J. AOAC Int. 104, 975-982 (2021). HPTLC of methionine (1) and paracetamol (2) on silica gel with butanol - dioxane - toluene - methanol 80:25:35:3. Quantitative determination by absorbance measurement at 220 nm. The hRF values for (1) and (2) were 26 and 83, respectively. Linearity was between 2 and 12 µg/zone for (1) 5 and 30 µg/zone for (2). Inter-day and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 612 and 1856 ng/zone for (1) and 1525 and 4620 ng/zone for (2), respectively. Mean recovery was 101.3 % for (1) and 100.6 % for (2). 

J. AOAC Int. 104, 1719-1725 (2021). HPTLC of diflunisal (1) and its impurity biphenyl-4-ol (2) on silica gel with toluene - acetone - acetic acid 7:13:2. Quantitative determination by absorbance measurement at 254 nm. The hRF values for (1) and (2) were 59 and 79, respectively. Linearity was between 0.5 and 3 µg/zone for (1) and 0.3 and 1.7 µg/zone for (2). Inter-day and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 131 and 398 ng/zone for (1) and 72 and 219 ng/zone for (2), respectively. Mean recovery was 100.2 % for (1) and 100.5 % for (2). 

J. AOAC Int. 104, 1430-1441 (2021). HPTLC of eight different fixed-dose combination products of aspirin (1) with ramipril (2), caffeine (3), metoprolol (4), paracetamol (5), atorvastatin (6) and simvastatin (7) on silica gel with toluene - ethyl acetate - 1 % formic acid in methanol 35:65:3. Quantitative determination by absorbance measurement at 229 nm. The hRF values for (1) to (7) were 88, 15, 34, 49, 59, 66 and 78, respectively. Linearity was between 2000 and 6000 ng/zone for (1) and (5), 100 and 300 ng/zone for (2), 600 and 1800 ng/zone for (3), 1000 and 3000 ng/zone for (4), 200 and 600 ng/zone for (6) and 800 and 2400 ng/zone for (7). Inter-day and intra-day precisions were below 2 % (n=3). The LOD and LOQ were 107 and 323 ng/zone for (1), 32 and 98 ng/zone for (2), 17 and 51 ng/zone for (3), 3 and 10 ng/zone for (4), 9 and 27 ng/zone for (5), 109 and 331 ng/zone for (7), respectively. Recovery ranged 99.2-100.8 % for (1), 99.2-100.2 % for (2), 98.2-101.3 % for (3), 99.4-100.6 % for (4), 100.2-101.4 % for (5), 98.7-101.3 % for (6) and 99.6-101.3 % for (7).

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, 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, 1620, 460970 (2020). Samples were ethyl acetate extracts of Lavandula angustifolia herb and flowers and of aerial parts of other Lamiaceae (Ocimum basilicum, Origanum vulgare, Thymus vulgaris, Rosmarinus officinalis, Salvia officinalis), as well as standards. HPTLC on silica gel (pre-washed with methanol and heated 30 min at 105 °C) with n-hexane – ethyl acetate – acetic acid 70:27:3. Documentation at UV 254 nm and 365 nm and white light before and after A) derivatization with anisaldehyde – sulfuric acid reagent, followed by 10 min heating at 110 °C; B) spraying with DPPH• (0.2 % in methanol), followed by 30 min incubation in the dark; C) α-amylase inhibition assay by immersion into enzyme solution, incubation 30 min at 37 °C, immersion into substrate solution (starch 1 % in water), incubation 20 min at 37 °C and immersion into Gram’s iodine solution for detection (inhibition zones appear blue on white background). Quantification was performed on pictures using image processing software, and expressed as equivalents to the respective standards used for calibration curves: A) β-sitosterol (LOQ 1.5 µg/band), B) gallic acid (LOQ 60 ng/band), C) acarbose (LOQ 8 µg/band). An amylase inhibiting zone (hRF 68) present in all samples (except L. angustifolia), scraped from untreated plates and washed with ethyl acetate, was tentatively identified by ATR-FTIR analysis as oleanolic acid (pentacyclic triterpene).