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, bmad045 (2022). Standards were azilsartan medoxomil (AZL) and cilnidipine (CLN). Samples were acetonitrile solutions of commercial tablets of AZL and CLN, and purified human blood plasma as biological fluid spiked with AZL and CLN. The following method was developed by a software-assisted AQbD approach (analytical quality by design): (1) Taguchi orthogonal array design was implemented in 8 screening experiments in order to identify the 3 critical method variables (CMVs), which were: volume ratio of toluene – ethyl acetate, volume of methanol and saturation time. These CMVs had statistically significant impact (one-way ANOVA and Pareto charts) on the 3 critical analytical attributes (CAAs, they were: resolution between AZL and CLN and their hRF values). (2) To optimize these CMVs, the Box–Behnken design was implemented in 15 software-proposed experiments; the impacts of the 3 CMVs on the 3 CAAs were evaluated by ANOVA, multiple regression analysis, and 2D and 3D contour plots; the response surface analysis allowed the software to find a mathematical (quadratic or linear) equation for each CAA, based on the CMVs values. (3) The optimal CMVs ranges were determined by defining an analytical design space (ADS) 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 15 min at 110° C. Separation with toluene – ethyl acetate – methanol 13:3:4 after 15 min pre-saturation with 35 % relative humidity. Absorption measurement at UV 254 nm. The hRF values were 49–51 for AZL and 70–71 for LRT. Linearity range was 400–2000 ng/zone for AZL and 100–500 ng/zone for CLN. Intermediate precision was below 1.6 % (n=3). LOQ were 121 ng/zone for AZL and 34 ng/zone for CLN. Recovery rates were 99.3–99.7 % for AZL and 98.1–99.5 % for CLN. Recovery rates from spiked plasma were 83.3 % for both molecules.

J. Planar Chromatogr. 28, 234-240 (2015). HPTLC of (1) omeprazole, (2) pantoprazole, (3) rabeprazole and (4) diclofenac from tablets on silica gel previously washed with methanol and activated at 105 °C for 20 min, with toluene - n-butanol - 25 % ammonia 30:70:2. Quantitative determination by absorbance measurement at 290 nm. The hRF values were 67 for (1), 38 for (2), 57 for (3) and 27 for (4). Linearity was between 50 and 500 ng/zone for (1), (2) and (3), and between 150 and 1500 ng/zone for (4). The interday and intraday precisions were below 2 %. The LOD and LOD respectively for (1) were 7 ng/zone and 24 ng/zone, for (2) 9 ng/zone and 30 ng/zone, for (3) 13 ng/zone and 43 ng/zone, and for (4) 25 ng/zone and 82 ng/zone. Recovery was 99.6 % for (1), 100.1 % for (2), 100.4 % for (3) and 100.1 % for (4).

J. Liquid Chromatogr. 14, 3213-3239 (1991). Proposal of a new combination of four organic solvents for the optimization of TLC separations of basic drugs and alkaloids using response surface modelling and mixture designs. Adjustment of solvent strength and selectivity using a four component mixture space of tetrahedron. Discussion of the selection of the four solvents defining the factor space, the selection of the design space and of the experimental design, the optimization criterion, and the POEM software used for modelling the response surface and locating the optimal solvent composition.

J. Planar Chromatogr. 6, 296-299 (1993). Integration of four computer-assisted methods (the monofactor optimization system (MOS); the multicomponent solvent optimization system (MSOS); the difactor optimization system (DOS); and the stepwise gradient optimization (SGOS)) for optimizing HPTLC separation in order to produce the optimization system of TLC (OS T), resulting in a method development strategy which obtains simple solutions for simple separation problems and reserves the more complex solutions for difficult separations.

Proc. 9th Internat. Symp. Instr. Chromatogr., Interlaken, April 9.-11., 337-339 (1997). Prediction of retention data using multiple development and circular techniques from a single development.

J. Planar Chromatogr. b, 178-182 (2001). Evaluation of molecular interactions in liquid adsorption chromatography with mixed mobile phases. Two equations based on different retention mechanism models were verified experimentally. TLC on silica gel; development in horizontal chambers with cyclohexane - carbon tetrachloride, cyclohexane - ethylene chloride, n-heptane - ethylene chloride, and n-heptane - acetone.

J. Chromatogr. Sci. 53 (3), 436-442 (2015). Review on the most important aspects of forced-flow TLC, including the set-ups developed and the progress of detection methods used. Description of mobile phase progress in planar stationary phase, evoked by either internal forces, capillarity, or external forces, e.g., gravity, electric field, a pump and centrifugal forces. Emphasizing on overpressured layer chromatography and forced-flow planar chromatography, as a special bridge between HPLC and TLC. Characterization of a simple and special rule of the progress of mobile phase: optimal efficiency is composed by the doubled effect of flow resulting from the pump-forced mobile phase (convex profile of laminar flow) and capillary forces on the dry stationary phase (concave laminar flow).