J. Planar Chromatogr. 33, 79-87 (2020). HPTLC of quercetin in the aerial parts of Juniperus communis, J. horizontalis and J. chinensis on silica gel with ethyl acetate - methanol - water - acetic acid 900:80:40:7. Assessment of peroxidase inhibition activity by dipping into peroxidase enzyme solution (10 mg/mL solution of peroxidase in cold phosphate buffer (pH 7), followed by dilution with 50 mL of phosphate buffer, pH 7) for 3 s, followed by heating at 35 ºC for 2 min, dipping into a hydrogen peroxide solution and finally dipping into a benzidine solution (4 g in 700 mL methanol). Linearity was between 0.85 and 9 µg/zone for quercetin. Intermediate precisions were below 3 % (n=3). The LOD and LOQ were 280 and 850 ng/zone. Recovery was between 96.6 and 99.7 %.

J. Planar Chromatogr. 33, 27-32 (2020). HPTLC of rutin (1), chlorogenic acid (2) and gallic acid (3) in the seeds of Moringa oleifera on silica gel with ethyl acetate - acetone - water - formic acid 6:3:2:2. Quantitative determination by absorbance measurement at 254 nm. The hR_F values for (1) to (3) were 51, 72 and 83, respectively. Linearity was between 1000 and 7000 ng/zone for (1), 100 and 700 ng/zone for both (2) and (3). Intermediate precisions were below 1 % (n=6). The LOD and LOQ were 5 and 17 ng/mL for (1), 7 and 22 ng/mL for (2) and 7 and 20 ng/mL for (3), respectively. Recovery rate was between 98.1 and 99.5 % for (1), 98.8 and 99.5 % for (2) and 97.6 and 98.6 % for (3).

J. Planar Chromatogr. 33, 11-18 (2020). HPTLC of lutein in dietary supplements on silica gel with n-heptane – ethyl acetate 9:1. The part of the TLC chromatogram containing the zone visible in day light was cut off, followed by developing in the opposite direction with n-heptane – acetone – ethyl acetate 11:5:4. Quantitative determination by absorbance measurement at 450 nm. Linearity was between 90 and 500 ng/zone for lutein. Intermediate precisions were below 2 % (n=9). The LOD and LOQ were 50 and 90 ng/zone, respectively. Recovery rate was between 87 and 102 %.

J. Planar Chromatogr. 33, 33-41 (2020). HPTLC fingerprint of the kernel and seed of Allanblackia parviflora fruit (extracted with methanol - water 4:1) on silica gel with methanol - water - ethyl acetate 33:27:200. Detection by spraying with vanillic acid - sulfuric acid reagent (1 g of vanillic acid in 100 mL of 96 % ethanol, followed by the dropwise addition of 2 mL concentrated sulfuric acid). Different formulations of the derivatization reagent were investigated and the use of vanillic acid instead of the more frequently used vanillin provided a better result. Qualitative determination under UV 254 and 366 nm. Consistent hR_F values of the main zones under UV 254 nm were 39, 35 and 12. For the derivatized plate, consistent hR_F values of the main zones were 39, 34, 31 and 22.

J. Planar Chromatogr. 33, 51-57 (2020). HPTLCS (high-performance thin-layer chromatography scanning) of ethyl p-methoxycinnamate in the rhizome of Kaempferia galanga on silica gel with hexane - ethyl acetate 18:1. Quantitative determination by absorbance measurement at 309 nm. The hR_F value for ethyl p-methoxycinnamate was 29. Linearity was between 2 and 6 ng/zone. Intermediate precisions were below 2.4 % (n=3). Mean recovery rate was 100.1 %. Results were compared with a validated HPLC method and the HPTLCS method was more environmetnally friendly..

J. Planar Chromatogr. 33, 71-77 (2020). HPTLC of ledipasvir (1) and sofosbuvir (2) on silica gel with ethyl acetate - hexane - methanol  32:5:3. Quantitative determination by absorbance measurement at 256 nm. Linearity was between 60 and 1980 ng/zone for (1) and 45 and 3600 ng/zone for (2). Intermediate precisions were below 2 % (n=3). The LOD and LOQ were 16 and 50 ng/zone for (1) and 13 and 40 ng/zone for (2), respectively. Mean recovery rate was 99.4 % for both (1) and (2).

J. Planar Chromatogr. 33, 79-87 (2020). HPTLC of velpatasvir (1) and sofosbuvir (2) on silica gel with chloroform - methanol 19:1. Quantitative determination by absorbance measurement at 265 nm. The hR_F values for (1) and (2) were 29 and 19, respectively. Linearity was between 5 and 50 µg/zone for (1) and 10 and 70 µg/zone for (2).  Intermediate precisions were below 2 % (n=3). The LOD and LOQ were 3 and 5 µg/zone for (1) and 8 and 10 µg/zone for (2), respectively. Mean recovery rate was 100.2 % for (1) and 100.9 % for (2).

J. Planar Chromatogr. 33, 59-70 (2020). HPTLC of metformin (1), saxagliptin (2) and dapagliflozin (3) on silica gel with chloroform - methanol - water - acetic acid 740:260:50:1. Quantitative determination by absorbance measurement at 224 nm. The hR_F values for (1) to (3) were 14, 50 and 66, respectively. Linearity was between 30 and 350 µg/mL for (1), 140 and 1500 µg/mL for (2) and 50 and 600 µg/mL for (3).  Intermediate precisions were below 2 % (n=6). LOD and LOQ were 7 and 23 µg/mL for (1), 39 and 130 µg/mL for (2) and 14 and 47 µg/mL for (3), respectively. Recovery rate was between 98.9 and 100.5 % for (1), 99.2 and 100.5 % for (2) and 99.2 and 100.7 % for (3). Comparable results were obtained when compared with a HPLC method.