Search results for "Analytical"
showing 10 items of 9586 documents
Isolation and structural characterization of polypeptide antibiotics of the peptaibol class by high-performance liquid chromatography with field deso…
1984
Abstract A number of polypeptide antibiotics of the peptaibol class, i.e., trichotoxin, alamethicin, suzukacillin, hypelcin and paracelsin, have been separated into components and isolated by high-performance liquid chromatography on spherical, porous octadecylsilyl bonded phases. All peptaibols were found to reveal a strong microheterogeneity due to single or multiple amino acid exchange. Most of the closely related and partially isobaric sequence analogue could be resolved using mixed alcohol—water eluents. As demonstrated by the structure analysis of the paracelsins and the main component of trichotoxin A-50, high-performance liquid chromatography with field desorption and fast atom bomb…
Micellar liquid chromatographic separation of amino acids using pre- and post-column o -phthalaldehyde/ N -acetylcysteine derivatization
2000
Abstract The isocratic analysis of primary proteic amino acids using a C18 column, micellar mobile phases of sodium dodecyl sulphate (SDS) and 1-propanol at varying pH, and pre- and post-column formation of the o-phthalaldehyde (OPA)/N-acetyl- l -cysteine (NAC) isoindoles, is examined. An interpretive optimization strategy was applied to find the best separation conditions. For this purpose, empirical polynomial models were used to describe the elution behavior of the isoindoles and free amino acids, using as separation factors the concentrations of surfactant and modifier (two-factor problem), or these two factors and the pH of the mobile phase (three-factor problem). The separation of the…
Phase transitions in some n-alkanes and petroleum waxes — investigation by photoacoustic and exoelectron emission techniques
2000
Abstract The use of the photoacoustic (PA) effect and photostimulated exoelectron emission (EEE) technique in the investigation of first- and second-order phase transitions in pure n -alkanes such as n -C 22 , n -C 28 and n -C 32 and in three petroleum waxes having different carbon number distributions, have been examined. Changes in the amplitude and phase of the PA signal with temperature and the temperature dependence of the intensity of photostimulated EEE across the phase transitions have been measured. These measurements have shown that both the polymorphic phase transitions and melting of these hydrocarbons are accompanied by jumps or peaks of the PA amplitude and phase and EEE inten…
Characterization of waxes used in pictorial artworks according to their relative amount of fatty acids and hydrocarbons by gas chromatography.
2005
A study attempted to characterize natural waxes used in pictorial works of art was carried out by means of gas chromatography. The analytical treatment requires prior hydrolysis of the waxes to release the fatty acids (FA) (myristic (myr), palmitic (pal), oleic (ole), stearic (ste), araquidic (ara), behenic (beh), lignoceric (lig), cerotic (cer)) from the main esters of the waxes. The formation of volatile derivatives of the fatty acids was carried out by derivatization with ethyl choroformate (ECF). This derivatization reagent was chosen due to the speed, safety and quantitativity of the reaction. The analyzed hydrocarbons were n-eicosane, n-heneicosane, n-docosane, n-tricosane, n-tetracos…
Solid state solvation effect and reduced amplified spontaneous emission threshold value of glass forming DCM derivative in PMMA films
2015
Abstract Molecule crystallization is one of the limitations for obtaining high-gain organic laser systems. One of the examples is well known red laser dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). The lowest threshold value of amplified spontaneous emission was achieved by doping 2 wt% of DCM molecule in tris-(8-hydroxy quinoline) aluminum (Alq3) matrix. Further increase of the DCM dye concentration makes the system less efficient as its threshold value increases. It is due to large intermolecular interaction, which induces photoluminescence quenching. Compounds with reduced intermolecular interaction could be prospective in organic laser systems due to higher …
Evaluation and comparison of tailor-made stationary phases based on spherical silica-based beads for capillary electrochromatography via peptide sepa…
2004
Small cyclic peptides have been employed to elucidate the performance of novel sorbents as stationary phases in capillary electrochromatography (CEC). In this paper chain length dependencies for ordinary liquid chromatographic sorbents are reported together with findings acquired on beads specifically designed to suit CEC. The latter, tailor-made, spherical, porous silica exhibits a distinguished surface modification to meet the criteria anticipated to enhance performance profiles in CEC. With well-characterised peptides resembling the analytes, probing of the CEC system in a systematic manner (predominantly via the organic modifier content of the background electrolyte (BE)) reveals insigh…
Chromatographic peak profile of ionogenic analytes upon elution with unbuffered eluents
1998
Experimental proof of the model was carried out for the separation of benzoic acid on a LiChrospher RP-18 column. The observed chromatographic peak profile coincides with the peak profile predicted by the model. The retention times of the dissociated and non-dissociated species determined by using an appropriate fitting procedure were 2.2 and 4.3 min, respectively. Based on these values, a theoretical peak profile was calculated, demonstrating a close agreement with the experimentally observed peak profile. An unexpectedly large difference was found for the retention times of the dissociated and non-dissociated species calculated by a fitting procedure and those experimentally measured on t…
Transport mechanism of peptides through supported liquid membranes
2007
Abstract The transport of selected dipeptides through supported liquid membranes impregnated with di(2-ethylhexyl) phosphoric acid in n-dihexylether has been investigated. The fluxes depend on the side chain of amino acids, presence in the peptide structure. The highest fluxes were obtained for the peptides extracted with the highest efficiency. It has been found that the hydrophobicity of investigated peptides, was not the major factor, influences their SLM permeation. In the conditions studied, it has been observed that the transport of peptide–carrier complex was depending on the acidic–basic properties of the analyte. The linearly least-square fittings of log {K1 + [H+]D} and log[(HR)2]…
Use of pH gradients in continuous-flow systems and multivariate regression techniques applied to the determination of methionine and cysteine in phar…
1997
Abstract The simultaneous spectrophotometric determination of methionine and cysteine in presence of cystine and other compounds in pharmaceuticals, using a multivariate calibration method, was studied. The method is based on the reaction between the analytes and the o- phthalaldehyde -N- acetyl - l - cysteine (OPA-NAC) reagent performed in a continuous-flow system (FI). The FI system allows the generation of a local pH gradient in order to produce spectral and/or kinetic changes in the UV-Vis spectra of the amino acid-OPA-NAC derivatives. This information is used to improve the prediction ability of the Partial Least-Squares (PLS) models. The performance of two FI assemblies, the selection…
Extraction of dansylated amino acids using the supported liquid membrane technique
1997
Extraction using the supported liquid membrane (SLM) technique demands conditions where the extracted compounds can be made uncharged allowing them to pass through the membrane. For amino acids, being bifunctional, such conditions can not be obtained directly. One way to overcome this problem is to block one of the functionalities by derivatization, utilising the other group for the transport. The SLM extraction of dansylated amino acids was investigated and optimized. It was possible to obtain high extraction efficiencies (>90%) for most amino acids. For amino acids with polar side chains, such high extraction efficiencies were only obtained at low analyte concentrations ( 10 nmol 1-l). Fo…