J Chromatogr A 1653, 462442 (2021). Samples were peptides obtained through tryptic hydrolysis of the 5 most abundant milk proteins: α-lactalbumin (α-LA), β-lactoglobulin (β-LG), α-, β- and κ-casein (CA). As standards, synthetic whey and pea (Pisum sativum, Fabaceae) peptides (selected based on the in silico tryptic digest of α-LA, β-LG, legumin A, and vicilin with one or zero miscleavages) were only used in the last assay for prediction of the RF values of peptides with known amino-acid (AA) sequences. Two-dimensional HPTLC on silica gel (pre-washed with methanol and activated 10 min at 100°), first with basic mobile phase sec-butanol – pyridine – ammonia – water 39:34:10:26, and (after 12h drying) in the orthogonal direction with acidic mobile phase sec-butanol – pyridine – acetic acid – water 11:8:2:5. Derivatization for peptides and proteins by immersion into fluorescamine (0.05 % in acetone); visualization under UV 254 nm and 365 nm. Computer-assisted determination of the x- and y-coordinates of the derivatized zones. Repeatability (n=8) of the 2D-HPTLC was statistically tested with the Kolmogorov-Smirnov test for normal distribution and with Dixon’s Q test for outliers. Relative standard deviation (RSD) for the RF values was 12.9 % for the first dimension (y-coordinates) and 16.5 % for the second dimension (x-coordinates). According to their higher intensity and sharpness, 15 – 20 detected zones from each protein hydrolyzate were selected, manually scraped from the derivatized layer, dissolved in formic acid solution (0.1 % in acetonitrile – water 3:2), mixed with an equal volume of matrix (dihydroxybenzoic acid 2 % in acetonitrile – water 3:7), crystallized on air on a ground steel target, before being desorbed by the laser beam of the MALDI-TOF-MS/MS (matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry). Direct hyphenation of HPTLC to MS was not performed, to avoid zone diffusion during plate coating with the matrix and to circumvent the stronger binding of polar peptides on the layer.  The MS spectra were acquired in positive reflector mode in m/z range 340 – 4000 (10 – 2500 for fragments), using an external peptide as calibration standard. Identification of 51 from the 85 selected peptides according to AA sequences was performed, using software programs allowing m/z calculation of protein fragments and estimation of cleavage sites. Correlation of the retention behaviour of the peptides with their properties (molecular weight MW, isoelectric point IEP, charges, polarity) was tested with Student’s two-sided t-test after calculation of Pearson’s correlation coefficients. The correlation was significant with IEP, percentages of anionic AA and of non-polar AA; but not with the following properties: MW, percentages of cationic AA and of uncharged polar AA. Finally, based on the correlation results, regression formulas were found to calculate the x- and y-coordinates of any known peptide from the percentage of non-polar AA (or vice-versa). The prediction power of these formulas was verified by repeating the complete 2D-HPTLC-MS experiment with the standard peptides of whey and of peas, and measuring the absolute and relative deviations between the actual x- and y-coordinates and the predicted values. The absolute deviations were higher in the lower RF zones. The average, relative RF value deviations (range 22.1 – 25.7 %) were not different between whey and pea peptides.

J. Liq. Chromatogr. Relat. Technol. 44, 820-828 (2021). HPTLC of Gentiana extracts from in vitro cultures on silica gel with acetate - methanol - water 4:1:1 in sandwich mode. Detection under UV light at 254 nm and fluorescence at 312 nm (emission above 370 nm). Principal component analysis (PCA), hierarchical cluster analysis and the novel proposal—nonnegative PCA was performed to identify common and distinct features.

J Chromatogr Sci, 60 (4), 372-386 (2022). Investigation of the dual retention mechanism in TLC taking place on three stationary phases of different polarity (C-18, silica gel and DIOL)  using binary mobile phases composed of acetonitrile as the main component and water, or methanol as a modifier. The test analytes were 12 compounds of pharmaceutical importance and considerably different chemical structure, i.e. the imidazoline and serotonin receptor ligands, and their related compounds. Determination of retention of each analyte in each investigated chromatographic system in a wide enough range of the mobile phase composition, with volume fraction of the mobile phase modifier ranging from 0.10 to 0.90. Calculation of the exact turning point values as a proof of occurrence of the reversed-phase hydrophilic interaction chromatography (HILIC/RP) retention mechanism based on the multimodal retention model. Analysis of the dual retention mode with the use of the volume fraction of the mobile phase modifier, the total polarity and the total solubility models, allowing the dual (HILIC/RP) retention mechanism for the DIOL, C-18 and silica gel stationary phase to be confirmed. The observed retention mechanism was more complicated than the dual HILIC/RP one in the case of the DIOL stationary phase and acetonitrile/methanol mobile phase.

Part II – is silica gel a reliable adsorbent for lipophilicity estimation? J. Planar Chromatogr. 25, 5-9 (2012). TLC of 35 simple compounds with known literature lipophilicity on silica gel with nine concentrations of six modifiers: acetone, dioxane, ethyl acetate, methylethylketone, propan-2-ol, and tetrahydrofuran as mobile phases. Different approaches for lipophilicity determination such as single TLC run, Soczewiñski-Wachtmeister equation coefficients, principal component analysis (PCA) of the retention matrix, and PARAFAC on a three-way array were applied.

J. Chromatogr. 435, 397-416 (1988). Study of the formation of multiple fronts when pure liquids such as methanol and heptane and multi-component liquids such as ethanol - toluene mixtures flow through dry TLC layers of silica or octadecyl-silica. Measurement of the dynamics, and explanation of the formation and motion by using a model.

J. Planar Chromatogr. 3, 389-396 (1990). Forced flow development (OPLC) was used to determine the porosity, permeability, and apparent average particle size of commercially manufactured TLC plates and Empore sheets. Compared with columns, layers exhibit smaller values for the total porosity (eT - 0.69) and interstitial porosity (e U - 0.42).

Chromatographia 34, 431-432 (1992). Reverse-phase TLC of porphyrin ether glycerides on RP-18 silica with acetone - methanol 1:1, and paraffin oil - impregnated silica with acetone - methanol 1:1. Also HPLC. Supplementary physico-chemical characteristics are given for the compounds.

Part I. Linearly increasing development distances. J. Planar Chromatogr. 8, 279 - 283 (1995). Determination of the value RFn, the retention factor after the nth development step (i.e. the ratio of the total migration distance of the component during consecutive development steps to the chromatographic distance of the last development step). The zone width dn of a given spot (after the nth step) is also predicted. The elaborated models are supported with experimental results. - TLC and HPTLC of mixtures of furocoumarin isomers, cannabinoids, and poppy alkaloids (isopimpinellin, xanthotoxin, bergapten, psoralen, angelicin; cannabigerol, cannabichromene, cannabidiol; morphine, codeine, narcotoline, thebaine, papaverine, narcotine) on silica with chloroform and toluene as monocomponent mobile phases for furocoumarins and cannabinoids, resp. chromatography of poppy alkaloids was performed with ethyl acetate - acetone - hexane - methanol - dichloromethane - diethylamine 113:113:226:19:19:1. Detection and evaluation under UV 313 nm for furocoumarin isomers, at 200 nm for cannabinoids, and at 280 nm for alkaloids.