J Chromatogr A, 1616, 461434 (2020). Samples were acetonic extracts of Malus domestica fruit peels (Rosaceae) and of Salvia officinalis, Thymus vulgaris and Origanum vulgare spice powders (Lamiaceae), as well as standards of maleic acid (dicarboxylic acid), carvacrol, thymol (phenolic monoterpenes), rosmanol (phenolic diterpene), betulinic acid, corosolic acid (CA), maslinic acid (MA), oleanolic acid (OA) and its isomer ursolic acid (UA) (triterpenes). HPTLC on silica gel, when intended for MS and NMR experiments, layers were prewashed twice with methanol – water 3:1, followed by 30 min drying at 120 °C. When intended for quantitative densitometry, start zones were submitted to prechromatographic derivatization with iodine solution (10 g/L in chloroform) allowed to migrate up to 12 mm, incubated 10 min at 27 °C and dried under cold air stream; this allowed separation of isomeric triterpenes. Separation with toluene – methanol – ethyl acetate 17:2:1 after 5 min chamber saturation at 50 % relative humidity. CA coeluted with MA, and OA with UA. Four hyphenations: A) Quantitative HPTLC densitometry for active analytes was performed by measuring absorption at 665 nm with a tungsten lamp after immersion of the chromatograms in anisaldehyde sulfuric acid reagent and heating 5 min at 110 °C. Linear range was obtained at 25 - 200 ng/band for OA and 100 - 400 ng/band for UA. B) Effect-directed analysis by immersing the chromatograms into Gram-positive Bacillus subtilis suspension for antibacterial activity and into acetyl-cholinesterase and tyrosinase solutions for enzymatic inhibition. C) Active bands were eluted with methanol through the oval elution head and in-line filter frit of a TLC-MS interface pump, into a quadrupole-Orbitrap mass spectrometer. Full scan mass spectra (m/z 100−1000) in the positive and negative ionization modes were recorded using heated electrospray ionization (HESI, spray voltage 3.5 kV, capillary temperature 270 °C, probe heater temperature 200 °C). D) With higher amounts applied, preparative HPTLC, by scraping the multipotent band corresponding to OA and UA, and dissolving these analytes in methanol, for NMR analyses (1H raw or deconvoluted, and 2D 1H–13C Heteronuclear Single Quantum Coherence). Both isomers were distinguished by their allylic H-18 protons and separately quantified by applying PULCON method (PUlse Length-based CONcentration). LOQ was 267 μM for OA and 173 μM for UA; optimal range was 300 – 4600 mM, corresponding to 126 - 2090 μg of triterpenes.

CBS 125. HPTLC of estrogen-active compounds in a migrate of a food contact material on silica gel with chloroform - acetone - petroleum ether 11:4:5. Planar Yeast Estrogen Test (P-YES) was performed by spraying 2 mL yeast cells onto HPTLC plates, followed by incubation at 30 °C for 3 h and spraying with 2 mL 0.5 mg/mL 4-methylumbelliferyl-beta-D-galactopyranoside and incubation for 20 min at 37 °C. The method was compared with microtiter bioassay (L-YES). P-YES was more sensitive than L-YES and results can be repeated upto one year later.

CBS 127, 13-15 (2021). HPTLC of rutin and quercetin in Ginkgo biloba (1), rosmarinic acid in rosemary (2) and oleuropein in olive oil (3) on silica gel with ethyl acetate - formic acid - acetic acid - water 100:11:11:26. Detection by spraying with NP reagent (1 g 2-aminoethyl diphenylborinate in 100 mL methanol) for (1) and (2) or with anisaldehyde reagent (0.5 mL p-anisaldehyde in 85 mL methanol, 10 mL acetic acid and 5 mL sulfuric acid), followed by heating at 100 °C for 3 min. Absorbance measurement at 254 nm and 238 nm for oleuropein and in fluorescence mode at 366>/400 nm for rosmarinic acid. The method showed the application of Quantified Reference Extracts for the identification of plant materials and quantification of markers by HPTLC.

Sens. Actuators B Chem. 299, 126902 (2019). Thin layer chromatography combined with surface-enhanced Raman spectroscopy (TLC-SERS) of melamine in milk on silica gel with acetone - chloroform - ammonia 14:1:4. 2 μL gold nanoparticles were drop casted onto the analyte spot, followed by measurement using a  Raman spectrometer equipped with a diode laser emitting at 785 nm wavelength for illumination over a 100 μm diameter was used to obtain the SERS signals. A parallel representation model of the triple-spectral data was constructed using a pure quaternion matrix. Quaternion principal component analysis (QPCA) was utilized to build a quantitative model using support vector regression (SVR) algorithm. The method allowed the determination of melamine-contaminated milk with concentrations from 1 to 250 ppm.

Front. Pharmacol. 12, 755941 (2021). High-throughput eight-dimensional (8D) hyphenation of normal-phase HPTLC with multi-imaging by ultraviolet, visible and fluorescence light detection as well as effect-directed assay and heart-cut of the bioactive zone to orthogonal reversed-phase high-performance liquid chromatography-photodiode array detection-heated electrospray ionization mass spectrometry. The method allowed the analysis of 68 powdered plant extracts (botanicals) which are added to food products in food industry and the study of antibacterials, estrogens, antiestrogens, androgens, and antiandrogens, as well as acetylcholinesterase, butyrylcholinesterase, α-amylase, α-glucosidase, β-glucosidase, β-glucuronidase, and tyrosinase inhibitors in an array of 1,292 profiles.

J. Planar Chromatogr. 35, 181-187 (2022). HPTLC of gallic acid (1) and gallic acid ester (2) in Turkish gall on silica gel with dichloromethane - ethyl acetate - formic acid 5:3:1. Detection by spraying with 2 % ferric chloride ethanol solution. Quantitative determination by absorbance measurement at 280 nm. The hRF values for (1) and (2) were 67 and 81, respectively. Linearity was between 507 and 3045 ng/zone for (1) and 499 and 2994 ng/zone for (2). Interday and intra-day precisions were below 2 % (n=6). Average recovery was 100.6 % for (1) and 97.8 % for (2). The method was used to analyze the changes in the content of components which was treated by static simulated gastrointestinal digestion.

J. Planar Chromatogr. 35, 169-179 (2022). HPTLC of arjungenin (1) and arjunetin (2) in the bark of Terminalia arjuna on silica gel with toluene - ethyl acetate - formic acid 5:4:1. Detection by spraying with 10 % solution of sulfuric acid dissolved in methanol. Quantitative determination by absorbance measurement at 420 and 475 nm for (1) and (2). The hRF values for (1) and (2) were 43 and 67, respectively. Linearity was between 100 and 1000 ng/zone for (1) and (2). The method facilitated the detection of traces amount of adulterants in herbal products.

J. Planar Chromatogr. 35, 153-159 (2022). HPTLC of glucuronic acid in gum samples of Sterculia urens on silica gel with 1-propanol - water 7:3. Detection by spraying with napthoresorcinol sulfuric acid reagent, followed by heating at 105 °C for 5 min. Quantitative determination by absorbance measurement at 580 nm. The hRF value for glucuronic acid was 43. Linearity was between 300 and 700 ng/zone. Interday and intra-day precisions were below 2 % (n=3). Recovery was between 100.4 and 102.3 %.