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Trimethylsilyl Derivatives (trimethylsilyl + derivative)
Selected AbstractsGas chromatography/negative-ion chemical ionisation mass spectrometry for the quantitative analysis of morphine in human plasma using pentafluorobenzyl carbonate derivativesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2002H. J. Leis A sensitive and specific method for the quantitative determination of morphine in human plasma is presented. Morphine was extracted from plasma by solid phase extraction on C18 and converted to its pentafluorobenzyl carbonate trimethylsilyl derivative. The derivatives were analysed without further purification. Using gas chromatography/negative ion chemical ionisation mass spectrometry, a useful diagnostic fragment ion at m/z 356 is obtained at high relative abundance. Deuterated morphine was used as internal standard. Calibration graphs were linear within the range 1.25 to 320,nmol/L. Intra-day precision was 3.82% (15,nmol/L), 2.85% (75,nmol/L) and 4.13% (225,nmol/L), inter-day variability was found to be 1.77% (15,nmol/L), 4.95% (75,nmol/L) and 9.88% (225,nmol/L). Inter-day accuracy showed deviations of 2.18% (15,nmol/L), ,0.72% (75,nmol/L) and ,0.13% (225,nmol/L). The method is rugged and robust and has been applied to the batch analysis of morphine during pharmacokinetic profiling of the drug. Copyright © 2002 John Wiley & Sons, Ltd. [source] Quantification of free and esterified steryl glucosides in vegetable oils and biodieselEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2009Florence Lacoste Dr. Abstract Steryl glucosides (SG) are minor components that dramatically modify the low temperature performance of fatty acid methyl esters (FAME) used as biodiesel. SG are naturally present in vegetable oils but they may also be the result of the transesterification of esterified steryl glucosides (ESG). These are present in vegetable oils at a level of a few hundred milligrams per kilogram, depending on the nature of the feedstock. We developed an analytical method to quantify SG and ESG in vegetable oils and in FAME. The purification of SG and ESG was performed by liquid chromatography on silica gel, and the analysis of the trimethylsilyl derivatives was achieved by gas chromatography and flame ionization detection. The filterability of biodiesel is affected when the SG content is higher than 20,mg/kg. Therefore, the sensitivity of this new method is adapted for this purpose since the quantification limit is 10,mg/kg of SG and ESG. The recoveries are acceptable, between 75% and 90% depending on the species and content, and the reproducibility relative standard deviation, evaluated at 10%, is comparable to other studies. [source] Porphyromonas gingivalis lipids and diseased dental tissuesMOLECULAR ORAL MICROBIOLOGY, Issue 2 2006F. C. Nichols Background/aim:,Porphyromonas gingivalis synthesizes several classes of dihydroceramides and at least one of these lipid classes promotes proinflammatory secretory reactions in gingival fibroblasts as well as alters fibroblast morphology in culture. The purpose of this investigation was to determine whether the dihydroceramide lipids of P. gingivalis are recovered in lipid extracts of subgingival plaque, diseased teeth, and diseased gingival tissue samples. Methods:, Lipids were extracted from P. gingivalis, subgingival plaque, subgingival calculus, teeth laden with gross accumulations of subgingival calculus, and gingival tissue samples obtained from chronic severe periodontitis sites. Lipid samples were analyzed by gas chromatography-mass spectrometry as trimethylsilyl derivatives or by electrospray-mass spectrometry as underivatized products. High-performance liquid chromatography fractions of P. gingivalis lipids and gingival tissue lipids were also analyzed by electrospray-mass spectrometry analysis. Results:,P. gingivalis phosphorylated dihydroceramides were recovered in lipid extracts of subgingival plaque, subgingival calculus, calculus contaminated teeth, and diseased gingival tissue samples. However, the distribution of phosphorylated dihydroceramides varied between these samples. Conclusion:, Subgingival plaque, subgingival calculus, diseased teeth, and gingival tissue are contaminated with phosphorylated dihydroceramides produced by P. gingivalis. The previously reported biological activity of these substances together with the recovery of these lipids at periodontal disease sites argues strongly for their classification as virulence factors in promoting chronic inflammatory periodontal disease. [source] A gas chromatography/mass spectrometry method for the determination of sildenafil, vardenafil and tadalafil and their metabolites in human urineRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2010Sabina Strano-Rossi Sildenafil (SDF), vardenafil (VDF) and tadalafil (TDF) are phosphodiesterase type 5 enzyme inhibitors (PDE5Is), used in the treatment of erectile disorders and to improve breathing efficiency in pulmonary hypertension. The increasing incidence of their use among young athletes has drawn the attention of the anti-doping authorities to the possible abuse of PDE5Is by athletes due to their pharmacological activities. This paper describes a method for the determination in urine of PDE5Is and their metabolites by gas chromatography/mass spectrometry (GC/MS) after liquid/liquid extraction of the analytes from urine and derivatisation to obtain trimethylsilyl derivatives. The metabolic profile was studied on real samples collected from subjects taking PDE5Is (Viagra®, Levitra® or Cialis®); the main urinary metabolites were identified and their MS fragmentation characterized. The sample pre-treatment and GC/MS conditions for the detection of the metabolites have been optimised. A method for their preliminary screening and subsequent confirmation is described that takes into account the general requirements of a routine doping analysis to be used for the screening of large numbers of samples. The main metabolites identified can be included in a general purpose screening method and all the metabolites in a more specific confirmation method. The method developed has been applied for the screening of PDE5Is in 5000 urine samples. Based on the obtained results, the proposed method appears to be of practical use in analytical and forensic toxicology, including doping analysis. Copyright © 2010 John Wiley & Sons, Ltd. [source] Trimethylsilyl transfer during electron ionization mass spectral fragmentation of some , -hydroxycarboxylic and , -dicarboxylic acid trimethylsilyl derivatives and the effect of chain lengthRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2004J.-F. Rontani The electron ionization (EI) mass spectral fragmentation of , -hydroxycarboxylic and , -dicarboxylic acid trimethylsilyl derivatives was investigated. The mass spectra of these compounds exhibited fragment ions resulting from classical fragmentation of the trimethylsilyl ether and ester groups, and others resulting from the interactions between the two functionalities (m/z 147, 204, 217, [M,31]+ and [M,105]+ in the case of , -hydroxycarboxylic acid derivatives and m/z 147, 204, 217 and [M,131]+ in the case of , -dicarboxylic acid derivatives). Several fragmentation pathways were proposed to explain the formation of these different fragment ions. It is proposed that the ions at m/z 204 and 217 are formed via an initial trimethylsilyl transfer between the ether and the ester group or between the two ester groups. This transfer appeared to be more favoured in the case of , -dicarboxylic acid derivatives and to be dependent on the chain length. A more efficient transfer was in fact observed for compounds with a relatively long alkyl chain. In the case of shorter , -hydroxycarboxylic and , -dicarboxylic acid trimethylsilyl derivatives the formation of the ions at m/z 204 and 217 suffers strongly from competition from production of the ion at m/z 147. Copyright © 2004 John Wiley & Sons, Ltd. [source] Application of tandem mass spectrometry combined with gas chromatography and headspace solid-phase dynamic extraction for the determination of drugs of abuse in hair samplesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2003Dirk W. Lachenmeier A new method combination, headspace solid-phase dynamic extraction coupled with gas chromatography/tandem mass spectrometry (HS-SPDE/GC/MS/MS), is introduced to determine drugs of abuse in hair samples. This highly automated procedure utilizes SPDE for pre-concentration and on-coating derivatization as well as GC and triple quadrupole MS/MS for selective and sensitive detection. All these steps, apart from washing and cutting of the hair samples, are performed without manual intervention on a robot-like autosampler. SPDE is a solventless extraction technique related to solid-phase microextraction (SPME). The analytes are absorbed from the sample headspace directly into a hollow needle with an internal coating of polydimethylsiloxane by repeated aspirate/dispense cycles. The HS-SPDE/GC/MS/MS procedure was applied to the analysis of methadone, the trimethylsilyl derivatives of cannabinoids and the trifluoroacetyl derivatives of amphetamines and designer drugs. The method was shown to be sensitive with detection limits between 6 and 52 pg/mg hair matrix and precision between 0.4 and 7.8% by the use of an internal standard technique. Linearity was obtained from 0.1,20,ng/mg with coefficients of correlation between 0.995 and 0.999. Compared with conventional methods of hair analysis, HS-SPDE/GC/MS/MS is easier to use, substantially faster, with the degree of sensitivity and reproducibility demanded in clinical and forensic toxicology. The main advantage of the SPDE technique in relation to SPME is the robustness of the capillary. Copyright © 2003 John Wiley & Sons, Ltd. [source] Chirally Modified Platinum Generated by Adsorption of Cinchonidine Ether Derivatives: Towards Uncovering the Chiral SitesCHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007Norberto Bonalumi Abstract The adsorption behavior of O -methyl and O -trimethylsilyl derivatives of cinchonidine (CD), employed as chiral modifiers for heterogeneous enantioselective hydrogenations on supported Pt catalysts, has been investigated by using attenuated total reflection infrared spectroscopy (ATR-IR) and density functional theory (DFT) electronic structure calculations. The ATR-IR spectroscopic investigation provided detailed insight of the adsorbed modifiers under conditions close to those employed during catalytic processes, and electronic structure calculations were used as a complement to the experiments to uncover the implications of conformational changes in generating the topology of the surface chiral site. The structural investigation of the adsorbed modifiers revealed a relationship between the spatial positions of the ether substituents and the enantiodifferentiation induced by the modified catalyst observed in the hydrogenation of ,-activated ketones. Experiments and calculations corroborate a model, according to which the addition of a bulky ether group to CD reshapes the chiral sites, thus generating catalytic chiral surfaces with different and, in some cases (e.g. hydrogenation of ketopantolactone), even opposite enantioselective properties to those obtained with CD without altering the absolute configuration of the modifier. The study also confirms that active surface conformations of cinchona modifiers are markedly different from those existing in vacuum and in solution, thus underlying the necessity of investigating the surface-modifier interaction in order to understand enantioselectivity. [source] | ||||||||||