Normal-phase TLC

From the general framework of the Snyder and Soczewinski model of the linear adsorption TLC, two very simple relationships were derived, which proved extremely useful for rapid prediction of solute retention in the thin-layer chromatographic systems employing binary mobile phases. One of them (known as the Soczewinski equation) proved successful in the case of the adsorption and the normal phase TLC modes. Another (known as the Snyder equation) proved similarly successful in the case of the reversed-phase TLC mode. 

Pelander et al. [81] developed a computer program for optimization of the mobile phase composition in TLC. They used the desirability function technique combined with the PRISMA model to enhance the quahty of TLC separation. They apphed the statistical models for prediction of retardation and band broadening at different mobile phase compositions they obtained using the PRISMA method the optimum mobile phase mixtures and a good separation for cyanobacterial hepatotoxins on a normal phase TLC plate and for phenolic compound on reversed-phase layers. 

SOLVENT STRENGTH PARAMETERS FOR SOLVENTS COMMONLY VSBD IN NORMAL PHASE TLC... 

Normal-phase TLC has been employed for the separation of two new flavans in the extract of the undergorund tubers of Cyperus conglomeratus Rottb. (family Cyperaceae). The underground tubes were dried, ground and were extracted with with petroleum ether diethyl ether-methanol (1 1 1, v/v) for 24 h at ambient temperature. The extract was defatted with cold methanol. The components of the extract were preliminarily separated by traditional column chromatography followed by GC/MS and TLC. New flavans (5-hydroxy-7,3, 5 -trimethoxyflavan and 5,7-hydroxy-3, 5 -dimethoxyflavan) were separated on silica TLC layers using petroleum ether-diethyl ether (1 3, v/v) with the RF values of 0.50 and 0.37 for dimethoxy and trimethoxy derivatives, respectively [115]. 

Normal-phase TLC using a silica stationary phase was employed for the optimization of the separation of flavonoid content of Matricariae flos (Chamomilla recutita L. Rauschert). Air-dried and powdered plant material was extracted by refluxing for 10 min with methanol. The suspension was filtered, evaporated and the residue was redissolved in methanol. The mobile phases included in the experiments were 1 = ethyl acetate-methylethylketone-formic acid-water (50 30 10 10, v/v) 2 = ethyl acetate-methanol-water (75 15 10 v/v) 3 = ethyl acetate-formic acid-water (80 10 10, v/v) 4 = ethyl acetate-formic acid-water (100 20 30, v/v) 5 = ethyl acetate-formic acid-acetic acid-water (100 11 11 27, v/v) 6 = n-butanol-acetic acid-water (66 17 17, v/v) 7 = ethyl acetate-methanol-formic acid-water (75 10 5 10, v/v) 8 = ethyl acetate-acetic acid-water (80 10 10, v/v). Development was carried out in the linear ascending mode at... 

Flavonoids in propolis have also been investigated by TLC using a silica stationary phase and various mobile phases. Samples of 14 propolis with different geographical origin were extracted with 80 per cent ethanol and analysed with normal-phase TLC. The retention data are compiled in Table 2.47. 

Normal-phase TLC has been employed for the control of the synthesis of some new reactive azo dyes containing the tetramethylpiperidine fragment. The chemical structure of the basic molecule and the substituents of the new derivatives are shown in Fig. 3.16. The new derivatives were characterized by their RF values determined in different mobile phases. Compositions of mobile phases were n-propanol-ammonia (1 1, v/v) for dye 1.2 (Rp = 0.84) n-propanol-ammonia (2 1, v/v) for dyes 1.3 (RF = 0.50) and 1.4 (RF = 0.80) and n-heptane-diethyl ether (1 1, v/v) for dyes 1.5 (RF = 0.80) and 1.6 (RF = 0.76). The results indicated that together with other physicochemical methods such as IR and H NMR, normal-phase TLC is a valuable tool for the purity control and identification of new synthetic dyes [96],... 

The elution factors in normal-phase TLC and RP-HPLC, using a fixed set of chromatographic parameters, were determined for a series of saturated triacylglycerides with TCN from C30 to Ceo, serving as reference compounds and various oxidation derivatives of analogous unsaturated triglycerides, including hydroperoxides, peroxides, epoxides, core aldehydes and their DNP derivatives. From these measurements, a series of incremental... 

A normal phase TLC system has been developed for brinzolamide. The operating parameters for this method are summarized in Table 8. 

Any sample type that has been separated by normal-phase TLC is appropriate for a liquid-solid chromatographic (LSC) separation. An example of this is shown in Figure 5-45. In this separation, both the TLC plate and HPLC separations were done using the same mobile phase. Several good references on the early work in TLC (22,23) and on adsorption chromatography (24-26) should be consulted by those interested in a historical perspective of the use of normal-phase chromatography. 

Besides normal-phase TLC, reversed-phase TLC was used by impregnating the silica gel layer with paraffin or silicone oil and using hydrophilic solvents as mobile phases. By this method, it is possible to achieve a good separation of alcohols belonging to groups with the same number of carbon atoms. 

Combining different separation methods, governed by different separation mechanisms, to multidimensional methods is suitable for multiplying the potential of the individual techniques. Reversed-phase chromatography high-performance columns (RP-HPLC) can be coupled with normal phase TLC [9,10]. 

The isolation by TLC yielded an active compound which was homogeneous in several normal phase TLC systems. The addition of a small amount of formic acid to the developing solvent resulted in a much sharper TLC spot, indicating an acidic group in the active compound. The active area was not visible under ultraviolet light at 254 nm on indicator TLC plates but was visualized by spraying with 5% phosphomolybdic acid in ethanol and heating to 110°C for 10 min. Infrared spectroscopy indicated hydroxyl and... 

Nonetheless, RPTLC is the method of choice in a wide range of application areas and has a number of advantages compared with normal phase TLC ... 

To analyse an analgesics mixture by normal phase TLC using single and multiple development techniques. To analyse analgesic mixtures by reverse phase TLC. 

Single elution normal phase TLC Materials and equipment... 

Duncan, JD and DW Armstrong (1990). Normal phase TLC separation of enantiomers using chiral ion interaction agents. Journal of Liquid Chromatography, 13(6). 

TLC is still regarded as a cheap and effective technique for ochratoxin A estimation, particularly because of its low cost and adaptability. New methods include extraction with a mixture of phosphoric acid and dichloromethane and purification by liquid-liquid partitioning into sodium hydrogen carbonate, before separation by normal-phase TLC and detection by fluorescence as usual (Pittet Royer, 2002) and extraction with a mixture of methanol and aqueous sodium bicarbonate solution, followed by partitioning into toluene before TLC (Ventura et al.,2005). 

High-performance TLC (HPTLC) has now largely replaced conventional TLC as a method of lipid resolution and quantification. Scanning of charred and radioactive spots provides improved quantitative estimates due to increased resolution of all components compared to conventional TLC. It serves as an efficient method of sample isolation for sensitive MS identification of various lipids. Modern TLC is a fully instrumental technique distinguished from conventional TLC. Because the technique is optimized to achieve maximum separation with high levels of automation, the results are largely independent of operator skill. Both one-dimensional and two-dimensional HPTLC are commonly employed. Normal phase TLC on Chromarods (latroscan) with FID constitutes a special application to separation and quantification of both neutral and polar lipid classes. The order of resolution of the lipid classes is directly related to the polarity of the solutes, which may be modified to some extent by the preparation of derivatives or altering the polarity of the adsorbent. 

Normal phases. Silica is generally the normal phase used in lipid separations. The average particle sizes in traditional TLC range between 10 pm and 50 pm, with a fairly wide size distribution. In normal phase TLC the stationary phase (such as silica) is polar and the mobile phase is relatively non-polar. Scott (1982) has extensively reviewed silica gel and its properties, the water absorption of the silica surface and its interaction with polar and non-polar solvents. 

Source From Comparison of retention of phenols, aniUne derivatives and quinoUne bases in normal-phase TLC with binary isoeluotropic eluents, in J. Planar Chromatogr. ... 

Fig. 1 Photograph taken with a videodensitometer of a Whatman Multi-K SC5 plate showing the 2-D separation of a 16-component mixture of pesticides. The fluorescence-quenched zones are outlined for clarity. Direction 1 ethyl acetate-diisopropyl ether (2.5 97.5) mobile phase on the 20 cm x 3 cm K5F silica gel strip (normal phase TLC) direction 2 acetonitrile-water (85 15) on the adjacent 20 cm x 17 cm C-18F bonded silica gel layer (RPTLC). X Origin. Pesticides 1, propaquizafop 2, quizalofop-P 3, triadimefon 4, triadimenol 5, fenoxycarb 6, quinoxyfen 7, cyromazine 8, oxyfluorfen 9, fluoroglycofen 10, acetochlor 11, metazachlor 12, piperonyl butoxide 13, fur-alaxyl 14, pyriproxyfen 15, buprofezin 16, clofentezine. Source From Separation of a mixture of pesticides by 2D-TLC on two-adsorbentlayer Multi-K SC5 plate, in J. Liq. Chromatogr. Relat. Technol. with permission of Marcel Dekker, Inc.

General classification of the modes of thin-layer chromatography (TLC) is based on the chemical nature of the stationary and mobile phases. Three types of TLC are widely recognized as different modes adsorption TLC, normal-phase TLC, and reversed-phase (RP)/TLC. 

Similarly to dye standards, drug standards (3,4-methylenedioxy-Af-methylamphetamine, lysergic acid diethylamide, flunitrazepam) were resolved on a normal-phase TLC plate using chloroform/methanol (9 1). After drying, LIAD/ESI analysis was performed using the same procedure as for dye standards. All drugs were detected in positive-ion mode as [M+H]+ ions [54]. 

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