extracts. J. Planar Chromatogr. 28, 178-183 (2015). TLC of (1) chlorogenic acid and (2) caffeine in coffee samples on silica gel with ethyl acetate - methanol - water 77:13:10 to a distance of 8 cm using a horizontal sandwich chamber. The plates were dried at room temperature for 1 h. Detection of polyphenols with NP-PEG reagent, of terpenoids with anisaldehyde-sulfuric acid reagent followed by heating at 110 °C for 5 min, of purine derivatives with iodine-hydrochloric acid reagent. Quantitative determination of (1) and (2) at UV 254 nm using VideoScan software. The hRF value of (1) was 14, and of (2) 51. The antibacterial activity of green and roasted coffee seeds and pomace was evaluated against Bacillus subtilis using TLC-direct bioautography. TLC-2,2-diphenyl-1-picrylhydrazyl (DPPH) test was used to determine the antioxidant properties. For bioautography with Bacillus subtilis, the plates were immersed for 8 s in the bacterial suspension, placed in a moistened plastic box, and incubated at 37 °C for 17 h. Detection after spraying with 0.2 % MTT aqueous solution. For the DPPH test, plates were sprayed with 0.2 % methanolic DPPH solution. Detection of antioxidant activities as yellow zones against a purple background.

CBS 116, 13-15 (2016). HPTLC of nicotine in e-liquids on silica gel with chamber saturation (with filter paper) for 20 min with toluene – acetone –diethylamine 10:10:1 to the migration distance of 70 mm. Detection under UV 254 nm. Quantitative determination by absorbance measurement at 260 nm. Elution of the zones with methanol (with 0.1 % formic acid) into a single quadrupole MS and detection in positive ionization mode. The hRf value of nicotine was 56 and separation from other ingredients (propylene glycol, glycerol, flavors) was good. Visual evaluation of the samples for presence of nicotine was confirmed with MS and UV spectra.

CBS 118, 5-7 (2017). Presentation of two HPTLC methods for 1) detection and identification of UV filter substances in suncream and 2) detection of phenolic markers in Edelweiss species (Leontopodium spp.). For 1) HPTLC of sun cream samples and standards octocrylene, avobenzone, octisalate and ensulizole on silica gel first with heptane – ethyl acetate 4:1 with chamber saturation, migration distance 70 mm, then with isopropanol, without saturation, migration distance 28 mm. Densitometric evaluation by absorbance measurement at UV 254 nm. Direct elution of target zones into a single quadrupole MS, detection in positive and negative ionization mode. For 2) HPTLC of methanolic and glycerol-based Edelweiss extracts and standards chlorogenic acid, apigenin, luteolin, luteolin-4-O-glucoside, luteoline-7-O-glucoside, leontopodic acids A and B, cynarine, and 3,5-dicaffeoylquinic acid on silica gel with butyl acetate – formic acid – water 280:100:3 with chamber saturation, migration distance 70 mm. Detection by heating the plate at 100 °C for 3 min and immersing (while still hot) into natural products reagent (1 g of 2-aminoethyl diphenylborinate in 200 mL ethyl acetate). Evaluation under UV 366 nm.

J. Planar Chromatogr. 31, 129-134 (2018). HPTLC of hydroxysafflor yellow A in safflower on silica gel with 3.6 % hydrochloric acid – methanol – ethyl acetate 7:3:1. Quantitative determination by absorbance measurement at 399 nm. The hRf value for hydroxysafflor yellow A was 60. Linearity (starting from LOD) was in the range of 62-793 ng/zone with r=0.9991. The intermediate precision was below 3 % (n=6). The LOD and LOQ were 59 and 169 ng/zone, respectively. Recovery was between 96 and 102 %.

J. Chromatogr. Sci., 56 (9), 846–852 (2018). Simultaneous determination of theophylline (THP), guaifenesin (GUI) and guaiacol (GUA, a guaifenesin impurity) by HPTLC on silica gel with ethyl acetate – hexane – methanol - ammonia 65:35:10:2. Detection and quantification by densitometry at 275 nm. The hRf values were 13, 35 and 80 for THP, GUI and GUA, respectively. The linearity range was 0.4–2 μg/band for both THP and GUI, and 0.4–1.2 μg/band for GUA. Validation of the proposed method according to ICH guidelines. Statistical comparison of the results with RP-HPLC showed no difference regarding accuracy and precision.

Proc. Intern. Symposium on TLC with special Emphasis on OPLC, Szeged, 93, (1984). TLC and OPTLC of L-lysine, formaldehyde on silica with citrate buffer pH 6.1. Detection with ninhydrin and heating at 80 °C for 10 minutes. Densitometry.

J. Chromatogr. 292, 117-127 (1984). HPTLC of phenylurea herbicide hydrolysates and their aniline metabolites on silica with dichloromethane or dichloromethane - methanol 99:1 and on RP-18 with acetonitrile -3 % aq. sodium chloride solution 85:15. Prior to development, the applied spots were overspotted with 4 mL of 0.25 DNS chloride solution. An increased fluorescence intensity was obtained by dipping the plates into paraffin - hexane 2:1. Scanning by fluorescence, excitation at 360 nm. Detection limit 1 ng.

1. Separation on silica by thin-layer and high-performance liquid chromatography. J. Chromatogr. 328, 279-287 (1985). HPTLC of bis-quaternary aminosteroids (pipecuronium bromide and related steroids) on silica with methanol - acetonitrile - conc. NH3 514:386:100 containing 0.005 mole/l ammonium chloride and 0.08 mole/l ammonium carbonate. Detection by immersion of the plate in Dragendorff reagent. Densitometry by absorbance at 525 nm.