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The presence of phenolic content in overground extracts of Euonymus verrucosus Scop. — commonly growing in Europe — has been reported recently. The chromatographical and spectral data revealed the presence of several simple phenolic acids (gallic, protocatechuic, p-hydroxybenzoic, vanillic, syringic, caffeic, p-coumaric, ferulic, and m-coumaric acids), both as free and conjugated with other secondary metabolites. The comparison of two-dimensional TLC systems on cellulose stationary phases with HPLC— DAD reversed-phase chromatography was performed to assess a cheap and rapid technique in the identification process of major phenolic constituents. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging tests, expressed as IC50, revealed the most beneficial results for the fraction after alkaline hydrolysis and yielded 205 ± 8 μg mL−1.

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Conditions have been established for TLC separation of a mixture of nine quinolizidine alkaloid standards (lupanine, methylcytisine, cytisine, hydroxylupanine, sophocarpine, lusitanine, retamine, sparteine, and l - α -isosparteine) and of alkaloid fractions from a variety of Genista species and from in-vitro cultures of members of this species. Optimization of the one-dimensional TLC separation of the nine alkaloid standards was performed on two types of layer, RP-18W and silica gel. The mixture of standards was also chromatographed by two-dimensional TLC on diol F 254S layers and by 2D TLC with an adsorbent gradient. In the last variant (so-called graft TLC) the first development was performed on a TLC diol plate and the second, in the perpendicular direction, on an RP-18W TLC plate. Only by 2D TLC with an adsorbent gradient was it possible to achieve full separation both of the standards and of alkaloid fractions from plant material. Under these conditions the presence of retamine, cytisine, sparteine, l - α -isosparteine, lupanine, and methylcytisine was discovered in all Genista species and in shoot cultures of G. tinctoria .

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Summary

A new objective chromatographic response function, R K, based on the kernel density estimate, is introduced for estimation of the fingerprinting performance of a particular TLC system (uniformity of retention) for which a large set of experimental R F values of possible components of the mixture is available. The R K criterion is insensitive to large numbers (hundreds or thousands) of R F values, when the previously proposed criteria cease. It can be applied to one and two-dimensional TLC and is easily computed. As an example of its application, the performance of twelve general screening systems was evaluated in the context of herbal extract fingerprinting (88 phytochemical standards) by both one and two-dimensional TLC.

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Grażyna Matysik, Agnieszka Skalska-Kamińska, Beata Stefańczyk, Magdalena Wójciak-Kosior, and Dariusz Rapa

In this publication a new technique in planar chromatography is presented. The technique connects two-dimensional chromatography with multiple gradient development. It enables separation of multicomponent mixtures such as plant extracts with simultaneous qualitative identification of components. On the same plate less polar aglycones and more polar glycoside derivatives can be identified simultaneously. The new technique was applied to analysis of anthraquinone derivatives in Rhamnus frangulae cortex methanol extract.

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Phenolic acids in the leaves, roots, and fruits of Peucedanum verticillare L. Koch ex Dc have been qualitatively determined for the first time by the method of one- and two-dimensional TLC on cellulose layers. Phenolic acids in P. verticillare have not previously been studied.

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Two-dimensional separations were performed on polar bonded stationary phase of type cyanopropyl-silica and diol-silica by use of non-aqueous eluents (polar modifier dissolved in n-heptane) as the first direction eluents and aqueous eluents (organic modifier — MeOH dissolved in water) as the second direction eluents. The chromatographic process was performed in micro scale using 5 × 5 cm plates, small volumes of eluents, and 10 μL of plant extracts to obtain satisfying separation. Plates developed in horizontal chambers were dried and observed in UV light (254 nm and 366 nm) photographed by digital camera and derivatized by 1,1-diphenyl-2-picrylhydrazyl (DPPH) to detect antioxidants (free radical scavengers) or derivatized by Naturstoff reagent to detect phenolic compounds (characteristic luminescence of some phenolic compounds). The above experiments give the possibility to construct fingerprints for investigated Mentha species and varieties and preparations containing the herb. It can be used in quality control of the plant material and its antioxidative activity.

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Two-dimensional planar chromatography (2D TLC) on cellulose layers, solid phase extraction (SPE), and reversed-phase high-performance liquid chromatography (HPLC) have been used for purification, separation, and identification of the phenolic acids in the foliage and fruits of Peucedanum tauricum Bieb. ( Umbelliferae = Apiaceae ). Methanolic extracts of the foliage and fruit were purified and the free phenolic acids fractions were isolated by means of the classical method of Ibrahim and Towers . Hydrolysis of the esters and glycosides was performed by the method of Schmidtlein and Herrmann . Isolated fractions containing phenolic acids were investigated by comparison with standards, by means of analytical 2D TLC on cellulose layers, by use of derivatization reagents (gaseous NH 3 , 3% FeCl 3 and diazotized sulfanilic acid in 20% sodium carbonate solution), and by RP HPLC with isocratic elution (mobile phase methanol-water, 20:80 ( v / v ) containing 1% ( v / v ) acetic acid) and UV spectroscopy (by means of the diode-array detector of the liquid chromatograph).By use of this procedure the cinnamic acid derivatives caffeic acid, p -coumaric acid, and ferulic acid, the benzoic acid derivatives vanillic acid, p -hydroxybenzoic acid, protocatechuic acid, gentisic acid, and syringic acid, and the depside chlorogenic acid were detected and identified in the foliage of Peucedanum tauricum Bieb. Caffeic, p -coumaric, vanillic, p -hydroxybenzoic, protocatechuic, and syringic acids were also detected and identified in the fruit of the plant. This is the first time these phenolic acids have been isolated, detected, and identified in the foliage and fruit of P. tauricum Bieb.

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Two mixtures of pesticides have been separated by two-dimensional thin-layer chromatography with adsorbent gradients of the type silica-wettable with water octadecyl silica or silica-cyanopropyl. The pesticides were identified by R F values in both chromatographic systems and by comparison of UV spectra.

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Two-dimensional thin-layer chromatography (2D TLC) has been used as a screening method for detection of the metal ions Al 3+ , Cr 3+ , Cu 2+ , Ni 2+ , Mg 2+ , Zn 2+ , Mn 2+ , Pb 2+ , Sn(IV), and Fe 3+ in honey. Different mobile phases and visualization reagents were tested. The best separation was achieved on precoated microcrystalline cellulose TLC plates with acetonitrile-HCl-water, 73 + 15 + 12 ( v/v ), as mobile phase in the direction x , and 2-pentanol-acetonitrile-HCl, 30 + 20 + 50 ( v/v ), in the direction y . A mixture of quercetin, dimethylglyoxime, and NH 3 was used for visualization of the chromatographic spots. This reagent mixture produced intensely colored spots for all the ions tested and enabled their identification at concentrations ranging from 50 to 1000 ng per spot.The method was used to identify metal ions in honey samples, dissolved in 2 mol L −1 hydrochloric acid, after microwave digestion. Seven metal ions, Al 3+ , Cr 3+ , Fe 3+ , Mn 2+ , Pb 2+ , Ni 2+ and Sn(IV), were identified.

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