J. Planar Chromatogr. 34, 157-163 (2021). HPTLC of berberine in the stem of Tinospora cordifolia on silica gel with n-hexane - ethyl acetate - methanol - formic acid 8:8:4:1. Quantitative determination by absorbance measurement at 360 nm. The hRF value for berberine was 48. Linearity was between 30 and 100 ng/zone. Intermediate precision was below 2 % (n=6). The LOD and LOQ were 10 and 30 ng/zone. Recovery was between 100.7 and 104.0 %. 

J. Planar Chromatogr. 34, 147-155 (2021). HPTLC of berberine (1), berbamine (2), palmatine (3), magnoflorine (4) and jatrorrhizine (5) on silica gel with ethyl acetate - formic acid - glacial acetic acid - water 100:11:11:26. Quantitative determination by absorbance measurement at 254 nm. The hRF values for (1) to (5) were 47, 12, 38, 14 and 40. Linearity was between 1000 and 6000 ng/zone for (1) and (2), 200 and 700 ng/zone for (3), 500 and 2000 ng/zone for (4) and 300 and 1800 ng/zone for (5). Intermediate precision was below 2 % (n=3). The LOD and LOQ were 323 and 979 ng for (1), 227 and 688 ng for (2), 56 and 169 ng for (3), 89 and 289 ng for (4) and 87 and 289 ng for (5). Average recovery was 99.4 % for (1), 100.0 % for (2), 98.6 % for (3), 99.4 % for (4) and 98.9 % for (5). 

J. Planar Chromatogr. 34, 31-38 (2021). HPTLC of reserpine (1), scopoletine (2), piperine (3), bacoside A (4) and lupeol (5) in a polyherbal formulation (containing Rauwolfia serpentina, Nardostachys jatamansi, Convolvulus pluricaulis, Bacopa monnieri, Piper longum) on silica gel with benzene - ethyl acetate - glacial acetic acid - n-butanol 57:30:10:3 for (1), (2) and (3), n-butanol - glacial acetic acid - water 18:3:4 for (4) and benzene - ethyl acetate 9:1 for (5). Detection by spraying with 5 % methanolic sulfuric acid solution, followed by heating at 80 °C for 20 min. Quantitative determination by absorbance measurement at 254 nm for (1) to (3), 598 nm for (4) and 580 nm for (5). The hRF values for (1) to (5) were 17, 53, 73, 34 and 48, respectively. Linearity was between 1 and 2 µg/zone for (1), 2.5 and 4.5 µg/zone for (2), 10 and 50 µg/zone for (3), 12 and 24 µg/zone for (4) and 1 and 5 µg/zone for (5). Intermediate precision was below 2 % (n=6). The LOD and LOQ were 6 and 20 ng/zone for (1), 13 and 38 ng/zone for (2), 11 and 33 ng/zone for (3), 377 and 1143 ng/zone for (4) and 324 and 982 ng/zone for (5), respectively. Average recovery was 98.1 %for (1), 99.9 % for (2), 99.9 for (3), 99.7 % for (4) and 99.5 % for (5).

Sci. World J. 2020, 7367836 (2020). TLC of ethyl acetate fractions of hydro ethanolic extracts obtained from Cassia siamea leaves (Caesalpiniaceae) on silica gel with chloroform – ethanol 17:3, as well as cassiarin A (an isoquinoline alkaloid, hRF 34) as standard. Visualization under UV light. Densitometry scanning at 368 nm for cassiarin A. Linearity was in the range of 400–1400 ng; intra-day precision was below 4 %; LOD and LOQ values were 3 and 8 ng, respectively; recovery rates were 102.8–120.1 %. The cassiarin A concentrations in the samples (given as w/v, the volumes being those of the first undried hydro-ethanolic extracts) varied depending on the origin (ground and climate) of the leaves.

3 Biotech 10(8), 344 (2020). Rauvolfia serpentina (Apocynaceae) was cultivated in vitro as leaf-derived callus and as plantlet cultures obtained from tissues of nodal explants, without or with cadmium chloride as elicitor of alkaloid production. TLC of methanol – ammonia 10:1 extracts of callus and plantlet organs (leaves, stems and roots) on silica gel, along with indole alkaloids reserpine and ajmalicine in different concentrations. Development with chloroform – toluene – ethyl acetate – diethyl amine 7:7:4:1. Detection under UV light and by densitometry scanning in absorbance mode at 240 nm and 280 nm. The highest alkaloid yields were obtained for reserpine (hRF 15) in roots (191µg/g) and for ajmalicine (hRF 45) in callus (131µg/ml) when culture had been done with elicitor 0.15 mM for 6 days and 4 days, respectively (at 0.20 mM, an inhibiting effect was observed).

J Am Soc Mass Spectrom 31(9), 1981-1993 (2020). Low-temperature plasma-mass spectrometry was studied for comparison between direct desorption (DD) and diode laser assisted desorption (LD) in terms of quantitative and qualitative analysis of compounds from cellulose vs. silica gel TLC layers. Compounds (the 20 common amino acids, propofol, nicotine, cotinine, salicylamide, acetylsalicylic acid, paracetamol, caffeine, valprolactone and its isomer 4-ene-valproic acid) were applied on the TLC plates (without development) at different concentrations; a commercial mixture of acetylsalicylic acid, paracetamol and caffeine was also applied on TLC plates, developed with dichloromethane – ethyl acetate 1:50, detection at UV 254 nm and quantitative MS. In general, DD provided good results on cellulose, where LODs where between 0.01 and 2.55 ng/mm2, whereas several compounds remained undetected on silica gel. LD however provided LODs on silica gel from 0.3 to 84 pg/mm2. Tandem MS with collision-induced dissociation was implemented to improve signals, LODs and to characterize the other analytical figures-of-merits (including detection of the main fragment ions, determination of optimal laser beam width and irradiance depending on the compounds). For the two metabolites of valproic acid, the ions and fragments had identical values; therefore, a mix of the two isomers had to be applied and separated with dichloromethane – methanol 50:1 before MS; one half of the plate was visualized for control by dipping into potassium permanganate reagent (7.5g KMnO4, 50g K2CO3, 0.75g NaOH in 1L water).

J. Planar Chromatogr. 33, 599-607 (2020). HPTLC of vasicine (1) and vasicinone (2) in different parts of Justicia adhatoda on silica gel with ethyl acetate - methanol - ammonia 40:10:1. Quantitative determination by absorbance measurement at 270 nm. The hRF values for (1) and (2) were 37 and 57, respectively. Linearity was between 100 and 400 ng/zone for (1) and (2). Intermediate precision was below 2 % (n=3). The LOD and LOQ were 6 and 10 ng/zone for (1) and 20 and 32 ng/zone for (2). Recovery was between 98.0 and 99.3 % for (1) and 97.3 and 97.8 % for (2).

Phytochem. Anal. 31, 711-721 (2020). HPTLC of 13 aporphine and four benzylisoquinoline-type alkaloids in the twigs of Ocotea spixiana on silica gel with propanol - water - ammonium hydroxide 18:2:1. Detection by desorption electrospray ionisation mass spectrometry (DESI-MS).