Food Chem. 260, 344-353 (2018). HPTLC profiling of phenolic compounds in 50 commercially available beers on silica gel with methyl ethyl ketone – toluene – formic acid 25:15:2. Detection by dipping into a 0.5 % methanolic 2-aminoethyl diphenylborinate solution, followed by drying in the air for 5 min and immersion for 3 s in a 5 % methanolic PEG 400 solution. Image acquisition at UV 366 nm. The HPTLC method was hyphenated to four different assays to demonstrate the fast discovery of single DPPH scavengers, Gram negative (A. fischeri) and Gram positive (B. subtilis) antimicrobials as well as AChE inhibitors in beers. For the DPPH assay, the plate was immersed into a 0.02 % methanolic DPPH_x000D_ solution, followed by drying at ambient temperature (25 °C) in the dark for 30 s and then heated for 30 s in a stream of warm air. Images were acquired every 30 s for a period of 10 min. For the B. subtilis bioassay, the plate was immersed_x000D_ in the prepared bacterial suspension, incubated at 37 °C for 2 h, immersed in a 0.2 % PBS-buffered MTT solution and incubated again at 37 °C for 0.5 h. For the luminescent A. fischeri bioassay, the plate was immersed in the bacterial suspension for 2 s and instant bioluminescence was captured. For the AChE assay, the plate was immersed in the enzyme solution (AChE 666 units plus 100 mg BSA ad 100 mL 0.05M TRIS buffer, pH 7.8), incubated at 37 °C for 25 min, and immersed in a substrate solution (25 mg α-naphthyl acetate and 50 mg Fast Blue salt B ad 90 mL with ethanol – water 1:2). Phenolic compounds in active zones were also characterized by HPTLC-HRMS. Effect-directed fingerprints were investigated for image processing and multivariate data analysis. Isoxanthohumol was found to be the main phenolic beer component that showed the widest spectrum of activities.

Biochem. Biophys. Res. Commun. 500, 103-109 (2018). 2D-TLC of glycerolipid classes in Arabidopsis thaliana seedlings on silica gel with chloroform – methanol – ammonia 15:10:1 in the first dimension and chloroform – methanol – acetic acid – water 170:20:15:3 in the second dimension. Detection by spraying with 0.01 % primuline in 80 % acetone. Lipid zones were scraped off from the TLC plate and separated lipids were analyzed by gas chromatography.

J. Planar Chromatogr. 31, 163-168 (2018). HPTLC bioautography of the essential oil in the bark of Ocotea quixos on silica gel with toluene – ethyl acetate – petroleum ether 97:7:20. After separation, the Mueller‒Hinton culture medium was deposited on the Petri dish which contained the chromatographic plate. The medium contained the selected microorganisms: 500 μL Bacillus subtilis ATCC 6633 ATCC and 500 μL P. aeruginosa ATCC 9027. The plate was incubated at 37 °C for 48 h. The molecule with activity proved to be cinnamyl acetate at an hRF value of 53.

Phytochemistry. 155, 1-11 (2018). Review of recent developments in plant sources of propolis and innovative phytochemical approaches to propolis analysis, including TLC application for the assessment of its authenticity and HPTLC fingerprinting and HPTLC-DART-MS for metabolomic approaches in determining geographical origin.

J. Chromatogr. A, 1572, 145-151 (2018). Introduction of on-surface reactions as a new strategy for rapid structure elucidation. This was illustrated by a miniaturized on-surface synthesis-guided identification of two new degradation products (impurities) occurring in a pharmaceutical formulation of the anti-cancer drug ifosfamide, especially in the presence of urea. The respective reagents were applied in the nanomole scale accurately and automated on a HPTLC silica gel plate. After a fast reaction in the start zone, the plate was developed, followed by online elution to high-resolution MS, whereby the on-surface reaction highlighted the impurities. As proof of concept and for benchmarking, it was compared to a reaction mixture obtained from conventional preparative synthesis in a round-bottom flask as well as to different formulations. Image evaluation was performed by videodensitometry. Discussion of the advantages such as: 1) the combination of all relevant steps on one HPTLC plate and its resulting efficiency made surface synthesis on chromatographic phases an optimal tool for signal highlighting in MS, and thus for the assignment of impurities in drugs; 2) the miniaturization of the chemistry process scale down to the μg-level per synthesis (in total 30-60 μg chemicals/reaction), setting a new state-of-the-art standard; 3) the contribution to a greener chemistry by reducing the consumption of chemicals and enhancing the analytical efficiency, when adapted for the quality control of any other chemical product.

using high-performance thin-layer chromatography. J. Planar Chromatogr. 31, 309-317 (2018). HPTLC of gardenin-E (1), gardenin-D (2), xanthomicrol (3), 5-desmethynobiletin (4), gardenin-A (5), and gardenin-B (6) in the sum resin of Gardenia lucida on silica gel with n-hexane – diethyl ether – 1,4-dioxane 4:6:1. Detection by dipping into natural product reagent (10 mL of 1 % methanolic diphenyl boryloxyethylamine), followed by dipping into PEG reagent (8.0 mL of 5 % ethanolic polyethylene glycol 4000). Quantitative determination by absorbance measurement at 335 nm. Linearity was between 0.33 and 1.67 μg/zone. LOD and LOQ were 90 and 300 ng for (1), 90 and 290 ng for (2), 90 and 320 ng for (3), 100 and 320 ng for (4), 60 and 210 ng for (5) and 80 and 280 ng for (6), respectively. The intermediate precision was <2 %. Recovery ranged from 96.0 to 99.3 %.

by high-performance thin-layer chromatography method. J. Planar Chromatogr. 31, 337-342 (2018). HPTLC of betulinic acid (1), oleanolic acid (2) and lupeol (3) in Achyranthes aspera on silica gel with benzene – ethyl acetate – formic acid 679:227:94 for (1), n-hexane – ethyl acetate – glacial acetic acid 40:20:1 for (2) and n-hexane – ethyl acetate 4:1 for (3). Detection by spraying with anisaldehyde sulfuric acid reagent for (1) and (2) and ceric ammonium sulfate for (3), followed by heating at 105-110°C for 5-10 min. Quantitative determination by absorbance measurement at 530 nm for (1) and (2) and 366 nm for (3). The hRF values for (1) to (3) were 79, 46 and 44, respectively. Linearity was between 2-10 μL/zone. LOD and LOQ were 1 and 4 ng/zone for (1), 1 and 3 ng/zone for (2), and 2 and 5 ng/zone for (3), respectively.

J. AOAC Int. 101, 981-991 (2018). HPTLC of triamcinolone acetonide (1) and econazole (2) on silica gel with ethyl acetate – tetrahydrofuran – ammonia 100:70:1. Quantitative determination by absorbance measurement at 225 nm. The hRF values for (1) and (2) were 77 and 56, respectively. Linearity ranged between 0.2-28.0 μg/zone for (1) and 0.5-55.0 μg/zone for (2). LOD and LOQ were 56 and 170 ng/zone for (1) and 160 and 480 ng/zone for (2), respectively. The intermediate precision was <2 % (n=9). Average recovery was 99.5 % and 99.3 %.