J. Sep. Sci. 43, 105-119 (2020). Review of the role of chromatography for discovering new drugs from natural resources, including the application of TLC and HPTLC in qualitative and quantitative separations of compounds in mixtures. The review also described reverse-phase and 2D chromatography applications.

J. Sep. Sci. 43, 2477-2486 (2020). HPTLC of urea produced by arginase as a bioautographic method for the detection of arginase inhibitors in Myrtus communis on silica gel with ethyl acetate - methanol - water - formic acid 800:100:100:1. Detection by spraying with arginase solution (50 U in 3 mL of a buffer containing Tris–HCl 50 mM, pH 7.5 and 0.1 % of BSA), followed by spraying with 3 mL of L-arginine solution (200 mM, pH 9.7) and incubation at 37 ºC for 60 min. Visualization by spraying with 3 mL of sulfuric acid - phosphoric acid - water 2:7:91 and 2 mL of alpha-isonitrosopropiophenone solution (5% in absolute ethanol) followed by heating at 100 ºC for 1h. The hRF value for the inhibitor N-trans-caffeoyltyramine was 27. Sensitiviy was estimated for the arginase inhibitor Nω-hydroxy-nor-Arginine (nor-NOHA), resulting in a LOD of 0.1 µg/zone.

Phytochem. Anal. 31, 57-67 (2019). HPTLC of gymnemagenin in the leaves of Gymnema sylvestre on silica gel with toluene - chloroform - methanol 5:8:3. Detection by spraying with vanillin sulphuric acid reagent, followed by heating at 110 ºC for 5 min. Quantitative determination by absorbance measurement at 610 nm. The hR_F value for gymnemagenin was 37. Linearity was between 400 and 3000 ng. The LOD and LOQ were 68 and 206 ng, respectively.

Phytochem. Anal. 31, 57-67 (2019). HPTLC profiling of the leaves of Fraxinus excelsior on silica gel with ethyl acetate - water - formic acid 8:1:1. Qualitative identification under UV light at 254 and 366 nm. The hR_F value of chlorogenic acid was 90.

J. Liq. Chromatogr. Relat. Technol. 43, 291-299 (2020). Review of available software and methods for HPTLC image analysis, including preprocessing of data and multivariate treatment of obtained fingerprints. HPTLC fingerprint analysis and quantitative evaluation of HPTLC images for the analysis of food and natural products was also described.

J. Liq. Chromatogr. Relat. Technol. 43, 361-366 (2020). HPTLC of the dried root and rhizome of Rhodiola rosea on silica gel with ethyl acetate - methanol - water 77:13:10. Detection by spraying with 1) a solution of p-anisaldehyde (0.5 mL in 85 mL methanol, 10 mL acetic acid and 5 mL sulfuric acid), followed by heating at 105 ºC for 5-7 min, 2) a solution of 2-isopropyl-5-methylphenol (0.5 g in 95 mL ethanol and 5 mL sulfuric acid), followed by heating at 120 ºC and 3) NP solution (1 g diphenylboryloxyethylamine in 100 mL methanol) and PEG solution (5 g PEG-4000 in 100 mL ethanol). Detection under UV 254 and 366 nm. Effect directed detection was performed using 1) DPPH* radical reagent assay: spraying with 0.2 % 2,2-diphenyl-1-picrylhydrazyl solution in methanol, 2) AChE assay: spraying with the enzyme solution (20 units of AChE and 150 mg BSA in 150 mL 0.05 M TRIS buffer, pH 7.8), follwed by incubation at 37 ºC for 20 min and spraying with 50 mg Fast Blue B salt diluted in 100 mL of water and 3) Bacillus subtilis bioassay: dipping into bacterial suspension for 8 s, followed by incubation at 37 ºC for 17 h and spraying with 0.2 % MTT aqueous solution. The bioautographic tests showed presence of both antioxidants (DPPH assay) and antibacterials (Bacillus subtilis assay) in the methanolic plant extract, however no acetylcholinesterase inhibitors were found. As marker compound, rosavin was detected.

J. Liq. Chromatogr. Relat. Technol. 43, 305-318 (2020). Review of the application of TLC in the evaluation of different biological activities of natural compounds, focusing on antioxidant (using 2,2-diphenyl-1-picrylhydrazyl radical assay and decoloration of beta-carotene), enzymatic (using enzyme inhibition assays), antimicrobial (bioautographic assays) and hormonal (using yeast strains screening) activities.

J. Liq. Chromatogr. Relat. Technol. 43, 344-350 (2020). HPTLC of hydrodistilled Plectranthus amboinicus essential oil on silica gel with n-hexane - ethyl acetate - ethanol 95:3:2. Detection by dipping into anisaldehyde sulfuric acid reagent, followed by heating at 100 ºC for 5 min. HPTLC-bioprofiling was performed using the following assays by dipping the chromatogram into the respective solution, followed by drying, incubation and documentation at white light or measuring bioluminescence: DPPH* radical reagent assay (using a 0.2 mg/mL 2,2-diphenyl-1-picrylhydrazyl solution in methanol), AChE inhibitory assay, tyrosinase inhibitory assay, alpha- and beta-glucosidase inhibitory assays, alpha-amylase inhibitory assay, Gram-negative antimicrobial bioassay (chromatogram immersion into a A. fischeri suspension), and Gram-positive antimicrobial bioassay (chromatogram immersion into a B. subtilis bacterial suspension). Direct analysis in real time mass spectrometry allowed the detection of five bioactive compounds: caryophyllene oxide (hR_F 20), a-humulene (hR_F 26), carvacrol (hR_F 40), methyl carvacrol ether (hR_F 76) and caryophyllene (hR_F 84).