Food Chem. 242, 601-610 (2018). Review of recent research on L-theanine, including the use of HPTLC for the rapid quantitative determination in Camellia sinensis and the combination with other non-chromatographic techniques.

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. Chromatogr. A 1506, 109-119 (2017). HPTLC of seven important steviol glycosides on silica gel, which may degrade in food products under certain processing and storage conditions, and additionally as a sum parameter their reported breakdown products steviol and isosteviol. Detection with 2-naphthol and primuline reagent. Baseline separation of steviol and isosteviol was achieved after a plate cut and subsequent short development (two-step method). The HPTLC method was robust with regard to varying sample matrix loads, provided a high sample throughput (23 separations in parallel on one plate), and was fast (total analysis time of 1 h: 30 min application, 15 min separation and 15 min derivatization/densitometry, leading to 2.6 min per sample). The solvent consumption was low (0.4 mL per analysis) and accuracy of the densitometric quantification was good. Confirmation of the results with HPTLC-ESI-MS of only the zones of interest instead of matrix or background so that there was less need for MS cleaning. Hyphenation to Aliivibrio fischeri bioassay to obtain information on bioactive compounds in Stevia leaf extracts.

J. Chromatogr. Sci. 56 (4), 376-381 (2018). Investigation of the lipophilicity of new anticancer active 10-substituted 1,6- and 3,6-diazaphenothiazines using RP TLC. Determination of their lipophilicity (RM0 and log PTLC) with mixtures of acetone and Tris buffer as mobile phases. The obtained results showed significant intercorrelation between RM0 and the specific hydrophobic surface area b, revealing congeneric classes of diazaphenothiazines. Transformation of the parameter RM0 into parameter log PTLC by use of the calibration curve. Comparison of the parameter log PTLC with computationally calculated lipophilic parameters log Pcalcd. Discussion of the lipophilicity with the structure elements and correlation with molecular descriptors, ADME properties and in vitro anticancer activities.

J. Chromatogr. A 1558, 69-76 (2018). Development of an HPTLC method for monoacylglycerols (MAG), diacylglycerols (DAG), triacylglycerols (TAG) and free fatty acids (FFA) in E 471 food emulsifiers, as a simple, rapid, sensitive and convenient screening alternative to HPLC and GC analysis. HPTLC of the samples in t-butyl methyl ether on primuline pre-impregnated LiChrospher silica gel by two-fold development, first with diethyl ether to 18 mm, then with n-pentane – n-hexane – diethyl ether 13:5:7 to 75 mm. Quantitative determination by fluorescence measurement at UV 366/>400 nm, using the cumulative signal for each lipid class and 1,2-distearin for calibration. The amounts of the lipid classes were calculated using response factors and expressed as monostearin, distearin, tristearin and stearic acid. The LOD and LOQ for 1,2-distearin were 1 and 4 ng/zone, respectively. The visual detection by fingerprint enabled an easy characterization and the direct comparison of emulsifiers through the lipid class pattern.

J. Chromatogr. Sci. 55 (5), 571-577 (2017). Proposal of a rapid, easy and efficient method for calcium oxalate crystal inhibition in the agar gel system analogous to antimicrobial well diffusion assay, and TLC-agar-overlay bioautography (note that the term "direct bioautography" is wrongly used in the title) to detect the antilithiatic metabolites and to localize the active metabolites in Phyllanthus niruri, an Ayurvedic plant. The agar well diffusion method showed 50 % inhibitory concentration (IC50) value at 229 and 494 mg/mL for tri-sodium citrate and Phyllanthus niruri extract, respectively, with the lowest concentration showing visible crystal inhibition (minimum inhibitory concentration, MIC) of 20 mg/mL in both samples. With this method the successful screening, detection and confirmation of calcium oxalate crystal inhibitory metabolites from P. niruri was possible. Detection of tuberonic acid in the bioactive fraction of P. niruri by HPLC-HRMS.

Phytochemistry 155, 37-44 (2018). HPTLC of pine resins collected from Abies grandis, Pseudotsuga menziesii, Picea abies, Pinus sylvestris L. and Pinus strobus L. in a forest area of The Netherlands during early and late spring on silica gel with toluene – isopropyl alcohol – diethyl ether 16:1:3. Detection by spraying with 2 mL of anisaldehyde sulfuric acid solution, followed by heating at 100 ºC for 3 min. Qualitative identification under UV light at 366 nm. Most of the metabolites detected in GC-MS were confirmed by HPTLC analysis. HPTLC proved to be an important technique for metabolic profiling.

J. Chromatogr. A 1572, 137-144 (2018). Development of a method for the analysis of anthocyanes within the foodstuffs of plant origin by TLC on RP-18 phase (which ensures mixed-mode retention mechanism with the localized adsorption on the non-bonded silanols) with acetic acid as the mobile phase component, using two anthocyanins (cyanin and keracyanin) and two anthocyanidins (pelargonidin and delphinidin) as phytochemical standards. By triple development, distinct and symmetrically shaped chromatographic zones were obtained. Further analysis of the products of hydrolytic degradation of the test anthocyanins by MS. Identification of the hydrolytically split fractions by using the p-aminobenzoic acid reagent. Investigation of the calibration curves for cyanin, keracyanin, pelargonidin and delphinidin, and the respective LOD and LOQ values. Application of the method to identify and quantify cyanin, keracyanin, pelargonidin and delphinidin in selected alimentary products (syrups, juices and herbal infusions).