Thin-layer chromatography artifacts

The identification of bromocriptine mesilate in the dosage form can be carried out by thin layer chromatography using Merck plates with dichloromethane/methanol/formic acid 78 20 2 (v/v/v) and subsequent uv-visualization at 254 and 360 nm. Using this method, it is important to only air-dry the spot after application to the plate, since more vigorous evaporation of the solvent will give rise to artifacts (32). 

The study of the dyes, mordants, and other coloring materials used in pre-Columbian textile artifacts remains an inadequately explored area of analytical endeavor. Thin layer chromatography and related techniques should prove productive in the identification of vegetable dyes (7). Inorganic materials can be readily identified by x-ray diffraction methods. 

RCl by using reverse-phase HPLC for separation and purification and concluded that Chl-RC 1 was a preparation artifact formed during the TLC separation step. The conclusion appeared reasonable as it is known that chlorophyll is easily chlorinated at the C20 position and readily hydroxylated on the silica-gel material used in thin-layer chromatography. 

Impurities in and additives to solvents can cause several problems and artifacts in liquid and gas chromatography. " Primarily they can be the origin of irreproducible separations, enhanced UV-background and even of mechanical problems. De Schutter and Col have investigated this problem in purity of solvents used in high-performance thin-layer chromatography. 

See also-. Archaeometry and Antique Analysis Dating of Artifacts. Electrophoresis Overview. Fourier Transform Techniques. Gas Chromatography Pyrolysis. Mass Spectrometry Overview. Microscopy Techniques Light Microscopy Scanning Electron Microscopy. Thin-Layer Chromatography Overview. X-Ray Fluorescence and Emission Energy Dispersive X-Ray Fluorescence. 

Under physiological conditions rhenium is most stable as rhenium(VlI), and thus the determination of perrhenate (ReO in biological samples is an important concern. Many HPLC and thin-layer chromatography (TLC) techniques developed for pertechnetate also succeed for perrhenate, although the greater sensitivity of reduced rhenium radiopharmaceuticals to reoxidation creates ample opportunity for the appearance of analytical artifacts. In this context, a dual-column HPLC procedure designed to avoid redox artifacts in the analysis of pertechnetate is especially useful in the analysis of perrhenate [18]. 

In each case, spectra of pigments eluted from layers matched those from unaltered, authentic pigment standards prepared in the laboratory by repeated column and thin-layer chromatography of extracts from large masses of leaves. No artifacts except for a possible trace of pheophytin should be noted if instructions are carefully followed. 

Table II shows the PRT-ase activities of the various mutants expressed as percent of wild-type activity. The hpt mutant is primarily affected in its IMP activity. The remaining activity is due to G-PRT and can be completely inhibited by the addition of guanine to the reaction mixture (data not shown). The gpt mutant is deficient in GMP and XMP activity with only minimal decrease in IMP activity. The residual activity for XMP in all gpt strains is an artifact imposed by the rapid assay using DE-81 Whatman discs to capture the nucleotide. The bases are usually washed off by NH4HCO3 and water, but this washing does not allow complete removal of the Cl4 xanthine substrate. In a more tedious method involving separation of base and nucleotide by thin layer chromatography, XMP activity in the gpt strains is virtually undetectable.

Isolation of the hydrocarbons from other lipids The total lipid extract may be subjected to removal of elemental sulphur by passage through an activated copper column (Blumer, 1957) and then to chromatographic separation on adsorbent columns or thin layer plates. For column chromatography, silic el is used with a short alumina bed on the top of the silic el. Both adsorbents should be partially deactivated by the addition of water (2—5%) to prevent the formation of artifacts (Blumer, 1970). Elution with a non-polar solvent such as hexane or pentane and subsequently with mixtures of non-polar and polar solvents, e.g. benzene and methanol, permits the isolation of several fractions containing saturated, unsaturated, aromatic hydrocarbons and more polar compounds (methyl esters, alcohols, acids, phenols and heterocyclic compounds). The interference from esters encountered in the isolation of aromatic hydrocarbons can be avoided prior to separation by saponification of the esters of fatty acids, which are easily removed. 

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