Search results for "SEPARATION"
showing 10 items of 865 documents
Crown-ether mediated transport of amino acids through an immobilized liquid membrane
1988
Poly(ethylene glycol) diacrylate based monolithic capillary columns for the analysis of polar small solutes by capillary electrochromatography
2018
Monolithic stationary phases based on poly(ethylene glycol) diacrylates for capillary electrochromatography were developed. Several poly(ethylene glycol) diacrylates (Mn 250, 575, and 700) were used as single monomers and the resulting columns were carefully compared. Methanol and ethyl ether were selected as porogenic solvents, and in all cases ultraviolet radiation was selected as initiation method to prepare polymeric monoliths. The influence of the monomer chain length and ratio monomer/porogen on the morphological and electrochromatographic properties of the resulting monoliths was investigated. Several families of compounds with different polarity (alkyl benzenes, organophosphorous pe…
A fast method for determining low-molecular-mass aliphatic carboxylic acids by high-performance liquid chromatography–atmospheric pressure chemical i…
2006
A fast quantitative high-performance liquid chromatographic separation method with atmospheric pressure chemical ionization mass spectrometric detection (HPLC-APCI-MS) was developed for the determination of low-molecular-mass aliphatic mono- and dicarboxylic acids typically present in different industrial process waters. A mixture of glycolic, lactic, a-glucoisosaccharinic, oxalic, maleic, fumaric, succinic, malic, glutaric, methylsuccinic, and adipic acids was separated using an RP chromatographic system. Adipic acid was used as an internal standard to calculate correlation coefficients for the acids studied. The chromatographic analysis of these acids was primarily carried out by means of…
Encapsulation of cytochrome C by multilayer microcapsules. A model for improved enzyme immobilization
1997
Cytochrome C was used as a model compound to study the behavior of proteins during the encapsulation procedure in alginate microcapsules and the loss by diffusion during storage. Alginate gel beads were coated with a multilayer membrane consisting of alternating layers of poly(N-vinylamine) and poly(acrylic acid) or water soluble anionic cellulose derivatives, respectively. To obtain high encapsulation yields, it is recommended to use the lowest possible concentration of salts in the precipitation bath. Loss during storage (and use) is minimized by applying at least two polycation/polyanion double layers for the membrane. Cellulose derivatives are superior over poly(acrylic acid). Single la…
Single-pump bi-dimensional LC applied to the characterization of derivatized fatty alcohol ethoxylates.
2010
A column selection valve and a 6-port 2-position injection valve were combined to implement bi-dimensional LC in a system driven by a single pump. The system was applied to the separation of linear fatty alcohol ethoxylates with 12-18 carbon atoms in the hydrocarbon moiety, previous derivatization with diphenic anhydride. Separation on the first separation dimension (C(1)) was carried out with a propyl-diol column and an acetonitrile/aqueous ammonium acetate gradient. Fatty alcohol ethoxylate hydrocarbon series (oligomers with the same number of carbon atoms in the alkyl chain but differing in the number of ethylene oxide units) were resolved without distinguishing the oligomers within the …
Reversed-phase liquid chromatography without organic solvent for determination of tricyclic antidepressants
2012
The chromatographic behavior of seven tricyclic antidepressants (amitryptiline, clomipramine, doxepin, imipramine, maprotiline, nortryptiline, and trimipramine) was examined with micellar mobile phases containing the nonionic surfactant Brij-35. Acetonitrile-water mixtures were also used for comparison purposes. Tricyclic antidepressants are moderately polar basic drugs, which are positively charged in the usual working pH. This gives rise to a strong association with the alkyl chains and residual ionized silanols in silica-based stationary phases, which is translated in a high consumption of organic solvent to get appropriate retention times. Brij-35 modifies the surface of the stationary …
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…
Lattice fluid model generalized for specific interactions: An application to ternary polymer solutions
2011
Abstract The phase diagram of the Poly- l -Lactic-Acid (PLLA), dioxane and water system was derived by using the lattice fluid model generalized for specific interactions. A qualitative analysis of Hansen solubility parameters together with empirical observations were adopted to reduce the number of adjustable parameters. The as-selected model parameters were derived by fitting a set of cloud point curves; consequently, the complete phase diagram of the system was computed. The use of specific interactions between species gave out a quantitative agreement with a set of experimental data, whereas changing the polymer polydispersity the agreement is only qualitative. In principle, the present…
Analysis of amino acids using serially coupled columns.
2017
Single conventional columns in reversed-phase LC are insufficient for analysing the isoindoles of primary amino acids, due to their limited functionality. An interesting possibility for increasing the separation power is the combination of several columns of different nature, where the length is modified by coupling small segments. This approach may require a considerable investment to have multiple lengths for each stationary phase. However, the combination of only two columns of fixed length can be enough to resolve satisfactorily relatively complex mixtures, provided that an optimised gradient program is applied. In this work, a mixture of 19 primary amino acid isoindoles found in protei…
Determination of optical purity of phosphonic acid analogues of aromatic amino acids by capillary electrophoresis with alpha-cyclodextrin.
2000
A simple and efficient method for the determination of enantiomeric purity of structurally diverse phosphonic and phosphinic acid analogues of phenylalanine and phenylglycine using capillary electrophoresis is presented. These preliminary studies indicated that the enantiomer separation is strongly dependent on the structure of the aminophosphonic acid.