J. Planar Chromatogr. 35, 383-393 (2022). HPTLC of baicalin in the stem barks of Oroxylum indicum on silica gel with acetone - ethyl acetate - water - formic acid 4:20:1:1. Quantitative determination by absorbance measurement at 318 nm. The hRF value for baicalin was 49. Linearity was between 0.2 and 1.0 µg/zone. Interday and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 56 and 188 ng/zone. Average recovery was 99.2 %.

J. Planar Chromatogr. 35, 229-241 (2022). Review of the advances, limitations and challenges faced by the application of HPTLC for lipidomic analysis. The paper described methods for the separation of phospholipids (PL) and/or sphingolipids (SL) on silica gel HPTLC plates from different samples in lipidomic studies, including matrices and development conditions. HPTLC methods for separating lipid classes and subclasses, combined with semi-quantification by UV‒FL densitometry and mass spectrometry were also described. HPTLC and genetic knockouts was also discussed as an emerging field. 

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.

J. Planar Chromatogr. 35, 273-279 (2022). HPTLC of sweetener saccharin (1), acesulfame-K (2), neohesperidin (3), aspartame (4), stevioside (5), rebaudioside A (6), sucralose (7), and Na-cyclamate (8) in food samples on silica gel with ethyl acetate - methanol - acetic acid 5:1:1. Detection by dipping into the following reagent sequece, followed each by plate heating and image documentation or densitometry: 1) Primuline reagent (100 mg primuline in 20 mL water and 80 mL acetone), followed by solvent evaporation and detection at 366 nm; 2) ninhydrin reagent (0.3 g ninhydrin dissolved in 95 mL isopropyl alcohol and 5 mL glacial acetic acid), followed by heating at 120 °C for 5 min and detection at white light; 3) 2-naphthol sulfuric acid reagent (1 g 2-naphthol dissolved in 90 mL ethanol and 6 mL 50 % sulfuric acid added dropwise), followed by heating at 120 °C for 5 min and detection at white light. Quantification by absorbance measurement at 200 nm for (1), 230 nm for (2), 290 nm for (3), 500 nm for (4) to (7) and 650 nm for (8).  Linearity was between 30 and 600 ng/zone for (5) and (6) and 800 and 1600 ng/zone for (8).   

Molecules 25 (17), E3928 (2020). Samples were curcumin (as standard) and methanolic extracts of Curcuma xanthorrhiza and C. aeruginosa (Zingiberaceae) rhizomes, both separately and in mixtures. Separation on TLC silica gel with chloroform – methanol – formic acid 94:3:3. Densitometry of curcumin (hRF 50) in absorption mode at UV 427 nm. This method was validated with curcumin standard for selectivity (vs. demethoxycurcumin hRF 32), linearity range (250 - 450 ng), LOD (21 ng) and LOQ (69 ng), accuracy and precision. Curcumin contents were between 0.74 and 1.23 % in pure C. xanthorrhiza extracts, but decreased when adulterated with C. aeruginosa.

Plant Cell, Tissue and Organ Culture (PCTOC) 146 (2), 225–236 (2021). Samples were hydro-ethanolic extracts of Musa acuminata and M. balbisiana (Musaceae) plantlets, obtained from in vitro meristem-derived gel cultures with saccharose, temperature or jasmonic acid as elicitors of production of secondary metabolites. HPTLC on silica gel  (RP18W phase for genotoxicity assay) with ethyl acetate – toluene – formic acid – water 34:5:7:5. Evaluation under white light, UV 254 nm and 366 nm. Effect-directed assays (EDA) were performed (by immersion or by automated piezoelectrical spraying) for free radical (DPPH•) scavengers, and, after neutralization, for enzymatic inhibitors (acetyl-cholinesterase, α-glucosidase) and for genotoxicity (SOS response – UMU-C test). For comparison, positive control standards were applied but not developed, before the assays (gallic acid, physostigmine, acarbose, nitroquinoline-1-oxide, respectively). After the first assay, absorbance densitometry was performed through inverse scanning at 546 nm using mercury lamp (fluorescence mode without optical filter). Antioxidant activity was found the highest when cultures were maintained at 20 °C (vs. 15 and 26 °C) and supplemented with saccharose (40-50 g/L) or jasmonic acid (200 µM).

ALTEX - Alternatives to animal experimentation, 38(3), 387-397 (2021). Samples were standards of food contact contaminants with genotoxicity (4-nitroquinoline-1-oxide (NQO), aflatoxin B1, hexachloroethane, nitroso-ethylurea, phenformin, PhIP) or negative controls (alosetron, mannitol), and extracts of coated tin cans (extracted with n-hexane – acetone at 25°C for 16 h or by heating at 60 °C with ethanol 95 % for 240 h). HPTLC on RP18W layer, pretreated to harden the binder by heating 1 h at 120 °C, prewashed with methanol and with ethyl acetate and dried 4 min in cold air stream after each development. Application areas were focused to their upper edges by a two-fold elution with ethyl acetate, followed by 1 min drying in cold air stream. Development with toluene – ethyl acetate 8:5, followed by 5 min drying, neutralization with citrate buffer (pH 12) and 4 min drying. Effect-directed analysis for genotoxicity (SOS response – UMU-C test, using NQO as positive control) by immersion (speed 3.5 cm/s, time 3 s) into Salmonella typhimurium suspension and, after 3 h incubation at 37 °C and 4 min drying in cold air stream, into one of two fluorogenic substrate solutions (methylumbelliferyl- vs. resorufin-galactopyranoside). After 1 h incubation at 37 °C, visualization of mutagenic compounds as (blue vs. red) fluorescent zones at FLD 366 nm, and densitometry performed with mercury lamp for fluorescence (at  366 / >400nm vs. 550 / >580 nm, respectively). Further validation experiments, including spiking extracts with NQO, were performed showing good mean reproducibility, no quenching or other matrix effects. Lowest effective concentration of NQO was 0.53 nM (20 pg/band), 176 times lower than in the corresponding microtiter plate assays.

J Chromatogr A, 1602, 458–466 (2019). HPTLC of caffeine, physostigmine (alkaloids) and hydroethanolic extract of Peganum harmala seeds (Nitrariaceae, Zygophyllaceae) on silica gel prewashed twice with methanol – water 3:1, followed by 1 h drying at 120 °C. Separation, after 5 min chamber saturation, with ethyl acetate – methanol – ammonia (25%) 85:11:4 (basic mobile phase) or ethyl acetate – toluene – formic acid – water 16:4:3:2 (acidic mobile phase, requiring neutralization with phosphate-citrate buffer). Derivatization with Dragendorff’s reagent and with anisaldehyde sulfuric acid. Effect-directed analysis by spraying A) with Gram-negative bioluminescent Aliivibrio fischeri suspension for antibacterial activity (caffeine was used as standard); B) with acetyl- and butyryl-cholinesterase (AChE / BChE) solutions for enzymatic inhibition. For AChE and BChE asssays, classical immersion into the enzyme solutions was also used for comparison, and inhibition densitometry for active analytes was performed by inverse scan measurement (fluorescence without optical filter) at 546 nm using a mercury lamp; activity was expressed as physostigmine equivalents. Active bands were eluted (only after basic MP) 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 50−750) in positive ionization mode were recorded using heated electrospray ionization (HESI, spray voltage 3.5kV, capillary temperature 270°C). By comparison to literature, AChE inhibitors (also active against A. fischeri) were assigned to be harmine, harmaline and ruine (β-carboline alkaloids), and BChE inhibitors were harmol (same class) and vasicine and deoxyvasicine (quinazoline alkaloids, also called peganine and deoxypeganine). Piezoelectric spraying had the following advantages over automated immersion: (1) it covered the whole plate surface; (2) required much lower volumes of solutions; (3) applied always fresh enzyme or reagent solutions, thus avoiding gradual inactivation; (4) avoided zone distortions, shifts or tailings occurring during immersion or withdrawal of the plate, or due to the hydrophilicity of compounds.