J Chromatogr A 1638, 461830 (2021). The purpose was to find the first universal HPTLC mixture (UHM), a mixture of reference compounds that could be used for the system suitability test (SST) for the full RF range in all HPTLC experiments.
(Part 1) UHM composition: First, 56 organic molecules, detectable without derivatization, were tested on HPTLC silica gel with 20 different mobile phases (MP) belonging to different Snyder’s selectivity groups and with several polarity indices. Visualization under UV 254 nm and 366 nm. Densitometry scanning at 254 nm in absorption mode, and at 366 nm in a fluorescence mode (mercury lamp 366 nm, with wavelength filter <400 nm). For selected bands, spectra were recorded in absorbance-reflectance mode (wavelength range 190 – 450 nm, deuterium and tungsten lamp). This procedure allowed 8 molecules to be selected for their better spot resolution and for their specific RF values (at least 3 different values distributed throughout the full RF range for each MP). The final composition of UHM was: thioxanthen-9-one (0.001 %), guanosine (0.05 %), phthalimide (0.2 %), 9-hydroxyfluorene, octrizole, paracetamol, sulisobenzone and thymidine (each 0.1 %), in methanol.
(Part 2) UHM validation: Afterwards, UHM was submitted again to a panel of HPTLC assays with always two MP: (A) toluene – methanol – diethylamine 8:1:1; (B) ethyl acetate – formic acid – water 15:1:1; and for each MP, the means, standard deviation and 95 % confidence intervals of the RF values were calculated. (a) UHM was validated for intermediate intra-laboratory precision, as well as for inter-laboratory reproducibility, with ΔRF 0.045. (b) The capacity of UHM to detect small variations was demonstrated by significant changes in at least some RF values, when separation was deliberately performed at different levels of relative humidity (0 %, 33 %, 75 %, 100 %), or with smaller humidity variations (7 % compared to 0–5 %, and 49 % compared to 33 %), or when performing vs. omitting the 10min chamber pre-saturation, or when modifying the MP (+/-10% of one solvent at each time). These response characteristics (the opposite of robustness) made UHM a powerful tool for SST. (c) Finally, UHM stability was studied with UHM aliquots under several storage conditions (-78 °C, -20 °C, 4 °C, room temperature, 45 °C; or 40 °C with 75 % relative humidity) and durations (2 weeks or 2 months). The densitometric peak profiles at 254 nm were compared to those of the fresh compounds, qualitatively (RF value, UV spectrum) and quantitatively (peak area). UHM was stable at room temperature or below, for 2 months (at higher temperature, guanosine, phthalimide and paracetamol degraded).

J. Liq. Chromatogr. Relat. Technol. 41, 15-16 (2019). HPTLC of thymine (1), uracil (2), adenine (3), cytosine (4), guanine (5) and guanosine (6) in Ganoderma lucidum and Cordyceps sinensis on silica gel with dichloromethane - methanol - formic acid 160:45:16. Quantitative determination by absorbance measurement at 254 nm. Identification of nucleobases in the samples was reconfirmed by hyphenated HPTLC-MS. The hRF values for (1) to (6) were 83, 73, 46, 32, 23 and 10, respectively. The intermediate precision was below 5 % (n=3). 

J. Chromatogr. 268, 311-314 (1983). TLC on cellulose with a) water, b) solutions of inorganic salts. Detection by UV 254 nm.

J. Chromatogr. 589, 301-306 (1992). Chromatographic behavior of twelve barbituric acid derivatives by OPLC using silica, impregnated with tricaprylmethyl-ammonium chloride (TCMA). The retention of barbiturates decreased with increasing TCMA on the layer. The Rf values increased with increasing methanol content of the eluent. The pH and the inorganic salt concentration in the eluent had no effect on the retention. Discussion of many other parameters. The results of the best separation are given.

Asian Journal of Chemistry 23(1), 309-311 (2011). TLC on silica gel with toluene - isopropyl alcohol - acetic acid 12:12:1. The hRf values was 63 for etophylline and 75 for theophylline. Densitometric evaluation at 261 nm. The method was linear in the range of 200-400 ng/band for etophylline and 60-80 ng/band for theophylline.

TLC of mononucleotides on silica with isopropanol - NH3 - water 12:8.3. Determination by spectrophotometry at 250 nm after elution.

Chinese J. Chromatogr. (Sepu) 11, 146-148 (1993). TLC of oligonucleotides on silica with 1) isopropanol - water - NH3 6:3:1, 2) propanol - water - NH3 6:3:1, and 3) propanol - water - NH3 11:7:2. Detection under UV 254 nm.

J. Chromatogr. A 773, 285-290 (1997). Determination of the TLC detection limits of the phosphorothioate analogs of nucleotides and related compounds by means of UV, iodine, HCl vapors, the iodine-azide reagent and the molybdate reagent. Application of the iodine-azide reagent for the selective TLC detection of the phosphorothioate analogs of nucleotides.