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, 326-330 (1990). Optimization of mobile phase composition for the separation of phenylurea and s-triazine herbicides on silica by means of the „ELUO“ method in which solvents are selected from an eluotropic series based on solvent power. The method is complementary to the „PRISMA“ method for optimizing the compositions of binary, ternary and quaternary mobile phases for OPLC, or even HPLC and HPTLC. TLC of 13 herbicides on silica with five different binary solvent systems.

J. Planar Chromatogr. 6, 144-146 (1993). Investigation of a computer assisted retardation factor prediction system (RFPS) for 15 O-ethyl-O-aryl-N-isopropyl phosphoroamidothioates in HPTLC. The system is based on the use of 4 physico-chemical parameters: hydrophobicity, electric affect, field effect, and steric effect, all of which have a significant influence on HPTLC retention mechanism. The system has been evaluated by comparison of measured retardation factors with those predicted data and experimental results.

J. Planar Chromatogr. 9, 192-196 (1996). Optimization procedures in TLC require unambiguous goals, and optimization criteria express such goals in mathematical terms. If the retardation factor, Rf, varies as a function of the parameters to be optimized criteria should be selected that enable simultaneous optimization of retention and selectivity. It is demonstrated that the result of an optimization process depends on the optimization criterion selected. Substances chromatographed: Metalaxy, pyridaphenthion, trademefon, thiobencarb on HPTLC silica with hexane - ethyl acetate in different compositions.

J. Planar Chromatogr. 13, 88-92 (2000). TLC of cephalosporins (cephalexine, cefaclor, ceftriaxone, cefixime, cefotaxime) on silica gel developed with a variety of binary mobile phases containing different amounts of organic modifier. The influence of type, chemical character, and position of the substitution of functional groups (steric and structural effects) on the retention was of particular interest.

J. Planar Chromatogr. 21, 315-323 (2008). The role of the mobile phase in controlling selectivity for adsorption chromatography - with either thin-layer plates or columns - is reviewed and expanded. The use of different solvent mixtures of varying selectivity in normal-phase chromatography is now on a firm theoretical and practical basis. The choice of a more polar component (B-solvent) of a binary solvent mixture (A/B) largely determines relative retention and resolution. Maximum differences in selectivity are achieved by the use of two mobile phases where the B-solvent is either very polar (requiring a lower % B for desirable values of k) or relatively nonpolar (requiring a higher % B).

J. Planar Chromatogr. 3, 425-528 (1990). It is proposed the RM values of substances analyzed on silica with tertiary mobile phases may be predicted from one-parameter regression equations. Experimental RM values for a group of isomers investigated have been compared with theoretical values calculated both on the basis of the author’s own studies (RMy = f(RMx)), and from Oscik’s theory. Substances chromatographed: o-, m- and p-isomers of aminophenol, ethylphenol, cresol, nitroaniline, nitrophenol, toluidine, chloroaniline, chlorophenol, nitrotoluene, chlorotoluene.