in different_x000D_ growth stages by thin-layer chromatographic scanning. J. Planar Chromatogr. 31, 190-196 (2018). HPTLC of rupestonic acid (1), vitexicarpin (2), apigenin (3), and luteolin (4) in Artemisia rupestris on silica gel with chloroform – methanol – formic acid – water 650:63:17:7. Quantitative determination by absorbance measurement at 250 nm for (1) and 352 nm for (2) to (4). The hRf values for (1) to (4) were 56, 67, 34 and 18, respectively. Linearity was in the range of 128-725 ng/zone for (1), 70-400 ng/zone for (2), 26-145 ng/zone for (3) and 17-97 ng/zone for (4). The intermediate precision was below 5 % (n=6). Average recoveries for (1) to (4) were 100.0 %, 103.6 %, 98.1 % and 99.9 %.

J. AOAC Int. 3, 686-694 (2018). HPTLC of 11 chemical dyes, namely, Sudan I (1), II (2), III (3), and IV (4); 808 Scarlet (5); Sudan Red 7B (6); malachite green (7); Basic Orange 2 (8); auramine (9); Orange II (10); and erythrosine (11) in traditional Chinese medicine raw materials and Chinese patent medicines on silica gel with cyclohexane – trichloromethane 7:3 saturated with ammonia vapor for the separation of (1) to (8). The plate was developed a second time in the same direction with ethyl acetate – alcohol – water – aqueous ammonia 16:4:2:1 for (9) to (11). Quantitative evaluation by densitometry from 200 to 700 nm. The hRf values for (1) to (11) were 74, 78, 74, 68, 44, 23, 8, 2, 56, 28 and 20, respectively. The LODs were 2 to 3 ng/zone, except for (6) 10 ng/zone. HPTLC combined with ESI-MS was assessed for proof of the effective separation of dyes and their identification in herbal matrices.

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.

J. Ethnopharmacol. 232, 135-144 (2019). HPTLC of hesperidin in Citrus reticulatae pericarpium on silica gel with ethyl acetate – formic acid – acetic acid – water 15:1:1:2. Qualitative identification at UV 275 nm. The hRF value for hesperidin was 26.

J. Soil Sci. Plant Nutr. 18, 881-892 (2018). HPTLC of vasicine in Adhatoda zeylanica on silica gel with toluene – methanol – dioxane – ammonia 2:2:5:1. Qualitative identification under UV light at 343 nm. The hRF value for vasicine was 83.

J. Planar Chromatogr. 31, 297-308 (2018). HPTLC of zopiclone in the presence of its degradation products, namely, 7-oxo-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazin-5-yl-4-methylpiperazine-1-carboxylate (hydrolytic DEG) and 5H-pyrrolo[3,4-b]pyrazine-5,7(6H)-dione (oxidative DEG) on silica gel with ethyl acetate – methanol – ammonia 33% 17:2:1. Quantitative determination by absorbance measurement at 303 nm. The hRF value for zopiclone was 44. Linearity was between 0.1 and 2 μg/zone. LOD and LOQ were 30 and 80 ng/zone. The intermediate precision was <2 % (n=3). Average recovery was 99.5 %.

J. High Resol. Chromatogr. 8, 44-45 (1985). TLC of glycyrrhetinic acid on HPTLC silica, treated with 0.7 % benzene solution of 3-APTS, with butanol - NH3 - ethanol 5:2:1. Detection by UV. In situ densitometry. Detection limit 50 ng.

of Oil Refinement (Shiyou Lianzhi) 8, 37-40 (1984). (Chinese) (The analysis of the additives in lubricating oil by thin-layer chromatography.) TLC of dispersing agents (alkyl-salicylates, thio-alkyl-phenolates), antioxidants (dithio-phosphates, dialkyl-dithio-phosphates) and their intermediates on silica with various developing systems. Detection by UV. Sensitivity 10 ng.