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.

J. Planar Chromatogr. 20, 267-274 (2007). Comparison of retention factors in pure water, log kw, determined by linear extrapolation and by a numerical method based on Oscik’s equation, and calculated values of log P as hydrophobicity indices for nine homologues s-triazines. The effect of mobile phase pH on solute retention was investigated as well as the effect of mobile and stationary phase properties on chromatographic behavior; 3 different organic modifiers (dioxane, acetonitrile, and tetrahydrofuran) and two stationary phases (RP-8 and RP-18) were used. Correlations of calculated log P values and log kw with carbon number confirm the usefulness of chromatographic techniques for studying the hydrophobicity of organic compounds. TLC on RP-18 with buffer - methanol mixtures in saturated sandwich chambers. Detection under UV light at 254 nm.

J. Chromatogr. A 1458, 136–144, (2016). The soil-water partition coefficient normalized to the organic carbon content (KOC) influences the fate of organic compounds in the environment. This paper proposes a RP-TLC method for KOC determination as a simpler, yet equally accurate method as the official HPLC method. TLC on different systems, including RP-18 and cyano phases developed with methanol – water and acetonitrile – water mixtures. 50 different compounds such as phenols, benzodiazepines, triazine herbicides, and polyaromatic hydrocarbons were selected. A calibration set of 29 compounds with known logKOC values was used to build simple univariate calibrations, Principal Component Regression (PCR) and Partial Least Squares (PLS) models between logKOC and TLC retention parameters. The models exhibit good statistical performance and indicate that the cyano phase contributes better to logKOC modeling than the RP-18 phase. Comparison of the proposed TLC methods, the official HPLC method, and four in silico estimation approaches by using the non-parametric Sum of Ranking Differences(SRD) approach. The best estimations of logKOC values were achieved by simple univariate calibration of TLC retention data from cyano phase developed with 40–50 % methanol. In a Linear Solvation Energy Relationship study it was found that the more polar cyano phase in combination with methanol – water mixtures is the key to better modeling of logKOC through significant diminishing of dipolar and proton accepting influence of the mobile phase as well as enhancing molar refractivity in excess of the chromatographic systems.

Phytochemistry 28, 87-981 (1989). TLC of pisatin and maackiain on silica with chloroform - methanol 4:1. Detection with vanillin - HCl reagent. Determination of RM: TLC on RP-18 254 plates activated by heating at 120°C for 15 min. with acetonitrile - water 13:7. Visualization under UV and by exposing to iodine vapor.

J. Chromatogr. 543, 195-2000 (1991). Measurement of the RM values of arylsulfonylalkanoic and arylsulfonylcycloalkane carboxylic acids by TLC on polyamide. Analysis of the RM vs. Rekker hydrophobicity relation. Excellent correlations, esp. within strictly congeneric sub-series, were established.

Acta Chromatographica 1, 81-90 (1992). Introduction of a new thermodynamic definition of the Rf coefficient and furnish of empirical evidence to support it. Concept is the mental division of the multicomponent mobile phases into the individual liquid moieties. Practical example: Solute : methyl undecyl ketone; stationary phases : RP-2, RP-8, RP-18; mobile phases : methanol : water, binary mixtures in varying proportions.