165 resultados para ethyl lactate


Relevância:

10.00% 10.00%

Publicador:

Resumo:

A simple and sensitive high-performance liquid chromatographic (HPLC) method with fluorescence detection and mass spectrometric identification has been developed for analysis of 30 long-chain and short-chain free Fatty acids (FFAs). The fatty acids were derivatized to their esters with 1-[2-(p-toluenesulfonate)ethyl]-2-phenylimidazole-[4,5-f]-9,10-phenanthrene (TSPP) in N,N-dimethylformamide (DMF) at 90 degrees C with anhydrous K2CO3 as catalyst. A mixture Of C-1-C-30 fatty acids was completely separated within 60 min by gradient elution on a reversed-phase C-8 column. Qualitative identification of the acids was performed by atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) in positive-ion mode. The fluorescence excitation and emission wavelengths were 260 and 380 nm, respectively. Quantitative determination of the 30 acids in two Tibetan medicines Gentiana straminea and G. dahurica was performed. The results indicated that the medicines contained many FFAs. Linear correlation coefficients for the FFA derivatives were > 0.9991. Relative standard deviations (RSDs, n = 6) for the fatty acid derivatives were < 3%. Detection limits (at a signal-to-noise ratio of 3:1) were 3.1-38 fmol. When the fatty acid derivatives were determined in the two real samples results were satisfactory and the sensitivity and reproducibility of the method were good.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A sensitive method for the determination of free fatty acids using 2-(2-(anthracen-10-yl)-1H-naphtho[2,3-dimidazol-1-yl) ethyl-p-toluenesuIfonate (ANITS) as tagging reagent with fluorescence detection has been developed. ANITS could easily and quickly label fatty acids in the presence of the K2CO3 catalyst at 90 degrees C for 40 min in N,N-dimethylformamide solvent. From the extracts of rape bee pollen samples, 20 free fatty acids were sensitively determined. Fatty acid derivatives were separated on a reversed-phase Eclipse XDB-C8 column by HPLC in conjunction with gradient elution. The corresponding derivatives were identified by post-column APCI/MS in positive-ion detection mode. ANITS-fatty acid derivatives gave an intense molecular ion peak at mlz [M+H](+); with MS/MS analysis, the collision-induced dissociation spectra of m/z [M+H](+) produced the specific fragment ions at mlz [M-345](+) and mlz 345.0 (here, m/z 345 is the core structural moiety of the ANITS molecule). The fluorescence excitation and emission wavelengths of the derivatives were lambda(ex) = 250 nm and lambda(em) = 512 nm, respectively. Linear correlation coefficients for all fatty acid derivatives are > 0.9999. Detection limits, at a signal-to-noise ratio of 3 : 1, are 24.76-98.79 fmol for the labeled fatty acids.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A simple and sensitive method for evaluating the chemical compositions of protein amino acids, including cystine (Cys)(2) and tryptophane (Try) has been developed, based on the use of a sensitive labeling reagent 2-(11H-benzo[alpha]-carbazol-11-yl) ethyl chloroformate (BCEC-Cl) along with fluorescence detection. The chromophore of the 1,2-benzo-3,4-dihydrocarbazole-ethyl chloroformate (BCEOC-Cl) molecule was replaced with the 2-(11H-benzo[alpha]-carbazol-11-yl) ethyl functional group, yielding the sensitive fluorescence molecule BCEC-Cl. The new reagent BCEC-Cl could then be substituted for labeling reagents commonly used in amino acid derivatization. The BCEC-amino acid derivatives exhibited very high detection sensitivities, particularly in the cases of (Cys)(2) and Try, which cannot be determined using traditional labeling reagents such as 9-fluorenyl methylchloroformate (FMOC-Cl) and ortho-phthaldialdehyde (OPA). The fluorescence detection intensities for the BCEC derivatives were compared to those obtained when using FMOC-Cl and BCEOC-Cl as labeling reagents. The ratios I (BCEC)/I (BCEOC) = 1.17-3.57, I (BCEC)/I (FMOC) = 1.13-8.21, and UVBCEC/UVBCEOC = 1.67-4.90 (where I is the fluorescence intensity and UV is the ultraviolet absorbance). Derivative separation was optimized on a Hypersil BDS C-18 column. The detection limits calculated from 1.0 pmol injections, at a signal-to-noise ratio of 3, ranged from 7.2 fmol for Try to 8.4 fmol for (Cys)(2). Excellent linear responses were observed, with coefficients of > 0.9994. When coupled with high-performance liquid chromatography, the method established here allowed the development of a highly sensitive and specific method for the quantitative analysis of trace levels of amino acids including (Cys)(2) and Try from bee-collected pollen (bee pollen) samples.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A highly sensitive and accurate method based on the precolumn derivatization of bile acids (BA) with a high ionization efficiency labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-ethyl-benzenesulfonate (BDEBS) coupled with LC/MS has been developed. After derivatization, BA molecules introduced a weak basic nitrogen atom into the molecular core structure that was readily ionized in commonly used acidic HPLC mobile phases. Derivatives were sufficiently stable to be efficiently analyzed by atmospheric pressure chemical ionization (APCI)-MS/MS in positive-ion mode. The MS/MS spectra of BA derivatives showed an intense protonated molecular ion at m/z [M + H](+). The collision-induced dissociation of the molecular ion produced fragment ions at [MH - H2O](+), [MH - 2H(2)O](+), [MH - 3H(2)O](+). The characteristic fragment ions were at m/z 320.8, 262.8, and 243.7 corresponding to a cleavage of N - CO, O - CO, and C - OCC, respectively, and bonds of derivatized molecules. The selected reaction monitoring, based on the m/z [M + H]+ -> [MH - H2O](+), [MH - H2O](+), [MH - 2H(2)O](+), [MH-3H(2)O](+), 320.8, 262.8, and 243.7 transitions, was highly specific for the BA derivatives. The LODs for APCI in a positive-ion mode, at an S/N of 5, were 44.36-153.6 fmol. The validation results showed high accuracy in the range of 93-107% and the mean interday precision for all standards was < 15% at broad linear dynamic ranges (0.0244-25nmol/mL). Good linear responses were observed with coefficients of > 0.9935 in APCI/MS detection. Therefore, the facile BDEBS derivatization coupled with mass spectrometric analysis allowed the development of a highly sensitive and specific method for the quantitation of trace levels of the free and glycine-conjugated BA from human serum samples.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Ochotona curzoniae and Microtus oeconomus are the native mammals living on the Qinghai-TibetanPlateau of China. The molecular mechanisms of their acclimatization to the Plateau-hypoxia remain unclear. Expressions of hepatic hypoxia-inducible factor (HIF)-1 alpha, insulin-like growth factor-I (IGF-I)/IGF binding protein (BP)-1(IGFBP-1; including genes), and key metabolic enzymatic genes [lactate dehydrogenase (LDH)-A/isocitrate dehydrogenase (ICD)] are compared in Qinghai-Tibetan- Plateau mammals andsea- level mice after injection of CoCl2 (20, 40, or 60 mg/ kg) and normobaric hypoxia (16.0% O-2, 10.8% O-2, and 8.0% O-2) for 6 h, tested by histochemistry, Western blot analysis, ELISA, and RT-PCR. Major results are CoCl2 markedly increased 1) HIF-1 alpha only in mice, 2) hepatic and circulatory IGF-I in M. oeconomus, 3) hepatic IGFBP-1 in mice and O. curzoniae, and 4) LDH-A but reduced ICD mRNA in mice (CoCl2 20 mg/kg) but were unchanged in the Tibetan mammals. Normobaric hypoxia markedly 1) increased HIF-1 alpha and LDH-A mRNA in mice and M. oeconomus (8.0% O-2) not in O. curzoniae, and 2) reduced ICD mRNA in mice and M. oeconomus (8.0% O-2) not in O. curzoniae. Results suggest that 1) HIF-1 alpha responsiveness to hypoxia is distinct in lowland mice and plateau mammals, reflecting a diverse tolerance of the three species to hypoxia; 2) CoCl2 induces diversities in HIF-1, IGF-I/IGFBP-1 protein or genes in mice, M. oeconomus, and O. curzoniae. In contrast, HIF-1 mediates IGFBP-1 transcription only in mice and in M. oeconomus (subjected to severe hypoxia); 3) differences in IGF-I/IGFBP-1 expressions induced by CoCl2 reflect significant diversities in hormone regulation and cell protection from damage; and 4) activation of anaerobic glycolysis and reduction of Krebs cycle represents strategies of lowland-animals vs. the stable metabolic homeostasis of plateau- acclimatized mammals.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A simple and sensitive method for the determination of free fatty acids (FFAs) using acridone-9-ethyl-p-toluenesulfonate (AETS) as a fluorescence derivatization reagent by high performance liquid chromatography (HPLC) has been developed. Free fatty acid derivatives were separated on an Eclipse XDB-C-8 column with a good baseline resolution and detected with the fluorescence of which excitation and emission wavelengths of derivatives were set at lambda(ex) 404 and lambda(em) 440 nm, respectively. Identification of 19 fatty acid derivatives was carried out by online post-column mass spectrometry with an atmospheric pressure chemical ionization (APCI) source under positive-ion detection mode. Nineteen FFAs from the extract of Lomatogonium rotatum are sensitively determined. The results indicate that the plant Lomatogonium rotatum is enriched with an abundance of FFAs and FFAs of higher contents, which mainly focus on even carbon atoms, C-14, C-16, and C-18. The validation of the method including linearity, repeatability, and detection limits was examined. Most linear correlation coefficients for fatty acid derivatives are > 0.9989, and detection limits (at signal-to-noise of 3: 1) are 12.3-43.7 fmol. The relative standard deviations (RSDs) of the peak areas and retention times for 19 FFAs standards are < 2.24% and 0.45%, respectively. The established method is rapid and reproducible for the separation determination of FFAs from the extract of Lomatogonium rotatum with satisfactory results.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A pre-column derivatization method for the sensitive determination of amines using the labeling reagent 1,2-benzo-3,4-dihydrocarbazole-9-isopropyl chloroformate (BCIC-Cl) followed by high-performance liquid chromatography with fluorescence detection has been developed. Identification of derivatives is carried out by high performance liquid chromatography/atmospheric pressure chemical ionization (LC-APCl-MS-MS). The chromophore of 2-(9-carbazole)-ethyl chloroformate (CEOC) reagent is replaced by 1,2-benzo-3,4-dihydrocarbazole-9-isopropyl functional group, which results in a sensitive fluorescence derivatizing reagent BCIC-Cl. BCIC-Cl can easily and quickly label amines. Derivatives are stable enough to be efficiently analyzed by high-performance liquid chromatography and show an intense protonated molecular ion corresponding m/z [MH](+) under APCl in positive-ion mode. The collision-induced dissociation of protonated molecular ion formed a product at m/z 260 corresponding to the cleavage of CH2-OCO bond. Studies on derivatization demonstrate excellent derivative yields over the pH 9.0-10.0. Maximal yields close to 100% are observed with a 3 to 4-fold molar reagent excess. In addition, the detection responses for BCIC derivatives are compared with those obtained using CEOC and FMOC as derivatization reagents. The ratios of l(BCIC)/l(CEOC) and l(BCIC)/l(FMOC) are, respectively, 1.23-3.14 and 1.25-3.08 for fluorescent (FL) responses (here, l is relative fluorescence intensity). Separation of the derivatized amines had been optimized on reversed-phase Eclipse XDB-C-8 column. Detection limits are calculated from 1.0 pmol injection, at a signal-to-noise ratio of 3, are 10.6-37.8 fmol. The mean interday accuracy ranges from 94 to 105% for fluorescence detection with the largest mean %CV < 7.5. The mean interday precision for all standards is < 6.0% of the expected concentration. Excellent linear responses are observed with coefficients of > 0.9997.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A simple, sensitive, and mild method for the determination of amino compounds based on a condensation reaction with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC-HCI) as the dehydrant with fluorescence detection has been developed. Amines were derivatized to their acidamides with labeling reagent 2-(2-phenyl-1H-phenanthro-[9,10-d]imidazole-1-yl)-acetic acid (PPIA). Studies on derivatization conditions indicated that the coupling reaction proceeded rapidly and smoothly in the presence of a base catalyst in acetonitrile to give the corresponding sensitively fluorescent derivatives with an excitation maximum at lambda(ex) 260nm and an emission maximum at lambda(em) 380nm. The labeled derivatives exhibited high stability and were enough to be efficiently analyzed by high-performance liquid chromatography. Identification of derivatives was carried out by online post-column mass spectrometry (LC/APCI-MS/MS) and showed an intense protonated molecular ion corresponding m/z [MH](+) under APCI in positive-ion mode. At the same time, the fluorescence properties of derivatives in various solvents or at different temperature were investigated. The method, in conjunction with a gradient elution, offered a baseline resolution of the common amine derivatives on a reversed-phase Eclipse XDB-C-8 column. LC separation for the derivatized amines showed good reproducibility with acetonitrile-water as mobile phase. Detection limits calculated from 0.78 pmol injection, at a signal-to-noise ratio of 3, were 3.1-18.2 fmol. The mean intra- and inter-assay precision for all amine levels were < 3.85% and 2.11%, respectively. Excellent linear responses were observed with coefficients of > 0.9996. The established method for the determination of aliphatic amines from real wastewater and biological samples was satisfactory. (c) 2006 Elsevier B.V. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A rapid and sensitive liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS) assay for the determination of five pharmacologically active compounds (PAC) extracted from the traditional Chinese medicine, Rhodiola , namely salidroside, tyrosol, rhodionin, gallic acid, and ethyl gallate has been developed. In this method, PAC could be baseline separated and detected with DAD at 275 nm. The validation of the method, including sensitivity, linearity, repeatability, and recovery, was examined. The linear calibration curves were acquired with correlation coefficient >0.999 and the limits of detection LOD (at a signal-to-noise ratio=3:1) were between 0.058 and 1.500 mu mol/L. It was found, that the amounts of PAC varied with different species of Rhodiola . The established method is rapid and reproducible for the separation of five natural pharmacologically active compounds from extracts of Rhodiola with satisfactory results.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A rapid capillary electrophoresis method for the separation of five natural pharmacologically active compounds from extracted Rhodiola, namely salidroside, tyrosol, rhodionin, gallic acid and ethyl gallate has been developed. The separation of five natural pharmacologically active compounds was carried out in a fused-silica capillary with 14 mM boric acid, 30 mM SDS and 2.5% acetonitrile, adjusted to pH 10.7 with NaOH. Applied potential was 21 kV. The temperature of the capillary was maintained at 25 degreesC by the instrument thermostating system, with the correlation coefficients of 0.9805-0.9989 for migration time, and relative standards of < 3.52% for peak areas. The established method is rapid and reproducible for the separation of five natural pharmacologically compounds from extracts of Rhodiola with satisfactory results.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

It has been suggested that endothelial apoptosis is a primary lesion in the pathogenesis of thrombotic thrombocytopenic purpura (TTP). We tested this hypothesis by examining the phenotypic signatures of endothelial microparticles (EMP) in TTP patients. In addition, the effect of TTP plasma on microvascular endothelial cells (MVEC) in culture was further delineated. EMP released by endothelial cells (EC) express markers of the parent EC; EMP released in activation carry predominantly CD54 and CD62E, while those in apoptosis CD31 and CD105. We investigated EMP release in vitro and in TTP patients. Following incubation of MVEC with TTP plasma, EMP and EC were analysed by flow cytometry for the expression of CD31, CD51, CD54, CD62E, CD105, CD106 and von Willebrand factor (VWF) antigen. EMP were also analysed in 12 TTP patients. In both EC and EMP, CD62E and CD54 expression were increased 3- to 10-fold and 8- to 10-fold respectively. However, CD31 and CD105 were reduced 40-60% in EC but increased twofold in EMP. VWF expression was found in 55 +/- 15% of CD62E(+) EMP. Markers of apoptosis were negative. In TTP patients, CD62E(+) and CD31(+)/CD42b(-) EMP were markedly elevated, and preceded and correlated well with a rise in platelet counts and a fall in lactate dehydrogenase. CD62E(+) EMP (60 +/- 20%) co-expressed VWF and CD62E. The ratio of CD31(+)/42b(-) to CD62E(+) EMP exhibited a pattern consistent with activation. In conclusion, our studies indicate endothelial activation in TTP. EMP that co-express VWF and CD62E could play a role in the pathogenesis of TTP.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A simple and sensitive method for the determination of short and long-chain fatty acids using high-performance liquid chromatography with fluorimetric detection has been developed. The fatty acids were derivatized to their corresponding esters with 9-(2-hydroxyethyl)-carbazole (HEC) in acetonitrile at 60 degreesC with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride as a coupling agent in the presence of 4-dimethylaminopyridine (DMAP). A mixture of esters of C-1-C-20 fatty acids was completely separated within 38 min in conjunction with a gradient elution on a reversed-phase C-18 column. The maximum fluorescence emission for the derivatized fatty acids is at 365 nm (lambda (ex) 335 nm). Studies on derivatization conditions indicate that fatty acids react proceeded rapidly and smoothly with HEC in the presence of EDC and DMAP in acetonitrile to give the corresponding sensitively fluorescent derivatives. The application of this method to the analysis of long chain fatty acids in plasma is also investigated. The LC separation shows good selectivity and reproducibility for fatty acids derivatives. The R.S.D. (n = 6) for each fatty acid derivative are <4%. The detection limits are at 45-68 fmol levels for C-14-C-20 fatty acids and even lower levels for

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The polymer-supported bimetallic catalyst FVP-PdCl2-2CuCl(2) (PVP, poly(N-vinyl-2-pyrrolidone), obtained in situ by the addition of CuCl2 to an alcoholic solution of PVP-PdCl2, exhibits high selectivity and activity for the oxidative carbonylation of aniline with carbon monoxide and oxygen to ethyl N-phenylcarbamate in the presence of a base (NaOAc) under atmospheric pressure. The strong synergic effect of Pd-Cu gives rise to a clear increase in the selectivity and activity. (C) 2000 Elsevier Science B.V. All rights reserved.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

A bench scale reaction test for methane aromatization in the absence of an added oxidant was performed and its reaction result evaluated based on the carbon balance of the system. The result was compared with those obtained from the micro-reaction test to ensure the accuracy of the internal standard analyzing method employed in this paper. The catalytic performances of modified Mo/HZSM-5 catalysts were examined. It was found that pre-treatment by steam on HZSM-5 weakened the serious deposition of coke, and pre-impregnation of n-ethyl silicate on HZSM-5 could improve the conversion of CH4, but had little effect on coke formation. A low temperature activation procedure including pre-reduction of the catalyst with methane prevents the zeolite lattice from being seriously destroyed by high valence state Mo species when the Mo loading is high. It was suggested that Mo2C species detected by XRD spectra was the active phase for CH4 aromatization.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Alcohols were derivatised to their carbazole-9-N-acetic acid (CRA) esters with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC . HCl) as the dehydrating agent. Studies on derivatisation conditions indicated that the coupling reaction proceeded rapidly and smoothly in the presence of a base catalyst in acetonitrile to give the corresponding sensitively fluorescent derivatives. The retention behaviour of alcohol derivatives was investigated by varying mobile phase compositions (ACN-water and MeOH-water). The parameters from the equation log k'=A-BX were evaluated by retention data of derivatives using an isocratic elution with different mobile phases. The results indicated that the parameters derived allowed computation of retention factors in good agreement with experiments. At the same time, a general equation was derived that makes possible predictions of partition coefficient in binary mobile phases with different proportions of organic solvent to water based on some simple regression analysis. The LC separation for the derivatised alcohols containing higher carbon alcohols showed good reproducibility on a reversed-phase C-18 column with gradient elution. The detection limits (excitation at 335 nm, emission at 360 nm) for derivatised alcohols (signal-to-noise ratio=3:1) were in the range of 0.1-0.4 pg per injection. (C) 2001 Elsevier Science B.V. All rights reserved.