra-shallow junctions by molecular beam epitaxy. We test three different approaches to doping: homogeneous co-deposition, single δ-layer (continuous) doping, and triple δ-layer (pulsed) doping. We demonstrate the formation of technologically suitable n++-In0.25Ga0.75As junctions 5–7 nm deep, grown under As-rich conditions with a single δ-layer at temperatures as low as 400 °C. These junctions have peak Si concentrations between 6 × 1019 and 1 × 1020 cm?3 and high crystal quality. The surface self-organizes into smooth ripples or mounds, up to a peak dopant concentration of ~2 × 1020 cm-3. Above this value, enhanced diffusion of Si and In due to a large population of Ga vacancies increases lattice strain in the semiconductor epilayer, triggering a transition from 2D growth to 3D growth and the formation of In0.85Ga0.15As clusters on the surface.
关键词： Time-of-flight secondary ion mass spectrometry,Indium gallium arsenide,Semiconductor growth,Ultra-shallow junctions,Self-organization,Solid-state diffusion
更新于2025-09-19 17:13:59
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Direct inlet probe atmospheric pressure photo and chemical ionization coupled to ultra-high resolution mass spectrometry for the description of lignocellulosic biomass
摘要： Lignocellulosic biomass, in particular wood, is a complex mixture containing cellulose, hemicellulose, lignin, and other trace compounds. Chemical analysis of these biomasses, especially lignin components, is a challenge. Lignin is a highly reticulated polymer that is poorly soluble and usually requires chemical, enzymatic, or thermal degradation for its analysis. Here, we studied the thermal degradation of lignocellulosic biomass using a direct insertion probe (DIP). DIP was used with two ionization sources: atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) coupled to ultra-high-resolution mass spectrometry. Beech lignocellulosic biomass sample were used to develop the DIP-APCI/APPI methodology. Two other wood species (maple and oak) were analyzed after optimization of DIP parameters. The two ionization sources were compared at first and showed different response towards beech sample, according to the source specificity. APPI was more specific to lignin degradation compounds, whereas APCI covered a larger variety of oxygenated compounds, e.g., fatty acids, polyphenolics compounds, in addition to lignin degradation products. The study of the thermo-desorption profile gave information on the different steps of lignocellulosic biomass pyrolysis. The comparison of the three feed sample types (oak, maple, and beech), using principal component analysis (PCA) with DIP-APCI experiments, showed molecular level differences between beech wood pellets and the two others wood species (maple and oak).
关键词： high-resolution mass spectrometry,APPI,APCI,direct inlet probe,biomass
更新于2025-09-19 17:13:59