J Chromatogr A, 1598, 196-208 (2019). Samples were acertone – water 7:3 extracts of Reynoutria japonica (= Fallopia japonica = Polygonum cuspidatum) rhizomes (Polygonaceae) as well as flavanols (catechin, epicatechin, epicatechin gallate, epigallocatechin gallate) and procyanidins (A1, A2, B1–B3 and C1) as standards. HPTLC on diol silica gel with: (MP1) acetonitrile; (MP2) ethyl acetate; (MP3) ethyl acetate – formic acid 90:1; or (MP4) toluene – acetone – formic acid 3:6:1. Prewashing of the plates with mobile phase was needed only with MP1. After drying under hot air stream, derivatization by automated immersion into DMACA (dimethylaminocinnamaldehyde) – HCl solution (60 mg in 13 mL HCl + 187 mL ethanol), followed by 2 min drying under warm air stream. Visualization under UV 366 nm and white light, densitometry in absorption/reflectance mode at 280 nm (before derivatization) or 655 nm (10 min after derivatization). Bands of interest were eluted from layer with acetonitrile – methanol 2:1 through the oval elution head of a TLC-MS interface pump, into a RP18 liquid chromatography guard column, followed by a quadrupole ion trap mass spectrometer. Full scan mass spectra (m/z 150–2000) were recorded in negative mode using electrospray ionization (spray voltage 4 kV, capillary temperature 200◦C, capillary voltage -38.8 V). Monomer gallates to hexamer gallates were detected, separated with MP1, MP2 or MP4; monomers and oligomers (not gallates) were separated with MP3 (up to hexamers) and with MP1 and MP4 (up to decamers). Moreover, enhanced absorption of standards was also studied for influence of mobile phases, of layers (diol silica gel vs. classical silica gel vs. cellulose) and of luminosity (light vs. dark).

J Chromatogr A, 1598, 209-215 (2019). Samples were methanolic extracts of honeys from Robinia pseudoacacia (Fabaceae) or from Tilia spp. (Tiliaceae / Malvaceae), as well as standards: abscisic acid (sesquiterpenoid), caffeic acid, chlorogenic acid, cinnamic acid, ferulic acid (phenolic acids), chrysin (flavone), myricetin, quercetin (flavonols), naringenin (flavanone). HPTLC on silica gel with chloroform – ethyl acetate – formic acid 5:4:1. Visualization under UV 254 nm and 366 nm, before and after derivatization by spraying with aluminium chloride (1 % in methanol), which rendered flavone bands bright yellow. Quantitative absorbance measuremet by densitometry at 366 nm. Linearity was in the range of 12,5–200 µg/mL for most standards (25–400 µg/mL for chrysin). Main differences observed in samples: 1) abscisic acid (hRF 56) and chrysin (hRF 82) were present only in Tilia honey samples, quercetin (hRF 55) only in Robinia honey; 2) ferulic acid (hRF 60) was the most prominent blue band in Tilia honey samples (1.35–18.73 g/kg of honey), and less intense in Robinia honey (0–1.24 g/kg of honey). Multivariate analysis was performed in two different ways with principal component analysis.

Antioxidants, 10(1), 117 (2019). Samples were methanolic extracts of Camellia sinensis leaves or commercial black, white or green tea powdered extracts (Theaceae), as well as standards of caffeine (methylxanthine alkaloid), of flavonols (quercetin, rutin) and of flavanols (catechin, catechin-gallate, epicatechin, epicatechin-gallat, epigallocatechin, epigallocatechin-gallate, gallocatechin, and the thearubigin theaflavin). HPTLC on RP18-W phase (with classical irregular particles (SP1) vs. LiChrospher phase with spherical particles (SP2)), prewashed with methanol – water 4:1 and dried 20 min at 110 °C, developed with citric acid 0,295 % in acetonitrile – water 3:10 for SP1, with citric acid 0,17 % in acetonitrile – water 1:2 for SP2. Visualization under white light, UV 254 nm and 366 nm. Absorbance densitometry was performed at UV 275 nm (deuterium lamp). Derivatization with A) Fast Blue B salt reagent followed by 3 min heating at 100 °C, and by absorbance densitometry at 546 nm for flavanols (mercury lamp); B) natural product reagent (on the same plate), followed by fluorescence densitometry of flavonols at FLD 366/>400 nm (mercury lamp); C) anisaldehyde sulfuric acid reagent, followed by 2 min heating at 110 °C, to detect all flavonoids. Effect-directed analysis was performed using piezoelectric spraying: A) for free radical (DPPH•) scavengers (vs. gallic acid as positive control); B) for activity against Gram-negative Aliivibrio fischeri (bioluminescence assay, vs. caffeine) or Gram-positive Bacillus subtilis (vs. tetracycline); C) for enzymatic inhibition of acetyl-cholinesterase, α- and β-glucosidase, β-glucuronidase, tyrosinase (vs. rivastigmine, acarbose, imidazole, D–saccharolactone and kojic acid, respectively). When SP2 was used, previous neutralization was required through spraying of sodium bicarbonate buffer (2.5 %, pH 8). AChE inhibition assay was performed with indoxyl acetate (0.1 % in ethanol) as substrate, sprayed before the enzyme. After incubation (30min at 37°C), inhibition bands appeared indigo or blue under white light, but the substrate coloured theaflavin in yellow.

J Chromatogr A, 1605, 460371 (2019). HPTLC of toluene – ethyl acetate extracts of Primula boveana leaves and of P. veris (Primulaceae) on silica gel with n-hexane – ethyl acetate 7:3. Visualization under white light, UV 254 nm and 366 nm. Derivatization by spraying with anisaldehyde sulfuric acid reagent, followed by heating for 4 min at 105 °C. Effect-directed analysis: A) for activity against Gram-negative (Aliivibrio fischeri bioluminescence assay) or Gram-positive bacteria (Bacillus subtilis bioassay) using automated immersion; B) for enzymatic inhibition (acetyl- and butyryl-cholinesterase) using piezoelectric spraying, with rivastigmine as standard, and absorbance spectra (500 nm) for P. boveana active bands measured by inverse scanning. Active bands were eluted from the untreated layer with methanol through the oval elution head of a TLC-MS interface pump, into a quadrupole-Orbitrap mass spectrometer to record full scan mass spectra (m/z 100−1000) using electrospray ionization (ESI voltage 3.5kV for P. boveana, -3kV for P. veris, source temperature 250°C). With the further help of preparative HPLC – NMR, they were identified as linoleic and linolenic acids in P. veris, and as flavone and its derivatives: hydroxyflavone, methoxyflavone and zapotin, in P. boveana.

Molecules, 26 (5), 1468 (2021). Summary: Samples were fortified extracts produced with iPowder technology (involving spray-drying of a rich first extract on a new batch of the same plant) from following plants: Camellia sinensis final bud and two leaves (Theaceae), Cynara scolumus leaves and Echinacea purpurea roots (Asteraceae), Eleutherococcus senticosus roots (Araliaceae), Equisetum arvense aerial part (Equisetaceae), Eschscholzia californica aerial parts (Papaveraceae), Humulus lupulus cones (Cannabaceae), Ilex paraguariensis leaves (Aquifoliaceae), Melissa officinalis aerial parts and Rosmarinus officinalis leaves (Lamiaceae), Passiflora incarnata aerial part (Passifloraceae), Raphanus sativus var. niger roots (Brassicaceae), Ribes nigrum leaves (Grossulariaceae), Spiraea ulmaria floral tops (Rosaceae), Valeriana officinalis roots (Caprifoliaceae), Vitis vinifera leaves or pomace (Vitaceae). HPTLC on silica gel with 1) ethyl acetate – toluene – formic acid – water 16:4:3:2,  or 2) cyclohexane – ethyl acetate – formic acid 30:19:1. Detection under white light, UV 254 nm and 366 nm. Extract stability after 2 years was also checked through HPTLC. Neutralization by spraying phosphate-citrate buffer, and drying in cold air stream. Effect-directed analysis using automated piezoelectrical spraying: A) for enzymatic inhibition (acetyl-cholinesterase, glucosidase, glucuronidase, tyrosinase); B) for activity against Gram-negative bacteria (Aliivibrio fischeri bioluminescence assay). Active bands of multipotent compounds were eluted from HPTLC layers with methanol through the oval elution head of a TLC-MS interface pump, into a quadrupole-Orbitrap mass spectrometer. Full scan mass spectra (m/z 100−1000) in the positive and negative ionization modes were recorded using heated electrospray ionization (HESI, spray voltage 3.5 kV, capillary temperature 270 °C). By comparison to literature, the following compounds were assigned: caffeine, catechins, carnosol, chlorogenic acid, cynaratriol, dicaffeoylquinic acid, feruloyl quinic acid, gallic acid, linoleic and linolenic acids, oleanic or ursolic acid, rosmarinic acid.

CBS 127, 13-15 (2021). HPTLC of rutin and quercetin in Ginkgo biloba (1), rosmarinic acid in rosemary (2) and oleuropein in olive oil (3) on silica gel with ethyl acetate - formic acid - acetic acid - water 100:11:11:26. Detection by spraying with NP reagent (1 g 2-aminoethyl diphenylborinate in 100 mL methanol) for (1) and (2) or with anisaldehyde reagent (0.5 mL p-anisaldehyde in 85 mL methanol, 10 mL acetic acid and 5 mL sulfuric acid), followed by heating at 100 °C for 3 min. Absorbance measurement at 254 nm and 238 nm for oleuropein and in fluorescence mode at 366>/400 nm for rosmarinic acid. The method showed the application of Quantified Reference Extracts for the identification of plant materials and quantification of markers by HPTLC.

J. Food Biochem. 44, e13137 (2020). HPTLC of kaempferol-3-O-rutinoside (1) and rutin (2) in Musa acuminata Colla on silica gel with ethyl acetate - toluene - formic acid - water 34:5:7:5. Detection by dipping into natural products reagent (0.5 % methanolic solution of 2-aminoethyl diphenylborinate), followed by dipping into a 5 % methanolic polyethylene glycol 400 solution. Qualitative identification under UV light at 366 nm. Radical scavenging activity was studied by dipping into a 0.2% methanolic DPPH* solution. The hRF values for (1) and (2) were 32 and 25, respectively. 

J. Planar Chromatogr. 35, 161-167 (2022). HPTLC of catechin in the seeds of Parkia roxburghiion silica gel with ethyl acetate - acetic acid - formic acid - water 40:4:3:4. Quantitative determination by absorbance measurement at 302 nm. The hRF value for catechin was 61. Interday and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 12 and 37 ng/zone, respectively. Recovery was found in the range of 99.1-99.5 %.