Silica gel for TLC

Trace impurities in silica gel for TLC can be removed by heating at 300° for 16h or by Soxhlet extraction for 3h with distilled chloroform, followed by 4h extraction with distilled hexane. 

Fig. 81. Silica gel blanks in the UV region. Equal amounts of silica gel for TLC from different manufacturers /, II and III extracted with the same amount of methanol, centrifuged and light absorption compared with that of the methanol used...

As with silica gels, the chromatographic separation efficiency of aluminas is determined by the mean particle size and the particle size distribution. The respective numerical values are of the same order of magnitude as in the case of silica gels for TLC and PLC. Methods of measurement for these parameters are identical with those described in Section II. A. 1. 

The separation of 34 commercial acid dyes of the monoazo, biazoanthraquin one, and triphenyl-methane types was studied by reverse-phase TLC by application of the dyes on layers of oc-tadecylsilyl-bonded silica gel for TLC with use of aqueous methanol or aqueous 60% acetone as developing solvent (101). 

FIGURE 9.15 The CD spectrum of the binder-free silica gel for TLC sample recorded in the nujol suspension. (From Sajewicz, M., Hauck, H.-E., Drabik, G., Namyslo, E., G16d, B., and Kowalska, T., J. Planar Chromatogr. —Mod. TLC, 19, 278—281, 2006. With permission.)... 

To ascertain that aminomethylphosphonic acid ( ) but not glycine (4) is a photolysis product, the primary amino product was identified by comparison of TLC Rf values. Possible products and their formation pathways from photolytic cleavage of N-nitrosoglyphosate are shown in Figure 1 (5). The TLC Rf values on silica gel for different solvent systems are shown in Table II (5). The data clearly indicate that aminomethylphosphonic acid... 

Vitamin Bjj compounds with different upper (L) and lower (R) ligands were fonnd in natnre (Figure 10.3). Some commercially available vitamin Bjj reagents, hydroxo-cobalamin and dicyanocobinamide, contain small amounts of impnrities [9]. Each vitamin Bjj reagent should be purified with silica gel 60 TLC [2-pro-panol/NH40H(28%)/water (7 1 2, v/v) as a solvent] and then used for experiments as an authentic standard material (Figure 10.4). 

To evalnate whether some foods contain true vitamin B,2 or inactive vitamin B,2 analogs, some vitamin B[2 compoimds were purified and characterized using silica gel 60 TLC [11-15]. An algal health food, spirulina tablets, contained considerable amounts of a vitamin Bjj analog (pseudovitamin Bjj) inactive for humans (Figure 10.6) [11]. 

Silica gel sintered TLC plates pretreated with K2Cr2C>7 and activated at 100°C for 2 hours. 4-dimethylamino- benzaldehyde 48... 

A solution of the aldehyde (1 mmol), the diene (1.5 mmol) and bis(trimethylsilyl) sulfide (2 mmol) in acetonitrile (0.5 ml) was treated at room temperature with a solution of CoC12.6H20 (0.2 mmol) in acetonitrile (2.5 ml). Progress of the reaction was monitored by GC/MS analysis. The reaction mixture was quenched with saturated ammonium chloride, extracted with ether and dried over sodium sulfate, and the solvent removed under vacuum. The crude reaction product was then purified by column chromatography or TLC on silica gel. For R1 = Ph a 94% yield was secured. 

A soln of the acid from hydrolyzed dipeptide 20 (40 mg, 0.115 mmol) in DMF (lmL) was treated with bithiazole 19 (30 mg, 0.088 mmol), HOBt (12 mg, 0.088 mmol), EDC (17.8 mg, 0.093 mmol), and NaH-C03 (30 mg, 0.35 mmol) at 0°C, and the mixture was stirred at 25 °C for 50 h. Brine was added, and the mixture was extracted with EtOAc (5x5 mL). The extracts were washed with sat. aq NaHC03 and brine, dried (MgS04), and concentrated. Chromatography (silica gel, preparative TLC, CH2Cl2/MeCN 2 1 and MeCN/CH2Cl2/MeOH 3 6 0.2) gave the jV-Boc tetrapeptide methyl sulfide yield 50 mg (85%). This was methylated with Mel/MeOH in 97% yield and then deprotected in 99% yield to give tetrapeptide S (21). 

Rf Values of Vitamin Do on Silica Gel GF254 TLC Plates for Common Solvents... 

Analytical thin layer chromatography (TLC) was conducted on pre-coated TLC plates, silica gel 60 F254, layer thickness 0.25 mm, manufactured by E. Merck and Co., Darmstadt, Germany. Silica Gel for flash column chromatography was obtained from Silicycle Chemical Division Silica Gel, 60 (particle size 0.040 - 0.063 mm) 230-240 mesh ASTM. All columns were prepared, loaded, and fractions collected according to the specification of Still.37 Ethyl acetate used for chromatography was dried over 4 A molecular sieves for at least 24 hours prior to use. Hexanes are the mixed hydrocarbon fraction (bp 60-70 °C), principally n-hexanes, which was purified as follows the commercial solvent was stirred concentrated sulfuric acid for at least 24 hours, decanted, stirred over anhydrous sodium carbonate for 6 hours, decanted, then distilled. 

The activity of the alumina on TLC plates is usually about III. Silica gel for column chromatography, 70-230 mesh, has a surface area of about 500 mVg and comes in only one activity. 

All materials are handled under an inert gas atmosphere in Schlenk-type vessels and in well-ventilated hoods. All solvents must be dried by Na-K alloy, degassed, and distilled. The silica gel for chromatography (Macherey-Nagel 0.06-0.2 mm) is dried for 12 h at 160°C in high vacuum. For thin layer chromatography (TLC) tests, silica gel on aluminum (Merck-60 F254) is used. The term hexane is used for the petroleum ether fraction boiling between 60 and 70 C. 

Thin-layer chromatographic silica gels have specihc pore volumes ranging from 0.5 to 2.0 mL/g sorbents with the highest values are preferred for partition chromatography. Typical applications of silica gel in TLC separation of classes of organic compounds are listed in Table 2. 

A method for the complete structural analysis of complex mixrnres of methyl esters of saturated and un-samrated fatty acids has been performed by 2-D TLC. Adsorbent silica gel impregnated with a 10% solution of dodecane was used for the first direction with acetonitrile-acetone (1 1, v/v) as eluent. The silica gel for the second direction was impregnated with a 20% AgNOs and dipropyl ether-hexane (2 3, v/v) was used as eluent. In this way, complete separation of a standard mixture of the methyl esters of six saturated, nine monoethylenic, and three polyenic esters were achieved. 

The 2-D TLC on bilayers, silica gel for normal phase (NP) and reversed phase (RP), offer the special possibility to carry out two different separation processes on the same plate. Normal-phase chromatography can be performed in the first direction on silica gel after the evaporation of the solvent, the plate was impregnated with paraffin oil dissolved in petroleum ether. After removal of the excess solvent, the plate was reversed phase developed in the second direction. 

The silica gel 60 TLC and reversed-phase HPLC patterns of the pink-colored compound purified from each laver are identical to those of authentic B12, but not to those of Bi2 compounds inactive for humans. 

Stationary Phase Silica Gel 60 TLC plate Mobil phase Chloroform/Methanol/Water = 65 25 4 UV light is used for general visualization. Rf value of initial NGPE = 0.37... 

---