Mass spectrometry最新文献

Congenital disorders of glycosylation (CDG) are inherited metabolic diseases that affect the synthesis of glycoconjugates. Defects in mucin-type O-glycosylation occur independently or in combination with N-glycosylation disorders, and the profiling of the O-glycans of apolipoprotein CIII (apoCIII) by mass spectrometry (MS) can be used to support a diagnosis. The biomarkers are site occupancy and sialylation levels, which are indicated by the content of non-glycosylated apoCIII0a isoform and by the ratio of monosialylated apoCIII1 to disialylated apoCIII2 isoforms, respectively. In this report, electrospray ionization (ESI) quadrupole MS of apoCIII was used to identify these biomarkers. Among the instrumental parameters, the declustering potential (DP) induced the fragmentation of the O-glycan moiety including the Thr-GalNAc linkage, resulting in an increase in apoCIII0a ions. This incurs the risk of creating a false positive for reduced site occupancy. The apoCIII1/apoCIII2 ratio was substantially unchanged despite some dissociation of sialic acids. Therefore, appropriate DP settings are especially important when transferrin, which requires a higher DP, for N-glycosylation disorders is analyzed simultaneously with apoCIII in a single ESI MS measurement. Finally, a reference range of diagnostic biomarkers and mass spectra of apoCIII obtained from patients with SLC35A1-, TRAPPC11-, and ATP6V0A2-CDG are presented.

Electrospray ionization (ESI) mass spectrometry of transferrin can be used to diagnose congenital disorders of glycosylation (CDG) by detecting abnormal N-glycosylation due to reduced site occupancy or processing failure. Time-of-flight mass spectrometers are widely used to separate 25-45 charged ions in the m/z 1,700-3,000 range, and a summed zero-charge mass distribution is generated despite the risk of improper deconvolution. In this study, the low m/z region of the multiply-charged ion mass spectrum enabled a robust analysis of CDG. A triple quadrupole mass spectrometer, the standard instrument for newborn screening for inborn errors of metabolism, permitted the identification of the key ions characteristic of different types of CDG affecting PMM2, ALG14, SLC35A1, SLC35A2, MAN1B1 and PGM1 in the m/z 1,970-2,000 region. Charge deconvolution was used as a complementary tool for validating the findings. It was necessary to set a cutoff level for the evaluation, since small peaks indicating glycosylation failure or reduced sialylation were observed, even in control subjects. This method and workflow facilitates the implementation of MS-based analyses and the screening of CDG in clinical laboratories.

Mass spectrometry imaging (MSI) without labeling has the potential for faster screening in drug development. Matrix-assisted laser desorption/ionization (MALDI) is typically used, but it has a large matrix size and uneven drug distribution. Surface-assisted laser desorption/ionization (SALDI) using nanoparticles (NPs) may overcome these issues. Here, the influence of NPs, solvent ratio, and order of dropping of NPs on SALDI-MSI of protoporphyrin IX (PpIX), a cancer drug, are reported. A solution of PpIX in a 50% aqueous solution of 50% acetonitrile at a concentration of 10 μM was used. The NPs include ZnO, Fe₃O₄, and four types of TiO₂. The NPs were fabricated by dissolving them on an aqueous 90% acetonitrile solution. Mass spectra were obtained with a time-of-flight mass spectrometer using a Nd:YAG laser at a 355-nm wavelength. The signal intensity using TiO₂ at a 0.5 mg/mL concentration in 50% acetonitrile was increased by 1.6-fold compared to that without TiO₂. Changing the solvent to 90% acetonitrile gave a uniform TiO₂ distribution and a 9-fold increase in the signal intensity for PpIX. Among the four types of TiO₂ with different particle sizes and crystal structures, TiO₂ with a smaller particle size and a rutile crystal structure produced the highest signal intensity. Forming a layer on top of the PpIX also resulted in an increased signal intensity. Hence, SALDI using TiO₂ provides effective ionization of the drug. In the future, we plan to investigate a spray method for the ionization of PpIX using TiO₂ for the MSI of various drugs.

The gas-phase adsorption of N₂ on protonated serine (Ser, C₃H₇NO₃), threonine (Thr, C₄H₉NO₃), glycine (Gly, C₂H₅NO₂), and 2-aminoethanol (C₂H₇NO) was investigated using a tandem mass spectrometer equipped with an electrospray ionization source and a cold ion trap. N₂ molecules were adsorbed on the free X-H (X=O and N) groups of protonated molecules. Gas-phase N₂ adsorption-mass spectrometry detected the presence of free X-H groups in the molecular structures, and was applied to the structural elucidation of small molecules. When the 93 structures with an elemental composition of C₃H₇NO₃ were filtered using the gas-phase N₂ adsorption-mass spectrometry results for Ser, the number of possible molecular structures was reduced to 8 via the quantification of the X-H groups. Restricting and minimizing the number of possible candidates were effective steps in the structural elucidation process. Gas-phase N₂ adsorption-mass spectrometry combined with mass spectrometry-based techniques has the potential for being useful for elucidating the molecular structures of a variety of molecules.

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.

CO₃ ^-• and O₂ ^-• are known to be strong oxidizing reagents in biological systems. CO₃ ^-• in particular can cause serious damage to DNA and proteins by H^• abstraction reactions. However, H^• abstraction of CO₃ ^-• in the gas phase has not yet been reported. In this work we report on gas-phase ion/molecule reactions of CO₃ ^-• and O₂ ^-• with various molecules. CO₃ ^-• was generated by the corona discharge of an O₂ reagent gas using a cylindrical tube ion source. O₂ ^-• was generated by the application of a 15 kHz high frequency voltage to a sharp needle in ambient air at the threshold voltage for the appearance of an ion signal. In the reactions of CO₃ ^-•, a decrease in signal intensities of CO₃ ^-• accompanied by the simultaneous increase of that of HCO₃ ^- was observed when organic compounds with H-C bond energies lower than ∼100 kcal mol^-1 such as n-hexane, cyclohexane, methanol, ethanol, 1-propanol, 2-propanol, and toluene were introduced into the ion source. This clearly indicates the occurrence of H^• abstraction. O₂ ^-• abstracts H⁺ from acid molecules such as formic, acetic, trifluoroacetic, nitric and amino acids. Gas-phase CO₃ ^-• may play a role as a strong oxidizing reagent as it does in the condensed phase. The major discharge product CO₃ ^-• in addition to O₂ ^-•, O₃, and NO _x ^• that are formed in ambient air may cause damage to biological systems.

Temperature-resolved proton transfer reactions of multiply-protonated angiotensin I, disulfide-intact and -reduced lysozyme, and ubiquitin ions to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for the proton transfer were determined from the intensities of the parent and product ions in mass spectra. Dramatic changes were observed in the distribution of product ions and the reaction rate constants. In particular, the rate constants for disulfide-intact lysozyme ions changed more drastically with the change in charge state and temperature compared to the corresponding values for disulfide-reduced ions. Proton transfer reactions were enhanced or suppressed as the result of the formation of complexes between the ions with gaseous molecules, which is related to changes in their conformation with changing.

We measured the Re/Os (¹⁸⁵Re/¹⁸⁸Os) and ¹⁸⁷Os/¹⁸⁸Os ratios from nanoparticles (NPs) using a multiple collector-inductively coupled plasma-mass spectrometer equipped with high-time resolution ion counters (HTR-MC-ICP-MS). Using the HTR-MC-ICP-MS system developed in this study, the simultaneous data acquisition of four isotopes was possible with a time resolution of up to 10 μs. This permits the quantitative analysis of four isotopes to be carried out from transient signals (e.g., <0.6 ms) emanating from the NPs. Iridium-Osmium NPs were produced from a naturally occurring Ir-Os alloy (ruthenosmiridium from Hokkaido, Japan; osmiridium from British Columbia, Canada; iridosmine from the Urals region of Russia) through a laser ablation technique, and the resulting nanoparticles were collected by bubbling water through a suspension. The ¹⁸⁷Os/¹⁸⁸Os ratios for individual NPs varied significantly, mainly due to the counting statistics of the ¹⁸⁷Os and ¹⁸⁸Os signals. Despite the large variation in the measured ratios, the resulting ¹⁸⁷Os/¹⁸⁸Os ratios for three Ir-Os bearing minerals, were 0.121±0.013 for Hokkaido, 0.110±0.012 for British Columbia, and 0.122±0.020 for the Urals, and these values were in agreement with the ratios obtained by the conventional laser ablation-MC-ICP-MS technique. The data obtained here provides a clear demonstration that the HTR-MC-ICP-MS technique can become a powerful tool for monitoring elemental and isotope ratios from NPs of multiple components.