J. Liq. Chromatogr. Relat. Technol. 44, 484-489 (2021). HPTLC of caffeic acid (1), rutin (2), naringin (3), and hesperidin (4) in samples of citrus fruits on polyamide plates with a microemulsion - formic acid 47:1. Microemulsion was prepared as follows: 2.7 g of SDS in 90 mL water, followed by adding 6.3 mL n-butanol and 1.0 mL n-heptane, and the mixture was shaken to produce a uniform and transparent O/W microemulsion. Detection by spraying with 1 % aluminum trichloride aqueous solution and photographed using a smartphone under UV light at 365 nm. Image retrieval techniques combined with support vector machine (SVM) directly classified the chromatograms based on migration path images.

J. Liq. Chromatogr. Relat. Technol. 44, 760-765 (2021). HPTLC of chrysin in chrysin loaded phytosomes on silica gel with n-hexane - ethyl acetate - methanol - formic acid 40:40:5:1. Quantitative determination by absorbance measurement at 268 nm. The hRF value for chrysin was 78. Linearity was between 50 and 250 ng/zone. Inter-day and intra-day precisions were below 2 % (n=3). The LOQ was 77 ng/zone. 

J. Liq. Chromatogr. Relat. Technol. 44, 809-819 (2021). HPTLC of major cannabinoids in Cannabis sativa on silica gel with hexane - ethyl acetate - methanol 7:2:1. Detection by spraying with anisaldehyde  sulfuric acid reagent. Quantitative determination by absorbance measurement at 525 nm for lupeol. The hRF values for Δ9-tetrahydrocannabinol and tetrahydrocannabinolic acid were 55 and 36, respectively. Analytical Quality by Design (AQbD) tools, such as the Design of Experiments (DoE) was used for a better understanding of the analytes’ chromatographic behavior as a function of the mobile phase composition. 

J. Liq. Chromatogr. Relat. Technol. 44, 599-609 (2021). HPTLC of lupeol in Betula alnoides on silica gel with chloroform. Detection by spraying with anisaldehyde sulfuric acid reagent. Quantitative determination by absorbance measurement at 525 nm for lupeol. The hRF value for lupeol was 44. Linearity was between 0.8 and 2.4 µg/zone. Inter-day and intra-day precisions were below 5 % (n=3). The LOD and LOQ were 0.2 and 0.5 µg/zone. Recovery was between 100.5 and 106.8 %.

J Chromatogr A, 1647, 462153 (2021). Samples were extracts of Pittosporum angustifolium leaves (Pittosporaceae), either pure or fermented 1-4 weeks in NaCl solution, as well as acarbose, gallic acid, β-sitosterol, caffeic and chlorogenic acids, as standards. HPTLC on silica gel (prewashed with methanol and dried 15 min at 105 °C) with n-hexane – ethyl acetate – acetic acid 15:9:1. Derivatization by immersion (speed 5 cm/s, time 1 s): (A) into DPPH• 0.2 % solution, to detect radical scavengers; (B) into neutralized ferric chloride (3 % in ethanol), followed by 5 min heating at 110 °C, for detection of phenolic compounds; (C) into anisaldehyde – sulphuric acid reagent, followed by 10 min heating at 110 °C, to detect terpenes and steroids. Effect-directed analysis (EDA) for α-amylase inhibition assay (D) by immersion into enzyme solution, incubation 15 min at 37 °C, immersion into substrate solution (starch 2 % in water), incubation 20 min at 37 °C and immersion into Gram’s iodine solution for detection (inhibition zones appear blue on white background). In all cases, visualization under white light. Quantification was performed on pictures using image processing software, and expressed as equivalents to the respective standards used for calibration curves: (A) and (B) gallic acid (LOQ 250 and 740 ng/band, respectively), (C) β-sitosterol (LOQ 1.5 µg/band), (D) acarbose (LOQ 8 µg/band). Zones of interest, scraped from untreated plates and washed with ethyl acetate, were submitted by ATR-FTIR analysis. An amylase inhibiting zone (hRF 85) present in all extracts was identified as fatty acid esters: ethyl palmitate in unfermented and methyl linoleate in fermented extracts. Moreover, fermented extracts contained antioxidant zones (hRF 15 – 20), identified as monomers and oligomers (including hydroxycinnamic, guaiacyl, syringyl derivatives) from decomposed lignin.

J Chromatogr A, 1625, 461230 (2020). Samples were methanolic extracts of commercial supplements containing Magnolia sp. bark (Magnoliaceae), as well as honokiol (1) and magnolol (2) (biphenyl neolignans) as separated or mixed standards. TLC and HPTLC on silica gel with n-hexane – ethyl acetate – ethanol 16:3:1. Visualization under UV 254 nm. Quantification of (1) and (2) by densitometric scanning in absorbance mode at 290 nm (hRF were 34 and 39, LOQ 200 ng and 280 ng/spot, respectively). Variability between samples from the same brand supplement was also determined, as well as extraction yields. Effect-directed analysis with 3 assays: A) to detect radical scavengers, immersion into DPPH• 0.02 % solution; B) to detect activity against Gram-negative bacteria, immersion into Aliivibrio fischeri suspension, followed by recording the bioluminescence; C) to detect activity against Gram-positive bacteria, immersion into Bacillus subtilis, followed by incubation 2 h at 28 °C and immersion into MTT 1 g/L. Compounds (1) and (2) were active in all assays. Identification of zones of interest by eluting with methanol from untreated TLC layer through the oval elution head of a TLC-MS interface directly to a single Quadrupole MS (electrospray ionization, interface temperature 350°C, heat block temperature 400°C, desolvation line temperature 250°C, detector voltage 4.5kV). Full mass scan spectra were recorded in the positive and negative ionization modes in m/z range 150–800. Other molecules (from other ingredients) were identified: piperine (alkaloid) and/or its geometrical isomers (active on A, hRF 29-30); and daidzein (active on A and B, hRF 18), isoflavone from Pueraria montana root (Fabaceae). Stability was assessed through 2D-HPTLC, by repeating the same development method in the orthogonal direction 4 h or 20 h after the first separation. Degradation products of (1) and (2) appeared after 20 h (but not at 4 h), including a honokiol dimer (formed in tracks of (1) and of (2)).

J Chromatogr A, 1628, 461461 (2020). Samples were hydro-methanolic extracts of 100 genuine saffron samples (Crocus sativus stigmata, Iridaceae) from South Khorasan (SK) and Razavi Khorasan (RK) provinces (Iran), pure or mixed in several proportions with common vegetal adulterants: C. sativus style, Calendula officinalis petals (Asteraceae, Asteroideae), Carthamus tinctorius petals (Asteraceae, Carduoideae), Rubia tinctorum rhizomes (Rubiaceae). Commercial saffron samples (containing artificial adulterants) were also tested. TLC on silica gel with ethyl acetate – methanol – water – acetic acid 66:23:11:1. Evaluation at 254 nm, 366 nm, and 440 nm. Crocin (carotenoid, hRF 38) was used for optimization of extraction (parameters being first calculated by chemometry), using multilinear regression and ANOVA. Image data (pixel intensities and colors of each sample under the three selected wavelengths) were unfolded into a data matrix and transformed into a vector, used for multivariate image analysis of the chromatogram fingerprints. This allowed: A) separation of genuine samples by principal component analysis (PCA) into 2 clusters according to origin (cold climate in Northern half of RK vs. warm climate in SK and Southern part of RK) with 92 % prediction accuracy; B) separation of samples according to purity / vegetal adulterant groups by partial least squares – discriminant analysis (PLS-DA) with 98 % accuracy (if 10 µL extract applied); C) separation with 100 % prediction accuracy by PCA between genuine, mixed, and commercial samples.

J Chromatogr A, 1624, 461239 (2020). Samples were chemical standards of acetylcholinesterase (AChE) inhibitors (azamethiphos, caffeine, donepezil, galanthamine, methiocarb-sulfoxide, paraoxon-ethyl) and of neurotoxic compounds, as well as drinking or contaminated water samples enriched through solid phase extraction. HPTLC on spherical silica gel (pre-washed twice by 20 min immersion in isopropanol, heated 20 min at 120 °C before and after pre-washing with acetonitrile). First separation (preparative TLC) with automated multiple development (16 steps). Effect-directed analysis for AChE inhibitors by immersion (speed 5 cm/s, time 1 s) into enzyme solution, incubation 5 min at 37 °C and immersion into substrate solution (indoxyl acetate 2 % in methanol); visualization under UV 366 nm. Active zones from untreated layers were eluted through the oval head of a TLC-MS interface to a second plate for a second separation with a panel of other mobile phases. Bands of interest were eluted from the second layer with water through the oval elution head of the TLC-MS interface pump, into a RP18 liquid chromatography guard column, followed by a quadrupole time-of-flight mass spectrometer. Full scan mass spectra (m/z 100–1200) were recorded in negative and positive modes using electrospray ionization (and collision-induced dissociation for MS2). Among the water contaminants, lumichrome (riboflavin photolysis product), paraxanthine and linear alkylbenzene sulfonates were identified as AChE inhibitors.