Capillary isoelectric focusing (cIEF) was online coupled to a Q‐TOF MS by a flow‐through microvial interface for the analysis of therapeutic mAb. Intact molecular weights obtained from the mass ...spectrum deconvolution of separated charge variants provided information on the structural heterogeneity of therapeutic mAbs. A sandwich cIEF–MS configuration composed of anolyte, sample, and catholyte segments sequentially injected into a neutrally coated capillary was used for the charge heterogeneity separation of four mAbs. Acetic acid and ammonium hydroxide were used in places of the non‐volatile acids and bases commonly used for IEF but are incompatible with online MS detection. Glycerol was added as the anti‐convective reagent. A chemical modifier was mixed with the cIEF effluent in the flow‐throw microvial to maintain the ESI stability and to mitigate ion suppression from the co‐eluted carrier ampholytes and glycerol. Analysis of mAb samples have shown relative populations of two basic variants originating from C‐terminal lysine process and acidic variant of deamidation. The lysine clippings, deamidation, and sialic acid modification in oligosaccharide chains were revealed in infliximab. Two lysine clipping variants and a deamidated variant were observed in adalimumab. The duplicate analyses of a reference mAb demonstrated five charge variants separated by cIEF due to some unidentified modifications, as their mass spectra shared close similarities. The mAb analyses demonstrated the feasibility of the cIEF–MS method, and they demonstrated how charge and structural variants and minor differences in therapeutic mAbs are observed with this technology. Online cIEF–MS is an information rich technology with high throughput, demonstrated by the initial data presented here.
We propose that the observed stellar halo around the globular cluster (GC) NGC 1851 is evidence of its formation in the central region of its defunct host dwarf galaxy. We numerically investigate the ...long-term dynamical evolution of a nucleated dwarf galaxy embedded in a massive dark matter halo under the strong tidal field of the Galaxy. The dwarf galaxy is assumed to have a stellar nucleus (or a nuclear star cluster) that could be the progenitor for NGC 1851. We find that although the dark matter halo and the stellar envelope of the host dwarf of NGC 1851 can be almost completely stripped during its orbital evolution around the Galaxy, a minor fraction of stars in the dwarf can remain trapped by the gravitational field of the nucleus. The stripped nucleus can be observed as NGC 1851 with no/little dark matter, whereas stars around the nucleus can be observed as a diffuse stellar halo around NGC 1851. The simulated stellar halo has a symmetric distribution with a power-law density slope of ∼−2 and shows no tidal tails within ∼200 pc from NGC 1851. We show that two GCs can merge with each other to form a new nuclear GC embedded in field stars owing to the low stellar velocity dispersion of the host dwarf. This result makes no assumption on the ages and/or chemical abundances of the two merging GCs. Thus, the observed stellar halo and characteristic multiple stellar populations in NGC 1851 suggest that NGC 1851 could have formed initially in the central region of an ancient dwarf galaxy. We predict that the stellar halo of NGC 1851 may have at least three different stellar populations. We also suggest some Galactic GCs with diffuse haloes, such as NGC 1904 and 5694, could be formed in a similar way to NGC 1851. We discuss the importance of GC merging within dwarfs in the formation of multiple stellar populations with abundance spreads in heavy elements in some Galactic GCs, such as M22 and NGC 2419. We also discuss other possible scenarios for the formation of the stellar halo around NGC 1851.
A quantification method for imatinib (IM), its major metabolite N‐desmethyl imatinib (NDI), and a degradation by‐product was developed using CE–MS combined with an online concentration technique. The ...use of multiple reaction monitoring (MRM)–MS/MS further improved the sensitivity of this technology. Liquid–liquid extraction (LLE) using tertiary butyl methyl ether yielded high recovery and reproducibility for the pretreatment of serum samples. The recovery rate exceeded 83% for all three analytes, and was 90% for IM. To improve quantification results, a conductivity‐induced online analyte concentration technique, field‐amplified sample stacking (FASS), was used. The S/N ratios were improved at least 10‐fold when compared with conventional capillary zone electrophoresis. The detection limits were 0.2 ng/mL for IM, 0.4 ng/mL for NDI, and 4 ng/mL for the degradation by‐product. These results are superior to those previously obtained by other reported methods. The new method was validated in terms of its selectivity, intra‐ and interday repeatability and accuracy, and sample storage stability, following the guidelines issued by the European Medicines Agency. Considering the convenient pretreatment procedure (LLE), superior sensitivity, and fast analysis speed (<15 min), this method can be useful in the determination of imatinib levels in blood.
We measure the C+N+O abundance sum in red giant stars in two Galactic globular clusters, NGC 1851 and NGC 6752. NGC 1851 has a split subgiant branch which could be due to different ages or C+N+O ...content while NGC 6752 is representative of the least complex globular clusters. For NGC 1851 and NGC 6752, we obtain average values of A(C+N+O) = 8.16 plus or minus 0.10 ( sigma = 0.34) and 7.62 plus or minus 0.02 ( sigma = 0.06), respectively. When taking into account the measurement errors, we find a constant C+N+O abundance sum in NGC 6752. The C+N+O abundance dispersion is only 0.06 dex, and such a result requires that the source of the light element abundance variations does not increase the C+N+O sum in this cluster. For NGC 1851, we confirm a large spread in C+N+O. In this cluster, the anomalous RGB has a higher C+N+O content than the canonical RGB by a factor of 4 ( similar to 0.6 dex). This result lends further support to the idea that the two subgiant branches in NGC 1851 are roughly coeval, but with different CNO abundances.
The compositions of stars are a critical diagnostic tool for many topics in astronomy such as the evolution of our Galaxy, the formation of planets, and the uniqueness of the Sun. Previous ...spectroscopic measurements indicate a large intrinsic variation in the elemental abundance patterns of stars with similar overall metal content. However, systematic errors arising from inaccuracies in stellar models are known to be a limiting factor in such studies, and thus it is uncertain to what extent the observed diversity of stellar abundance patterns is real. Here we report the abundances of 30 elements with precisions of 2% for 79 Sun-like stars within 100 pc. Systematic errors are minimized in this study by focusing on solar twin stars and performing a line-by-line differential analysis using high-resolution, high-signal-to-noise spectra. We resolve X/Fe abundance trends in galactic chemical evolution at precisions of 10−3 dex Gyr−1 and reveal that stars with similar ages and metallicities have nearly identical abundance patterns. Contrary to previous results, we find that the ratios of carbon-to-oxygen and magnesium-to-silicon in solar-metallicity stars are homogeneous to within 10% throughout the solar neighborhood, implying that exoplanets may exhibit much less compositional diversity than previously thought. Finally, we demonstrate that the Sun has a subtle deficiency in refractory material relative to >80% of solar twins (at 2 confidence), suggesting a possible signpost for planetary systems like our own.
ABSTRACT
The low-metallicity, kinematically interesting dwarf stars studied by Stephens & Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic ...line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with Fe/H > −2; however, large disagreements are found for stars with Fe/H ≤ −2, with offsets as large as ΔTeff ∼ +500 K and Δlog g ∼ +1.0. A subset of six stars (test cases) are analysed ab initio using high-resolution spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to include two α-challenged dwarf stars, suggestive of origins in a low-mass, accreted dwarf galaxy. The orbital parameters for the entire SB02 sample are re-determined using Gaia DR2 data. We find 11 stars that are dynamically coincident with the Gaia-Sausage accretion event and another 17 with the Gaia-Sequoia event in action space. Both associations include low-mass, metal-poor stars with isochrone ages older than 10 Gyr. Two dynamical subsets are identified within Gaia-Sequoia. When these subsets are examined separately, a common knee in α/Fe is found for the Gaia-Sausage and low orbital energy Gaia-Sequoia stars. A lower metallicity knee is tentatively identified in the Gaia-Sequoia high orbital energy stars. If the metal-poor dwarf stars in these samples are true members of the Gaia-Sausage and Gaia-Sequoia events, then they present a unique opportunity to probe the earlier star formation histories of these systems.
We present radial velocities and chemical abundances for nine stars in the old, distant open clusters Be 18, Be21, Be22, Be32, and PWM4. For Be 18 and PWM4, these are the first chemical abundance ...measurements. Combining our data with literature results produces a compilation of some 68 chemical abundance measurements in 49 unique clusters. All elements show negligible or small trends between X/Fe and distance (<0.02 dex kpc super(-1)), but for some elements, there is a hint that the local (R sub(GC) < 13 kpc) and distant R sub(GC) < 13 kpc samples may have different trends with distance. There is no evidence for significant abundance trends versus age (<0.04 dex Gyr super(-1)). We measure the linear relation between X/Fe and metallicity, Fe/H, and find that the scatter about the mean trend is comparable to the measurement uncertainties. Arguably, our understanding of the evolution of the outer disk from open clusters is currently limited by systematic abundance differences between various studies.
Concentration sensitivity is a key performance indicator for analytical techniques including for capillary electrophoresis‐mass spectrometry (CE–MS) with electrospray ionization (ESI). In this study, ...a flow‐through microvial interface was used to couple CE with MS and improve the ESI stability and detection sensitivity. By infusing a peptide mixture through the interface into an MS detector at a typical flow rate for CE‐MS analysis, the spatial region near the interface was mapped for MS signal intensity. When the sprayer tip was within a 6 × 6.5 × 5 mm region in front of the MS inlet, the ESI was stable with no significant loss of signal intensity for ions with m/z 239. Finite element simulations showed that the average electric field strength at the emitter tip did not change significantly with minor changes in emitter tip location. Experiments were conducted with four different mass spectrometer platforms coupled to CE via the flow‐through microvial interface. Key performance indicators, that is, limit of detection (LOD) and linearity of calibration curves were measured for nine amino acids and five peptides. Inter‐ and intraday reproducibility were also tested. The results were shown to be suitable for quantification when internal standards were used.
We present the chemical compositions for eight bright giants in the globular cluster NGC 1851. Our analysis reveals large star-to-star abundance variations and correlations of the light elements O, ...Na, and Al, a feature found in every well-studied globular cluster. However, NGC 1851 also exhibits large star-to-star abundance variations of the s-process elements Zr and La. These s-process elements are correlated with Al and anticorrelated with O. Furthermore, the Zr and La abundances appear to cluster around two distinct values. A recent study revealed a double subgiant branch in NGC 1851. Our data reinforce the notion that there are two stellar populations in NGC 1851 and indicate that this cluster has experienced a complicated formation history with similarities to to Centauri.
Polysaccharide characterization posts the most difficult challenge to available analytical technologies compared to other types of biomolecules. Plant polysaccharides are reported to have numerous ...medicinal values, but their effect can be different based on the types of plants, and even regions of productions and conditions of cultivation. However, the molecular basis of the differences of these polysaccharides is largely unknown. In this study, direct analysis in real time mass spectrometry (DART-MS) was used to generate polysaccharide fingerprints. Large saccharides can break down into characteristic small fragments in the DART source via pyrolysis, and the products are then detected by high resolution MS. Temperature was shown to be a crucial parameter for the decomposition of large polysaccharide. The general behavior of carbohydrates in DART-MS was also studied through the investigation of a number of mono- and oligosaccharide standards. The chemical formula and putative ionic forms of the fragments were proposed based on accurate mass with less than 10 ppm mass errors. Multivariate data analysis shows the clear differentiation of different plant species. Intensities of marker ions compared among samples also showed obvious differences. The combination of DART-MS analysis and mechanochemical extraction method used in this work demonstrates a simple, fast, and high throughput analytical protocol for the efficient evaluation of molecular features in plant polysaccharides.
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