J. Sep. Sci. 46, 2300198 (2023). HPTLC of asphaltenes-containing petroleum materials: saturated, aromatics, resins, asphaltenes group-type composition on silica-coated quartz rods with a reverse order of the subsequent elution steps, where the solvent polarity was simultaneously reduced and the chromatogram development distance increased in the following order: dichloromethane - methanol 19:1, 3 cm; toluene, 6 cm; and n-hexane, 10 cm. After each development step, the frame was placed in an oven at 70 °C until completely dried and placed in a desiccator for 10 min. Chromatograms were obtained based on the electrometer analog signal generated during the mechanical movement of individual rods in the air-hydrogen flame of the TLC–FID analyzer. 

J Chrom Sci, bmad055 (2022). Standards of antiglycemic drugs were metformin hydrochloride (S1, a biguanide), glibenclamide (S2 = glyburide, a sulfonylurea), pioglitazone hydrochloride (S3, a thiazolidinedione), repaglinide (S4, a glinide). Samples were methanolic solutions of commercial tablets of S1 with each of the other molecules. The following method was developed by a software-assisted AQbD approach (analytical quality by design): (1) Several TLC separations were tried with toluene together with other solvents and with acidic or basic modifiers, with also variations of 24 method or instrumental parameters. (2) Principal component analysis (PCA) was performed in order to identify two principal components (PCs) responsible for 98 % of the observed variations: namely, resolution and tailing factor. Three critical method parameters (CMPs) had a statistically significant impact on the PCs: mobile phase (MP) composition, ammonium acetate concentration in MP, and saturation time. (3) To optimize these CMPs, the Box–Behnken design was implemented in 15 software-proposed experiments; the impacts of the 3 CMPs on the 2 PCs were evaluated by ANOVA, multiple regression analysis, and 2D and 3D contour plots. (4) The optimal CMPs ranges were determined by defining a MODR (method operable design region) on the superposed contour plots, and one TLC condition was selected as analytical control point.
TLC on silica gel pre-washed with 10 mL methanol, dried and activated 10 min at 100° C. Separation with toluene – ethyl acetate – methanolic solution of 4 % ammonium acetate 7:7:6 after 15 min pre-saturation with 35 % relative humidity. Absorption emasurement at UV 254 nm. The hRF values were 13 for S1, 72 for S2, 82 for S3, 38 for S4. LOQ were 263, 387, 73 and 35 ng/zone, respectively. Linearity range was 25–75 µg/zone for S1, 100–300 ng/zone for S2 and S4, 750–2250 ng/zone for S3. Intermediate precision was below 2 %. For accuracy tests, recovery rates were between 97.6–101.4 %.

J Chrom Sci, bmad025 (2023). Standards (separated and mixed) were montelukast sodium (MKT) and loratadine (LRT). Samples were methanolic solutions of commercial tablets, and purified blood plasma as biological fluid, from patients taking MKT or LRT as oral treatment. TLC on silica gel with ethyl acetate – ethanol 9:1. Visualization under UV 254nm. The hRF values were 80 for MKT and 71 for LRT. Densitometric absorbance measurement at 260 nm (20 mm/s scanning speed). System suitability was verified by resolution, selectivity, capacity and absence of tailing. The method was validated for linearity range (0.3–3.6 μg/zone for MKT, 0.2–4 µg/zone for LRT), for precision, for reproducibility, for robustness, and for accuracy expressed as average recovery values (100 % overall mean) at different concentrations. The TLC-densitometric method was also found statistically equivalent (Student’s t-test and F-test) to a previously described method (HPLC – spectrophotometry), but was better in terms of environmental and health impacts, using green analytical procedure index (GAPI) and analytical eco-scale (scores based on solvents/reagents, energy consumption, occupational hazard and waste generation). The TLC method was also compared to three (equally “green”) different analytical methods of spectrophotometry (without chromatography): response correlation, absorptivity-centering and LRT-MKT ratio derivatives. The TLC method was more sensitive (LOQ values were 82 ng/zone for MKT, 20 ng/zone for LRT).

J. AOAC Int. 100, 922-934 (2017). HPTLC of monoacylglycerol, diacylglycerol, triacylglycerol, and glycerol in lubricating oils applied in cutting devices on silica gel in a three-step elution carried out toward increasing strength of the mobile phase: the elution up to 100 % of the plate’s height in n-hexane; step 2: the elution up to 60 % of the plate’s height in toluene; and step 3: the elution up to 30 % of the plate’s height in dichloromethane - methanol 19:1. Detection by exposure to iodine vapor and under UV light at 254 and 366 nm. Further analysis by coupling with a flame ionization detector.

J Chromatogr A, 1619, 460945 (2020). Samples were lamotrigin as standard, or extracted with an oil-in-water microemulsion (10 µL butyl acetate, 4 mL n-butanol, 925 mg sodium dodecyl sulphate, 8.6 mL water) either from patients’ raw plasma (for separation from blood proteins) after spiking, or from commercial tablets dissolved in methanol. TLC on silica gel with a water-in-oil microemulsion of 9 mL butyl acetate, 1 mL n-butanol, 250 mg sodium dodecyl sulphate, 250 µL water. Both optimal microemulsions were predicted using Taguchi orthogonal array and Plackett-Burman design. Evaluation in UV 254 nm, quantification from the digital picture using four image processing software programs. For lamotrigin (hRF 24), limits of quantification were 170 ng for pure drug and 10 ng for spiked plasma. Linearity (in range 20–200 ng/spot) was directly obtained for the calibration curve in spiked plasma; however, for pure drug, linearity was obtained only when using log values of the calculated densities (300–3000 ng/spot).

Chinese J Oil Refining & Chem. Ind. 32 (6), 70-72 (2021). The output of coal tar accounts for about 3-4 % of the coal quantity in the furnace, which mainly contains benzene, toluene, xylene, naphthalene, anthracene and other components, and can be refined into phenolic oil, anthracene oil, asphalt and other products. These are widely used in dyes, medicine, spices, pesticides and other industries. Presentation of a method by using rod chromatography (rod TLC) / FID under optimized experimental conditions: TLC of 0.04 g/mL coal tar on activated chrombars under constant humidity conditions were developed in turn (A) with heptane to 11 cm, (B) with toluene to 6.5 cm and (C) with dichloromethane to 4.0 cm. The chrombars were scanned by FID and the content of saturated hydrocarbons, aromatic hydrocarbons, glia and bitumen was calculated by referring to the correction factors used in the determination of the four components in decompression slag oil. The method has been applied to four batches of coal tar samples or coal tar intermediate products produced by different process with satisfactory results, and proved to be simple, fast, economically feasible and suitable for coal chemical enterprises to quickly detect the change of coal tar composition, and to provide data reference for adjusting the device process parameters.

ALTEX - Alternatives to animal experimentation, 38(3), 387-397 (2021). Samples were standards of food contact contaminants with genotoxicity (4-nitroquinoline-1-oxide (NQO), aflatoxin B1, hexachloroethane, nitroso-ethylurea, phenformin, PhIP) or negative controls (alosetron, mannitol), and extracts of coated tin cans (extracted with n-hexane – acetone at 25°C for 16 h or by heating at 60 °C with ethanol 95 % for 240 h). HPTLC on RP18W layer, pretreated to harden the binder by heating 1 h at 120 °C, prewashed with methanol and with ethyl acetate and dried 4 min in cold air stream after each development. Application areas were focused to their upper edges by a two-fold elution with ethyl acetate, followed by 1 min drying in cold air stream. Development with toluene – ethyl acetate 8:5, followed by 5 min drying, neutralization with citrate buffer (pH 12) and 4 min drying. Effect-directed analysis for genotoxicity (SOS response – UMU-C test, using NQO as positive control) by immersion (speed 3.5 cm/s, time 3 s) into Salmonella typhimurium suspension and, after 3 h incubation at 37 °C and 4 min drying in cold air stream, into one of two fluorogenic substrate solutions (methylumbelliferyl- vs. resorufin-galactopyranoside). After 1 h incubation at 37 °C, visualization of mutagenic compounds as (blue vs. red) fluorescent zones at FLD 366 nm, and densitometry performed with mercury lamp for fluorescence (at  366 / >400nm vs. 550 / >580 nm, respectively). Further validation experiments, including spiking extracts with NQO, were performed showing good mean reproducibility, no quenching or other matrix effects. Lowest effective concentration of NQO was 0.53 nM (20 pg/band), 176 times lower than in the corresponding microtiter plate assays.

J Chromatogr A, 1603, 355–360 (2019). Samples were ethyl acetate root macerates of fully flowered Tanacetum vulgare (Asteraceae). HPTLC on silica gel (classical irregular particles vs. Lichrosphere with spherical particles) previously washed with methanol, dried for 5 min at room temperature, perimeter-sealed with a polymer coat, and heated for 30 min at 100 °C. Separation with toluene or with toluene – n-hexane 7:3, in classical capillary flow or in OPLC (overpressured layer chromatography). For OPLC, off-line infusion was used (closed mobile phase (MP) outlet, automatically stopping development); external pressure 50 bar, rapid MP flush 175 and 350 µL, MP flow rate 250 and 500 µL/min, 1830 and 3475 µL MP, development time 446 s and 424 s. Derivatization by immersion into vanillin – sulfuric acid reagent, followed by 5 min heating at 110 °C; or into PABA reagent (500 mg p-aminobenzoic acid, 18 mL glacial acetic acid diluted, 20 mL water, 1 mL o-phosphoric acid, 60 mL acetone), followed by 5 min heating at 140 °C. Effect-directed analysis using automated immersion: A) for free radical (DPPH•) scavengers; B) for activity against Gram-negative bacteria using Aliivibrio fischeri bioluminescence assay; C) for activity against Gram-positive bacteria with Bacillus subtilis bioassay. Four active polyynes were identified as hexadiynylidene-epoxy-dioxaspiro-decane (1), pontica epoxyde (nonene-triynyl-vinyl-oxirane) (2), tetradeca-triine-en-one (3) and trans-(hexadiynylidene)-dioxaspiro-decene (4), by hyphenating OPLC to quadrupole-orbitrap HRMS without eluent, using a DART interface (Direct Analysis in Real-Time, needle voltage 4kV, grid voltage 50 V, helium as gas, temperature 500 °C, full scan in positive ionization mode in m/z range 100-750). Polyynes (3) and (4) were coeluting in HPTLC but not in OPLC, demonstrating that (4) is not produced by oxidation during the DART-MS procedure. Separation with OPLC compared to HPTLC was performed in a shorter time and with better resolution at the same time. Layers with spherical particles gave higher resolution; zone distortions occurring in OPLC due to dissolved air in MP were prevented by previous MP sonication.