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81.
A simple, rapid and efficient sample preparation technique, dispersive liquid-liquid microextraction, coupled with gas chromatography-flame ionization detection has been developed to determine N-methylpyrrolidine in cefepime. The effect of various experimental factors on the preparation procedure, such as the nature and volume of extraction and disperser solvents, extraction time, the nature of buffer and its pH, and salt effect, was investigated, optimized and the following results were obtained: extraction solvent, chloroform; dispersive solvent and solvent for dissolving cefepime, a mixture of methanol/water (88:12, v/v); salting out agent, NaCl; and buffer, carbonate/bicarbonate (C=0.5?M, pH=12). The optimized conditions were applied to the real sample (cefepime) for the extraction and determination of N-methylpyrrolidine. The calibration graph is linear from 0.02 to 850?mg/L with the square of correlation coefficient 0.999. LOD and LOQ are 6.4 and 21.2?μg/L in solution, respectively, and 0.2 (2×10(-5) ) and 0.6 (6×10(-5) ) μg/g (%, w/w) in cefepime powder, respectively, using sample size 50?mg. Repeatability of the method is good and RSD% for six repeated experiments (C=170?mg/L) is 6.35%. 相似文献
82.
Marli Roehsig Daniela Mendes Louzada de Paula Sidnei Moura Edna Maria de Albuquerque Diniz Mauricio Yonamine 《Journal of separation science》2010,33(14):2115-2122
A number of fatty acid ethyl esters (FAEEs) have recently been detected in meconium samples. Several of these FAEEs have been evaluated as possible biomarkers for in utero ethanol exposure. In the present study, a method was optimized and validated for the simultaneous determination of eight FAEEs (ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate) in meconium samples. FAEEs were extracted by headspace solid‐phase microextraction. Analyte detection and quantification were carried out using GC‐MS operated in chemical ionization mode. The corresponding D5‐ethyl esters were synthesized and used as internal standards. The LOQ and LOD for each analyte were <150 and <100 ng/g, respectively. The method showed good linearity (r2>0.98) in the concentration range studied (LOQ – 2000 ng/g). The intra‐ and interday imprecision, given by the RSD of the method, was lower than 15% for all FAEEs studied. The validated method was applied to 63 authentic specimens. FAEEs could be detected in alcohol‐exposed newborns (>600 ng/g cumulative concentration). Interestingly, FAEEs could also be detected in some non‐exposed newborns, although the concentrations were much lower than those measured in exposed cases. 相似文献
83.
Jafar Akbari Akbar Heydari Leila Ma’mani Seyed Hassan Hosseini 《Comptes Rendus Chimie》2010,13(5):544-547
An efficient and practical protocol for the chemoselective N-Boc protection of various structurally different aryl, aliphatic and heterocyclic amines was carried out with (Boc)2O using protic 1, 1, 3, 3-tetra-methylguanidinium acetate (10 mol%) as recyclable catalyst under solvent free condition at ambient temperature. No competitive side reactions (isocyanate, urea and N, N-di-Boc) were observed. α-Amino alcohols afforded the N-Boc-derivative without oxazolidinone formation. 相似文献
84.
85.
Rosa Maria da Rocha Esperidiana A.B. Moura José Carlos Bressiani Ana Helena A. Bressiani 《Radiation Physics and Chemistry》2010,79(3):301-305
Methylsilicone resin as a polymer precursor for a SiOC ceramic material was cured and foamed by electron beam (EB) irradiation in air prior to the pyrolysis under an inert atmosphere. Methylsilicone foams were obtained without additional foaming agent when exposed to accelerated electrons with radiation doses up to 9 MGy and dose rate of 2.8 kGy/s. During irradiation the polymer was melted and simultaneously gaseous products were formed by the methyl group oxidation and by the poly-condensation crosslinking reactions. The formed gases could not escape from the molten polymer and began to aggregate into bubbles. The effect of the radiation dose on the polymer foam molecular structure, the gel fraction and the ceramic yield was analyzed. The results indicate that the maximum amount of crosslinking in methylsilicone, when EB radiation is used, occurred between 1.0 and 2.0 MGy radiation dose. Methylsilicone foams were pyrolysed in N2 atmosphere at temperatures of 1200 and 1500 °C, resulting in amorphous SiOC and partially crystalline ceramic foams, respectively. A porosity of ~84% was achieved in the pyrolyzed foams, with cell size ranging from 30 to 300 μm and density of about 0.31 g cm?3. 相似文献
86.
Parvin Farshchi Seyed Khatiboleslam Sadrnezhaad Naser Moharram Nejad Mahmood Mahmoodi Leila Ibrahimi Ghavam Abadi 《Journal of nanoparticle research》2011,13(8):3511-3519
Using survey data, public awareness of and attitudes toward nanotechnology are examined in Iran (N = 759). Iran is a developing country with a national nanotechnology action plan for a ten year period starting from 2003
and has been active in the field of research and development of nanotechnology meanwhile. First, the results show that majority
of people are still not familiar with nanotechnology and perceived risks posed by this technology are not considered to be
a lot and most people feel its benefits outweigh the risks. The emotions toward this technology are of a hopeful and positive
nature and this technology is looked upon favorably in Iran. In particular, our results reveals that although the level of
trust is high specially in scientists to communicate the risks with the public, there are a great number who just have some
trust not quite a lot of it. Knowing that it is a hard and time-consuming effort to manage a nation’s view on nanotechnology,
extensive research as well as collaboration with other countries is needed to effectively communicate the risks in time. 相似文献
87.
A. E.B. Costa F.A.B.F. de Moura 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(1):59-63
In this paper we study the propagation of acoustic waves in an one-dimensional diluted random media which is composed of two
interpenetrating chains with pure and random elasticity. We considered a discrete one-dimensional version of the wave equation
where the elasticity distribution appears as an effective spring constant. By using a matrix recursive reformulation we compute
the localization length within the band of allowed frequencies. In addition, we apply a second-order finite difference method
for both time and spatial variables, and study the nature of the waves that propagate in the chain. We numerically demonstrate
that the diluted random elasticity distribution promotes extended acoustic modes at high-frequencies. 相似文献
88.
89.
Inorganic mercury concentration was measured in the muscle tissues of four types of fish in the aquatic international Anzali Wetland ecosystem in Guilan. In the same ecosystem, the northern pike is able to concentrate inorganic mercury in its body more than other fish. In each species, a fish with the highest amount of inorganic mercury was selected for determination of thermodynamic parameters of inorganic mercury extraction using calculation of the equilibrium constant and fitting of ln Kc versus inverse temperature at the atmospheric pressure. The origins of thermodynamic parameters were discussed. The extraction processes were done in the range of temperatures from 331.15 to 365.15 K and at atmospheric pressure. Results show that the extraction of mercury compounds from SH groups of sulfhydryl proteins in fish muscle tissue is an endothermic process with a positive value for entropy and Gibbs free energy changes at room temperature. 相似文献
90.
A dispersive liquid‐liquid microextraction method based on the dispersion of 1,2‐dichlorobenzene as an extraction solvent into an aqueous phase in the presence of ethanol as a dispersive solvent for the preconcentration of Co2+ and Ni2+ ions is discussed. 1‐Nitroso 2‐naphtol was used as a chelating agent prior to the extraction and the preconcentrated analyte was determined by flame atomic absorption spectrometry. The effect of various experimental parameters including the extraction and dispersive solvent type and volume, pH, amount of the chelating agent, etc. on the microextraction and complex formation was investigated for finding the optimum conditions. The enhancement factors were about 61.9 and 51.8, the calibration graphs were linear in the range of 10‐150 μgL?1 and 10‐250 μgL?1 with detection limits of 2.42 μgL?1 and 1.59 μgL?1, and RSD (n = 5) of 3.08% and 2.17% for cobalt and nickel, respectively. The method was successfully applied to the determination of Co and Ni in water and vitamin B12. 相似文献