J. Chromatogr. Sci. 43 (10), 542-548 (2005). The usefulness of TLC as an efficient measuring technique in the studies of oscillatory trans-enantiomerization of profens from the S to the R configuration (and vice versa) during their storage as 70 % ethanol solutions is demonstrated in the literature. S-(+)-ibuprofen, S-(+)-naproxen, and S,R-(±)-2-phenylpropionic acid are utilized as the test profens. It is proven possible to show oscillatory instability with the racemic S,R-(±)-2-phenylpropionic acid also. Correctness of the TLC assessment is successfully confirmed by means of polarimetry. Upon these preliminary results, it is concluded that the most probable mechanism might embrace the keto-enol tautomerism because of a convenient migration of the proton from one moiety of the profen molecule to another in an aqueous medium. To indirectly verify this hypothesis, profens are stored in dichloromethane, deliberately hampering their ability to dissociate and to re-structure. It is shown that the non-aqueous solvent considerably suppresses, although they do not completely eradicate, the oscillatory trans-enantiomerization of profens. In view of these findings, the reports which claim a predominant therapeutic potential of the respective S-profens become less convincing and certainly need reconsideration.

J. Planar Chromatogr. 3, 264-268 (1990). Comparison of various diluent + modifier - silica systems for 57 solutes by graphical methods; i.e. RM vs. eluent spectra plotted on the basis of equieluotropic series of RM1 vs. RM2 correlations. The spread of points was largest when the binary eluents differed in both diluent and modifier. The differentiated selectivity characteristics of the diluent - modifier binaries demonstrate good prospects for computer-aided selection of an optimal system for TLC analysis of a given set of compounds from the data base.

J. Chromatogr. 593, 329-337 (1992). Study of the retention behavior of 14 closely related coumarins in normal-phase TLC and HPLC with the aim of testing the suitability of TLC as a pre assay of HPLC when the optimization of the mobile phase has been carried out according to the PRISMA system. Measurement of the retention in TLC and HPLC at 37 and 13 selective points, respectively. Two and three dimensional evaluations of capacity factor k' against selectivity points showed similar retention behavior for the coumarins in TLC and HPLC. Discussion of the dependency of k' on the change in solvent strength.

J. Planar Chromatogr. 8, 341 - 345 (1995). Description of the vertical and horizontal correlations between the hRf values of apolar compounds and the selectivity points at constant and different solvent strength levels in saturated TLC chambers. - HPTLC of furocoumarins on silica, of anthraquinones on silica CN-phase and of opium alkaloids on NH2 silica with multicomponent solvent systems (dichloromethane, tetrahydrofuran, chloroform, n-hexane; ether, tetrahydrofuran, ethyl acetate, hexane; ethyl acetate, acetone, dichloromethane, hexane, methanol). - Anthraquinone aglycones: rhein, aloe-emodin, emodin, physicon, chrysophanic acid; furocoumarin isomers: bergaptene, iso-bergaptene, shondin, pimpinellin, iso-pimpinellin, xanthotoxin, angelicin, psoralen; opium alkaloids: morphine, codeine, narcotoline, thebaine, papaverine, narcotine. Densitometry at 425 nm (anthraquinones), or 280 nm (opium alkaloids).

J. Liq. Chrom. & Rel. Technol. 22, 1429-1441 (1999). Presentation of a new mathematical model for the optimization of the eluent composition used for the separation of a mixture of 1,4-benzodiazepines. HPTLC of 1-chlordiazepoxide, oxazepam, nitrazepam, medazepam and diazepam on silica gel with chloroform - acetone - isopropanol mixtures in different compositions. Quantitation by densitometry in reflectance mode at 254 nm.

J. Planar Chromatogr. 27, 1999-2020 (2014). HPTLC of methocarbamol in pharmaceutical mixtures with ibuprofen, paracetamol and diclofenac sodium and in the presence of its degradation product guaifenesin on silica gel with chloroform - methanol 47:3. Quantitative determination by absorbance measurement at 264 nm. A chemometric handling of the TLC peak responses involving the convolution of the derivative curves using 8-points sin x i polynomials, allowed the analysis of different mixtures of methocarbamol with enhancing of the regression parameters.

J. Planar Chromatogr. 10, 114-117 (1997). Using the analysis of addictive substances as an example an overview is given of the use of eight different development techniques to illustrate the improvements of the efficiency of thin-layer chromatography. Optical comparison of chromatograms and determination of separation numbers are used to provide information about the separation performance of each system. A comparison has been made of AMD, ADC and normal chamber developments of HPTLC and TLC plates with and without chamber saturation. The separation performance has been investigated using separation numbers according to Geiss and Kaiser. The highest separation number (23.5) was obtained by use of AMD. Separation numbers of approximately 18 were obtained with HPTLC plates. The worst separation numbers (7.7-15) were, as expected, obtained with TLC plates. The improvements in TLC techniques over recent years are emphasized. Substances chromatographed: anthranilic acid, codeine, DMT, etryptamine, morphine, DOB, theobromine, Sudan III.

Acta Chromatographica 20(3), 309-327 (2008). Presentation and discussion of an approach based on the distances to the closest spot and to the top or bottom of the plate in the optimization of two-dimensional thin-layer chromatographic separation. This is different to the method of relying on selection of the two most orthogonal chromatographic systems which best co-operate in the separation, which is mainly achieved by investigating the correlation between hRf values or scoring the distances between the spots. The theory arises from a well-known geometrical problem about equal-spreading of the points inside a unit square, proposing two coefficients, sensitive and insensitive, to complete separation. This is the two-dimensional version of the previously proposed criteria retention uniformity and retention distance, which describes the equal-spreading of the spots in one-dimensional chromatography. The coefficients range from 0 to 1 and their distribution as a random variable is well defined and not affected by the number of separated compounds.