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. 3, 417-421 (1990). Retention versus eluent composition relationships of 36 drugs and poisons have been determined using silica gel and 20 binary eluents - mixtures of four weakly polar diluents (heptane, chloroform, dichloromethane, and trichloroethylene) and four polar modifiers (MEK, ethyl acetate, ether, diisopropyl ether) or mixtures of the four polar modifiers with methanol. In accordance with the Snyder-Soczewinski model of adsorption, linear relationships of the type RM = RM - m log cmod were obtained in almost all cases.

Chromatographia 35, 102-108 (1993). Study of the optimization of TLC parameters. Comparison of the window diagram and overlapping resolution map methods. Use of the latter to take into account the spot diameter and the average plate height variations with the development distance, in order to improve the reliability of the method.

J. Planar Chromatogr. 8, 319-323 (1995). Application of a test mixture (thymol blue, methyl red, bromothymol blue, oracet blue) on silica with an automatic TLC sampler. Followed by radial development with a selection of solvents also delivered by the automatic TLC sampler. Chromatograms can be obtained by densitometry. Inspection enables selection of the approximate solvent strength (Snyder’s solvent classification table) for the separation. The results indicate which solvent group has the required selectivity. So a suitable solvent system can generally be determined in two to three methodical steps. Rapid, cost-effective method requiring minimal solvent and sample consumption.

J. Liq. Chrom. & Rel. Technol. 22, 15-27 (1999). Investigation of the dependence between retention of five different test solutes and the mobile phase composition in TLC systems with 3-cyanopropyl modified silica gel and binary 2-propanol - n-hexane eluents; calculation of regression parameters and conclusions regarding efficiency of the retention models.

J. Planar Chromatogr. 3, 216-221 (1990). Solvent systems for the separation of either steroids or esters of dansyl amino acids in both one-dimensional (1-D) and two-dimensional (2-D) planar chromatography solvent systems are ranked on the basis of simulations of optimized separations, the quality of which is quantified using suitable separation functions. The paper discusses the correlation between solvent ranking in the 1-D and the 2-D mode based upon either the solvent ranks or the actual values of the separation functions. The simulated separations are based on experimental results obtained using either TLC or overpressured layer chromatography.

J. Planar Chromatogr. 5, 334-337 (1992). Discussion of the possibility of calculating optimum values of the differences in chromatographic parameters for the components of separated mixtures on the basis of a retention model based on the law of mass action. The comparison of calculated values with those obtained experimentally on silica eluted with various mixed mobile phases has demonstrated the usefulness of the method.