Marine Drugs 20(2), 106 (2022). TLC was used to monitor the fractionation of hydro-methanolic extracts of Rhodophytes: Gracilaria gracilis (Gracilariaceae) (A), Porphyra sp. (Bangiaceae) (B), Spongoclonium pastorale (Ceramiaceae / Wrangeliaceae) (C); and to assess the purity of two isolated mycosporine-like amino acids: porphyra-334 and shinorine.  TLC on silica gel with n-butanol - acetic acid - water 3:1:1. Derivatization by spraying ninhydrin reagent for the detection of peptides and amino-acids; or by spraying anisaldehyde - sulfuric acid for most phytochemicals; in both cases, followed by 5 min heating at 100 °C. Visualization under white light and at 366 nm. Porphyra-334 (hRF 28) was isolated pure from (B) and (C). Shinorine (hRF 25), isolated from (A) and (B), contained a coeluting sugar (hRF 48), which was absent after further purification on solid phase extraction, and, only when isolated from (B), a coeluting peptide or amino-acid (hRF 35), which was absent after further purification on cyclodextrane column chromatography.

J Chromatogr A, 1616, 460774 (2020). Methanolic extracts of leaves of Musa acuminata, M. balbisiana and M. sapientum (Musaceae), either from fields or from in vitro cultures or from the plantlets derived from in vitro culture and acclimatized in isolated warm room, were separated on HPTLC silica gel layers with toluene – ethyl acetate – methanol 6:3:1 or ethyl acetate – toluene – formic acid – water 34:5:7:5. When intended for MS experiments, layers were previously washed twice with methanol – formic acid 10:1, once with acetonitrile – methanol 2:1 and air-dried. Evaluation under white light, UV 254 nm and 366 nm. Derivatization by immersion (2s, 2cm/s) into natural product reagent preceded by heating at 110 °C for 5 min, or into anisaldehyde sulfuric acid reagent, diphenylamine aniline reagent, ninhydrin reagent, followed by the same heating procedure. Besides, plates were neutralized by cold air stream followed with phosphate buffer (8 %, pH 7.5) piezoelectrically sprayed on the plates and automated plate drying. Thereafter, 9 effect-directed assays (EDA) were performed for free radical (DPPH•) scavengers, for enzymatic inhibitors (α-amylase, acetyl- and butyryl-cholinesterase, α- and β-glucosidase), for antimicrobial compounds (Gram-positive Bacillus subtilis assay, Gram-negative Aliivibrio fischeri bioluminescence assay), and for mutagenic compounds (SOS response – UMU-C test using Salmonella typhimurium suspension and 4-nitroquinoline 1-oxide as positive control). The bands of 4 active compounds were eluted with methanol through a TLC-MS interface pump into a quadrupole-Orbitrap mass spectrometer. Full scan mass spectra (m/z 50−800) in the positive and negative ionization modes were recorded using electrospray ionization (ESI, spray voltage 3.3kV, capillary temperature 320°C, collision energy 35 eV). By comparison to a standard, one band present in all samples was identified as linolenic acid. For the other bands, only present in in vitro grown accessions, only raw molecular formulas and phytochemical classes were assigned (a pyrrolidine alkaloid, an amino-acid, a phenolic derivative).

Food Chem. 341, 128271 (2021). HPTLC of finger millet (Eleusine coracana L.) on silica gel with n-butanol - water - acetic acid 4:1:1. Detection by spraying with ninhydrin, followed by heating at 100 °C. Amino acid profiling under UV light at 546 nm. The hRF values for 21 standard amino acids ranged from 2 to 51.

J. Planar Chromatogr. 34, 105-111 (2021). HPTLC of dansyl derivatives of amino acids on silica gel (1) and RP-18 (2) with acetonitrile in the concentration range from 0 to 40 % in water - formic acid solution for (1) and acetonitrile in the concentration range from 10 to 85 % in water - formic acid solution for (2). Pressurized planar electrochromatography (PPEC) under the same conditions with polarization voltage 0.500 kV and separation time of 15 min. Detection under UV light. The separation selectivity is different between HPTLC and PPEC due to the electrophoretic effect in PPEC.

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. Liq. Chromatogr. Relat. Technol. 43, 580-588 (2020). Retardation factor (hRF) of 42 amino acids in two different eluents (acetonitrile - sodium azide and 1,2 dioxane-sodium azide solutions) were predicted by different quantitative structure-retention relationship (QSRR) methods. The method analyzed the effect of sum of geometrical distances between N and O in separation of amino acids in RP-TLC.

J. Planar Chromatogr. 21, 299-304 (2008). HPTLC of 21 amino acids on silica gel impregnated with 5 % Ag ion with borate phosphate buffer pH 2.3. After drying at 50 °C detection by spraying with ninhydrin. With this system separation of alanine, phenylalanine and tryptophane could be achieved, as well as separation of alanine, tyrosine and tryptophan. Separation of these amino acids was neither achieved on conventional silical gel (without Ag impregnation) nor by addtion of buffered 5 % silver nitrate solution (pH 2.3) to the mobile phase.

J. Planar Chromatogr. 26, 31-36 (2013). TLC of a five-component mixture of the amino acids lysine (1), histidine (2), leucine (3), alanine (4) and glutamic acid (4) on silica gel with 1.0% aqueous urea solution pH 7.44. The hRf values of amino acids (1) to (5) were 38, 59, 78, 87 and 98, respectively. LOD for (1), (3) and (4) was 1.5 µg/zone, whereas for (2) and (5) it was 1.2 and 3.0 µg/zone, respectively.