Search results for "Analytical"
showing 10 items of 9586 documents
Non-porous polybutadiene-coated silicas as stationary phases in reversed-phase chromatography
1990
Abstract Non-porous silica of mean particle diameter 1.7 μm (Monospher) was coated with polybutadiene (PBD) following a published procedure. The silicas were prepared with graduated polymer loads up to 8% (w/w). Examination of the PBD-coated packings by means of electron spectroscopy for chemical analysis, scanning electron microscopy, diffuse reflection infrared fourier transform spectroscopy and differential thermal gravimetry indicated that the optimum polymer load was between 1 and 3% (w/w) with regard to a dense coverage corresponding to an average layer thickness of about 4 nm. No silanophilic interactions could be monitored using 1–3% (w/w) coated silicas under reversed-phase conditi…
Polymer-coated reversed-phase packings in high-performance liquid chromatography
1993
The synthesis and properties of polymer-coated RP stationary phases are reviewed. The sorbents are classified according to the method of synthesis. More flexibility in the tailoring of polymer-coated packings is noted. The impact of the polymer coating on the porosity of the oxides to be modified and their chromatographic properties is discussed.
Characterisation of Diarylheptanoid- and Flavonoid-type Phenolics in Corylus avellana L. Leaves and Bark by HPLC/DAD-ESI/MS
2013
Introduction The leaves of Corylus avellana L. (common hazel, Betulaceae), a plant with a wide distribution in Europe, have been used in folk medicine for various diseases, but phytochemical exploration of C. avellana is still incomplete. To the best of our knowledge there is no previous report concerning diarylheptanoids in C. avellana, although these compounds show a frequent occurrence among Betulaceae plants. Objective To improve existing online chromatographic methods for the investigation of the phenolic compounds in C. avellana leaves and bark, focusing on diarylheptanoid-type molecules. Methods Dried and powdered leaves and bark of C. avellana were extracted with increasing polarity…
t-Curves for n-Hexane
1992
The adsorption and desorption isotherms of n-hexane on powdered alumina and silica have been studied at 25°C over a wide range of relative pressures. Two t-curves for pore structure analysis are proposed, one for alumina (C = 12) and the second for silica (3 ≤ C ≤ 9). The statistical thickness t of the adsorbed n-hexane layer has been drawn as a function of the relative pressure assuming a maximal thickness of 0.55 nm and a mean thickness of 0.42 nm for the monolayer. The results are discussed in relation to previous published data.
Continuous fractionation and solution properties of PIB. II. CPF optimization
1987
The quality of polymer fractionation depends on the choice of the mixed solvent as well as on the particular conditions of operating the continuous countercurrent extraction. With a polyisobutylene (PIB) sample of medium molecular weight Mw = 98,400 g/mol and U = (Mw/Mn) − 1 = 1.4 plus the mixed solvents toluene/2-butanone (TOL/MEK) and n-heptane/2-butanone (HEP/MEK) (both giving comparably good fractionation in equilibrium experiments), possible ways to optimize the CPF were tested. The mixed solvent HEP/MEK turns out to be superior to TOL/MEK for kinetic reasons. Due to the larger gap between its density and that of the pure polymer, the coexisting phases can still move through the column…
Method for Synthesis and Screening of Large Groups of Molecularly Imprinted Polymers
2011
A technique for the synthesis of molecularly imprinted polymers (MIPs) in small scale (∼55 mg) coupled with direct in situ processing and batch rebinding evaluation is reported. The primary assessment is based on quantification by HPLC or UV absorbance measurement of the amount of template released from the polymer in a given solvent. This method allows a rapid screening of the parameters of importance to reach a desired level of binding affinity capacity and selectivity for a given target molecule. This was demonstrated for the triazine herbicide terbutylazine, where an initial screening was performed for the type of functional monomer used in the MIP preparation. Thus among the six functi…
Separation of isobutyl alcohol and isobutyl acetate by extractive distillation and pressure-swing distillation: Simulation and optimization
2006
Abstract We have studied, simulated and evaluated economically two separation alternatives of a mixture made up of 52 mole% of isobutyl alcohol and 48 mole% of isobutyl acetate by means of a practical case of a plant to treat 12,000 Tm/year of the original mixture. The simulation has been carried out satisfactorily by means of a package of commercial software (Aspen HYSYS ® ) using the thermodynamic model UNIQUAC with binary parameters obtained experimentally by us. The two processes evaluated (extractive distillation using n -butyl propionate as a solvent and pressure-swing distillation) have been optimized independently from each other and the best configurations have been evaluated econo…
Determination of indoor air quality of a phytosanitary plant.
2011
A new methodology has been developed to determine volatile organic compounds (VOCs) and pesticides in ambient air using membrane based devices as passive samplers. Pesticides were determined by gas chromatography with mass spectrometry detection (GC-MS) after their microwave-assisted extraction (MAE) from the passive sampler and the required clean-up. On the other hand, VOCs were also caught with the same samplers and directly determined by head space (HS) coupled to GC-MS. The use of samplers filled with florisil and activated carbon allows us to catch with a simple device both, VOCs and pesticides, with a high vapor pressure. Results obtained in the deployment of samplers in different sit…
Optimisation of fast protein separations on non-porous silica-based strong anion exchangers
1993
The adsorbed coating technology using various vinylpyrrolidone-vinylimidazole copolymer compositions was carried out on 1.7 μm non-porous monodisperse silica. It was shown that the retention properties and the loading capacity for bovine serum albumin (BSA) increases with the amount of vinylimidazole in the copolymer composition. The retention behavior of various proteins as a function of the salt composition in the eluent has been applied to find the optimal conditions for the synthesis of the anion-exchange stationary phase. The suitability of these supports for the fast separation of biological molecules is demonstrated. The best resolution and the highest speed in protein analysis was o…
Enzyme class identification in cleaning products by hydrolysis followed by derivatization with o-phthaldialdehyde, HPLC and linear discriminant analy…
2008
The enzymes present in raw materials of the cleaning industry (enzyme industrial concentrates) and in household cleaners were isolated by precipitation with acetone and hydrolyzed with HCl. The resulting amino acids were derivatized with o-phthaldialdehyde, and the derivatives were separated by HPLC. The peaks of 14 amino acids were observed using a C18 column and a multi-segmented gradient of acetonitrile-water in the presence of a 5 mM citric/citrate buffer of pH 6.5. Using either normalized peak areas (divided by the sum of the peak areas of the chromatogram) or ratios of pairs of peak areas as predictor variables, linear discriminant analysis models, capable of predicting the enzyme cla…