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, 543-548 (2021). HPTLC of mangiferin (1) and berberine (2) on silica gel with toluene - acetone - formic acid 7:11:2. Quantitative determination by absorbance measurement at 261 nm. The hRF values for (1) and (2) were 39 and 80, respectively. Linearity was between 400 and 800 ng/zone for (1) and 100 and 500 ng/zone for (2). Interday and intra-day precisions were below 2 % (n=5). The LOD and LOQ were 26 and 79 ng/zone for (1) and 19 and 18 and 56 ng/zone for (2), respectively. Average recovery was 101.2 % for (1) and 101.0 % for (2). The effect of various forced degradation conditions was observed.

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). 

J. Planar Chromatogr. 34, 503-512 (2021). HPTLC of β-acetoxyisovalerylalkannin (1), acetylshikonin (2) and β,β’-dimethylacrylalkannin (3) in Arnebia guttata on silica gel with petroleum ether (60-90°C) - xylene - ethyl acetate - formic acid 16:6:1:2. Quantitative determination by absorbance measurement at 522 nm. The hRF values for (1) to (3) were 31, 46 and 64. Linearity was between 200 and 1200 ng/zone for (1), 76 and 760 ng/zone for (2) and 201 and 1206 ng/zone for (3). Interday and intra-day precisions were below 5 % (n=6). The LOD and LOQ were 38 and 125 ng/zone for (1) and (3) and 50 and 167 ng/zone for (2). Average recovery was 100.7 % for (1), 98.9 % for (2) and 100.1 % for (3). 

J Chromatogr A, 1641, 462334 (2021). Validation of a newly built (using 3D-printing) and newly configurated on-surface multi-purpose autosampler, called “autoTLC−LC−MS system”, developed for orthogonal hyphenation of normal phase HPTLC with reversed phase HPLC and high-resolution MS. Details and protocols are given for the construction, installation and numerical control software programming of this autosampler. HPTLC of antibiotics cefoperazone (third-generation cephalosporin), clindamycin (lincosamide), erythromycin A (macrolide), ipronidazole (nitro-imidazole), nafcillin (penam), sulfaquinoxaline (sulphonamide), tiamulin (pleuromutilin), and trimethoprim (DHFR inhibitor) on silica gel without development. Bioassay with Bacillus subtilis: bacterial suspension was sprayed onto the plate, which was  horizontally incubated for 2 h at 37°C in a humid box; afterwards, the plate was sprayed with 0.2% MTT solution, incubated again for 30 min at 37°C, dried for 10 min at 50°C, and documented under white light. The image was uploaded as a template in the updated TLC–MS managing software, so that by clicking on the zones of the image showing antibacterial activity, the corresponding zones of the untreated plate, placed on a newly designed plate holder, were sequentially eluted by the round elution head of the automatic sampler into the RP-18 endcapped HPLC monolithic column connected to a Quadrupole-Orbitrap mass spectrometer. For the elution from the plate and HPLC separation, a gradient was used (flow rate 0.2 - 0.5 mL/min, depending on the step), with different proportions of two mobile phases: A) 0.1 % formic acid and 4 mM ammonium formate in water; B) 0.1 % formic acid and 4 mM ammonium formate in methanol. After separation in the column, antibiotics directly underwent electrospray ionization in positive mode (voltage 3.5 kV, capillary temperature 320 °C, probe heater temperature 350 °C) and were detected by HRMS. For validation, the achieved ranges were 2.1–14.1 % for intra-day and 2.5–16.1 % for inter-day precisions.

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.