J Chromatogr A 1666, 462863 (2022). Theoretical discussion on the factors determining the RF value of a given substance in a chromatographic system: A) the stationary phase (SP); B) the mobile phase (MP), the composition of which can be different from the solvent mixture prepared because of evaporation, saturation and liquid or gas adsorption effects over migration time; C) the difference of the free energies for the analyte transfer from SP to MP; D) external parameters like temperature and humidity. The universal HPTLC mixture (UHM) is a mixture of reference compounds that can be used for the system suitability test (SST) for the full RF range in all HPTLC experiments. Its composition is: thioxanthen-9-one (0.001 %), guanosine (0.05 %), phthalimide (0.2 %), 9-hydroxyfluorene, octrizole, paracetamol, sulisobenzone and thymidine (each 0.1 %), in methanol. The purpose was to study the potential of UHM to replace SST (described with specific markers in European Pharmacopoeia monographs) and to assess the quality of HPTLC results. TLC and HPTLC silica gel on different support (aluminium, glass) or with different granulometries and binders (classic, Durasil, Adamant), of the UHM, an acetonitrile extract of Abelmoschus manihot flowers (Malvaceae), a methanol extract of Sambucus canadensis flowers (Adoxaceae), and essential oils of Lavandula angustifolia, of Mentha × piperita (Lamiaceae) and of Myristica fragrans (Myristicaceae), as well as the following specific markers (standards): borneol, bornyl acetate, linalool, linalyl acetate (terpenoids), isoeugenol, isoeugenol acetate, chlorogenic acid (phenylpropanoids), gossypin (flavone), gossypetin-glucuronide, hyperoside (flavonol heterosides). Development (after 20 min plate conditioning with a saturated MgCl2 solution) with one of the following mobile phases: (MP1) toluene – ethyl acetate 19:1, especially for essential oils; (MP2) ethyl acetate – butanone – formic acid – water 5:3:1:1, especially for S. canadensis; (MP3) ethyl acetate – acetic acid – formic acid – water 100:11:11:26, especially for A. manihot. Documentation in UV 254 nm and 350 nm, and with white light (reflection + transmission), before and after derivatization. RF values were determined by scanning densitometry at 254 nm in absorption mode (for octrizole, at 366 nm in fluorescence mode with mercury lamp and optical filter K400 nm). For each HPTLC condition, intra-laboratory precision assay of UHM separation was performed (at least 5 analyses) with average RF values and 95 % prediction intervals, and calculating RF differences between pairs of UHM constituents and 95 % confidence intervals, which were max. +/-0.012 of the RF values for all UHM and markers. The sensitivity of UHM, and thus its usefulness as generic SST was demonstrated by repeating the HPTLC experiments with modifying by 10 % the quantity of one of the solvent each time. There were always significant changes in RF values of UHM components and/or in RF differences between pairs of UHM bands; it was often but no always the case with the official specific markers. UHM underwent also significant changes (although less than A. manihot extract) when several silica gel phases were compared under the same HPTLC conditions. This property is crucial to verify the right stationary phase before doing any RF correlations, and could make UHM a universal tool to identify discrepancies between different analyses. Finally, the use of UHM for a computer-supported evaluation of HPTLC results was discussed, either for zone identification and RF corrections (within confidence intervals), or for correlations of entire fingerprints as first step to implement machine learning algorithms.

J. Ethnopharmacol. 295, 115327 (2022). Review of modern applications for the analysis of Rauvolfia species, including traditional uses, phytochemistry, quality control, pharmacological properties, as well as clinical evidence that may be useful in the drug discovery process. The paper described qualitative and quantitative methods, including HPTLC methods for the analysis of targeted and non-targeted compounds in different extracts of plant parts of Rauvolfia species.

J. Ethnopharmacol. 305, 116004 (2023). Review of the ethnobotany, phytochemistry, and biological activities of the medicinally important Prunus africana. The paper described various TLC and HPTLC methods to isolate and analyse P. africana extracts, including the identification of myristic acid, palmitic acid, linoleic acid, oleic acid, stearic acid, arachidonic acid, n-docosonal, behenic acid, lignoceric acid, β-sitosterol, and ursolic acid.

Phytochem. Anal. 34, 5-29 (2023). Review of the plant resources, chemical ingredients, and biological activities of Euodiae fructus, focusing on the chromatographic and mass spectrometric technologies used for analysis of Euodiae fructus. The paper described TLC and HPTLC methods for the analysis of different analytes such as rutaecarpine and evodiamine and their application in traditional chinese medicine research. 

Trends Anal. Chem. 144, 116450 (2021). Review of analytical techniques for the forensic examination of photocopied documents. The papers described the application of chromatographic techniques, including TLC and HPTLC for the analysis of lifting toner samples from different brands. 

Trends Anal. Chem. 159, 116915 (2023). Review of analytical methodologies, distribution, ecotoxicity and removal of artificial sweeteners to determine the ecological and health risks that these substances may pose based on available data. The paper described analytical techniques, including HPTLC for the determination of artificial sweeteners in water samples.

Trends Anal. Chem. 154, 116654 (2022). Review of recent advances of sampling and sample preparation in effect-directed environmental analysis with a special focus on innovative approaches. The paper summarized sampling, enrichment and fractionation techniques for effect-directed analysis of water samples, including HPTLC methods for the analysis of potential toxicity contributors.

Trends Anal. Chem. 143, 116412 (2022). Comprehensive review on the recent progress (over the last 5 years) of riboflavin analytical methodologies in food, pharmaceutical and biological fields. The paper described HPTLC methods as a versatile auxiliary tool for riboflavin analysis.