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.

J. Chromatogr. Sci. 57 (4), 312-322 (2019). Development of a method for simultaneous analysis of five antipsychotic and medicinally important β-carboline alkaloids (βCAs), namely, harmalol, harmaline, harmine, harmane and norharmane, by HPTLC on silica gel with chloroform - methanol - glacial acetic acid 39:11:1. Quantification by densitometry in fluorescence mode at 366 nm. The linearity range of standard βCAs was 25-250 ng/band, with r² between 0.97 and 0.99. The recovery was between 83.9 and 112.4 %, repeatability of the application 0.6-2.4 %, repeatability of measurement 1.9-3.1 % and intermediate precision 0.6-11.2 %). LOD and LOQ were 4.9-6.6 and 16.5-21.9 ng/band, respectively. The method proved to be simple, cost-effective, precise, sensitive and specific for the determination of βCAs in the herbs Fagonia schweinfurthii, Peganum harmala and Tribulus terrestris, and was useful in forensic and industrial analysis and fingerprinting of various βCAs containing herbs and drug formulations.

J. Chromatogr. A 1594, 181-189 (2019). Development of a simple and rapid procedure for the determination of quinalphos in human whole blood by HPTLC on silica gel with n-hexane – acetone 9:1 after extraction from spiked blood samples with the optimum solvent, diethyl ether, at pH 3 (average recovery = 93.6%), detection and quantification by densitometry at 325 nm in absorbance mode. Validation by examination of the effect of different organic solvents and pH on the extraction yield of quinalphos, and by investigation of the interference of other organophosphorus pesticides of forensic relevance (not observed). The linearity was in the range of 1 to 100 μg/mL with r2 = 0.9981, the sensitivity (LLOQ) at 1 μg/mL. The within-day precision and between-day precision ranged from 0.2 to 1.0%, and 0.1 to 0.8%, respectively, with an overall average recovery of 91.1% at three concentrations 1, 10, and 50 μg/mL. For different storage conditions for the samples no significant decrease in the concentration of quinalphos was observed. Application of developed procedure in three fatal cases of poisoning.

Planta Medica 84(6/7), 465-474 (2018). The new concept “Comprehensive HPTLC Fingerprinting” was applied to define specifications for the identification and purity assessment of Angelica gigas roots, and for the quantification of its markers: the coumarins decursin and decursinol angelate. Methanolic root extracts of A. gigas (10 reference materials, 24 commercial samples), of 26 other Apiaceae species (including 10 Angelica, 9 Ligusticum, 2 Notopterygium, 4 Peucedanum, and Levisticum officinale) and of mixtures, were developed with toluene - ethyl acetate - acetic acid 90:10:1 on HPTLC silica gel (at 33% relative humidity, chamber pre-saturated for 20 min with filter paper and developing solvent) and dried for 5 min. Detection under white and UV lights before and after derivatization by dipping into 10% sulfuric acid in methanol and then heating 3 min at 100°C. Quantitative evaluation by densitometry in fluorescence mode at UV 313 nm, and luminance was also calculated from the image pixels. The study showed the presence in A. gigas of nodakenin, decursinol, 7-demethylsuberosin, imperatorin, osthole, and isoimperatorin at hRF 0, 4, 15, 33, 38 and 44 respectively. Z-ligustilide (hRF 59) was absent from A. gigas, allowing 1) to distinguish it from several other Apiaceae species; 2) to identify in mixtures with A. gigas two common adulterants (A. acutiloba, A. sinensis) even at 1% in the root powder. Minimal content of A. gigas fingerprint markers (decursin + decursinol acetate, co-eluting at hRF 27) was assessed as 3% (w/w) based on the quantified peaks from A. gigas reference materials.

J. Planar Chromatogr. 32, 339-342 (2019). HPTLC of withaferin A (1) and withanolide A (2) in Solanum nigrum on silica gel with toluene - ethyl acetate - formic acid - ethanol 60:30:1:6. Detection by spraying with p-anisaldehyde sulfuric acid (1 mL of p-anisaldehyde solution in 2 mL of concentrated sulfuric acid and 100 mL of acetic acid). Quantitative determination by absorbance measurement at 530 nm. The hRF values for (1) and (2) were 43 and 55, respectively. 

J. Liq. Chromatogr. Relat. Technol. 42, 563-569 (2019). HPTLC of spinosin in the fruits of Ziziphus jujuba on silica gel with ethyl acetate - dichloromethane - methanol - water 18:10:15:5. Quantitative determination by absorbance measurement at 334 nm. The hRF value for spinosin was 38. Linearity was between 10 and 120 ng/mL. Intermediate precision was below 2 % (n=6). The LOD and LOQ were 12 and 35 ng/mL, respectively. Recovery rate was between 98.7 and 101.3 %. The HPTLC method provided similar reproducibility, accuracy and selectivity for the quantitative determination of spinosin compared with a HPLC method.