Thin-layer chromatography vapor phase

The phenylthiohydantoins formed in the process of Edman degradation were compared with authentic phenylthiohydantoins prepared from amino acids and thus identified. Yet, in spite of numerous further improvements, such as application of thin layer chromatography, vapor-phase chromatography and even mass spectrometry for the identification of phenylthiohydantoins, the method... 

Thin-Layer Chromatography. Chiral stationary phases have been used less extensively in tic as in high performance Hquid chromatography (hplc). This may, in large part, be due to lack of avakabiHty. The cost of many chiral selectors, as well as the accessibiHty and success of chiral additives, may have inhibited widespread commerciali2ation. Usually, nondestmctive visuali2ation of the sample spots in tic is accompHshed using iodine vapor, uv or fluorescence. However, the presence of the chiral selector in the stationary phase can mask the analyte and interfere with detection (43). 

There is no other facet where thin-layer chromatography reveals its paper-chromatographic ancestry more clearly than in the question of development chambers (Fig. 56). Scaled-down paper-chromatographic chambers are still used for development to this day. From the beginning these possessed a vapor space, to allow an equilibration of the whole system for partition-chromatographic separations. The organic mobile phase was placed in the upper trough after the internal space of the chamber and, hence, the paper had been saturated, via the vapor phase, with the hydrophilic lower phase on the base of the chamber. 

Let s start with two components, A and B again, and follow their path through an adsorption column. Well, if A and B are different, they are going to stick on the adsorbant to different degrees and spend more or less time flying in the carrier gas. Eventually, one will get ahead of the other. Aha Separation—Just like column and thin-layer chromatography. Only here the samples are vaporized, and it s called vapor-phase chromatography (VPC). 

The product is pure by vapor phase and thin-layer chromatography infrared (carbon tetrachloride) cm-1 1740 proton magnetic resonance (carbon tetrachloride) S (multiplicity, number of protons, assignment) 4.14 (broad triplet, 2, CH20), 2.30 (broad triplet, 2, CH2CO), and 1.8-1.2 (multiplet, 16). 

Qual and quan identification of expls is often fraught with difficulty owing to the inherent thermal instability of the compds which limits the use of vapor phase analytical techniques. If the expl is present in reasonably pure and coned form, infrared spectroscopy is suitable. Many times, especially if the expl is present in trace amts (mictogram quantities) ox if it is diluted with fillers (as in proplnts), separation and conen prior to identification are required. The earlier method, thin layer chromatography,... 

Plasticizers include the esters of a few aliphatic and aromatic mono and dicarboxylic acids, aliphatic and aromatic phosphorus acid esters, ethers, alcohols, ketones, amines, amides, and non-polar and chlorinated hydrocarbons. These additives are used in various mixtures. For their separation and qualitative detection, thin-layer chromatography (TLC) is preferred. Usually Kieselgur plates, 0.25 mm thick, activated at 110°C for 30 min, in the saturated vapor are used. Methylene chloride and mixtures of diisopropyl ether/petether at temperatures between 40 to 60°C have been successfully used as the mobile phase. Refer to Table 1. 

A second way to resolve quench problems is to separate the sterols from the pigments by thin layer chromatography (TLC). Briefly, samples are concentrated by evaporation and redissolved in a small volume (<100 xl) of chloroform or hexane and spotted onto a pre-dried, silica gel G, TLC plate along with 5 xg of cholesterol standard. Components are resolved with a mobile phase comprised of petroleum ether, diethyl ether, and acetic acid at a 300 200 1 ratio. Sterols migrate 1/4 to 1/3 of the way to the top of the plate, while pigments stay at or near the origin. Spots are visualized with iodine vapor, marked with a pencil, scraped into scintillation... 

The products, which were obtained as viscous, pale amber oils, were purified by vacuum distillation or molecular distillation, whichever was best suited to the particular product. The yield of dialkylated p-cresol was 85-95%. Freedom from appreciable amounts of monoalkylated product was established by vapor phase chromatography (VPC), thin-layer chromatography (TLC), and molecular weight determination. The products obtained from propylene trimer and tetramer had no appreciable antioxidant activity) and will not be considered further here. 

Gresser et al. (1995) combined their PPF with VP and hydroxyapatite, crosslinking this mixture with benzoyl peroxide and DMT. Samples were allowed to crosslink at 37°C for 24 hours. These hardened samples were ground to analyze the amount of PPF and VP incorporated. The ground power was run in acetonitrile on reverse-phase thin layer chromatography plates, and developed with iodine vapor or ultraviolet light. Over 90% of the PPF was found to have been crosslinked in mixtures containing between 0.33 to 2 PPF/W ratios. The fraction of VP incorporated was dependent on the ratio of the two components. The fraction of PPF or VP incorporated was independent of the amount of hydroxyapatite, benzoyl peroxide, or DMT used. The VP monomer was found to add to poly( inyl pyrrolidinone) twice as often as it added to the fumarate double bond. 

Niederwieser, A. (1969). Recent advances in thin layer chromatography. IV. Gradient thin layer chromatography. Part II. Gradients of elution with special regard to vapor impregnation and flux of mobile phase. Chromatographia 2 362-375. 

Conventional methods of quantitation of fractions resolved by thin-layer chromatography (TLC) using techniques, such as in situ spectrophotometry or photodensitometry, are of limited utility to substances that contain weak or no chromophoric groups (1). Such fractions can be conveniently detected and quantitated by sensitive vapor phase detectors that are commonly used in gas chromatography (2,3). Several systems for quantitative TLC using vapor phase detectors have become known in recent years. 

During recent years, the problem of optimization of separation techniques in thin-layer chromatography has been tackled in both theoretical treatments (129-133) and in the development of instrumentation (134-136). In overpressured TLC (137) a pressurized ultramicrocham r is used. The essential feature of this chamber system is that, in contrast to the rigid glass plate used in the earlier ultramicrochamber (138,139), the sorbent layer is completely covered by an elastic membrane under external pressure, so that vapor phase above the layer is eliminated. Solvent is admitted into the chamber under overpressure by means of a pump system. This technique essentially combines the... 

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