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. Neurochem. 42, 12-15 (1984). TLC of 2', 3'-cAMP, 2'AMP, 3'AMP marked 8-3H on cellulose with ammonium sulfate- 0.5 M NaOAC- propanol 80:18:2. Detection by UV or autoradiography.

(Hungarian). Gyógysterészet 37, 161-163 (1993). TLC of allantoin on cellulose with butanol - acetic acid - water 3:1:1. Visualization by spraying with p-dimethylaminobenzaldehyde and heating at 100 °C for 10 min.

J. Pharm. Biomed. Anal. 54, 497-502 (2011). HPTLC of three bioactive steroidal glycoalkaloid markers, solasonine (SN), solamargine (SM) and khasianine (KN) in the plant Solanum xanthocarpum. The extraction effciency of targeted SGAs from plant matrix using methanol and acidified methanol were studied using percolation, ultrasonication and microwave techniques. HPTLC on silica gel with chloroform – methanol – water. The hRf values were 31, 37, and 52 for SN, SM, and KN, respectively. Quantitative determination by absorbance measurement at 520 nm after derivatization using Dragendorffs reagent. The linearity range was 2-10 µg/band for SN and SM and 6-30 µg/band for KN. Method specificity was confirmed using hRf values, correlation of UV spectra and comparison of ionization mass spectra (ESI-MS) of marker compounds in the sample track.

J. of Medicinal Chemistry 31, 1305-1308 (1988). TLC of 2'-deoxynucleosides and ribonucleosides on silica with n-propanol-2N aqueous ammonia 7:3. Detection under UV after spraying with cysteine/ sulfuric acid reagent for 2'-deoxynucleosides and tetramethyl-benzidine periodate reagent for ribonucleosides.

On the anomalous course of the Sheehan-Bose synthesis with 5-amino tetrazole. A novel synthesis of the 4,5,6,7-tetrahydrotetrazolo (1,5-a)pyrimidine ring system. Acta Chimica 130, 683-689 (1993). TLC of 4,5,6,7-tetrahydrotetrazolo (1,5-a)pyrimidine on silica with ethyl acetate - hexane - acetic acid 10:5:2. Detection by UV-irradiation, with iodine, or with 5% ethanolic molybdo-or tungstophosphoric acids as reagents.

J. Chromatogr. B 691, 155-160 (1997). TLC on polyethyleneimine. Detection by autoradiography. Detection limit 0.5 adducts/1010 nucleotides. Also HPLC with detection limit 3 adducts/1010 nucleotides. Comparison of the two techniques.