Phenolic compounds thin-layer chromatography

Wardas, W. Lipska, I. Bober, K. TLC fractionation and visuahzation of selected phenolic compounds applied as drugs. Acta Pol. Pharm. Drug Res. 2002, 57, 15-22. Wardas, W. Pyka, A. Visualizing agents for phenols in thin layer chromatography. J. Planar Chromatogr. Mod. TLC 1991, 4, 334 336. 

A common, simple, inexpensive and relatively fast method for the separation of phenolic compounds from a mixture is thin layer chromatography (TLC). A small amount of the extract (40-100 pi) is applied approximately 2 cm from the bottom of a thin layer chromatography... 

In addition to the need to monitor known problematic compounds, newer compounds are being identified as potential threats to humans and as such need to be monitored in the atmosphere. For example, researchers reported (10) that several chemical and instrumental analyses of HPLC fractions provided evidence for the presence of /V-nitroso compounds in extracts of airborne particles in New York City. The levels of these compounds were found to be approximately equivalent to the total concentrations of polycyclic aromatic hydrocarbons in the air. Since 90% of the N-nitroso compounds that have been tested are carcinogens (10), the newly discovered but untested materials may represent a significant environmental hazard. The procedure involved collecting samples of breathable, particulate matter from the air in New York City. -These samples were extracted with dichloro-methane. Potential interferences were-removed by sequential extractions with 0.2 N NaOH (removal of acids, phenols, nitrates, and nitrites) and 0.2 N H2S04 (removal of amines and bases). The samples were then subjected to a fractional distillation and other treatments. Readers interested in the total details should consult the original article (10). Both thin-layer chromatography (TLC) and HPLC were used to separate the compounds present in the methanolic extract. 

A comprehensive review of phenolic compounds in biochemical, environmental, industrial, and consumer products, as well as of sample preparation prior to thin-layer chromatography (TLC) has been effected by Tyman [1]. 

Thin-layer chromatography (TLC) is mainly applied in micropreparative taxoids separation [2-4]. Silica gel 6OF254 preparative plates are usually applied for this purpose. The problem of taxoids separation involves not only their similar chemical structure (e.g., paclitaxel versus cephalomannine) but also, due to different coextracted compounds usually encountered in crude yew extracts (polar compounds such as phenolics and nonpolar ones such as chlorophylls and biflavones), the separation is very difficult. The common band of paclitaxel and cephalomannine was satisfactorily resolved from an extraneous fraction in isocratic elution with ethyl acetate as a polar modifier [4] and n-heptane-dichloromethane as the solvent mixture and it was of suitable purity for high-performance liquid chromatography (HPLC) quantitative determination. 

Since the 1950s, many efforts have been made to isolate polyphenols directly from black tea, and the structures of the major phenolic compounds characteristic of fermented tea have been elucidated." ° However, the composition of black tea polyphenols is so complex that the minor phenolic substances, which cumulatively account for a substantial portion of black tea polyphenols, are difficult to separate even by high-performance liquid chromatography (HPLC). This difficulty associated with the purification is mainly due to the presence of uncharacterized substances that are detected as a broad hump on the baseline during HPLC analysis but do not produce any clear spots on thin-layer chromatography. These snbstances are probably a complex mixture of catechin oxidation products with higher molecular sizes, and usually account for the majority of black tea polyphenols. 

Finally, an attempt was made by using Buck and Kobrich s method (ref. 77), which yields phenols by the reaction of lithiated aryl compounds with nitrobenzene. Compound (81) was treated with n-butyllithium at -10010 in THF in the presence of tetramethylethylenediamine followed by the addition of nitrobenzene. The crude products, which were difficult to isolate as phenolic compounds, were immediately methylated with diazomethane in ether solution. The products were subjected to preparative thin layer chromatography, affording two substances. One, obtained from the upper layer, was recrystallized from ethanol as colorless needles. It showed mp 162.5 163.5lC and an optical rotation of [ o ]D -110° (c= 0.14 in CHClj). The other one, isolated from the lower layer, was recrystallized from ethanol as colorless needles. It showed mp 185 — 187"C and an optical rotation of... 

Polyamide (polycaprolactam) has been introduced only recently. It has been used almost exclusively for separations of phenolic compounds by thin-layer chromatography [e.g., Refs. (5,7J-75)], but aromatic nitro... 

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]. 

A wide variety of stationary phases have been used to separate substituted monocyclic phenols and phenolic acid compounds and their derivates by thin-layer chromatography (TLC). In particular, the composition of phenolic acids and flavonoids in leaves, roots, and fruits of several plants and in natural products has been extensively studied by the two-dimensional TLC by using cellulose or silica gel plates in one direction and silanized silica gel in the second direction. Quantitative determinations of flavonoids components of plant extracts were widely performed. 

Rastija, V. Momar, A. Jasprica, L. Srecnik, G. Medic-Saric, M. Analysis of phenolic compounds in Croatian red wines by thin layer chromatography. J. Planar Chromatogr. Mod. TLC 2004, 77 (1), 26-31. 

These workers point out that usually the additive must be separated in a pure state from co-extracted additives usually by thin-layer chromatography (TLC) and then identified by measurement of the UV, IR, nuclear magnetic resonance (NMR) and mass spectra of the compound. This full treatment is required only for new stabilisers - for a characterisation of well known compounds the simplest method is by direct comparison of the UV absorption spectra with those of a series of known stabilisers. For some compounds this will probably be sufficient, but many substituted phenols have similar spectra, and for three of the most frequently used antioxidants the UV spectra are identical. Topanol OC, lonox 330 and Binox M (see Table 2.11 for their chemical constitution) in ethanolic solution all have = 277 nm, with a shoulder at 282 nm. To extend this procedure Ruddle andWilson [66] prepared the spectra of alkaline solutions of the phenols, which were then measured either directly against a solvent blank or as difference spectra measured against the neutral solution. This still gives almost identical spectra for the three compounds mentioned previously. 

Gotti [95] described a procedure for the identification of antidegradants in vulcanised rubber mixes in which part of an extract of the sample is acetylated and then analysed by GC and the remainder is subjected to thin-layer chromatography. The results of the two analyses are interpreted separately, then, compared with each other. He discusses the characteristics displayed by a range of commercial antidegradants. The technique is suitable for compounds containing amino- or phenolic-hydroxy groups. 

Chromatography techniques, most commonly TEC (thin layer chromatography) and HPLC (high-performance liquid chromatography), are the most popular methods for the separation and detection of phenolic compounds. In recent... 

Both types of polyamides for thin-layer chromatography are available as bulk materials and as precoated layers on different carriers (plates, foils). The particle sizes are in the same ranges as used for other sorbents. Polyamides are applied for the separation of polarcompounds, which are able— because of their molecular structure—to interact with the amide group via hydrogen bonding. This is the reason why substance groups such as amino acids and derivatives (95,97), carboxylic acids (98), phenolic compounds (99-101), and preservatives (102) can be separated on polyamide as stationary phase. 

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