Magnetic resonance imaging of the neuroprotective effect of xaliproden in rats

RATIONALE AND OBJECTIVES: The neurotrophic effect of Xaliproden has been followed using sequential cerebral magnetic resonance imaging (MRI) in rats with vincristine-induced brain lesion as a model of Alzheimer disease. METHODS: Nineteen rats received an intraseptal injection of vincristine on day 0, followed by a daily gavage with either the vehicle (Tween-20 1%) (n = 10) or Xaliproden (10 mg/kg) (n = 9). Eight sham-operated controls received a daily gavage with either the vehicle (n = 4) or Xaliproden (n = 4). Brain MR imaging was performed at 4.7 T on a Biospec 47/30 MR system before surgery then 3, 7, 10, and 14 days after surgery. RESULTS: At day 3 following vincristine injection, an increase in MR signal intensity in the septum was observed on T2-weighted images. This increase was maximal at day 10, and remained stable until day 14. Daily treatment with Xaliproden delayed the appearance of hypersignals until day 7 and reduced by Ca. 50% the magnitude of the increase in signal intensity from day 10. No changes were observed in the hippocampus. CONCLUSION: Quantitative MRI objectifies noninvasively the neuroprotective effect of Xaliproden on rat brain anatomy

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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Compendio de física médica

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Silicon speciation by gas chromatography coupled to mass spectrometry in gasolines

cited By 14International audienceA method for the speciation of silicon compounds in petroleum products was developed using gas chromatography coupled to mass spectrometry (GC-MS). Prior to analysis, several precautions about storage and conservation were applied for all samples. In spiked gasoline samples, limits of detection between 24 and 69μgkg -1 for cyclic siloxanes (D 4-D 6) and between 1 and 7μgkg -1 for other species were obtained. In this study, cyclic siloxanes (D n) and one ethoxysilane were quantified for the first time in petroleum products by a specific method based on response factor calculation to an internal standard. This method was applied to four samples of naphthas and gasolines obtained from a steam cracking process. Cyclic siloxanes were predominant in four investigated samples with concentrations ranging between 101 and 2204μgkg -1. Cyclic siloxane content decreased with an increase in their degree of polymerization. During a steam cracking process, silicon concentrations determined by GC-MS SIM (single ion monitoring) significantly increase. This trend was confirmed by ICP-OES (inductively coupled plasma optical emission spectroscopy) measurements but a difference on the total silicon content was observed, certainly highlighting the presence of unknown silicon species. GC-MS SIM method gives access to the chemical nature of the silicon species, which is crucial for the understanding of hydrotreatment catalyst poisoning in the oil and gas industry. © 2011 Elsevier B.V

Combining fourier transform-ion cyclotron resonance/mass spectrometry analysis and kendrick plots for silicon speciation and molecular characterization in petroleum products at trace levels

cited By 13International audienceA new method combining FT-ICR/MS analysis and Kendrick plots for the characterization of silicon species at trace levels in light petroleum products is presented. The method provides efficient instrumental detection limits ranging from 80 ng/kg to 5 μg/kg and reliable mass accuracy lower than 0.50 ppm for model silicon molecules in spiked gasoline. More than 3000 peaks could be detected in the m/z 50-500 range depending on the nature of the gasoline sample analyzed. An in-house software program was used to calculate Kendrick plots. Then, an algorithm searched, selected, and represented silicon species classes (O 2Si, O 3Si, and O 4Si classes) in Kendrick plots by incorporating model molecules' information (i.e., exact mass and intensity). This procedure allowed the complete characterization of more than 50 new silicon species with different degrees of unsaturation in petroleum products. © 2012 American Chemical Society

Development of heart-cutting multidimensional gas chromatography coupled to time of flight mass spectrometry for silicon speciation at trace levels in gasoline samples

cited By 8International audienceTo improve the understanding of hydrotreatment (HDT) catalyst poisoning by silicon species, these molecules must be characterized in petroleum products using powerful analytical systems. Heart-cutting gas chromatography coupled to time of flight mass spectrometry (GC-GC/TOFMS) method equipped with a Deans switch (DS) system was developed for the direct characterization of target silicon compounds at trace level (μgkg-1) in gasoline samples. This method was performed to identify silicon compounds never characterized before. After the selection of the second dimension column using GC-GC-FID, GC-GC/TOFMS was performed. The calibration curves obtained by the GC-GC/TOFMS method were linear up to 1000μgkg-1. Limits of detection (LOD) were ranging from 5 to 33μgkg-1 in spiked gasoline. The method provided sufficient selectivity and sensitivity to characterize known silicon compounds thanks to their specific ions and their retention times. The analysis of a naphtha sample by GC-GC/TOFMS has shown the presence of cyclic siloxanes (Dn) as major compounds of PDMS thermal degradation with the occurrence of linear siloxanes, especially hexamethyldisiloxane (L2), which was never characterized in petroleum products but already known as severe poison for catalyst. © 2012 Elsevier B.V

Characterization of silicon species issued from PDMS degradation under thermal cracking of hydrocarbons: Part 1 - Gas samples analysis by gas chromatography-time of flight mass spectrometry

cited By 3International audienceSilicon species are becoming emergent contaminants in the oil and gas industry due to their severe poisoning effect on the hydrotreatment (HDT) catalysts. Using an experimental pilot plant, fresh and representative samples of PDMS degradation under thermal cracking of hydrocarbons were produced. To follow the evolution of silicon species, the gas fraction was immediately analyzed by GC/TOFMS after the production and also after 4 months of storage at 4 C. Cyclic siloxanes (Dn) as the major products of PDMS thermal degradation were characterized in the gas phase but these compounds are mainly present in the liquid fraction. Five volatile silicon compounds belonging to the families of silanes, siloxanes and silanols were characterized and quantified in the thermal cracking samples depending on the operating conditions applied in degradation tests. Under coking or visbreaking conditions (long residence time, absence of steam), silanes and siloxanes were preferentially formed. Under evaluated steam cracking conditions (short residence time and presence of steam), trimethylsilanol (TMSOH) was mainly produced by the hydrolysis of PDMS. The formation of the linear siloxane (L2) after several month of storage at 4 C by the self-condensation of TMSOH was also observed. The suspected poisoning effects of these molecules were discussed and could explain the deactivation of catalysts taking place in the refining of the light petroleum cuts. The new identified volatile silicon compounds could affect the performance of the catalyst by the reaction of hydroxyl groups potentially present at the surface of the support with reactive silicon molecules, more specifically silanols. © 2013 Elsevier Ltd. All rights reserved

Characterization of silicon species issued from PDMS degradation under thermal cracking of hydrocarbons: Part 2 - Liquid samples analysis by a multi-technical approach based on gas chromatography and mass spectrometry

cited By 5International audienceSilicon speciation has recently gained interest in the oil and gas industry due to the impact of silicon species on hydrotreatment (HDT) catalysts. The determination of the chemical structure of silicon compounds appears as essential to limit silicon poisoning as to improve the lifetime of catalysts. To achieve a representative speciation of silicon in petroleum products, fresh samples of PDMS degradation under thermal cracking of hydrocarbons were produced using a pilot plant. The samples were carefully stored in a dewar containing liquid nitrogen (-195 C) to minimize the possible evolution of silicon species and to allow their analysis in representative conditions. A complete analytical approach based on gas chromatography (GC) and mass spectrometry techniques (MS) was developed and applied to the samples produced at 500 C. Moreover, to resolve coelutions observed by GC/TOFMS, GC-GC/TOFMS was successfully applied to obtain the mass spectrum of only one silicon compound. Combining the GC/MS mass spectrum giving access to the fragmentation of the compound and the raw formula and double bond equivalent (DBE) obtained by ESI-FT-ICR/MS, chemical structures were proposed. Almost molecules were strengthened by MSn. Cyclic siloxanes (Dn) were confirmed as the major compounds of PDMS thermal degradation even in the presence of hydrocarbons with a relative amount generally around 95% or above. No significant difference on the formation of Dn were observed according to the different operating conditions under thermal cracking of hydrocarbons. For the first time, several other silicon compounds present at trace levels (<5% of the total area) were characterized. α,ω-dihydroxy polydimethylsiloxanes, methylhydroxy cyclic siloxanes, (n + 1)oxasilabicyclo alcanes or bis(cyclosiloxanyl) siloxane, α-hydroxy, ω-methyl polysiloxanes and (n)oxasilabicyclo alcanes were preferentially formed in the presence of steam. Under evaluated coking or visbreaking conditions (long residence time without steam), other compounds were mainly characterized such as dimethoxy polysiloxanes, methyl(hydroperoxy) cyclic siloxanes, or ethoxy methyl cyclic siloxanes, linear polysiloxanes and methylpropyl cyclic siloxanes. Around one hundred silicon compounds were highlighted belonging to 12 different chemical families. The same repetition pattern (C2H6OSi), initially in PDMS, was present in all silicon compounds characterized in this study. Molecules with a number of silicon atoms ranging from 1 to 40 silicon atoms clearly demonstrated the occurrence of silicon in all petroleum cuts through very different chemical structures. This study shows that silicon species can distillate from gas fractions to the heavy petroleum cuts depending on their boiling points and chemical properties. These silicon species contain reactive groups (hydroxy, hydroperoxy, methoxy and ethoxy) which are able to react at the surface of HDT catalysts and cause a severe deactivation. Thus, these results appear as a crucial advance in progressing in the understanding of silicon poisoning. © 2013 Elsevier Ltd. All rights reserved

Degradation processes of polydimethylsiloxane under thermal cracking conditions of hydrocarbons in an experimental pilot plant followed by size exclusion chromatography coupled to inductively coupled plasma high resolution mass spectrometry

cited By 14International audienceIn the oil and gas industry, silicon coming from antifoaming agents, is recognized to be an emergent contaminant for hydrotreatment catalyst due to its negative effect on their performance. Using a pilot plant, representative samples of the thermal degradation of antifoaming agent such as polydimethylsiloxanes (PDMS) were produced under evaluated thermal cracking of hydrocarbons with the presence or absence of steam. Micro size exclusion chromatography hyphenated to inductively coupled plasma high resolution mass spectrometry was used to characterize these samples. Under low temperature processing conditions at around 250 °C, PDMS was not degraded in the presence of hydrocarbons. Under thermal cracking of hydrocarbons at 500 °C, PDMS is degraded and formed intermediate polymers and low molecular weight compounds. A small amount of the initial PDMS can be present following the different operating conditions. The percentage of steam has a great influence on the degradation of intermediate polymers probably following a hydrolysis to produce low molecular weight species. The results presented bring preliminary results and a new insight on the degradation of PDMS under thermal cracking conditions. This work indicates that the different molecular weight silicon compounds can distillate in the various petroleum cuts and could be responsible for catalyst poisoning. © 2012 Elsevier B.V

Amine degradation in CO₂ capture. 3. New degradation products of MEA in liquid phase: Amides and nitrogenous heterocycles

International audienceTo reduce greenhouse gas emissions from fossil fuel power plants, post combustion CO2 capture with amine-based solvent is the most mature technology. Ethanolamine (MEA), the benchmark amine, is the most studied amine but some degradation products are still unknown and for an environmental acceptance, it is important to identify them. In this work eleven amides and nitrogenous heterocycles were identified in a pilot plant liquid sample. Among them seven molecules were never reported in literature. Different analytical methods were developed especially HS-SPME coupled to GC/MS. Mechanisms of formation were proposed for each molecule and were validated in most cases