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. Food. Biochem. 45, e13764 (2021). HPTLC of L-arabinose, D-fructose, D-fucose, D-galactose, D-glucose, D-mannose, D-rhamnose, D-xylose in the roots of Sechium edule on silica gel with chloroform - n-butanol - methanol - water - acetic acid 9:15:10:3:3. Detection by spraying with 5 % sulfuric acid in methanol containing 0.1 % orcinol, followed by heating at 80 °C for 5-10 min.

J. Food. Biochem. 45, e13608 (2022). HPTLC of kaempferol-3-O-β-D-glucoside in florets of Brassica oleracea on silica gel with toluene: acetone: formic acid 15:5:1. Quantitative determination by absorbance measurement at 240 nm. The hRF value for kaempferol-3-O-β-D-glucoside was 40.

J. Food. Biochem. 46, e13855 (2022). HPTLC of Amomum subulatum dry fruits on silica gel with toluene - ethyl acetate - methanol - formic acid 14:6:2:1. Qualitative identification under UV light at 254 and 366 nm. 

Front. Pharmacol. 13, 925298 (2022). HPTLC of milk thistle on silica gel with toluene - ethyl formate - formic acid 8:10:1. Detection by dipping in NP reagent and subsequently in PEG reagent, followed by heating at 100 °C for 5 min. Qualitative analysis under UV light at 254 and 366 nm. HPTLC of alkylamides in coneflower on silica gel with ethyl acetate - ethyl methyl ketone - water - formic acid 5:3:1. Detection by dipping in NP reagent and subsequently in PEG reagent, followed by heating at 100 °C for 5 min. Qualitative analysis under UV light at 254 and 366 nm. HPTLC of black cohosh on silica gel with toluene - ethyl formate - formic acid 5:3:2. Detection by dipping into sulfuric acid reagent (20 mL of sulfuric acid in 180 mL of methanol), followed by heating at 100 °C for 5 min. 

Anal. Bioanal. Chem. 414, 4481-4495 (2022). HPTLC of selected caffeine-containing standards and beverages (Red Bull, Coca-Cola, coffee, and black tea) on different stationary phases (silica gel, RP- and cyano-) with propan-2-ol - n-heptane - water 7:3:1. Direct surface analysis of the TLC plates with a flowing atmospheric pressure afterglow (FAPA) ambient desorption/ionization source (TLC-FAPA-MS). CN-HPTLC plates were the most efficient stationary phase, resulting in a significantly more intense caffeine signal.

Phytochem. Anal. 33, 564-576 (2022). HPTLC of flavonoids (1), anthocyanin (2) and antioxidant structures in sweet cherry (Prunus avium) on silica gel with ethyl acetate - dichloromethane - formic acid - acetic acid - water 100:25:10:10:11 for (1) and ethyl acetate - formic acid - acetic acid - water 100:11:11:26 for (2). Detection by spraying with natural product reagent/polyethylene glycol 400 (NP/PEG) solution or 0.1 % methanolic DPPH solution. Qualitative analysis under UV light at 366 nm. 

J. Food Compos. Anal. 114, 104763 (2022). HPTLC of ergosterol in wheat, on silica gel with ethyl acetate - petroleum ether 3:2. Quantitative determination by absorbance measurement at 282 nm. The hRF value for ergosterol was 45. Linearity was between 40 and 600 ng/zone. Inter-day and intra-day precisions were below 4 % (n=6). The LOD and LOQ were 11 and 36 ng/zone. Recovery was between 103.7 and 107.7 %.