Silver nitrate TLC

Figure 12.16 Silver nitrate TLC of acylglycerols. S, O and L denote the fatty acids in each compound.

Nishibe, S., H. Tsukamoto, I. Agata, S. Hisada, K. Shima, and T. Takemoto. Isolation of phenolic compounds from stems of Olea europaea. Shokugaku Zasshil981 35 251-254. Tsukamoto, H., S. Hisada, and S. Nishibe. Studies on the lignans from Oleaceae plants. Proc 26th Symposium on the Chemistry of Natural Products, Kyoto, Japan 1983 26 181—188. Paganuzzi, V. Use of silver nitrate TLC in the analysis of olive oil triterpene alcohols. I. Oils obtained from various anatomical parts of the olives. Riv Ital Sostanze Grasse 1981 58(8) 285-393. 

Separation of Ceramides Species on Borate and Silver Nitrate TLC Plates... 

The oil is obtained by pressing or solvent extraction. The refined oil is used for edible purposes. It is also widely used as a drying oil because of its nonyellowing characteristics and as a component of alkyd resins. Both the seed and the oil are free of nicotine. The meal is rich in protein and is used in cattle feed. The triglyceride composition determined by silver nitrate TLC and lipase hydrolysis is detailed in Table 3.128. 

Prior to the analysis a triacylglycerol internal standard, 1,3-diheptadecanoyl-2,6(Z)-octadecenoyl-glycerol (17 0, 18 1, 17 0), is added to the sample. The sample is then separated into its triacylglycerol components by silver nitrate TLC. The band for /8-SOS (symmetrically disaturated 2-oleoyl-l,3-diacylglycerols) is isolated and the total jS-SOS acylglycerols are converted to methyl esters which are then analysed by GLC. 

Approximately 4 mg of triacylglycerol as standard mixture is applied to the silver nitrate TLC plate as a narrow band by means of an applicator. The plate is developed in the developing solvent toluene/hexane (8 2, v/v) until the front is about half way up the plate (about 20 min). The plate is then removed from the TLC developing tank and all the solvent evaporated. The plate is returned to the developing tank and developed further (about 1.25 h). Finally, the solvent is removed again. 

Self-staining. Martinez-Lorenzo et al. (1994) observed that polyunsaturated fatty acid methyl esters, when separated by silver nitrate TLC using the... 

Separation with low temperature- and/or silver nitrate-TLC gas chromatography)... 

The elution characteristics of a wide variety of unsaturated esters have been studied. For example, the complete series of methyl cis- and trans-octadecenoates [323] and methylene-interrupted c s,c s-octadecadienoates [157] have been subjected to silver nitrate TLC. When run in order on a single TLC plate, each series migrates in the form of a sinusoidal curve similar to that observed with isomeric polar esters on silica gel alone (see below), with a minimum at the 6-18 1 isomer (or at 6,9-18 2 in the case of the dienes) and a maximum at the 13-18 1 isomer, frans-lsomers migrate consistently ahead of the corresponding c s-isomers, with the... 

With care, it is possible to separate positional isomers of unsaturated fatty acids by silver nitrate TLC. The most consistent and successful separations of this kind were achieved by Morris et al. [622], who utilised silica gel impregnated with up to 30 % silver nitrate, developing the plates several times in the same direction if necessary, with toluene as developing solvent at temperatures as low as -5 to -25 C (complex formation is stronger at low temperatures). With this system, the methyl 6-, 9-and 11-c/s-octadecenoates can be cleanly separated from each other. Layers containing such high proportions of silver nitrate are very friable, but are not required for more routine separations. 

Silver nitrate TLC is also useful for separation of monohydroxy acids. Dihydroxy or tetrahydroxy acids are best dealt with by TLC using borate or arsenate-impregnated silica gel. 

Imidazole derivatives 380 Imperatorin 65 Impregnation of TLC layers 86 -with caffeine 86 -with silver nitrate 86 -with tungstate 86 Indeno(l,2,3-cd)pyrene 39,85 Indicators, pH- 303 -, reagents 45 Indium cations 144 Indoleacetic acid 45... 

Silica-gel-precoated preparative TLC plates impregnated with AgNOj are widely applied in this technique [60,90]. To impregnate a silica-precoated plate with silver nitrate, the plate is dipped for 3 min in a 1% AgNOj solution in a methanol-water mixture (4 1, v v). The plate is then dried, first in air with exclusion of light, and next, it is activated at 80°C in a drying oven. If impregnated plates are not used immediately, they should be stored wrapped in black plastic film in a desiccator [90-92]. 

Trans olefins form weaker ir-complexes with silver ions than do cis olefins hence cis-trans isomers can be separated using silver ion chromatography. Initially silver ions were used in conjunction with TLC, with silver nitrate being incorporated in the silica gel layer. In recent years the technique has been adapted to HPLC. 

Thin-layer chromatography has also been employed in the analysis of these compounds (9,38,150,155-159). Several developers, such as silver nitrate (150,158), / -dimethyl-aminobenz-aldehyde (38), or UV light (150,158) have been used. Derivatization techniques, based on the urea hydrolysis to the corresponding aniline and ulterior reaction with dansyl chloride, have also been carried out (9,159). Moreover, TLC is frequently employed in studies of metabolization with radiolabeled compounds (155-157). 

Thin Layer Chromatography is used by major manufacturers of radiolabeled vitamin D3 (48) for monitoring purity. The systems described are 1) silica gel G with 10% acetone in hexane 2) silica gel G with acetone-hexane 1 1 and acetone-chloroform 1 1 3) silver nitrate-impregnated silica gel G with chloroform or chloroform-acetone 9 1 and 4) silica gel saturated with silicone oil using 4 1 acetone-water. It may be mentioned that these operations are carried out under very carefully controlled conditions to prevent or minimize decomposition. TLC is an excellent technique for separating vitamin Do from interfering materials, but it has to be used with due care in the quantita-... 

Organochloride. For the estimation of chlorine containing insecticides, the developed plate is sprayed with a 1.0% ethanolic silver nitrate solution containing five milliliters of concentrated ammonia solution. After drying the sprayed plate in air, it is irradiated with U.V. light (366 nm) for ten minutes. After exactly ten minutes, the area of the developed spots is measured and compared with that of the control insecticide run on the same TLC plate. 

Silica gel can also be used as a solid support on which liquids are immobilized to produce LLC systems. Most common are nonpolar phases for reverse phase work. Other chemicals used as stationary phases include cellulose and cellulose ion exchangers, polyamide, magnesium oxide, and Kieselguhr. Silver nitrate is added to silica gel to retain olefins selectively, as noted earlier. The review by Scott15 can be consulted for further information on the stationary phase in TLC. 

Analysis by TLC. Confirmation of the identity of the halogenated compounds in the soil samples was achieved by resolution of selected extracts on TLC plates, followed by gas chromatography of the separate compounds eluted from the plates. The thin layer chromatography system of Kovacs (6) was used, and the halogenated compounds were detected with the silver nitrate-2-phenoxyethanol reagent. Comparison with standards chromatographed on the same plates permitted an estimate of the pesticide concentrations. 

Monocarboxylic esters were further separated by argentation TLC [silica GF254 impregnated with 5% (w/v) silver nitrate] into saturated esters (Rf = 0.51), monounsaturated esters (R = 0.42), diunsaturated esters (Rf = 0.29), and poly unsaturated esters (Rf < 0.29) by development in n-heptane-diethyl ether-methanol (90 10 1, v/v/v) (19). 

The use of silica gel TLC plates (impregnated or not with arsenite) allows the separation of ceramide species into different groups of relative structural homology. This is based on the position and numbers of hydroxyl groups on the ceramide molecules. However, TLC allows a possible further fractionation of ceramide species according to the unsaturation of sphingoid bases or fatty acids. This is made possible by the impregnation of the silica gel plates with borate and silver nitrate. 

The impregnation of the layer is performed by immersing the plate in a solution of the silver salt in methanol, acetone or acetonitrile or by spraying the plate with one of these solutions. Preparative plates are usually treated with 1-20% silver nitrate solutions. For analytical Ag TLC, the concentration of silver nitrate varies in the range 0.5-10%. The impregnation procedures must be standardized to provide reproducible separation. Plates are left in the air for the solvent to evaporate and are usually activated prior to use (between 5 min and 1 h depending on the purpose) by heating at 110°C. 

A large number of impregnating agents have been tested, the most frequently used in TLC are silver nitrate, metal ions, cationic and anionic surfactants, silicone, and paraffin oil. Boric-acid-impregnated silica gel layers are suitable for the resolution of carbohydrates and lipids. 

Silver nitrate-impregnated silica gel has also been used successfully in the separation of some classes of compounds that contain double bonds in their structures. Thus it was used in the separation of glycerides and isomers of unsaturated fatty acid esters. The 2-D TLC on adjacent layers of silica gel G and sihca G impregnated with 5% of silver nitrate was used for development. The silica gel G layer covered a surface of 3 x 20 cm and the difference of the surface of 17 x 20 cm was covered with silica gel G impregnated with 5% AgNOs. The first direction was performed on silica gel G with petroleum ether-diethyl ether (9 1, v/v) as eluent. The second direction was carried out on the impregnated silica gel G and developed twice with the same eluent as in the first direction. After the first direction, the mixture was... 

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