Impurities thin layer chromatography

Approximately 0.4 g. of product 2 remaining in the supernatant solution can be recovered by repeated recrystallizations from the ethyl ether-pentane solution however, the presence of 10 impurities (thin-layer chromatography) makes this rather impractical. 

Verification—organic impurities Thin-layer chromatography (TLC) analysis... 

A radiopharmaceutical has adequate radiochemical purity when the fraction in the form of the wanted chemical form is high enough to meet specifications. Radiolysis (degradation due to own radiation) and the usual factors that affect stability (light, oxidation, reduction, pH shifts), may cause incomplete or slow labelling, degradation and create radiochemical impurities. Thin layer chromatography is the most widely used technique for the analysis of radiochemical purity. HPLC techniques may also be used, for instance for the assessment of the radiochemical purity of PET radiopharmaceuticals. 

Fig. 24. A thin layer chromatography (TLC) image, documenting detection of impurities in a series of dye intermediate samples under near-UV illuinination. Columns 1 and 7 represent reference materials. Photographed with Polaroid Type 339 film in a CU-5 closeup camera.

Many impurities are present in commercial caprolactam which pass into the liquid wastes from PCA manufacture from which caprolactam monomer may be recovered. Also, the products of die thermal degradation of PCA, dyes, lubricants, and other PCA fillers may be contained in the regenerated CL. Identification of die contaminants by IR spectroscopy has led to the detection of lower carboxylic acids, secondary amines, ketones, and esters. Aldehydes and hydroperoxides have been identified by polarography and thin-layer chromatography. 

A curious case of stepwise formation and subsequent decomposition was observed on thermal annealing of CpMn(CO)3, as is shown in Fig. 4. Zahn showed that CpMn(CO)3 undergoes only a small rapid rise to a flat plateau. Thus the effect shown in Fig. 4 must clearly result from the presence of an impurity which was carried along with the parent compound in the separation procedure. In the case cited, thin-layer chromatography in benzene was used. The compound which increases and decreases in its activity so strikingly has not yet been identified. 

Uniformly labeled 2,4-dichlorophenol- C (purchased from New England Nuclear Corp, Boston, Mass.) was used in the tracer preparation. This provided a label at all carbon positions in the dibenzo-dioxin structure. 2,7-Dichlorodibenzo-p-dioxin- C after initial cleanup by fractional sublimation, contained approximately 5% of an impurity, detected by thin layer chromatography (TLC) which gave mass peaks at 288, 290, 292, and 294 in the mass spectrometer, consistent with a trichloro-hydroxydiphenyl oxide. This is probably the initial condensation product of the Ullman reaction and is most likely 2-(2,4-dichlorophenoxy)-4-chlorophenol. It was removed easily by extractions with aqueous... 

It was preferred to first separate the impurities from bromocriptine by thin layer chromatography and then to isolate the substance by elution from the silica gel of the plate with methanol. The intact active ingredient is measured in 0.01 M methanolic methanesulphonic acid (26). 

Novatchev, N., and Holzgrabe, U. (2002). Comparison of the suitability of capillary electrophoresis and thin-layer chromatography for determination of impurities In amino acids. Pharmeuropa 14(4), 640-647. 

Owing to the polar and nonvolatile nature of most compounds used as medicinal drugs, reversed-phase HPLC is the most common technique for monitoring the dmg substance and its impurities. GC is also used, particularly for residual solvents, and capillary electrophoresis (CE) has been introduced in more recent times. Some older methods use thin-layer chromatography (TLC), but use of this methodology for the quantitative measurement of impurities is not common. 

Measurements of the common physical constants such as boiling point or refractive index are not sufficiently sensitive to determine the trace amounts of impurities in question. Besides the common spectroscopic methods, techniques like gas chromatography (GC), high-pressure liquid chromatography (HPLC), or thin-layer chromatography (TLC) are useful. The surest criterion for the absence of interfering foreign compounds lies in the polymerization itself the purification is repeated until test polymerizations on the course of the reaction under standard conditions are reproducible (conversion-time curve, viscosity number of the polymers). 

The structures of the investigated compounds and their abbreviations are shown in Fig. 1. The absence of impurity traces was confirmed by thin layer chromatography. All the solvents used were of Merck Uvasol quality. 

Fraudulent addition of sucrose is very difficult to detect (22) because some sucrose is normally present, and added sucrose is rapidly hydrolyzed. Since commercial sucrose contains small amounts of unfermentable impurities, it has been suggested (60) that GLC would detect these in wines. Synthetic sweetening agents can be detected by thin-layer chromatography (64, 65). 

The quality of FAME prepared by the methods described in this unit must be examined by GC analysis. Generally, impurities in the extracted lipid samples are not removed before methylation. If the GC results are not satisfactory due to sample contamination, additional steps may be necessary to clean the sample either before or after methylation. Commonly used techniques for purifying lipid samples are thin-layer chromatography (TLC), solid phase extraction (SPE), and column chromatography. 

Yasuda (Ref 42a) used thin layer chromatography to obtain qual and quan analyses of Tetryl impurities and decompn products... 

Gilford, Analysis of Impurities in Composition B by Thin-Layer Chromatography (1978) (AD A056313/0ST) 158) Ei Meir, L.C. 

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