Search results for "cyclic"
showing 10 items of 2439 documents
Volatile components from flower-heads of Centaurea nicaeensis All., C. parlatoris Helder and C. solstitialis L. ssp. schouwii (DC.) Dostál growing wi…
2008
The volatile constituents of the flowerheads of Centaurea nicaeensis All., C. parlatoris Helder and C. solstitialis L. ssp. schouwii (DC.) Dostal were extracted by hydrodistillation and analysed by GC and GC-MS. Altogether 113 components were identified. Fatty acids and hydrocarbons were the most abundant components in the oils. Caryophyllene and caryophyllene oxide were the main compounds of the sesquiterpene fraction. The study on the biological activity of the oils shows no significant activity.
Volatile compounds of flowers and leaves of Sideritis italica (Miller)Greuter et Burdet (Lamiaceae), a plant used as mountain tea
2010
Sideritis italica (Miller) Greuter et Burdet (Lamiaceae), widely used in ethnopharmacological medicine, occurs in Southern Italy and Sicily. The phytochemical composition of the essential oils of S. italica flowers and leaves, harvested in Piano Battaglia (Sicily), was analysed by GC and GC-MS. Of the 51 compounds, 43 in the oil from flowers and 29 in the oil from leaves were identified. Kaur-15-ene (20.0%) was recognised as the main constituent of the oil from flowers, together with beta-cubebene (12.1%), beta-pinene (8.5%), (Z)-nuciferol (6.5%), tricyclene (4.5%) and alpha-bisabolol (4.0%). In the oil from leaves, p-methoxyacetophenone (26.0%) prevailed, as did hexadecanoic acid (21.3%), …
Determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in goat milk and tissues by glass capillary gas chromatography and medium resolution mass fragme…
1981
Abstract An analytical method has been developed for the study of the elimination of 2,3,7,8-tetrachlodoribenzo-p-dioxin (TCDD) by lactation and its determination in various tissues of goat. The method is based on the alkaline hydrolysis of milk, liver, fat, muscle, blood, faeces and urine samples, extraction with n-hexane, treatment with sulphuric acid-saturated silica gel, chromatographic clean-up on silica gel and alumina micro-columns, and glass capillary gas chromatography—medium resolution mass fragmenography (resolution 2000). 1,2,3,4-Tetrachlorodibenzo-p-dioxin is used as the internal standard, the concentration of TCDD being determined from the calibration curve calculated from the…
Gas chromatographic and mass spectrometric analysis of chlorinated catechols occurring in pulp bleach liquors
1982
Chlorination step (C-step), spent bleach liquor from a kraft pulp mill and the product from the chlorination of guaiacol in aqueous solution have been investigated for their content of chlorinated catechols. After separation the samples were derivatized with diazoethane and analysed by glass capillary gas chromatography with an electron capture detector. The external standard mixture of all ethylated chlorocatechols was used in the measurements. The structures of the compounds identified were confirmed by gas chromatography/mass spectrometry. Eight chlorinated catechols were identified from a sample prepared by chlorination of guaiacol with Cl2 in aqueous solution. However, only four of the…
Channel flow at an immobilised liquid|liquid interface
2000
A novel rectangular channel flow electrochemical cell for the study of liquid | liquid interfaces is presented. The organic phase is immobilised by the use of a gelling agent, while the aqueous phase flows past the interface. This creates an asymmetric setup that allows us to establish diagnostic criteria to determine, for example, the direction of the ion transfer. The effects of varying flow rate and sweep rate have been considered both theoretically and experimentally. By comparison with two-dimensional simulations, it is demonstrated that a simple one-dimensional theory can be used to describe the cyclic voltammetry response of the channel flow cell.
Gas chromatographic study of acetyl derivatives of chlorinated 4-hydroxybenzaldehydes
1982
The GC retention times of 4-hydroxybenzaldehyde and its chloro derivatives have been measured on three nonpolar capillary columns. Multiple linear regression analysis has been used to explain the mobility of chlorinated compounds relative to the reference compound 4-hydroxybenzaldehyde. The most important effects have shown to be due to the number of chlorine atoms and the substituents ortho to the formyl group. Other effects have also been observed but found to be unable to explain the GC data.
Isolation of chlorinated dibenzothiophenes by high-performance thin-layer chromatography
1991
Abstract Chlorinated dibenzothiophenes can cause environmental problems analogous to chlorinated dibenzodioxins and dibenzofurans. In the analysis of chlorinated dibenzodioxins by gas chromatography—mass spectrometry some unknown chlorinated compounds have been found. The chlorinated dibenzothiophenes have the same m/z values as the corresponding dioxins in low-resolution mass spectrometry and they are found in same planar aromatic compound fraction in alumina and carbon column chromatography. Some chlorinated dibenzothiophenes were synthesized to serve as model compounds in analytical work. High-performance thin-layer chromatography (TLC) with different plates and several eluents was tried…
A Study of Lipid-Lipid and Lipid-Polypeptide Interactions by High Performance Liquid Chromatography
1984
Abstract Ternary systems containing phosphatidylcholine-cholesterol, phosphatidylcholine-gramicidin A or cholesterol-gramicidin A in tetrahydrofuran have been examined by high performance liquid chromatography. Preferential solvation of cholesterol and especially gramicidin A by phosphatidylcholine is observed. These results are interpreted in terms of hydrophobic interactions between membrane components.
Off-line dansylation of amines using C18 solid-phase packings: study of the fluorescence and chemiluminescence detection by post-column derivatizatio…
1999
Abstract Dansylation of amines (primaries and secondaries) using C18 solid-phase supports is described. The time of analysis and the handing sample have been markedly improved with respect to those required for solution dansylation. The dansylated amine derivates were injected onto the liquid chromatography system and fluorescence detected. The sensitivity and selectivity is better than the other dansylation procedures described in the literature and also better than other derivatization reagents such 1,2-napthoquinone 4-sulfonate (NQS) or 3,5-dinitrobenzoyl chloride (3,5-DNB). Dansyl compounds can also form chemiluminescent derivatives, therefore a post-column derivatization procedure with…
Direct Analysis of Phase I Metabolites, Phenol Sulfates, Glucuronides and Glutathione Conjugates of Benzo[a]pyrene in Freshly Isolated, Hypothermical…
1996
Abstract The complex biotransformation of benzo[a]pyrene (BaP), the prototype of the class of carcinogenic polycyclic aromatic hydrocarbons, can be used as a tool to characterize the capacity of in vitro systems for the biotransformation of xenobiotics. In order to account for the ability of liver parenchymal cells to metabolize BaP, a method was developed for the isolation, separation and quantitation of its phase I metabolites, e.g. tetrahydrotetraols, trans-dihydrodiols, quinones and phenols, as well as its phase II metabolites, e.g. sulfates, glucuronides and glutathione conjugates, employing a combination of extractive and chromatographic steps. Upon incubation of BaP with freshly isol…