Journal Chromatogr A, 1641, 461727 (2021). HPTLc of an ethanolic maceration of Solidago gigantea roots (Asteraceae) on silica gel with n-hexane – isopropyl acetate – acetone 16:3:1, or n-hexane – isopropyl acetate – acetic acid 40:9:1. With the second mobile phase, acid residues had to be eliminated by 20 min automated drying or by 2 h incubation with potassium hydroxide in the opposite twin trough (followed by 15 min cold air streaming); this latter mobile phase allowed to obtain higher hRF values, but some butyrylcholinesterase (BChE) inhibiting activities were lost. The chromatograms were documented at UV 254 nm and 365 nm and white light before and after A) derivatization with vanillin – sulfuric acid reagent; B) enzymatic reaction by immersion into acetylcholinesterase, BChE, glucosidase and amylase solutions; C) Aliivibrio fischeri and Xanthomonas euvesicatoria bioassays, to detect activity against Gram-negative bacteria; D) Bacillus subtilis bioassay to detect activity against Gram-positive bacteria; E) a new antifungal assay with Fusarium avenaceum. For this assay, the chromatograms were immersed 6 s into the isolated mycelium suspension (diluted to OD600 0.4-0.8) and incubated in a vapor chamber at 21 °C for 48-72 h. Inhibition zones were indicated by the lack of visible white fungal hyphae. An aqueous solution of iodonitrotetrazolium (INT, 1 mg/ml) was sprayed on the plate to enhance the contrast (bright zones on a purple background). Benomyl (a benzimidazole fungicide) was used as positive control. Eight clerodane diterpenes (including kingidiol, hautriwaic lactone, and solidagoic acids A and B) were identified from six multipotent zones by bioassay-guided purification through preparative flash chromatography and HPLC, followed by HRMS and NMR, as well as by HPTLC hyphenated to quadrupole-orbitrap HRMS: A) by eluting with methanol (flow 100 µL/min) the compounds from the plate through the oval elution head of an interface of heated electro-spray ionization (spray voltage 3.5 kV, capillary temperature 270 °C, nitrogen as sheath and auxiliary gas, full scan in negative and positive ionization modes in m/z range 50-750); B) without eluent with a DART interface (Direct Analysis in Real-Time, needle voltage 4 kV, grid voltage 50 V, helium as gas, temperature 500 °C, full scan in positive ionization mode in m/z range 100-750).

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. Planar Chromatogr. 34, 361-366 (2021). HPTLC of 19 iridoids, including ten iridoid glycosides (catalpol, aucubin, ajugol, hastatoside, loganin, geniposide, harpagoside, verbenalin, agnuside, nuzhenide), six secoiridoid glycosides (harpagide, sweroside, swertiamarin, gentiopicroside, oleuropein, amarogentin) and three nonglycosylated iridoids (loganic acid, genipin, valtrate) in samples of Gentiana lutea, Verbena officinalis, Olea europaea and Harpagophytum procumbens on silica gel with nine different mobile phases. Detection by spraying with anisaldehyde reagent, vanillin reagent, sulfuric acid reagent, respectively, followed by heating at 100 °C for 3 min. After derivatizing the plate with Ehrlich’s reagent, the plate was heated at 100 °C for 5 min. Digital images were recorded under UV light at 254 nm and 366 nm. The data is part of a HPTLC database under development for different families of phytochemicals.

Phytochem. Anal. 3078 (2021). HPTLC of thymoquinone on silica gel with cyclohexane - ethyl acetate 9:1 (1) and on RP with ethanol - water 4:1 (2). Quantitative determination by absorbance measurement at 259 nm. The hRF value of thymoquinone was 42 for system 1 and 51 for system 2. Linearity was between 25 and 1000 ng/zone for (1) and 50 and 600 ng/zone for (2). The intermediate precision was below 1 % (n=6) for (1) and (2). The LOD and LOQ were 8 and 25 ng/zone for (1) and 17 and 50 ng/zone for (2), respectively. Recovery rate was between 99.0 % and 100.9 % for (1) and 98.4 % and 101.2 % for (2). Analytical GREEnness (AGREE) scores for the systems were predicted using the AGREE software according to the 12 principles of green analytical chemistry.

Food Chem. 357, 129135 (2021). HPTLC of cinnamon on silica gel with toluene - ethyl acetate - methanol 6:5:3. Nine detection modes were used: 1) white light illumination, 2) UV 366 nm, 3) UV 254 nm, and six different derivatization reagents applied by immersion: 4) primuline reagent (100 mg primuline, 20 mL water and 80 mL acetone), 5) p-anisaldehyde sulfuric acid reagent (1 mL methoxy benzaldehyde, 140 mL methanol, 16 mL acetic acid and 8 mL sulfuric acid), 6) vanillin sulfuric acid reagent (1 g vanillin, 80 mL ethanol and 0.8 mL sulfuric acid), 7) diphenylamine aniline o-phosphoric reagent (2 % each of diphenylamine and aniline in 100 mL isopropanol plus 20 mL o-phosphoric acid), 8) Fast Blue B salt reagent (100 mg Fast Blue B salt in 100 mL ethanol, 70 %) and 9) natural product reagent (1 g 2-aminoethyl diphenyl borate in 100 mL ethanol), followed by heating at 110 °C (5), 120 °C (4, 6) or 140 °C (7, 8) for 3-5 min. Effect-directed profiling was performed through eight different assays: HPTLC–Aliivibrio fischeri bioassay, HPTLC–Bacillus subtilis bioassay, HPTLC–tyrosinase inhibition assay and densitometric evaluation, HPTLC–α–glucosidase and β–glucosidase inhibition assays, HPTLC–AChE and BChE inhibition assays, HPTLC–DPPH assay. Compounds were further characterized by heated electrospray ionization high–resolution mass spectrometry (HESI–HRMS).

J. Food. Sci. 75, 239-243 (2010). HPTLC of tea made of Camellia sinensis on silica gel with chloroform - methanol - water 13:7:1. DPPH bioautography assay by spraying with 2,2-diphenyl-1-picrylhydrazyl (1 mg/mL in ethanol) under dark conditions. Detection under UV light at 254 and 366 nm. 

J. Planar Chromatogr. 33, 609-616 (2020). HPTLC of oleuropein in the leaves of Olea europaea on silica gel with ethyl acetate - methanol - water 16:2:1 (method 1) and on RP-18 phase with ethanol - water 11:9 (method 2). Quantitative determination by absorbance measurement at 200 nm. The hRF values for oleuropein were 47 and 78 for methods (1) and (2), respectively. Linearity was between 200 and 1400 ng/zone for both methods, respectively. Intermediate precision was below 2 % (n=6). The LOD and LOQ were 68 and 203 ng/zone for method (1) and 69 and 206 ng/zone for method (2). Recovery was between 99.7 and 98.2 % for method (1) and 99.7 and 99.3 % for method (2).

J. Planar Chromatogr. 33, 647-661 (2020). HPTLC of empaglifozin (1) and linagliptin (2) on silica gel with chloroform - methanol - ammonia (25 %) 100:10:1. Quantitative determination by absorbance measurement at 225 nm. The hRF values for (1) and (2) were 31 and 71, respectively. Linearity was between 100 and 5000 ng/zone for (1) and 50 and 2500 ng/zone for (2), respectively. Intermediate precision was below 2 % (n=3). The LOD and LOQ were 32 and 97 ng/zone for (1) and 14 and 42 ng/zone for (2), respectively. Average recovery was 100.1 % for (1) and 99.9 % for (2). Comparison with a similar TLC method showed no significant statistical differences.