Impregnation, with caffeine

Silica gel 60, impregnated with caffeine for PAH determination Charge transfer complexes Polycyclic aromatic hydrocarbons (PAH) acc. to German drinking water specification (TVO)... 

Normally, impregnated TLC plates are only used for special separations, i.e. rarely, so that commercially produced plates of this type would be too expensive. Thus, A. Koch describes the separation of plant hpids on 5 x 5 cm HPTLC sUica gel 60 plates which were impregnated with 0.5 % phosphoric acid especially for this application [27]. The six relevant polycyclic aromatic hydrocarbons are tested for rather more frequently in the monitoring of drinking water. An HPTLC precoated layer impregnated with caffeine is manufactured commercially especially for this apphcation. 

NANO-SIL-PAH = Macherey-Nagel, impregnated with caffeine. 

Impregnating agents that are able to form charge transfer complexes. An example is the HPTLC precoated plate silica gel 60 impregnated with caffeine, which has been introduced in 1994. 

Imidazole derivatives 380 Imperatorin 65 Impregnation of TLC layers 86 -with caffeine 86 -with silver nitrate 86 -with tungstate 86 Indeno(l,2,3-cd)pyrene 39,85 Indicators, pH- 303 -, reagents 45 Indium cations 144 Indoleacetic acid 45... 

Knaff and Schlunder [9] studied the evaporation of naphthalene and caffeine from a cylindrical surface (a sintered metallic rod impregnated with the solute) to high-pressure carbon dioxide flowing over an annular space around the rod. They studied the diffusion flux within the bar and in the boundary layer. The mass-transfer coefficient owing to forced convection from cylinder to the gas flowing in the annular duct was correlated, using the standard correlation due to Stephan [7]. For caffeine, it does not require a free-convection correction, as the Reynolds dependence is that expected by a transfer by forced convection. This is... 

In contrast to the decaffeination of coffee, which is primarily executed with green coffee, black tea has to be extracted from the fermented aromatic material. Vitzthum and Hubert have described a procedure for the production of caffeine-free tea in the German patent application, 2127642 [11]. The decaffeination runs in multi-stages. First, the tea will be clarified of aroma by dried supercritical carbon dioxide at 250 bar and 50°C. After decaffeination with wet CO2 the moist leaf-material will be dried in vacuum at 50°C and finally re-aromatized with the aroma extract, removed in the first step. Therefore, the aroma-loaded supercritical CO2 of 300 bar and 40°C will be expanded into the extractor filled with decaffeinated tea. The procedure also suits the production of caffeine-free instant tea, in which the freeze-dried watery extract of decaffeinated tea will be impregnated with the aromas extracted before. 

Additions of 1/10 to 2 1/2% of urea to dilute procaine solutions increase materially their potency, to ten times, on direct application to nerve trunks, presumably by favoring penetration. The effect is not due to alkalinization. The action of local anesthetics is reported to be increased by intravenous injection of methylene blue, by the local application of caffeine or theophylline, by morphine, and by the antipyretic analgesics. Cocaine anesthesia is said to be ineffective in tissue impregnated with oxalic acid. Inflamed tissues are less susceptible to local anesthesia, probably because of their difficult penetration. 

In a similar study,an olive oil impregnated Millipore membrane was employed to determine the transport kinetics of several drugs between two aqueous compartments buffered at pH 1.2 and 7.4. Apparent first-order rate constants obtained for the drugs alone can be correlated with reported in vivo absorption rate constants. Each of the drugs is known to complex with caffeine, and in each case caffeine significantly reduces the rate of transport. Furthermore, calculated m vitro rate constants agree well with reported in vivo rote constants for the drug-caffeine complexes. 

Fig. 42 Chromatogram of polycyclic aromatic hydrocarbons on caffeine-impregnated precoated silica gel 60 HPTLC plates with concentrating zone (Merck). The following can be recognized in increasing Rf value. — 1. benzo(ghi)perylene, 2. indeno(l,2,3-cd)pyrene, 3 benzo(a)pyrene, 4. benzo(b)fluoranthene, 5. benzo(k)fluoranthene, 6. fluoranthene.

A,S.ergotamine,ergo tami nine,caffeine Butalbital.phenobarbital Separation on silver impregnated silica gel Lichrosorb Si 100 5iim,imp. with 1.09% Agl... 

For special separations, an impregnation of the layer is often necessary, e.g. of unsaturated fatty acids with silver nitrate or of antibiotics of the tetracycline type with EDTA. Whereas the user must perform these impregnations himself, a caffeine-impregnated HPTLC precoated layer is available for the determination of polycyclic aromatic hydrocarbons. 

In the determination of polycychc aromatic hydrocarbons (PAHs), the separation is performed either on caffeine-impregnated HPTLC silica gel 60 plates, on HPTLC-RP-18 plates with a concentration zone or on precoated HPTLC silica gel 60 plates with a concentration zone (Merck Item Nos. 1.15086,1.15037,1.13728). Subsequent dipping in paraffin/n-hexane (1 4) gives not only stabilization of the PAHs on the plate but also an increase in the fluorescence intensity by a factor of 4-5 [83a]. 

After the addition of an internal standard, samples were extracted with acetone/ methanol. Without further cleanup, the separation was performed on caffeine-impregnated HPTLC plates NANO-SIL-PAH, 20 x 10 cm (Macherey-Nagel), developed with /-hexane/methyl ethyl ketone (5/1, v/v). Interfering fat-soluble natural dyes (carotenoids) were bleached by UV irradiation, followed by multi-wavelength... 

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