Mobile thin layer chromatography

Refs. 293 and 294. Mobility ranking based on soil thin-layer chromatography (sdc). 

Immobilization. The abiUty of cyclodextrins to form inclusion complexes selectively with a wide variety of guest molecules or ions is well known (1,2) (see INCLUSION COMPOUNDS). Cyclodextrins immobilized on appropriate supports are used in high performance Hquid chromatography (hplc) to separate optical isomers. Immobilization of cyclodextrin on a soHd support offers several advantages over use as a mobile-phase modifier. For example, as a mobile-phase additive, P-cyclodextrin has a relatively low solubiUty. The cost of y- or a-cyclodextrin is high. Furthermore, when employed in thin-layer chromatography (tic) and hplc, cyclodextrin mobile phases usually produce relatively poor efficiencies. 

THIN-LAYER CHROMATOGRAPHY OF BENZOIC ACIDS WITH EXTERNAL CONTROL PROPERTIES OF THE MOBILE PHASE... 

One of trends of development of thin-layer chromatography implies that replacement of aqueous-organic eluents by micellar surfactants solution. This is reduces the toxicity, flammability, environmental contamination and cost of the mobile phases, reduce sample prepar ation in some cases. 

The new way of quantitative determination of the ascorbic acid (AC) by means of ion-pair thin layer chromatography (TLC) in organo-aqueous mobile phases containing cetyltrimethylammonium bromide (CTAB) has been alaborated. 

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. 

In the case of thin-layer chromatography there is frequently no wait to establish complete equilibrium in the chamber before starting the development. The chamber is usually lined with a U-shaped piece of filter paper and tipped to each side after adding the mobile phase so that the filter paper is soaked with mobile phase and adheres to the wall of the chamber. As time goes on the mobile phase evaporates from the paper and would eventually saturate the inside of the chamber. 

A more concentrated (1000 ppm) solution of dibenzo-p-dioxin in methanol was irradiated for 1.5 hours under a 450-watt lamp fitted with a borosilicate glass filter while nitrogen was bubbled continuously through, the solution. Unchanged starting material was recovered to the extent of 85%. The principal photolysis product again was a dark brown insoluble gum similar to that described above. Its mobility on thin layer chromatography (TLC) was very low in the benzene/ethyl acetate (4 1) solvent used to separate the other products. 

Chromatographic characterisation of hydrolysis products Hydrolysis products from sodium polypectate were analysed by thin-layer chromatography on silica gel G-60, using ethyl acetate / acetic acid / formic acid / water (9 3 1 4, by volume) as the mobile phase system. Sugars were detected with 0,2% orcinol in sulphuric add-methanol (10 90ml) [14]. 

In reversed-phase thin-layer chromatography (RP-TLC), the choice of solvents for the mobile phase is carried out in a reversed order of strength, comparing with the classical TLC, which determines a reversed order of values of compounds. The reversed order of separation assumes that water is the main component of the mobile phase. Aqueous mixmres of some organic solvents (diethyl ether, methanol, acetone, acetonitrile, dioxane, i-propanol, etc.) are used with good results. 

Morita et al. [69] optimized the mobile phase composition using the PRISMA model for rapid and economic determination of synthetic red pigments in cosmetics and medicines. The PRISMA model has been effective in combination with a super modihed simplex method for fadhtating optimization of the mobile phase in high performance thin layer chromatography (HPTLC). 

Gocan, S., Mobile phase in thin-layer chromatography, in Modern Thin-Layer Chromatography, Grinberg, N., Ed., Chromatographic Science Series, 52, Marcel Dekker, New York, 1990, chap. 3. 

Bodoga, R, Marufoiu, C., and Coman, M.-V., Faze mobile (mobile phases), in Cromatografia pe Strat Sublire. Analiza Poluanlilor (Thin-Layer Chromatography. Pollutant Analysis), Analytical chemistry series. Technical Publishing House, Bucharest, 1995, chap. 3 and references cited therein. 

Touchstone, J.C. and Dobbins, M.E, The mobile phase, in Practice of Thin Layer Chromatography, John Wiley Sons, New York, 1978, chap. 5. 

FIGURE 6.19 Circular chromatography of dyes on precoated silica gel high-performance TLC plate lipophilic dyes, mobile phase hexane-chloroform-NH3, 70 30. (From Ripphahn, J. and Halpaap, H., HPTLC High Performance Thin Layer Chromatography, Zlatkis, A. and Kaiser, R. E., Eds., Elsevier, Amsterdam, 1977, pp. 189-221. With permission.)... 

The identification of separated componnds is primarily based on their mobility in a snitable solvent, which is described by the Rp valne of each compormd. Kowalska et al. have nicely discnssed in greater detail the theory of planar chromatography and separation efficiency parameters in Chapter 2 of the third edition of the Handbook of Thin-Layer Chromatography, published in 2003. 

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