J. Planar Chromatogr. 30, 313-322 (2017). HPTLC of cyclobenzaprine hydrochloride (1) and asenapine maleate (2) on silica gel with toluene ‒ methanol ‒ chloroform ‒ ammonia solution 33 % 50:30:60:1. Quantitative determination under UV light at 290 and 220 nm for (1) and (2), respectively. The hRF values for (1) and (2) were 45 and 75, respectively. Linearity was between 5 and 50 μg/zone for (1) and (2). The intermediate precision (n=2) was <2 %. The LOD and LOQ for (1) were 1.3 and 4.4 μg/zone for (1) and 1.2 and 3.9 μg/zone for (2), respectively. Average recovery rate was 99.2 % for (1) and 99.7 % for (2). There were no significant differences between the mean percentage recoveries and the precisions compared with a validated HPLC mehod.

J. Planar Chromatogr. 30, 363-374 (2017). HPTLC of acetylsalicylic acid (1) and its related compound salicylic acid (2) on silica gel with n-hexane – diethyl ether – 80 % acetic acid 7:2:1. Good quality densitograms with well separated and symmetric peaks of (1) and (2) were achieved. Detection with the following reagents: Janus blue, bromophenol blue, bromocresol blue, hydrogen peroxide (without heating and with heating to 90 °C during 60 min), 1 % sodium hydroxide (with heating to 45 °C and also with heating to 90 °C during 60 min), brilliant green, malachite green, and thymol blue.

J. Chromatogr. A 1524, 266-272 (2017). Demonstration of the antibacterial profiling of Onopordum acanthium L. leaf extract and subsequent targeted identification of active compounds. Investigation of the extract against eight bacterial strains including two plant and three human pathogens and a soil, a marine and a probiotic human gut bacteria by TLC and off-line overpressured layer chromatography (OPLC) coupled with direct bioautography. Transfer of antibacterial fractions obtaining infusion-transfusion OPLC to HPLC-MS/MS analysis resulted in the characterization of three active compounds, two of them were identified as linoleic and linolenic acid. Adoption of OPLC method to preparative-scale flash chromatography for the isolation of the third active compound, which was identified after a further semi-preparative HPLC purification as the germacranolide, sesquiterpene lactone onopordopicrin. Pure onopordopicrin exhibited antibacterial activity that was specified as minimal inhibitory concentration in the liquid phase as well.

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. Liq. Chromatogr. Relat. Technol. 41, 83-86 (2018). TLC of gardenia blue in foods on RP-18 with 0.2 % trifluoroacetic acid – acetonitrile – ethanol 1:2:3 and on cellulose with acetone – 3-methyl-1-butanol – water 6:5:5. The hRf values of gardenia blue coloring were 35, 18 and 13 on RP-18 and 72, 56 and 48 on cellulose layer.

J. Chromatogr. A 1577, 101-108 (2018). In order to overcome the difficulty of the interpretation of the MS signals present at a low intensity for unknown degradation products or impurities, a new strategy and open-source software called eicCluster was developed. It offered unsupervised machine learning algorithms and powerful interactive visualization tools that made data processing fast and intuitive. The low-intensity HPTLC-HRMS signals were highlighted in a stressed formulation by using eicCluster. Thus, even compound ions present at low intensities were separated in subclusters from background signals (in silico highlighting). The respective preprocessing led to intensity-agnostic signals and the t-SNE algorithm clustered mass signals based on their similarity. The resulting 2D maps allowed a new view on the data set to such low-intensity target molecules in complex mixtures. Moreover, the targeted on-surface synthesis of degradation products (in situ highlighting) was shown to support a fast structure elucidation, when standards are not commercially available. It allowed a better understanding of the proposed degradation reactions in the formulation. Comparison with the results of stressed samples as well as the proposed degradation products of on-surface synthesis proved that in silico and in situ signal highlighting substantially eased structure elucidation and data processing.

J. Ethnopharmacol. 233, 141-147 (2019). HPTLC of gentiopicrin in the dried roots and rhizomes of Gentiana scabra on silica gel with ethyl acetate – ethanol – water 8:2:1. Detection by spraying with chromogenic reagent (acetic acid – sulfuric acid – p-anisaldehyde 100:2:1). Qualitative evaluation at UV 254 nm. The hRF value for gentiopicrin was 58.

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).