Journal of Mass Spectrometry最新文献

MS analysis of cyclic peptides in negative ion mode has been a challenge, in particular if the peptide does not contain acidic functional groups. In this paper, we present a way to easily produce negative ions from anionic peptide adducts, utilising collision-induced dissociation (CID)-mediated elimination. Using two different mass spectrometers, we have generated series of adducts of three cyclic and one linear peptide with various anions. They were then isolated and subjected to CID with a range of collision energies. The deprotonation percentage was then calculated from the resultant spectrum, and compared between the spectrometers, as well as with an external reference—proton affinity values. The susceptibility to deprotonate by detaching a HX moiety is proportional to the proton affinity of the X⁻ species. Also, the linear peptide deprotonated more readily than the cyclic ones. On the other hand, lack of amino or acidic groups resulted in higher collision voltage (CV) necessary for the formation of deprotonated species. Moreover, the exact propensity for neutral loss depends on the ion temperature, which differs between mass spectrometers. We have developed a facile method for generating peptide anions for MS analysis of cyclic peptides, which works even if the peptide in question does not have easily ionisable groups. The deprotonated species generated in this way can be fragmented again in order to identify the peptide.

The development of LA-ICPMS and LA-MC-ICPMS resulted in analytical methods for zircon geochronology using a 20- to 60-μm laser spot size. A high amount of complexly zoned zircons promotes the requirement of U–Pb dating at smaller spot sizes. When spot size reduces, downhole fractionation (DHF) increases, increasing the DHF discrepancy between zircon grains and the primary reference zircon standard and resulting in inaccurate results. With MC-ICPMS's high sensitivity and multi-collector capabilities, this work attempts to accurately determine age with spatial resolutions below 20 μm. Three well-characterized zircon standards (91500, GJ-1, and Plešovice) were tested at spot sizes of 35, 20, 15, and 10 μm. Laser and mass spectrometry tuning, laser shot count, and ablation time have been optimized to reduce the DHF effect on measurement accuracy. Static ablation of 35- to 15-μm spots with 150 laser shot counts (30 s) yielded precision of less than 1.5% and age offset of less than 2%. The DHF differs significantly from the reference standard and two test zircon samples used for validation, with an age offset of 4% at 10-μm spot sizes. Masking shot counts from the end enhanced accuracy, notably for lower laser shot counts and shorter ablation times. At 75 laser shot counts, precision reached 1.4% and age offsets reduced to 1.6% for ²⁰⁶Pb/²³⁸U age. This method minimizes laser shot counts to avoid sampling two age groups. Higher zircon DHF variability at smaller spot sizes may influence a well-calibrated, sensitive LA-MC-ICP-MS analytical figure of merit.

Ethyl propionate (C₅H₁₀O₂, EP) has been extensively studied in the fields of biofuels and atmospheric chemistry. However, its vacuum ultraviolet (VUV) photoionization has not been investigated. This study examines the photoionization process of EP using tunable VUV synchrotron radiation, coupled with a reflectron time-of-flight mass spectrometer. This method yielded the photoionization mass spectrum of EP and photoionization efficiency (PIE) spectra of 10 identified fragment ions (i.e., C₄H₇O₂^+., C₃H₇O₂^+., C₃H₆O₂^+., C₃H₅O₂^+., C₃H₆O^+., C₃H₅O^+., C₃H₄O^+., C₂H₅O^+., C₂H₅^+., and C₂H₄^+.). The results, interpreted with the aid of high-accuracy theoretical calculations, conclude possible formation mechanisms for each fragment ion. In the dissociation pathway of EP's cation, intramolecular hydrogen shifts and bond cleavage are the predominant processes. The C₃H₇O₂^+. and C₂H₄^+. reaction channels do not arise from one-step bond cleavage, but their reaction energy barriers are influenced by product energy, making them comparable to direct reaction channels. The active reaction sites within the molecules are elucidated using Laplacian bond order (LBO). Rate constants are calculated using RRKM theory, which confirms the kinetic factors governing the EP reaction process. This study provides a detailed understanding of the photoionization and dissociation of the main ions of EP within the 9.35–15.50 eV photon energy range.

This study focuses on investigating the conformational structure and zinc(II) affinity of a zinc finger-like motif (ZFM) peptide with the sequence acetyl-His₁-Cys₂-Gly₃-Pro₄-Gly₅-His₆-Cys₇, where bold highlights the potential zinc(II) binding sites. Zinc fingers are crucial protein motifs known for their high specificity and affinity for zinc ions. The ZFM peptide's sequence contains the 2His-2Cys zinc-binding sites similar to those in natural zinc finger proteins but without the hydrophobic core, making it a valuable model for studying zinc(II)–peptide interactions. Previous research on related peptides showed that collision cross sections and B3LYP modeling predicted that the His-2Cys-carboxyl terminus coordination of zinc(II) was more stable than the 2His-2Cys. Employing a comprehensive approach integrating ion mobility–mass spectrometry and theoretical modeling techniques, various zinc(II) binding modes of the ZFM have been thoroughly compared to ascertain their influence on the competitive threshold collision-induced dissociation method for measuring the relative gas-phase Zn(II) affinity of the ZFM peptide. The measured Zn(II) affinity of ZFM is greater than those measured recently for two peptides with similar primary structures, acetyl-His₁-Cys₂-Gly₃-Pro₄-Gly₅-Gly₆-Cys₇ and acetyl-Asp₁-His₂-Gly₃-Pro₄-Gly₅-Gly₆-Cys₇, indicating the preference for the His₁-Cys₂-His₆-Cys₇ side groups for coordinating zinc(II) over the His-2Cys-carboxyl terminus or Asp-His-Cys-carboxyl terminus in these related heptapeptides.

The development of a real-time system for characterizing individual biomolecule-containing aerosol particles presents a transformative opportunity to monitor respiratory conditions, including infections and lung diseases. Existing molecular assay technologies, although effective, rely on costly reagents, are relatively slow, and face challenges in multiplexing, limiting their use for real-time applications. To overcome these challenges, we developed digitalMALDI, a laser-based mass spectrometry system designed for single-particle characterization. digitalMALDI operates as a near real-time platform that directly samples aerosols, bypassing the need for complex and time-consuming sample preparation. To demonstrate the feasibility of this approach, intact insulin protein was used as a representative target. Results showed that digitalMALDI is capable of detecting 1 pg of insulin protein in single aerosol particles, suggesting that the system has a broad application for disease diagnosis, environmental monitoring, and biosecurity management.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a class of emerging contaminants that have been in use industrially since the 1940s. Their long-term and extensive commercial use has led to their ubiquitous presence in the environment. The ability to measure the bioconcentration and distribution of PFAS in the tissue of aquatic organisms helps elucidate the persistence of PFAS as well as environmental impacts. Traditional analysis by LC–MS/MS can measure total PFAS concentrations within an organism but cannot provide comprehensive spatial information regarding PFAS concentrations within the organism. In the current study, we used infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) to determine the limit of detection (LOD) of several PFAS utilizing a commercial standard mix spotted on mouse liver tissue. The traditional ice matrix and an alternative matrix, 1,8-bis (tetramethylguanidino)naphthalene (TMGN), were explored when determining the limits of detection for various PFAS by IR-MALDESI. The ice matrix alone resulted in a higher response than the combination of TMGN and ice. The resulting LOD for perfluorooctane sulfonic acid (PFOS) on a per voxel basis was 0.16 fmol/voxel. For comparison, zebrafish that were exposed to perfluorooctanoic acid (PFOA), PFOS, and perfluorohexanesulfonic acid (PFHxS) at different concentrations were homogenized, and PFAS were extracted by solid–liquid extraction, purified by solid phase extraction, and analyzed by LC–MS/MS to determine the level of bioaccumulation in the zebrafish. PFOS resulted in the highest level of bioaccumulation (731.9 μg/kg, or 234.2 fg/voxel). A zebrafish that had been exposed to a PFAS mixture of PFOA (250 ng/L), PFOS (250 ng/L), and PFHxS (125 ng/L) was cryosectioned and analyzed by IR-MALDESI. Images could not be generated as the accumulation of PFAS in the sectioned tissue was below detection limit of the technique.

This study presents a comprehensive evaluation of the application of online multi-internal standard calibration (M.ISC) in determining iodine concentrations through inductively coupled plasma mass spectrometry (ICP-MS). Notably, M.ISC streamlines the calibration process by requiring only a single standard solution, thereby enhancing sample throughput and minimizing liquid waste. In addition, unlike conventional internal standard (IS) methods, M.ISC omits the need for time-consuming species identification by utilizing multiple IS species simultaneously to minimize signal biases. The effectiveness of M.ISC was validated through the analysis of six standard reference samples, with the results of LOD and LOQ also being calculated by the error propagation approach. The traditional chemical analytical methods (TCAM), external standard calibration (EC) and single IS methods were also evaluated as comparative purpose. Nonetheless, M.ISC emerges as a straightforward matrix-correction strategy, offering a simple and efficient alternative to traditional calibration methods for iodine detection by ICP-MS.