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861.
Jesús Ibarz M Ferreira V Hernández-Orte P Loscos N Cacho J 《Journal of chromatography. A》2006,1116(1-2):217-229
A procedure has been developed for the GC-MS analysis of the aromas released in fast acid hydrolysis of precursor fractions from grape musts and skins. Different sorbents for the extraction of the precursors were compared. The best results were obtained with LiChrolut EN polymeric resins which displayed two and six-fold more extraction capacity than Amberlite XAD-2 resins and C18 sorbents, respectively. C18 sorbents are more suitable for selective extraction of less polar precursors. The initial version of the method was imprecise and so the imprecision of the different steps was assessed. The maceration of the solid parts and the liquid-liquid extraction of the aromas released in the acid hydrolysis proved to be the critical steps. Greater crushing of the solid parts and solid-phase extraction (SPE) instead of liquid-liquid extraction (LLE) improved reproducibility. In the method finally proposed about 100 aromatic components belonging to four large groups (lipid derivatives, shikimic acid derivatives, norisoprenoids and terpenes) were determined with good reproducibility. Important aroma compounds, such as cis-rose oxide or wine lactone were detected in non-Muscat grapes. 相似文献
862.
This forum article outlines some of the major challenges in present day biomarker discovery research. Notably the dilemma of reaching sufficient concentration sensitivity versus the required analysis time per sample is highlighted using a model calculation. A number of possible developments and recent research findings are considered to show possible ways out of this dilemma. Finally, the challenge of processing large, megavariate datasets prior to statistical analysis is presented. 相似文献
863.
864.
Koryagina NL Savelieva EI Khlebnikova NS Goncharov NV Jenkins RO Radilov AS 《Analytical and bioanalytical chemistry》2006,386(5):1395-1400
A novel procedure has been developed for determination of fluoroacetic acid (FAA) in water and biological samples. It involves
ethylation of FAA with ethanol in the presence of sulfuric acid, solid-phase microextraction of the ethyl fluoroacetate formed,
and subsequent analysis by GC-FID or by GC-MS in selected-ion-monitoring mode. The detection limits for FAA in water, blood
plasma, and organ homogenates are 0.001 μg mL−1, 0.01 μg mL−1, and 0.01 μg g−1, respectively. The determination error at concentrations close to the detection limit was less than 50%. For analysis of
biological samples, the approach has the advantages of overcoming the matrix effect and protecting the GC and GC-MS systems
from contamination. Application of the approach to determination of FAA in blood plasma and organ tissues of animals poisoned
with sodium fluoroacetate reveals substantial differences between the dynamics of FAA accumulation and clearance in rabbits
and rats. 相似文献
865.
Poór B Michniewicz N Kallay M Buma WJ Kubinyi M Szemik-Hojniak A Deperasiñska I Puszko A Zhang H 《The journal of physical chemistry. A》2006,110(22):7086-7091
We have unraveled the effects of an amino substituent in the ortho position on the excited-state dynamics of 4-nitropyridine N-oxide by studying the picosecond fluorescence kinetics and femtosecond transient absorption of a newly synthesized compound, 2-butylamino-6-methyl-4-nitropyridine N-oxide, and by quantum chemical calculations. Similar to the parent compound, the S(1) state of the target molecule has significant charge-transfer character and shows a large (approximately 8000 cm(-1)) static Stokes shift in acetonitrile. Analysis of the experimental and the theoretical results leads, however, to a new scenario in which this intramolecular charge transfer triggers in polar, aprotic solvents an ultrafast (around 100 fs) intramolecular proton transfer between the amino and the N-O group. The electronically excited N-OH tautomer is subsequently subject to solvent relaxation and decays with a lifetime of approximately 150 ps to the ground state. 相似文献
866.
Amelichev SA Konstantinova LS Obruchnikova NV Rakitin OA Rees CW 《Organic letters》2006,8(20):4529-4532
Fused aromatic and heterocyclic 1,2,3,4,5-pentathiepins react with triphenylphosphine and alkynes bearing electron-withdrawing groups to give the corresponding 1,4-dithiins in high yields. Unsymmetrical alkynes add regioselectively to afford products in agreement with the electron distribution in a proposed reaction intermediate. A mechanism for these reactions is proposed. 相似文献
867.
Alexander A. Simenel Svetlana V. Samarina Lubov' V. Snegur Zoya A. Starikova Larissa A. Ostrovskaya Natalia V. Bluchterova Margarita M. Fomina 《应用有机金属化学》2008,22(5):276-280
The antitumor activity of o‐carboxybenzoylferrocene sodium salt ( 1 ) was studied in vivo . Interaction between o‐carboxybenzoylferrocene ( 2 ) and N,N′‐carbonyldiimidazole in boiling methylene dichloride leads to 3‐(N‐imidazolyl)‐3‐ferrocenylisobenzofuran‐1(3H)‐one ( 5 ). The structure of compound 5 was established by X‐ray analysis. Aminolysis of compound 5 in toluene gave rise to ferrocenoylbenzamides ( 6a – d )–derivatives of dimethylamine, piperidine, pyrrolidine and morpholine. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
868.
869.
Highly sensitive detection of five typical fluoroquinolones in low‐fat milk by field‐enhanced sample injection‐based CE in bubble cell capillary
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Yan Deng Natalia Gasilova Liang Qiao Ying‐Lin Zhou Xin‐Xiang Zhang Hubert H. Girault 《Electrophoresis》2014,35(23):3355-3362
Fluoroquinolones are a group of synthetic antibiotics with a broad activity spectrum against mycoplasma, Gram‐positive, and Gram‐negative bacteria. Due to the extensive use of fluoroquinolones in farming and veterinary science, there is a constant need in the analytical methods able to efficiently monitor their residues in food products of animal origin, regulated by Commission Regulation (European Union) no. 37/2010. Herein, field‐enhanced sample injection for sample stacking prior the CZE separation was developed inside a bubble cell capillary for highly sensitive detection of five typical fluoroquinolones in bovine milk. Ethylenediamine was proposed as the main component of BGE for the antibiotics separation. The effect of BGE composition, injection parameters, and water plug length on the field‐enhanced sample injection‐based CE with UV detection was investigated. Under the optimized conditions, described field‐enhanced sample injection‐based CE‐UV analysis of fluoroquinolones provides LODs varying from 0.4 to 1.3 ng/mL. These LOD values are much lower (from 460 to 1500 times) than those obtained by a conventional CE in a standard capillary without bubble cell. The developed method was finally applied for the analysis of fluoroquinolones in low‐fat milk from a Swiss supermarket. Sample recovery values from 93.6 to 106.0% for different fluoroquinolones, and LODs from 0.7 to 2.5 μg/kg, were achieved. Moreover, the proposed ethylenediamine‐based BGE as volatile and compatible with MS system, enabled the coupling of the field‐enhanced sample injection‐based CE with a recently introduced electrostatic spray ionization MS via an iontophoretic fraction collection interface for qualitative fluoroquinolones identification. 相似文献
870.