J. Planar Chromatogr. 32, 481-493 (2019). HPTLC of metformin hydrochloride (1) and ursodeoxycholic acid (2) on silica gel with toluene - ethanol - acetone - formic acid 90:40:50:17. Quantitative determination by absorbance measurement at 234 and 700 nm for (1) and (2), respectively. The hRF values for (1) and (2) were 19 and 80, respectively. Linearity was between 5000 and 40000 ng/zone for (1) and 1500 and 12000 ng/zone for (2). Intermediate precision was below 1 % (n=3). The LOD and LOQ were 195 and 592 ng/zone for (1) and 150 and 455 ng/zone for (2), respectively. Recovery rate was 100.5 % for (1) and 99.9 % for (2).

J. Planar Chromatogr. 32, 501-504 (2019). HPTLC of aspirin (1) and omeprazole (2) on silica gel with ethyl acetate - dichloromethane - glacial acetic acid 80:20:1. Quantitative determination by absorbance measurement at 241 nm. The hRF values for (1) and (2) were 79 and 19, respectively. Linearity was between 160 and 960 ng/zone for (1) and 80 and 480 ng/zone for (2). Intermediate precision was below 1 % (n=3). The LOD and LOQ were 11 and 32 ng/zone for (1) and 3 and 8 ng/zone for (2), respectively. Recovery rate was between 101 and 106 % for both (1) and (2).

J. Planar Chromatogr. 32, 517-520 (2019). HPTLC of tramadol (1), caffeine (2), paracetamol (3), ibuprofen (4), naproxen (5), and diclofenac (6) on RP-18 WF, LiChrospher RP-18 WF, and RP-18 WF with concentration zone, developed with various ratios of methanol in water with 0.1 M potassium chloride. Qualitative identification under UV light at 254 nm. Potassium chloride may be used to suppress ion–ion interactions between the solutes and the silica gel surface.  HPTLC RP-18WF plates with concentration zone and developed with methanol - water 13:7 with addition of 0.15 mol/L KCl were suitable for the qualitative and quantitative analyses of tramadol, paracetamol, caffeine, naproxen, and ibuprofen or diclofenac. The method allowed to study subtle differences in the efficiency of the separation of analgesic drugs by HPTLC with similar octadecyl silica-based adsorbents.  

J. Planar Chromatogr. 32, 401-409 (2019). HPTLC of losartan potassium in plasma on silica gel with toluene - ethyl acetate - acetone - formic acid 8:8:2:1. Quantitative determination by absorbance measurement at 240 nm. The hRF value for losartan was 57. Linearity was between 50 and 1200 ng/mL. Intermediate precision was below 3 % (n=6). Recovery rate was between 95 and 99 %.

J. Planar Chromatogr. 32, 411-420 (2019). HPTLC of fosinopril sodium (1), hydrochlorothiazide (2), and chlorothiazide (3) on silica gel with ethyl acetate - chloroform - methanol - formic acid 120:80:10:1. Quantitative determination by absorbance measurement at 215 nm. The hRF values for (1) to (3) were 53, 39 and 29, respectively. Linearity was between 1 and 10 µg/zone for (1), 0.2 and 3 µg/zone for (2) and 0.2 and 2 µg/zone for (3).  Intermediate precisions were below 2 % (n=6). The LOD and LOQ were 280 and 860 ng/zone for (1), 90 and 350 ng/zone for (2) and 50 and 160 ng/zone for (3). Recovery rate was 100.2 % for (1), 100.1 % for (2) and 99.9 % for (3).

Phytochem. Anal. 30, 405-414 (2019). HPTLC fingerprint of 70 standard medicinal plants on silica gel with ethyl acetate – ethyl methyl ketone – formic acid 98% – water 5:3:1:1. Derivatization with anisaldehyde, Liebermann–Burchard, 3 % iron(III) chloride (FeCl₃) and phosphomolybdic acid reagent. Detection before and after derivatization under visible light and UV light (254 and 366 nm). A similarity search algorithm based on color (RGB, HSV and Lab) information alone or together with hRF values was built  to assess the fingerprinting of medicinal plants. The method showed better results than principal components analysis (PCA), classification and regression trees (CART) and partial least squares discriminant analysis (PLS‐DA).

Phytochem. Anal. 30, 332-345 (2019). TLC fingerprint of Musa paradisiaca fruits on silica gel with hexane - acetone 7:2. Detection by dipping into 5 % anisaldehyde sulfuric acid solution in methanol. Densitometric absorption measurement at 540 nm. To determine antioxidant activity, the plate was dipped into 0.05 mM DPPH* radical reagent solution in methanol and kept at room temperature in dark conditions for 30 min. Further analysis of zones by gas chromatography‐mass spectrometry.

J. AOAC Int. 102, 776-780 (2019). HPTLC of sibutramine, phenolphthalein, and three PDE5 inhibitors (sildenafil, vardenafil and tadalafil), as well as caffeine, fluoxetine, theophylline, and acetaminophen as adulterants in weight loss products on silica gel with methyl tert-butyl ether – toluene – methanol 8:2:1. Densitometric absorption measurement at 225 nm. The hR_F values of reference substances increased in the following order: fluoxetine, sildenafil, vardenafil, caffeine, theophylline, tadalafil, acetaminophen, phenolphthalein and sibutramine. The method was successfully used for the screening of 12 commercial products. Of those, nine products tested positive for at least one undeclared component.