J. Planar Chromatogr. 34, 521-530 (2021). HPTLC of piperine in Piper nigrum on silica gel with toluene - ethyl acetate 3:2. Quantitative determination by absorbance measurement at 254 nm. The hRF value for piperine was 63. Linearity was between 200 and 1000 ng/zone. Interday and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 611 and 1778 ng/zone, respectively. Average recovery was 98.3 %.

J. Planar Chromatogr. 34, 559-560 (2021). HPTLC fingerprint of Ginkgo biloba finished products on silica gel with n-butyl acetate - methanol - water - formic acid 15:4:2:2. Detection by dipping into anisaldehyde reagent (1 mL of p-anisaldehyde in 200 mL of a mixture of methanol, acetic acid and sulphuric acid 17:2:1). Qualitative identification under UV light at 254 nm and 366 nm. 

J. Planar Chromatogr. 34, 531-542 (2021). HPTLC of betulinic acid (1), β‑sitosterol (2) and lupeol (3) in fruits, leaves, root and stem bark of Dillenia pentagyna on silica gel with petroleum ether - ethyl acetate - acetonitrile 82:18:1. Detection by dipping into anisaldehyde sulfuric acid reagent, followed by heating at 105 °C for 5 min. Quantitative determination by absorbance measurement at 580 nm. The hRF values for (1) to (3) were 17, 23 and 36. Linearity was between 120 and 440 ng/zone for (1), 200 and 1000 ng/zone for (2) and 60 and 220 ng/zone for (3). Interday and intra-day precisions were below 2 % (n=5). The LOD and LOQ were 91 and 276 ng/zone for (1), 304 and 921 ng/zone for (2) and 41 and 125 ng/zone for (3), respectively. Average recovery was 100.7 % for (1), 101.7 % for (2) and 102.0 % for (3). 

J. Planar Chromatogr. 34, 493-502 (2021). HPTLC of quercetin (1), beta-sitosterol (2), piperine (3), gallic acid (4) and resveratrol (5) in Krishnadi Churna on silica gel with toluene - chloroform - methanol 4:4:1 for (3), toluene - ethyl acetate - ethanol - methanol - formic acid 20:15:10:5:1 for (4), toluene - ethyl acetate - methanol - formic acid 50:40:10:2 for (1) and toluene - ethyl acetate - methanol - formic acid 60:30:10:3 for (2) and (5). Quantitative determination by absorbance measurement at 366 nm. The hRF values for (1) to (5) were 52 for (1), 64 for (2), 77 for (3), 61 for (4) and 45 for (5). Linearity was between 2 and 14 µg/mL for (1), (2) and (5), 1 and 18 µg/mL for (3) and 3 and 15 µg/mL for (4). The LOD and LOQ were 3 and 8 µg/zone for (1), 2 and 6 µg/zone for (2), 5 and 16 ng/zone for (3), 8 and 3 µg/zone for (4) and 8 and 3 µg/zone for (5). Average recovery was 99.2 % for (1), 98.4 % for (2), 98.6 % for (3), 98.9 % for (4) and 99.1 % for (5). 

Journal of Chromatography B, 1184, 122956 (2021). Test for acetyl- and butyrylcholinesterase (AChE and BChE) inhibition without development of piperin (standard inhibitor of AChE and BChE) and ethanol – water (3:2) extracts of Iranian plants, on HPTLC silica gel prewashed twice with methanol – water 3:2 and dried 60 min at 120°C. After sample application the plate was immersed (speed 3.5 cm/s, time 2 s) into enzyme solution (6.6 units/mL AChE or 3.3 units/mL BChE in TRIS buffer 0.05 M, with bovine serum albumin 0.1 %, pH 7.8), incubation 25 min at 37°C and immersion (speed 3.5 cm/s, time 1 s) into chromogenic substrate solution (α-naphthyl acetate 0.1 % and Fast Blue salt B 0.2 % in ethanol – water, 1:2). Seven mobile phases were tested for the active samples. Best separation was obtained with toluene – ethyl acetate – formic acid – water 4:16:3:2 and with toluene – ethyl acetate – methanol 6:3:1. Before enzymatic assay, plates developed with acidic mobile phases were neutralized by spraying 3 mL citrate phosphate buffer (Na2HPO4 8 %, citric acid q.s. ad pH 7.5) followed by 10 min of automatic drying. Enzymatic assay was performed using a piezoelectric spraying device: a) pre-wetting by spraying 1 mL TRIS buffer (0.05 M, pH 7.8); b) spraying 3 mL of the enzyme solution; c) incubation 25 min in a humid box at 37°C; d) spraying 0.5 mL substrate solution; e) 5 min drying at room temperature, and then 10 min of automatic drying. By spraying, zone shift and zone diffusion, which occurred with plate immersion, were avoided. For development control, derivatization was done by piezoelectrically spraying 4 mL of sulfuric anisaldehyde reagent (anisaldehyde – sulfuric acid – acetic acid – methanol, 1:10:20:170), followed by heating 3 min at 110°C. For identification of zones of interest, direct elution with methanol from underivatized HPTLC plates through a TLC-MS interface directly to a MS. Identified zones were 3-O-acetyl-β-boswellic acid (triterpenoid) from Boswellia carteri gum-resin (Burseraceae), pimpinellin and psoralen (furocoumarins) from Heracleum persicum flowers (Apiaceae), oleuropein (seco-iridoid) from Olea europaea leaves (Oleaceae), harmine, harmaline, vasicine, deoxyvasine (alkaloids) from Peganum harmala seeds (Zygophyllaceae), costic acid (sesquiterpene) from Nardostachys jatamansi hypocotyl (Valerianaceae), elaidic, linoleic, palmitic, palmitoleic acids (fatty acids) from Pistacia atlantica fruits (Anacardiaceae).

J Chromatogr. A, 1652, 462377 (2021). Samples were vanilla tinctures, water − ethanol − ethyl acetate 1:1:1 extracts of vanilla-flavored food products and of natural Vanilla sp. (Orchidaceae) pods, oleoresin, paste and powders, as well as calibration standards of vanillin (1) and ethylvanillin (2). HPTLC on silica gel with n-hexane – ethyl acetate 1:1 for profiling, 3:2 for quantification. Other mobile phases were also tested and given in the supplement. Compounds (1) and (2) (hRF 68 and 82, respectively) were quantified by absorbance densitometry (at maximal wavelength 310 nm, deuterium lamp, scanning speed 10mm/s). Contents were found to be between 1 μg/g and 36 mg/g for (1) and null for (2) except in one tincture (62 µg/mL). Derivatizations performed for five assays: A) to detect radical scavengers, immersion (speed 3 cm/s, time 5 s) into DPPH• (0.5 mM in methanol), followed by drying for 90 s at room temperature and 30 s at 60 °C; B) to detect activity against Gram-negative bacteria, immersion (speed 2 cm/s, time 3 s) into Aliivibrio fischeri suspension, followed by recording the bioluminescence; C) to detect activity against Gram-positive bacteria, immersion (speed 3.5 cm/s, time 6 s) into Bacillus subtilis, followed by incubation 2 h at 37 °C, immersion in MTT solution, incubation for 30 min at 37 °C and heating for 5 min at 50 °C; D) to detect acetylcholinesterase (AChE) inhibitors, immersion (speed 2.5 cm/s, time 2 s) into AChE solution (666 units in TRIS buffer 0.05M, with bovine serum albumin 0.1 %, pH 7.8), incubation for 25 min at 37 °C and immersion into substrate solution (α-naphthyl acetate 0.1 % and Fast Blue salt B 0.18 % in ethanol – water, 1:2; E) to detect tyrosinase inhibitors, spraying with enzyme solution (400 unit/mL, in phosphate buffer 0.02 M, pH 6.8), followed by 2 min drying, immersion into substrate levodopa (18 mM in phosphate buffer, pH 6.8), 10 min incubation at room temperature and drying. For identification, zones of interest were transferred with methanol from underivatized HPTLC layer through a TLC-MS interface and a filter frit directly to a Quadrupole-Orbitrap MS (heated electrospray ionization, probe heater at 270°C, spray voltage 3.5kV, lock masses acetic acid for negative, dibutyl phthalate for positive ionization, mode full HR-MS scan in m/z range 50–750). Afterwards, the following substances assigned by MS were confirmed by using HPTLC comparison with standards: (1) and (2), vanillyl alcohol, vanillic acid, ethyl vanillyl ether, coumarin, 4-hydroxybenzoic acid, 4-methoxybenzoic acid, 4-hydroxybenzaldehyde, 4-allyl benzoic acid, oleamide, triacetin.

Chromatography Research International 2014, 626801 (2014). HPTLC of extracts of Gymnema sylvestre (Apocynaceae) in tablets, as well as standards for calibration, on silica gel (prewashed with methanol and activated at 120°C for 15 min) with toluene – ethyl acetate – methanol 65:25:14. Derivatization by immersing into sulfuric acid (5 % in methanol) and heating at 110°C for 4 min. Densitometric evaluation within 25 min in absorbance mode at 423 nm, which was the optimal wavelength for quantifying simultaneously the triterpenoid gymnemagenin (hRF 27, linearity range 100–1200 ng/band, LOD 32 ng/band, LOQ 53 ng/band) and β-sitosterol (hRF 78, linearity range 200–1200 ng/band, LOD 97 ng/band, LOQ 159 ng/band). Interday and intra-day precisions as well as recovery rates provided relative deviation values below 1 %. This method was used to determine the analyte contents in the tablets (0.041 % gymnemagenin and 0.138 % β-sitosterol), as well as to confirm the stability of the analytes in solution at room temperature after 48h.   

Frontiers in Marine Science 7, 266 (2020). Methanol extracts from marine sponge Haliclona cnidata (Chalinidae) submitted to different stresses (antibiotics and/or darkness) were separated on HPTLC silica gel with an automated 15-step gradient based on methanol, dichloromethane and n-hexane. Bioluminescence was recorded after immersing the HPTLC plates into Aliivibrio fischeri suspension. Antibacterial activity and quorum sensing enhancement were analysed on software, and Pearson’s similarity coefficient was applied to generate similarity matrices for cluster analysis (UPGMA, Unweighted Pair Group Method with Arithmetic Mean). Only slight differences were observed, especially in QS enhanced zones in stressed vs. control cultures.