Efforts to analyze trace levels of cyclic peroxides by liquid chromatography/mass spectrometry gave evidence that acetonitrile suppressed ion formation. Further investigations extended this discovery to ketones, linear peroxides, esters, and possibly many other types of compounds, including triazole and menadione. Direct ionization suppression caused by acetonitrile was observed for multiple adduct types in both electrospray ionization and atmospheric pressure chemical ionization. The addition of only 2% acetonitrile significantly decreased the sensitivity of analyte response. Efforts to identify the mechanism were made using various nitriles. The ion suppression was reduced by substitution of an acetonitrile hydrogen with an electron-withdrawing group, but was exacerbated by electron-donating or steric groups adjacent to the nitrile. Although current theory does not explain this phenomenon, we propose that polar interactions between the various functionalities and the nitrile may be forming neutral aggregates that manifest as ionization suppression.
Over the past 15 years,ambient ionization mass spectrometry has rapidly developed,greatly expanding the applications of single-cell analysis,food and agricultural,envi-ronmental,chemical analysis,biomedical analysis,mass spectrometry imaging,among other areas.Real time mass spectrometry evaluations of living sample,such as in vivo direct analysis for single cell,clinical applications,metabolic monitoring of living species and transient intermediates in organic reactions,have demonstrated the power and potential significance of ambient ionization mass spectrometry.Here-in,we want to introduce a partial of our works atmospheric ionization mass spec-trometry,related to ambient ionization mass spectrometry. 相似文献
The understanding of the gas dynamics of the atmospheric pressure interface is very important for the development of mass spectrometry systems with high sensitivity. While the gas flows at high pressure (>1 Torr) and low pressure (<10–3 Torr) stages are relatively well understood and could be modeled using continuum and molecular flows, respectively, the theoretical modeling or numeric simulation of gas flow through the transition pressure stage (1 to 10–3 Torr) remains challenging. In this study, we used the direct simulation Monte Carlo (DMSC) method to develop the gas dynamic simulations for the continuous and discontinuous atmospheric pressure interfaces (API), with different focuses on the ion transfer by gas flows through a skimmer or directly from the atmospheric pressure to a vacuum stage, respectively. The impacts by the skimmer location in the continuous API and the temporal evolvement of the gas flow with a discontinuous API were characterized, which provide a solid base for the instrument design and performance improvement.
Abstract On the basis of the reported low-resolution electron impact (EI) mass spectral decomposition patterns of a few underivatlsed simple disaccnarides1-3 and the results of a high-resolution electron impact mass spectrum of a model disaccharide β-methyl pachybioside,4 a common fragmentation pathway of such compounds could be worked out. Using the derived standard decomposition pathways, structure of a novel tetrasaccharide, orthenthose, has been elucidated as oleandrose tetrasaccharide. 相似文献
We present affinity capillary electrophoresis and mass spectrometry (ACE-MS) as a comprehensive separation technique for label-free solution-based affinity analysis. The application of ACE-MS for measuring affinity constants between eight small molecule drugs [ibuprofen, s-flurbiprofen, diclofenac, phenylbutazone, naproxen, folic acid, resveratrol, and 4,4'-(propane-1,3-diyl) dibenzoic acid] and β-cyclodextrin is described. We couple on-line ACE with MS to combine the separation and kinetic capability of ACE together with the molecular weight and structural elucidation of MS in one system. To understand the full potential of ACE-MS, we compare it with two other methods: Direct infusion mass spectrometry (DIMS) and ACE with UV detection (ACE-UV). After the evaluation, DIMS provides less reliable equilibrium dissociation constants than separation-based ACE-UV and ACE-MS, and cannot be used solely for the study of noncovalent interactions. ACE-MS determines apparent dissociation constants for all reacting small molecules in a mixture, even in cases when drugs overlap with each other during separation. The ability of ACE-MS to interact, separate, and rapidly scan through m/z can facilitate the simultaneous affinity analysis of multiple interacting pairs, potentially leading to the high-throughput screening of drug candidates. 相似文献
Collision-induced dissociation (CID) experiments were performed on atmospheric ion adducts [M + R]– formed between various types of organic compounds M and atmospheric negative ions R- [such as O2–, HCO3–, COO–(COOH), NO2–, NO3–, and NO3–(HNO3)] in negative-ion mode atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. All of the [M + R]– adducts were fragmented to form deprotonated analytes [M – H]– and/or atmospheric ions R–, whose intensities in the CID spectra were dependent on the proton affinities of the [M – H]– and R– fragments. Precursor ions [M + R]– for which R- have higher proton affinities than [M – H]– formed [M – H]– as the dominant product. Furthermore, the CID of the adducts with HCO3– and NO3-(HNO3) led to other product ions such as [M + HO]– and NO3–, respectively. The fragmentation behavior of [M + R]– for each R– observed was independent of analyte type (e.g., whether the analyte was aliphatic or aromatic, or possessed certain functional groups). 相似文献
The interaction between negative atmospheric ions and various types of organic compounds were investigated using atmospheric
pressure corona discharge ionization (APCDI) mass spectrometry. Atmospheric negative ions such as O2–, HCO3–, COO–(COOH), NO2–, NO3–, and NO3–(HNO3) having different proton affinities served as the reactant ions for analyte ionization in APCDI in negative-ion mode. The
individual atmospheric ions specifically ionized aliphatic and aromatic compounds with various functional groups as atmospheric
ion adducts and deprotonated analytes. The formation of the atmospheric ion adducts under certain discharge conditions is
most likely attributable to the affinity between the analyte and atmospheric ion and the concentration of the atmospheric
ion produced under these conditions. The deprotonated analytes, in contrast, were generated from the adducts of the atmospheric
ions with higher proton affinity attributable to efficient proton abstraction from the analyte by the atmospheric ion. 相似文献
It has been about ninety years since Hoesch reaction was first discovered in 1915. To our knowledge, although several authors[1,2] have studied the mechanism of Hoesch reaction, it has not been explained clearly. Here we represent an investigation on the mechanism with isotopic mass spectrometry. The effects of isotopes on mass spectra were illustrated obviously. FAB spectrum contained intermediate molecular ions at m/z 336 (M+, 19.3), 338 (M+, 18.2), 340 (M+, 12.3),etc and the peak 364 had already arose. This isotopic cluster demonstrated the positive ion 4 (M+, 336) was in existence (isotopes of Zn: 64, 66, 67, 68, 70). A possible intermediate molecular structure of the signal at m/z 364 could be assigned to 3 (M+, 364). Ions peaks of a possible intermediate negative ions suggested the structure 7. 相似文献
