Journal of the American Society for Mass Spectrometry最新文献

It is demonstrated here that a recently published LabView-based time-of-flight mass spectrometer (TOFMS) simulation program (named TOFSim) can accurately simulate data collected on a commercial Bruker Autoflex III matrix-assisted laser desorption/ionization (MALDI) TOFMS instrument operating in linear mode. Once the instrument distances are determined by matching measured and simulated flight times, it is shown that both overall flight times and peak widths are reproduced for data collected under both focused and slightly defocused conditions. This work confirms that TOFSim can be used not just for training new instrument operators in the principles of TOFMS but, as demonstrated here, to show how changing the voltage applied to grid G1 in the source or the delayed extraction delay time affects the focusing properties of the instrument. In the future we expect that this will also allow users to perform "what-if" experiments to investigate scenarios which may be difficult or impossible to do in a real instrument.

Since desorption electrospray ionization mass spectrometry (DESI-MS) was first presented in 2004, the fundamental design of the sprayer has undergone relatively minor modifications. This changed in 2022 when Takats and co-workers implemented the desorption electro-flow focusing (DEFFI) sprayer design by modifying the sprayer from a commercial DESI system, leading to significantly improved spatial resolution and robustness compared with the traditional DESI-MSI sprayer design. Here, we present the design of a new DEFFI sprayer that can be built from standard fittings and connectors in combination with an aluminum spray head that can be machined in most mechanic workshops. The new design represents a cost-efficient approach to improved DESI-MSI on mass spectrometers from all vendors, including high-resolution instruments such as Orbitraps and FT-ICR. The new DEFFI sprayer is demonstrated on a QExactive Orbitrap mass spectrometer, resulting in a massively improved ion yield compared with the classic DESI sprayer. The improved ion yield enables DESI-MSI at ion injection times down to 5 ms, allowing for DESI-MSI at a potentially very high speed. More importantly, the DEFFI sprayer delivers a more robust and focused spray, which is easier to use and requires less optimization. It provides high spatial resolution with limited effort compared with previous modifications of the traditional DESI design. Imaging of rat testis was performed at pixel sizes down to 12 μm, suggesting a spatial resolution of approximately 30 μm, which may have potential for further improvement.

Substances of misuse are becoming increasingly difficult to analyze as unique methods of smuggling are adopted and due to the rapid emergence of new psychoactive substances, increasing the pool of compounds to characterize and identify. Technologies such as gas chromatography and liquid chromatography coupled to mass spectrometry (MS) represent the gold standard for accurate and robust analysis, with on-site ambient- and portable-MS systems providing rapid methods of drug screening and testing. For many samples containing residual analyte quantities, methods to improve sensitivity through chemical derivatization are critical for accurate determination. Herein, we demonstrate for the first time the use of trimethylation enhancement using diazomethane (TrEnDi) to improve the MS-based sensitivity of 13 different drugs of misuse. All analytes were successfully permethylated, with 11 demonstrating improved analytical characteristics from TrEnDi with MS sensitivity enhancements ranging from 1.2-fold to as high as 24.2-fold in the case of psilocybin, as well as increases in reversed-phase chromatographic retention for most species. Derivatization using ¹³C-isotopically labeled TrEnDi reagents were used to successfully resolve isobaric interference issues between three pairs of controlled substances. By using an unconventional aprotic solvent system for electrospray ionization, the benefit of a fixed-permanent positive charge was highlighted as TrEnDi-modified amphetamine was easily measured while unmodified was not detected. Finally, TrEnDi was employed to boost the sensitivity of morphine in a real urine matrix. Our results demonstrate a percent recovery of 103.1% and a sensitivity enhancement of 2.4-fold, demonstrating the versatility and applicability of TrEnDi to pre-existing analytical workflows for trace analysis.

In some types of mass spectrometers, such as time-of-flight mass spectrometers (TOF-MSs), it is necessary to control pulsed beams of ions. This can be easily accomplished by applying a pulsed voltage to the pusher electrode while the ionizer is continuously flowing ions. This method is preferred for its simplicity, although the ion utilization efficiency is not optimized. Here we employed another pulse-control method with a higher ion utilization rate, which is to bunch ions and kick them out instead of letting them stream. The benefit of this method is that higher sensitivity can be achieved; since the start of new ions cannot be allowed during TOF separation, it is highly advantageous to bunch ions that would otherwise be unusable. In this study, we used analytical and numerical methods to design a new bunching ionizer with reduced resources, adopting the principle of the electrostatic ion beam trap. The test model experimentally demonstrated the bunching performance with respect to the sample gas density and ion bunching time using gas samples and electron impact ionization. We also conducted an experiment connecting the newly developed bunching ionizer with a miniature TOF-MS. As a result, the sensitivity was improved by an order of magnitude compared to the case using a nonbunching ionizer. Since the device is capable of bunching ions with low voltage and power consumption, it will be possible to find applications in portable mass spectrometers with reduced resources.

Profiling of steroid hormones is incredibly valuable in clinical settings for diagnosing endocrine disorders. However, the presence of matrix effects and labor-intensive manual work in LC-MS/MS analysis has hindered its routine application. In the present study, a highly efficient and automated magnetic bead extraction method was developed to address matrix effects and quantitatively profile 15 steroid hormones in human serum. Octadecyl (C18) and N-vinylpyrrolidone divinylbenzene (HLB) modified magnetic beads were compared for enriching steroids from human serum. Following enrichment, the beads were separated using a magnetic field; the matrix was cleaned, and the steroid hormones were eluted from the beads for LC-MS/MS analysis. This entire process of enrichment, cleanup, and elution was conducted automatically, making it simple, fast, and cost-effective. The results indicated that steroid hormones could be selectively enriched from human serum in just 1 min using C18 magnetic beads. The absolute matrix effect, evaluated as the relative response between human serum matrix and methanol solution, ranged from 89.2% to 113.1% for low levels, from 82.3% to 112.0% for medium levels, and from 91.7% to 111.0% for high levels. The intrabatch coefficients of variation (CVs) and interbatch CVs were between 3.1% and 13.4% and between 3.0% and 13.7%, respectively. Recoveries were between 87.6% and 114.3% for low levels, 94.0% and 105.0% for medium levels, and 91.9% and 111.7% for high levels. The clinical application was demonstrated by profiling steroid hormones in 160 pregnant women at various gestational weeks. The results suggested that the automated magnetic bead extraction method for LC-MS/MS could effectively address matrix effects in profiling steroid hormones. To our knowledge, this is the first automated magnetic bead extraction method for LC-MS/MS profiling of steroid hormones in clinical practice.

Paper spray mass spectrometry (PS-MS) often employs laser cutting to prepare paper substrates, potentially inducing localized thermal decomposition of the cellulose backbone. This work investigates how cellulose pyrolysis products and inherent background molecules within the paper affect PS-MS signal quality and evaluates paper pretreatment methods to enhance performance. Comparative analyses of laser-cut and razor-cut paper using mass spectrometry and ultraviolet-visible spectroscopy (UV-vis) showed significant differences. Laser-cut paper exhibited elevated MS blank signals and higher absorbance in the 200-400 nm UV region, indicating increased chemical abundance and complexity. Gas chromatography-mass spectrometry (GC-MS) identified over 20 residual compounds on laser-cut paper absent in razor-cut samples, half of which were identified as known cellulose pyrolysis products. Washing the paper substrates with methanol, water, or dilute nitric acid significantly reduced both pyrolysis products and background molecules, with water showing the most improvement. Analyses of morphine, fentanyl, methamphetamine, voriconazole, and fluconazole showed no reduction in the signal after washing, with fentanyl and methamphetamine exhibiting a significantly increased MS signal, regardless of the cutting method. This work reveals that while pyrolysis products from laser cutting contribute to increased chemical noise, inherent background molecules in the paper also play a significant role. A simple water wash mitigates both issues, potentially improving the overall PS-MS performance for a range of analytes.

Neuraminidase (NA) is a kind of glycoside hydrolase enzyme, functioning to remove terminal sialic acid (Sia) from glycans which are located on the cell surface. NA plays an essential role in cell interactions with ligands, microbes, and other cells during physiological and pathological processes. Additionally, NA is a major target for developing anti-influenza drugs and influenza vaccines. Herein, a matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) based method to quantify NA activity is demonstrated for the first time. A reactive matrix 2-hydrazinoquinoline (2-HQ) is used to on-target label the natural substrate (3-sialyllactose, 3'-SL) and its enzymatic product (Sia). The derivatization enhances the ionization efficiency of 3'-SL and Sia, especially in negative ion detection mode. Moreover, the lactose ion signals and noise are significantly suppressed. Consequently, NA activity in influenza vaccines has been successfully quantified by comparing the relative intensity of 2-HQ derivatized Sia and 3'-SL in the absence of an additional internal standard. Moreover, the inhibition efficiencies of NA inhibitors have also been measured. Due to its operating simplicity, high-throughput capacity, and quantification accuracy, the proposed method has potential to be applied for the detection of different kinds of NA activity to reveal the role of NA in immunity, vaccine, and infection processes.

Reactions with mobile protons occur under electrospray ionization (ESI) in many applications of mass spectrometry. Understanding how protonation isomers (protomers) form and how molecular structure influences protomer interconversion provides fundamental insight into ESI mechanisms, which can then be exploited to rationalize ion mobility and ion activation processes for robust analyte detection. Using ten arylamine protomer systems, this paper establishes the key substrate properties that influence protomer isomerism. Protomers from ten arylamines are separated by differential ion mobility spectrometry (DMS) mass spectrometry and identified by characteristic collision-induced dissociation mass spectra. These assignments are further rationalized using quantum chemical calculations (M06-2X/6-31G(2df,p)). Based on these assignments, mobility-selected protomers are then allowed to react with methanol vapor under atmospheric and reduced pressure conditions (2.5 mTorr, 300 K). The latter enabled measurements of the second-order rate coefficients for methanol-catalyzed protomer isomerization, which span 3.9 × 10^-11-2 × 10^-13 cm³ molecule^-1 s^-1. Double-hybrid quantum chemical calculations (DSD-PBEP86-D3(BJ)/aug-cc-pVDZ) show that the direction of proton transfer is controlled by protomer relative stability, whereas reaction rates are controlled by a key transition state that separates the protonation sites. Computational exploration of a larger substituted-arylamine test-set shows that the protomer proton affinity generally correlates with energy of the key transition state. Applying the Bell-Evans-Polanyi principle to this reaction set highlights that outliers in the predictive model correspond to transition states with significant displacements along the reaction coordinate. This archetype system of derivatized arylamines provides a foundation to understand how substrate functionalization influences protomer isomerism for ions during ESI and predicts protonation isomer distributions.

Electrospray ionization mass spectrometry has long been a prevalent ionization method in the analysis of low volatility molecules with biological, environmental, and industrial relevance. To address analytical challenges associated with molecules suffering from low ionization efficiencies (IEs), chemical derivatization (CD) strategies have been developed and are frequently adopted into workflows. However, only a minute number of CD techniques have been developed for negative polarity. To address this disparity, we evaluated 27 anions based on three criteria: (1) IE relative to a sodium dodecyl sulfate (11 + Na⁺) internal standard; (2) stability to collision induced dissociation; (3) diagnostic tandem mass spectrometry behavior. Highly fluorous ions exhibiting weakly coordinating and hydrophobic properties displayed enhanced IE. Trifluoromethanesulfonyl-containing ions proved to be unexpectedly labile, while tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (23) and bis(nonafluoro-1-butane)sulfonimidate (25) were determined to be of optimal IE of 332% ± 25% and 939% ± 92%, respectively, and in tandem MS exhibited survival yields of 100% ± 0% and 72.6% ± 0.8% at -50 eV. 23 and 25 were also comparable in IE across several solvents, and combinations thereof, that are ubiquitous in liquid chromatography. Various salts of 25 were evaluated for cation effects, where the IE of 25 ranged from 939% ± 92% to 3195% ± 145% across K⁺, NH₄⁺, Na⁺, and H⁺. Compared to tetra-n-butylammonium, tetra-n-butylphosphonium, and (4-methylphenyl)diphenylsulfonium cations, 25 displayed signal enhancements ranging from 136% ± 6% to 181% ± 14%, thereby making it an optimal candidate for CD development.