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, 381-385 (1990). The retention of 13 2-nitro-4-cyanophenyl esters and 10 trisubstituted symmetric triazine derivatives was determined on silica layers impregnated with silicone oils of various molecular mass, and vinyl content. The data were evaluated by principal component (PC) analysis performed on the covariance and correlation matrices of the original data set. It was established that the retention of each solute increases with increasing vinyl content, and that the molecular mass has a lower impact on retention than does the vinyl content. Application of multivariate mathematical methods in the evaluation of RP retention data.

I. Regular part of the model. J. Planar Chromatogr. 4, 460-466 (1991). Manual examination of the retardation behavior of 16 apolar, closely related coumarins in normal phase TLC using the regular part of the three-dimensional „PRISMA“ model. The results show a highly significant second order dependency between the retardation factor (Rt) and the solvent strength (vertical correlation), as well as between the retardation factor and the selectivity point (horizontal factor).

J. Planar Chromatogr. 7, 340-343 (1994). Comparative study of seven earlier reported (CBS 69 079) and six additional mobile phases for TLC of phospholipids. Best resolution and most sensitive detection of phospholipids was obtained by four unidimensional developments on silica with chloroform - methanol - isopropanol - 0.25 % potassium chloride - ethyl acetate 30:9:25:6:18. Visualization of amino lipids by spraying with 0.2 % ninhydrin in butanol saturated with water and of glycolipids by spraying with 0.5% a-naphthol in methanol - water 1:1, followed by drying, spraying with sulfuric acid - water 95:5 and heating at 100 °C. Quantification by densitometry at 400 nm.

J. Planar Chromatogr. 11, 191-194 (1998). Description of a new method used to optimize a ternary mobile phase used for separation of mixtures of organic compounds by HPTLC. Computer programs have been written to assist prediction of the optimum mobile phases. The method was found to be a rapid and efficient tool in mobile phase optimization. HPTLC of (chlordiazepoxide, oxazepam, nitrazepam, medazepam, diazepam) on silica gel with chloroform - acetone - i-propanol mixtures of different compositions. Densitometry at 254 nm.

J. Planar Chromatogr. 3, 430-431 (1990). TLC of 4 dithia[3.3]-phanes on RP-18 silica with methanol - water 9:1. Visualization under UV. Numerical values of the Rf coefficient were established for each solute-phase combination, regressionally fitted into a physically based equation resulting in good correlation.

Chromatographia 34, 303-307 (1992). Stepwise gradient TLC of mixture containing model colored solutes and glycosides from Digitalis species on silica with toluene - ethyl acetate system and ethyl acetate - methanol system. Determination of the optimal gradient programs by using a computer. Discussion of the separation and the agreement of predicted and experimental Rf values and the elution time with the non-aqueous system.