Browse

You are looking at 81 - 90 of 33,800 items for :

  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All

A high-performance thin-layer chromatographic method with densitometric detection has been used to determine the convallatoxine content of extracts from the various parts (flowers, leaves, and underground parts such as the rhizomes and buds on the rhizomes) of the plant. Plant extracts were separated on thin layers of silica gel Si 60F254 by multiple gradient development. The convallatoxine content was determined by densitometry and the results were evaluated statistically.

Restricted access

This review covers the use of topological indexes based on the adjacency and distance matrixes to predict the RF and RM values, and the physicochemical properties, of a variety of groups of organic compounds investigated by TLC. This review indicates that further investigations on the application of the topological indexes in TLC are justifiable.

Restricted access

The solvation parameter model has been used to characterize the retention properties of a varied group of solutes in silica gel thin-layer chromatography (TLC) and in silica gel and alumina column liquid chromatography. The model was unable to describe retention on silica gel TLC plates with the RM value as the dependent variable for five single-solvent mobile phases. The results were improved by fitting the retention data to the simple competition model and separating the solute and solvent contributions (denoted S and eºAS, respectively) to the free energy of adsorption on the inorganic oxide. Separate models were then constructed to enable estimation of values of S and AS from structure. These models were successful in describing retention in column liquid chromatography on silica gel with mixtures of methyl t-butyl ether and hexane as a mobile phase. This approach proved less reliable for calculating retention in TLC, probably because of non-equilibrium in the separation system. Evidence is presented that neither the solute adsorption parameter (S) nor the solute cross-section (AS) as used in these studies is unambiguously defined. Further refinements aimed at establishing clearly defined solute and solvent adsorption terms, and possibly including selective solute–solvent interactions in the mobile phase as a secondary contribution to retention, could result in improved model performance. The approach described here should be considered preliminary and thought of as a stepping stone in the direction towards a comprehensive model for structure-driven method development in normal-phase separations, which are currently less developed than models available for reversed-phase separations.

Restricted access

Persilben (3,5-methoxy-2-hydroxy-E-stilbene) was satisfactorily separated on thin layers of silica gel, by use of two-step gradient elution, and quantified by densitometric techniques. The results were evaluated statistically. Eight acetone extracts from herbs and rhizomes of six taxons of Polygonum L. genus: P. lapathifolium ssp nodosum (Pers.) Dans., P. lapathifolium ssp. tomentosum (Schrank) Dans., P. hydropiper L., P. bistorta L., P. amphibium L., P. convolvulus L. (Bilderdykia convolvulus L.) were studied. Persilben was detected in the herbs of five taxons of Polygonum L. The amounts of the compound ranged between 46.3 and 174.2 μg g1 dry herbs.

Restricted access

A new horizontal sandwich chamberis described in this paper. Mobile phase can be applied to any part of the plate by use of this chamber. This has enabled a new mode of development in TLC, in which the starting position of development can be anywhere instead of at the origin; we therefore call this new mode ‘half-way development’. Compared with traditional development, the new mode can be used to develop any separated spot again. Many other modes of development can also be performed with this chamber, for example relay development on an over-length plate, programmed multiple development, gradient development, band application, concentration, and micropreparative separation. These methods are simple and convenient and give good results.

Mixtures of dyes have been used to verify above supposition with the above-mentioned methods. The results obtained are satisfactory.

Restricted access

A thin-layer chromatographic and densitometric method has been developed for the identification and quantitation of gliclazide and its impurities on silica gel, using chloroform–methanol, 19 + 1 (v/v), as mobile phase. UV densitometric measurements were made at λ = 226 nm. The method is characterized by high sensitivity (15 ng), linearity over a wide concentration range (0.06 to 0.30 mg mL1), and high recovery (100.23%). It was found that the established conditions can be also used for determination of impurities in medicines.

Restricted access

Molecular interactions have been evaluated in liquid adsorption chromatography with mixed mobile phases. Two equations based on different retention mechanism models were verified experimentally. The parameters of both equations were calculated and interpreted. The parameters described the association phenomenon in analyzed systems. Solvation effects were taken into account. These effects were confirmed by use of two independent theories and two independent equations. The equation parameters were calculated for test substances in four chromatographic systems in which solvation phenomenon was present or not. A linear relationship was found between parameters analyzed. Chromatographic measurements were obtained by use of thin-layer chromatography.

Restricted access

This report describes the TLC separation of two classes of chiral drug, including β-blocking drugs and non-steroidal anti-inflammatory drugs (NSAID) on molecularly imprinted chiral stationary phases, in the same way as has been performed by HPLC. Several molecularly imprinted polymers (MIP) were prepared using the enantiomers of either the β-blocking drugs, R-(+)-propranolol, R-(+)- or S-(–)-atenolol, or the NSAID, S-(+)-naproxen and S-(+)-ibuprofen, as print molecules. Three different functional monomers, ITA, MAA, and VPD were employed in the imprinting process. The polymers prepared in the presence of MAA or VPD could be coated as thin layers on glass supports, but not those prepared in the presence of ITA. The MIP of R-(+)-propranolol, with 5% acetic acid in acetonitrile as mobile phase, resolved the racemate of propranolol into two spots, but tailing spots were obtained. The MIP prepared from S-(+)-naproxen, with 1% acetic acid in THF–heptane, 1 + 1, as mobile phase, resolved the racemate of ketoprofen into enantiomers, with a good separation factor (α = 5.2).

Restricted access

Gradient thin-layer chromatography and densitometry have been used for qualitative and quantitative analysis of caffeic acid in some Dipsacaceae family plants. The presence of caffeic acid was determined in complex plant extracts before and after acid hydrolysis.

Restricted access