Preparative layer chromatography plates used

Apply the mixture of compounds as a dichloromethane solution to a preparative thin-layer chromatography plate using a syringe. Allow the plate to air-dry, and then elute it with ethyl acetate. 

Other variations have been described by Szepesi and Nyiredy (1996) and Nyiredy (1996). Incremental multiple development (IMD) (Szabady et al., 1995 and 1997) involves rechromatography with the same composition mobile phase for distances that increase, usually by the same amount (linearly). If development occurs in the same direction with the same distance but different mobile phases having distinctive strength and selectivity, the method is termed gradient multiple development (GMD) this method most significantly increases the separation capacity of the system. In bivariate multiple development, the development distance and mobile phase composition are varied simultaneously for successive runs this method, which is effective for samples of differing polarity, has been used especially for preparative layer chromatography plates. 

Chromatographic development chambers for analytical pirrposes are commercially available in several different sizes. The most commonly used ones are rectangiflar glass tanks with inner dimensions of 21 X21 X9 cm, and they can be used to develop two plates simultaneously in the preparative scale. Even bigger tanks are available for much larger plates, for preparative layer chromatography. The width of the chamber should be varied depending on the size and the number of plates to be developed. 

TLC of larger quantities of materials (10 to 1000 mg) on thick layers (1-5mm), for the purpose of isolating separated substances for further analysis or use, is called preparative layer chromatography (PLC). Most preparative applications are carried out on 20 x 20 silica gel or alumina plates with a layer containing a fluorescent indicator to facilitate nondestructive detection. 

Examine by thin-layer chromatography (TLC) using a suitable TLC silica gel as the coating substance on the TLC plate. The method requires preparation of the following solutions ... 

Most of the reactions described in the following chapters were monitored by Thin Layer Chromatography (TLC) using plastic TLC plates coated with a thin layer of Merck 60 F254 silica gel. The products were detected by using an ultraviolet lamp or the TLC plates were treated with p-anisaldehyde reagent, prepared as explained below, and then heated to 120 °C to stain the spots. After visualization and measurement, the Rf values were recorded. 

In our laboratory crude preparations of aphantoxins and anatoxin-a(s) are extracted similarly except at the final stages of purification (Fig. 2). A Bio-gel P-2 column (2.2 x 80 cm) is used for aphantoxins gel filtration and a Sephadex G-15 (2.6 x 42 cm) column for ana-toxin-(s). Both toxins are eluted with 0.1 M acetic acid at 1.5 ml/ min. Fractions of aphantoxins from Bio-gel P-2 run are spotted on thin-layer chromatography plates (Silica gel-60, EM reagents) and developed according to Buckley et al. (1976) (31). The Rf values for the aphantoxins, saxitoxin and neosaxitoxin standards (Table 1) indicates that two of the aphantoxins (i.e. I and II) are similar to saxitoxin and neosaxitoxin. 

Silica-gel thin-layer chromatography plates—We purchase these from Fisher (catalog 05-713-317). The plates are prepared (activated) by heating in a 100°C oven for 5 to 10 min to remove any moisture from the matrix. Remove from the oven and store desiccated at room temperature until they are ready to be used. Approximately 2 5 plates will be required (1 plate/2 groups). 

The slower running material from the preparative thin layer chromatography plate (flf = 0.4) corresponds to the 2 2 cyclic adduct, that is, the desired 18-crown-6 derivative, 1,T,4,4 -tetra-0-benzyl-2,2 3,3 -oxydi-ethylenedi-L-threitol ll-1. Removal and isolation of this material from the silica (remember, caution, mask necessary when using silica) as in steps 14 and 15 for the smaller crown, affords a colourless oil ll-1 (274 mg, 11%), [a]D +5.8° (c = 3.5, chloroform). 

Powdered neutral imprinted polystyrene obtained at [H2O] = 2.78 M and [AOT] =0.2M, and having a surface area of 19.4m /g, was used for the preparation of a thin-layer chromatography plate and the separation of nitrobenzene, phenol, anUine, benzoic acid, and nitrophenol positional isomers. The plate showed fairly different Rf values for all these compounds, while the selectivity of a commercial sihca plate was found to be much worse [365]. 

The TLC Sample Streaker from Analtech (Fig. 4) is a manual device used to apply large volumes of solution to preparative-layer chromatography (PLC) plates. For PLC, large-volume initial zones are applied in the form of a continuous band across the layer, and this is accomplished with the sample streaker by the mechanical action of... 

Preparative-layer chromatography (PLC) can be used for the fractionation and/or isolation of compounds in amounts up to 1000 mg. According to the elution mode, it can be classified into classical PLC (i.e., conventional capillary-flow) and forced-flow PLC (e.g., OPLC and RPC). The main differences between analytical TLC/ HPTLC plates and preparative PLC plates are the layer thickness, mean particle size, and particle size distribution. In TLC and HPTLC, layer thickness is typically 0.2 or 0.25 mm. Mean particle size is about 12 jam in TLC and 5 jam in HPTLC, and the particle size distribution is up to 20 jam for TLC and about 10 jam for HPTLC. Consequently, HPTLC offers better resolution and lower limit of detections (LODs) than conventional TLC [17]. 

RPC involves the use of centrifugal force to accelerate the flow of solvent from the feed-point at the center to the periphery of a rotating plate. Up to 72 samples can be separated and quantified in situ by analytical RPC. One sample is applied as a circle for micropreparative and preparative RPC, for which separations can be carried out off-line or on-line with elution from the layer and recovery in a fraction collector (48). A variety of N- and S-type chambers with the prefix designations N (normal), M (micro), U (ultramicro), and C (column) are used for RPC, differing mostly in the size of the vapor space (153). Nyiredy (45) has described commercial instruments (Chromatotron and Rotachrom) and the various modes of RPC and covers preparative layer chromatography, including RPC, in Chapter 11 of this Handbook. 

Preparative-layer chromatography has been used in some cases, especially when small quantities of substance are involved. Culberson and Kristinsson (1969) separated some depsides on silica gel plates with Pastuska s mixture. Piattelli and Guidici de Nicola (1968) isolated anthraquinones, Santesson (1970a) isolated bis-anthraquinones and Santesson (1969b) isolated xan-thones, in all cases on silica-gel plates. Bloomer et al. (1970a,b) reported on preparative-layer chromatography of some aliphatic lichen acids and Aberhart et al. (1970) isolated portentol and its acetate by PLC. 

Stationary phases used in TLC are microparticulate sorbents with particle diameters of between 10 and 30/im. The smaller the mean particle size and the narrower the size range, the better the chromatographic performance in terms of band spreading (efficiency) and resolution (Topic D2). Thin-layer chromatography plates are prepared by coating sorbents onto rectangular plastic, aluminum or glass sheets in adherent uniform layers approximately 250/tm... 

Techniques for thin-layer chromatography jnay use similar solvent systems with either microcrystalline cellulose or silica gel being favoured. Additional solvent systems, for example benzene/methanol/acetic acid or pyridine/ethyl acetate/acetic acid/water are particularly useful for silica gel chromatography. Detailed descriptions of the technique have appeared elsewhere (Bobbit, 1963 Randerath, 1968 Stahl, 1969 Smith and Seakins, 1976), the latter containing a particularly good up-to-date account of the apparatus, materials and techniques used. The use of the technique is particularly facilitated by the availability of ready-prepared plates. 

Gas chromatography (gc) is inferior to hplc in separating abiUty. With gc, it is better to use capillary columns and the appHcation is then limited to analysis (67). Resolution by thin layer chromatography or dc is similar to Ic, and chiral stationary phases developed for Ic can be used. However, tic has not been studied as extensively as Ic and gc. Chiral plates for analysis and preparation of micro quantities have been developed (68). 

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. 

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