999 resultados para perdas de MS
Resumo:
Time-resolved DRIFTS, MS, and resistance measurements were used to study the interaction of undoped and Pd-doped SnO2 with H-2 in air and argon at 300 degrees C. Using first-order kinetics, we compare the time constants for the resistance drop and its partial recovery with those of the surface hydroxyl evolution and water formation in the gas phase upon exposure to hydrogen. In the case of the undoped oxide, resistance and bridging hydroxyls (BOHs) evolve similarly, manifesting a fast main drop followed by recovery at a similar rate. The rate of water formation for this material was found to be much slower than that of the main drop in both the resistance and BOHs. In contrast, the resistance change for SnO2-Pd appeared to be similar to that of water formation, and no correlation was found between the evolution of resistance and surface OHs. Isotopic exchange on both materials revealed that water formation occurs via fast and slow hydrogen transfer to surface oxygen species. While the former originates from just-adsorbed hydrogen, the latter appears to proceed from the preadsorbed OHs. Both surfaces exhibit close interaction between chemisorbed oxygen and existing bridging OH groups, indicating that the latter is an intermediate in the hydrogen oxidation and generation of donor states on the surface.
Resumo:
In the preparation of silica-supported nickel oxide from nickel nitrate impregnation and drying, the replacement of the traditional air calcination step by a thermal treatment in 1% NO/Ar prevents agglomeration, resulting in highly dispersed NiO. The mechanism by which NO prevents agglomeration was investigated by using combined in situ diffuse reflectance infrared fourier transform (DRIFT) spectroscopy and mass spectrometry (MS). After impregnation and drying, a supported nickel hydroxynitrate phase with composition Ni(3)(NO(3))(2)(OH)(4) had been formed. Comparison of the evolution of the decomposition gases during the thermal decomposition of Ni(3)(NO(3))(2)(OH)(4) in labeled and unlabeled NO and O(2) revealed that NO scavenges oxygen radicals, forming NO(2). The DRIFT spectra revealed that the surface speciation evolved differently in the presence of NO as compared with in O(2) or Ar. It is proposed that oxygen scavenging by NO depletes the Ni(3)(NO(3))(2)(OH)(4) phase of nitrate groups, creating nucleation sites for the formation of NiO, which leads to very small (similar to 4 nm) NiO particles and prevents agglomeration.
Th1 not Th17 cells drive spontaneous MS-like disease despite a functional regulatory T cell response
Resumo:
Multiple sclerosis is considered a disease of complex autoimmune etiology, yet there remains a lack of consensus as to specific immune effector mechanisms. Recent analyses of experimental autoimmune encephalomyelitis, the common mouse model of multiple sclerosis, have investigated the relative contribution of Th1 and Th17 CD4 T cell subsets to initial autoimmune central nervous system (CNS) damage. However, inherent in these studies are biases influenced by the adjuvant and toxin needed to break self-tolerance. We investigated spontaneous CNS disease in a clinically relevant, humanized, T cell receptor transgenic mouse model. Mice develop spontaneous, ascending paralysis, allowing unbiased characterization of T cell immunity in an HLA-DR15-restricted T cell repertoire. Analysis of naturally progressing disease shows that IFN?(+) cells dominate disease initiation with IL-17(+) cells apparent in affected tissue only once disease is established. Tregs accumulate in the CNS but are ultimately ineffective at halting disease progression. However, ablation of Tregs causes profound acceleration of disease, with uncontrolled infiltration of lymphocytes into the CNS. This synchronous, severe disease allows characterization of the responses that are deregulated in exacerbated disease: the correlation is with increased CNS CD4 and CD8 IFN? responses. Recovery of the ablated Treg population halts ongoing disease progression and Tregs extracted from the central nervous system at peak disease are functionally competent to regulate myelin specific T cell responses. Thus, in a clinically relevant mouse model of MS, initial disease is IFN? driven and the enhanced central nervous system responses unleashed through Treg ablation comprise IFN? cytokine production by CD4 and CD8 cells, but not IL-17 responses.
Resumo:
Tetrodotoxin (TTX) is one of the most potent marine neurotoxins reported. The global distribution of this toxin is spreading with the European Atlantic coastline now being affected. Climate change and increasing pollution have been suggested as underlying causes for this. In the present study, two different sample preparation techniques were used to extract TTX from Trumpet shells and pufferfish samples. Both extraction procedures (accelerated solvent extraction (ASE) and a simple solvent extraction) were shown to provide good recoveries (80-92%). A UPLC-MS/MS method was developed for the analysis of TTX and validated following the guidelines contained in the Commission Decision 2002/657/EC for chemical contaminant analysis. The performance of this procedure was demonstrated to be fit for purpose. This study is the first report on the use of ASE as a mean for TTX extraction, the use of UPLC-MS/MS for TTX analysis, and the validation of this method for TTX in gastropods.
Resumo:
The performances of four LC-MS/MS methodologies for determination of up to eight mycotoxin biomarkers in human urines were compared by involving three laboratories that analysed common urine samples spiked at two levels of each biomarker. Each laboratory received a calibration solution, spiked urines and the corresponding unspiked urine. The two spiking levels for each biomarker were chosen by considering the levels naturally occurring in human urines and the limits of quantification of the LC-MS/MS methodologies used by the participating laboratories. The results of each laboratory were evaluated for their z-score values. The percentage of satisfactory z-scores (vertical bar z vertical bar 2) were obtained for fumonisin B-1 (7/12 results), ochratoxin A (4/8 results) and alpha-zearalenol (1/8 results). The percentage of satisfactory z-scores for fumonisin B-1 and ochratoxin A increased from 42 to 83% for fumonisin B-1 and from 50 to 62% for ochratoxin A when laboratories 1 and 2 used own calibrants. Factors that could explain the different results obtained for fumonisin B-1 and ochratoxin A with provided and own calibration solutions could not be identified in this study and should be carefully investigated in future studies.
Resumo:
There are more than 300 potential mycotoxins that can contaminate food and feed and cause adverse effects in humans and animals. The data on the co-occurrence of mycotoxins in novel animal feed materials, such as distiller's dried grain with solubles (DDGS), are limited. Thus, a UHPLC-MS/MS method for the quantitation of 77 mycotoxins and other fungal metabolites was used to analyze 169 DDGS samples produced from wheat, maize, and barley and 61 grain samples. All DDGS samples analyzed were contaminated with 13-34 different mycotoxins. Fumonisins were present in all 52 maize DDGS samples (81.0-6890 μg/kg for fumonisin B1), and deoxynivalenol was present in all 99 wheat DDGS samples (39.3-1120 μg/kg). A number of co-occurring mycotoxins were also identified. Due to the high co-occurrence of mycotoxins, routine screening of the animal feed ingredients is highly recommended to allow the highlighted risks to be effectively managed.