Silica gel, in thin-layer chromatography

Dallas, M. S. J. (1968a). Reproducibility of values on silica gel in thin layer chromatography. J. Chromatogr. 33 58-61. 

Specific surface area Owing to the constant density of the silanol groups, the specific area is a direct indicator of the adsorption capacity of a silica gel in chromatogaphy (Section II.A.2). The specific surface area Sbet of silica gel in thin-layer chromatography ranges from 200 to 800 m /g. A possible method of determination of Sbet >s based on the measurement of nitrogen adsorption isotherms (9). 

Figure 2 Typical particle size distributions of silica gels in thin-layer chromatography determined with COULTER Multisizer AccuComp .

Preparative HPLC was used to separate sterols and triterpene alcohols from the unsaponifiable matter in plant oils from Camellia weiningensis L., Brassica juncea L., and Microula sikkimensis. The isolated compounds were acetylated and further purified by AgN03-impregnated silica gel preparative thin layer chromatography (TLC). The identification was done by IR and MS. 

In 1975, a group of Depaetment of Pharmacognosy, School of Pharmacy, University of Pittsburgh, Pittsburgh, USA confirmed an anthraquinone chrysophanic acid (chrysophanol. 53) and euparone (2,5-diacetyl-6-hydroxybenzofuran. 52) (Figure 17) from ethanol extraction of the dried powdered roots of Ruscus aculeatus L. by silica gel G thin-layer chromatography [21, 51],... 

The presence of lipids has been detected in Sp. The resolution of lipid class was achieved in silica gel G thin layer chromatography showing the presence of phosphatidyl choline, triacylglycerols, cholesterol and cholesterol esters. However the extraction of lipids with ether did not deactivate Sp. (Catala et al, 1975). 

Trucksess, M., Brumley, W., and Nesheim, S. (1984). A rapid quantification of aflatoxin in corn and peanut butter, using disposable silica gel column, thin layer chromatography and gas chromatography/mass spectometry. J. Assoc. Off. Anal. Chem., 67 973-975. 

Technique of thin-layer chromatography. Preparation of the plate. In thin-layer chromatography a variety of coating materials is available, but silica gel is most frequently used. A slurry of the adsorbent (silica gel, cellulose powder, etc.) is spread uniformly over the plate by means of one of the commercial forms of spreader, the recommended thickness of adsorbent layer being 150-250 m. After air-drying overnight, or oven-drying at 80-90 °C for about 30 minutes, it is ready for use. 

Tswett s initial column liquid chromatography method was developed, tested, and applied in two parallel modes, liquid-solid adsorption and liquid-liquid partition. Adsorption ehromatography, based on a purely physical principle of adsorption, eonsiderably outperformed its partition counterpart with mechanically coated stationary phases to become the most important liquid chromatographic method. This remains true today in thin-layer chromatography (TLC), for which silica gel is by far the major stationary phase. In column chromatography, however, reversed-phase liquid ehromatography using chemically bonded stationary phases is the most popular method. 

The difference between this technique and GC or HPLC is that the separation process occurs on a flat essentially two-dimensional surface. The separated components are not usually eluted from the surface but are examined in situ. Alternatively, they can be removed mechanically for further analysis. In thin-layer chromatography (TLC), the stationary phase is usually a polar solid such as silica gel or alumina which is coated onto a sheet of glass, plastic, or aluminium. Although some moisture is retained by the stationary phase, the separation process is predominantly one of surface adsorption. Thin layers are sometimes made from ion-exchange or gelpermeation materials. In these cases the sorption process would be ion-exchange or exclusion. 

The most commonly used approach in thin-layer chromatography (tic) entails separations on a silica gel plate where tire silica gel is coated as a thin layer on a glass plate. The plate is developed using the mobile phase... 

Exercises in thin-layer chromatography. Separation of amino acids. Prepare solutions of DL-alanine, L-leucine and L-lysine hydrochloride by dissolving 5 mg of each separately in 0.33 ml of distilled water, measured with a graduated 1 ml pipette (leucine may require warming to effect solution). Mix one drop of each solution to provide a mixture of the three amino acids and dilute the remainder of each solution to 1 ml to give solutions of the respective amino acids. The latter will contain about 5 pg of each amino acid per pi. Apply approximately 0.5 pi of each of the solutions to a Silica Gel G plate and allow to dry in the air (i.e. until the spots are no longer visible). 

The following table contains the common solvents used in thin-layer chromatography, with a measure of their strengths on silica gel and alumina. The solvent strength parameter, s°, is defined as the relative energy of adsorption per unit area of standard adsorbent.13 It is defined as zero on alumina when pentane is used as the solvent. This series is what was called the eluotropic series in the older literature. For convenience, the solvent viscosity is also provided. Note that the viscosity is tabulated in cP for the convenience of most users. This is equivalent to mPasec in the SI convention. Additional data on these solvents may be found in the tables on high-performance liquid chromatography. 

Background and principles Thin-layer chromatography is the other most commonly used form of planar chromatography and uses a very similar experimental approach to paper chromatography. The principal difference is that this technique relies on the separation of biomolecules from a mixture on the basis of partition and/or adsorption. There is a distinct difference between the process of adsorption and a/isorption, and they are not interchangeable terms Whereas molecules that are a/isorbed are taken up into , those that are adsorbed stick to a surface. So, in thin-layer chromatography, the mobile phase is adsorbed (sticks to) and subsequently moves along the stationary phase. The stationary phase consists of an adsorbent (sticky) layer on a flat plate or sheet. The most commonly encountered adsorbent layers comprise silica gel, alumina (not aluminium) or cellulose, while popular solvents include hexane, acetone and alcohol. 

E. Soczewinski, Solvent composition effects in thin-layer chromatography systems of the type silica gel-electron donor solvent, Ana/. Chem. 41 (1969), 179-182. 

Silica gel is the most extensively used adsorbent in thin layer chromatography because it leads to excellent, uncomplicated separations. It can be successfully employed for both qualitative and quantitative thin layer chromatographic analyses. It is usually used as a stationary phase in separations and analysis of alkaloids, various organic acids (especially amino acids and their derivatives), steroids, lipids, vitamins, plant pigments, pesticides, drugs, carbohydrates, phenolic substances, etc. 

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. 

In thin-layer chromatography, the stationary phase is a suspension made up of a material such as silica gel or cellulose in a solvent. The suspension is... 

Typical Mobile Phases used in Thin-layer Chromatography on Silica Gel... 

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