Solid thin layer chromatography

The mother liquorsand washings of fractions I and II are concentrated froma volume of about 1.7 liters to 250 ml, the pH is adjusted to 2.5 with 100% formic acid and the solution is stored overnight in a refrigerator, whereby further substance crystallizes. This is filtered off under suction and washed with a small amount of water. The residue on the suction filter is azeotropically distilled with ethanol. There is obtained solid, almost colorless title substance which is denoted as 8. 8 is purer than A according to thin-layer chromatography. 

Removal of solvent from the extracts leaves a residue that is purified by dry-column chromatography.2 The residue is dissolved in 40 ml. of acetone in a 300-ml., round-bottomed flask, 30 g. of silica gel (Note 8) is added, and the acetone is removed with a rotary evaporator. The resulting solid mixture is placed on top of 360 g. of dry silica gel (Note 8) packed in flexible nylon tubing (Note 9), and the column is developed with 420 ml. of 10 1 (vjv) benzene-acetone. Approximately 150 ml. of solvent drips from the bottom of the column toward the end of development, and this eluent is collected in 25-ml. fractions and checked for product by thin layer chromatography (Note 10). The column itself is then cut into 2-cm. sections, the silica gel in each section is eluted with three 25-ml. portions of ethyl acetate, and the eluent from each section is analyzed by thin-layer chromatography (Note 10). Combination of all the product-containing fractions yields 1.2-1.5g. (40-47%) of the benzylated compound as an oil, n 1.6083 (Notes 11 and 12). 

Tezuka s group (Tezuka and Ando, 1985 Tezuka et al., 1986) was able to isolate and characterize the benzenediazo ether of 1-naphthol (6.10). They stirred a solid mixture of the molecular complex 6.9 formed between an a-azohydroperoxide acid and benzene with an excess of 1-naphthol at room temperature in the dark for several hours. The separation of this solid by thin layer chromatography (silica gel, with a benzene-ethyl acetate mixture [9 1] as eluent) afforded the diazo ether 6.10 as a yellow oil in 17 % yield, together with 4- and 2-phenylazo-l-naphthol (6.11 and 6.12, 4% and 42%, respectively), 4-phenylbenzaldehyde (32%), benzoic acid (23%), and traces of other compounds (Scheme 6-6). Higher yields of the diazo ether (up... 

High performance liquid chromatography (HPLC) has been by far the most important method for separating chlorophylls. Open column chromatography and thin layer chromatography are still used for clean-up procedures to isolate and separate carotenoids and other lipids from chlorophylls and for preparative applications, but both are losing importance for analytical purposes due to their low resolution and have been replaced by more effective techniques like solid phase, supercritical fluid extraction and counter current chromatography. The whole analysis should be as brief as possible, since each additional step is a potential source of epimers and allomers. 

In conclusion, synthetic dyes can be determined in solid foods and in nonalcoholic beverages and from their concentrated formulas by spectrometric methods or by several separation techniques such as TEC, HPLC, HPLC coupled with diode array or UV-Vis spectrometry, MECK, MEECK, voltammetry, and CE. ° Many analytical approaches have been used for simultaneous determinations of synthetic food additives thin layer chromatography, " " derivative spectrophotometry, adsorptive voltammetry, differential pulse polarography, and flow-through sensors for the specific determination of Sunset Yellow and its Sudan 1 subsidiary in food, " but they are generally suitable only for analyzing few-component mixtures. 

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. 

Lipophilicity represents the affinity of a molecule or a moiety for a lipophilic environment. It is commonly measured by its distribution behavior in a biphasic system, either liquid-liquid (e.g. partition coefficient in 1-octanol-water) or solid-liquid (retention on reversed-phase high-performance liquid chromatography or thin-layer chromatography system). 

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. 

GLC, gas-liquid chromatography GSC, gas-solid chromatography—no high-boiling liquid, only solid HPLC, high-performance liquid chromatography TLC, thin-layer chromatography. 

Thin layer chromatography (TLC) Solid (silica gel) Liquid (solvent, often a mixture). Also called developer. 

Thin layer chromatography was carried out on 20x20cm glass plates coated 0.25mm thick with a suitable support and dried overnight. Silica gel G, silica gel H and cellulose were examined as the solid phases for chromatography of methanearsonate, arsenite and arsenate. Several sprays for the visualization of the arsenicals on plates were tested. Three of the more successful reagents and the colour produced with final product are shown in Table 13.2. 

The pure solid can be dried and weighed. A percentage yield can be calculated from its mass. The pure solid will often be subjected to analysis by melting point and thin-layer chromatography (see pp. 94-95). 

The precipitate was filtered off, washed with ether, and dried under vacuum to yield 4.7 g of dry product (A-poly-2). Thin layer chromatography on silica gel using dichloromethane/methanol (93 7) showed only a trace of free monomer. This activated copolymer was soluble in water, THF, CH2CI2 and DMF. It was reproducibly prepared in good quantity and stored in the solid state for months, protected from moisture, without loss of activity. 

The epothilone synthesis in Scheme 13.49 has been used as the basis for a combinatorial approach to epothilone analogs. 167 The acyclic precursors were synthesized and attached to a solid support resin by steps A-E in Scheme 13.58. The cyclization and disconnection from the resin were then done by the olefin metathesis reaction. The aldol condensation in step D is not highly stereoselective. Similarly, olefin metathesis gives a mixture of E- and Z-stereoisomers so that the product of each combinatorial sequence is a mixture of four isomers. These were separated by thin-layer chromatography prior to bioassay. In this project, reactants A (3 variations), B (3 variations), and C (5 variations) were used, generating 45 possible combinations. The stereoisomeric products increase this to 180 (45 x 4). 

---