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.

CBS 106, 5-6 (2011). HPTLC on 1) ProteoChrom silica gel with 2-butanol – pyridine – ammonia 25 % – water 39:34:10:26; on 2) ProteoChrom cellulose with 2-butanol – pyridine – acetic acid – water 15:10:3:12 by two-dimensional development and on 3) silica gel with the developing solvent from 2). Detection by spraying with ninhydrin, fluorescamine, or triethylamine reagent. Evaluation under daylight and UV 366 nm. Detection by mass spectrometry by scanning the plate with a self modified desorption electrospray beam. In one-dimensional HPTLC up to 20 bands can be separated. By two-dimensional separation this number can be increased. Particularly suited are cellulose HPTLC plates.

Clin. Chem. 29, 744-745 (1983). TLC of amino acids on cellulose with butanol - formic acid -water 12:3:5. Detection with ninhydrin.

J. Liquid Chromatogr. 6, 109-122 (1983). TLC of 24 amino acids on stannic tungstate with a) butanol (saturated with water)- acetic acid 3:1, b) acetone - formic acid-water 2:2:1. Detection with 0.2 % ninhydrin in butanol.

Merck Spectrum 1989 18-19. HPTLC of D-tryptophan and L-tryptophan on „chiral“ silica (converted with C-18 silane and impregnated with copper salt and the „chiral selector“) with methanol – water acetone 50:50:30. Detection by spraying with ninhydrin followed by heating at 120°C for 5 min. Quantification by densitometry at 510 nm.