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81.
The use of aerosol produced in a nebulization chamber is proposed as an alternative to gas sample capture in flow systems. This paper describes the coupling of a sampling interface with a flow system, for in situ gas monitoring. Aspects related with the behavior of aerosol formation and gas solubilization in liquid drops are discussed. The method is applied to the determination of residual lime in acidic soils. Aliquots of 5.0 ml of 1.0 mol l−1 HCl were mixed with soil samples (1 g). The CO2 released from these samples was captured by a nebulized aerosol and determined conductivity. The analytical curve from 1.0×10−2 to 5.0×10−2 mol kg−1 CaCO3 was ploted applying the matrix matching approach. This proposition, allowed an increase in the sensibility with detection limit of 6.0×10−3 mol kg−1. The precision was good (R.S.D. <3%) for an analytical frequency of 22 determinations per hour. A fair agreement, at 95% confidence level, was found between the results from the proposed method and certified values of the investigated samples. 相似文献
82.
Purification of plasmid DNA vectors by aqueous two-phase extraction and hydrophobic interaction chromatography 总被引:4,自引:0,他引:4
The current study explores the possibility of using a polyethyleneglycol(PEG)-ammonium sulphate aqueous two-phase system (ATPS) as an early step in a process for the purification of a model 6.1 kbp plasmid DNA (pDNA) vector. Neutralised alkaline lysates were fed directly to ATPS. Conditions were selected to direct pDNA towards the salt-rich bottom phase, so that this stream could be subsequently processed by hydrophobic interaction chromatography (HIC). Screening of the best conditions for ATPS extraction was performed using three PEG molecular weights (300, 400 and 600) and varying the tie-line length, phase volume ratio and lysate load. For a 20% (w/w) lysate load, the best results were obtained with PEG 600 using the shortest tie-line (38.16%, w/w). By further manipulating the system composition along this tie-line in order to obtain a top/bottom phase volume ratio of 9.3 (35%, w/w PEG 600, 6%, w/w NH4)2 SO4), it was possible to recover 100% of pDNA in the bottom phase with a three-fold increase in concentration. Further increase in the lysate load up to 40% (w/w) with this system resulted in a eight-fold increase in pDNA concentration, but with a yield loss of 15%. The ATPS extraction was integrated with HIC and the overall process compared with a previously defined process that uses sequential precipitations with iso-propanol and ammonium sulphate prior to HIC. Although the final yield is lower in the ATPS-based process the purity grade of the final pDNA product is higher. This shows that it is possible to substitute the time-consuming two-step precipitation procedure by a simple ATPS extraction. 相似文献
83.
Ribeiro da Silva MA Gomes JR Ferreira AI 《The journal of physical chemistry. B》2005,109(27):13356-13362
The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloroaniline were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high-temperature vacuum sublimation technique was used to measure the enthalpies of vaporization or sublimation of the three isomers. These two thermodynamic parameters yielded the standard molar enthalpies of formation of the three isomers of chloroaniline, in the gaseous phase, at T = 298.15 K, as 53.4 +/- 3.1 kJ.mol(-1) for 2-chloroaniline, 53.0 +/- 2.8 kJ.mol(-1) for 3-chloroaniline, and 59.7 +/- 2.3 kJ.mol(-1) for 4-chloroaniline. These values, which correct previously published data, were used to test the computational methodologies used. Therewith, gas-phase acidities, proton affinities, electron donor capacities, and N-H bond dissociation enthalpies were calculated and found to compare well with available experimental data for these parameters. 相似文献
84.
The L-dopa is the immediate precursor of the neurotransmitter dopamine. Unlike dopamine, L-dopa easily enters the central nervous system and is used in the treatment of Parkinson’s disease. A sensitive and selective method is presented for the voltammetric determination of L-dopa in pharmaceutical formulations using a carbon paste electrode modified with trinuclear ruthenium ammine complex [(NH3)5RuIIIORuIV(NH3)4ORuIII(NH3)5]6+ (Ru-red) incorporated in NaY zeolite. The parameters which influence on the electrode response (paste composition, potential scan rate, pH and interference) were also investigated. The optimum conditions were found to an electrode composition (m/m) of 25% zeolite containing 6.7% Ru, 50% graphite and 25% mineral oil in acetate buffer at pH 4.8. Voltammetric peak currents showed a linear response for L-dopa concentration in the range between 1.2×10−4 and 1.0×10−2 mol l−1 (r=0.9988) with a detection limit of 8.5×10−5 mol l−1. The variation coefficient for a 1.0×10−3 mol l−1 L-dopa (n=10) was 5.5%. The results obtained for L-dopa in pharmaceutical formulations (tablet) was in agreement with compared official method. In conclusion, this study has illustrated that the proposed electrode modified with Ru-red incorporated zeolite is suitable valuable for selective measurements of L-dopa. 相似文献
85.
Rodinei Augusti Marcos N. Eberlin Concetta Kascheres 《Journal of heterocyclic chemistry》1995,32(4):1355-1357
The reactions of carbethoxycarbene (:CH2-CO2Et, 2) with several acyclic enaminones (RCOCH=CR1NHR2, 3) lead to the unexpected formation of 2-Me, 3-CO2Et, 4-H, 5-R1-pyrroles 4 . Structural variations of the enaminones show that the structural fragments C(3)-CO2Et and C(2)-Me are provided by 2 and that the fragment C(5)-R1NHR2 originates from the enaminones 3 , while the RCO group from 3 is eliminated during the course of reaction. Reactions with cyclic and nitrogen-hindered enaminones do not lead to pyrrole formation but occur by simple insertion of 2 to the Cα-H bond. 相似文献
86.
Rosario Pardo Marcos Zayat David Levy 《Journal of Sol-Gel Science and Technology》2006,40(2-3):365-370
A photochromic naphthopyran derivative was embedded in sol-gel prepared thin ormosil films. The resulting samples show high
transparency and exhibit a strong red colouration upon irradiation with UV light. The photostability of the photochromic molecules
is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the
inner pore surface of the matrix allows tailoring the chemical environment where the dye molecules will be allocated, in terms
of the effectiveness of the interaction between the photochromic molecules and the Si-OH groups on the surface of the pores,
affecting the stability of the molecules upon prolonged exposition to UV light.
The photostability of the molecules was increased in matrices functionalized with larger organic groups, or with larger amount
of modifying groups. In this way the photodegradation of the photochromic molecules could be reduced by a factor of 5, as
compared with the photodegradation of the molecules in unfunctionalized silica matrix. 相似文献
87.
In this work a laboratory polymerization scale process was studied for the production of polybutadiene with high content of cis-1,4 repeating units. A Ziegler-Natta catalytic system based on neodymium versatate (catalyst), diisobutylaluminium hydride (cocatalyst) and tert-butyl chloride (chlorinating agent) was used. The influence of solvent nature (pure grade) and possible contaminants (electron donors) in a recovered solvent from a butadiene-styrene anionic polymerization industrial plant on the stereoselectivity and catalytic activity, molecular weight and molecular weight distribution of the resultant polybutadienes was studied. The polymers were characterized by infrared spectroscopy and size exclusion chromatography. Polybutadienes with cis-1,4 units content in the range of 99-98% were produced. The polymers weight-average molecular weight, , varied from 2.23 × 105 to 4.47 × 105 and the molecular weight distribution, MWD, from 3.1 to 5.1. 相似文献
88.
89.
A system has been developed for online preconcentration and determination of Cd using thermospray flame furnace atomic absorption
spectrometry (TS-FF-AAS). It is based on the solid-phase extraction of Cd in an Amberlite XAD-2 minicolumn loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol
(TAM), and the metal ion is eluted with 1 mol L−1 hydrochloridric acid, followed by its determination. The online system allows determining Cd with a detection limit of 8.0 ng L−1 and a quantification limit of 25.0 ng L−1. The precision (repeatability), calculated as the relative standard deviation (% RSD) in sample solutions containing 0.5
and 3.0 μg L−1 of Cd, was 6.1 and 4.5%, respectively. The preconcentration factor obtained was 24. The system’s accuracy was confirmed by
analyzing the following certified reference materials (CRMs): Rice flour NIES 10b, Apple leaves NIST 1515 and Orchard leaves
NBS 1571. This procedure was applied to the determination of Cd in cabbage and powdered guarana samples. 相似文献
90.
The complexes [Ru(salen)(NO)Cl] and [Ru(salen)(NO)(H(2)O)](+) were shown to release the nitrosyl ligand as nitric oxide upon exposure to visible light in organic and aqueous solutions respectively, by means of UV-visible, EPR, and FTIR spectroscopies. The former was prepared by a new synthetic route and had its structure determined by single-crystal X-ray diffraction. A crystal of the dichloromethane solvate is orthorhombic, space group Fdd2 (No. 43) and formula C(16)H(14)ClN(3)O(3)Ru.CH(2)Cl(2), with Z = 16 and cell parameters a = 25.489(4), b = 33.435(4), and c = 9.3716(9) A. The electronic absorption spectra of the complexes were calculated using the INDO/S method. The water-soluble complex is a potential drug for antitumoral phototreatment. 相似文献