J. Liq. Chromatogr. Relat. Technol. 45, 100-106 (2022). HPTLC of metformin (1), pioglitazone (2), glipizide (3), and glimepiride (4) in herbal as well as dietary supplements on silica gel with cyclohexane - dichloromethane - 1-propanol - saturated solution of ammonium acetate in acetic acid 7:5:2:2. Quantitative determination by absorbance measurement at 254 nm. The hRF values for (1) to (4) were 26, 46, 55 and 79. Linearity was in the range of 200-1200 ng/zone for (1) to (4). Intermediate precisions were below 10 % (n=9). LOD and LOQ were 186 and 565 ng/zone for (1), 192 and 581 ng/zone for (2), 154 and 465 ng/zone for (3) and 222 and 674 ng/zone for (4), respectively. Recovery was between 97.4 and 105.4 % for (1), 98.2 and 105.4 % for (2), 100.2 and 103.1 % for (3) and 98.8 and 104.4 % for (4).  

J. Liq. Chromatogr. Relat. Technol. 45, 217-225 (2022). HPTLC of capecitabine (1) and thymoquinone (2) on silica gel with toluene - methanol 3:1. Quantitative determination by absorbance measurement at 254 nm. The hRF values for (1) and (2) were 52 and 86, respectively. Intermediate precisions were below 2 % (n=3). LOD and LOQ were 17 and 54 ng/zone for (1) and 39 and 119 ng/zone for (2), respectively. 

J. Planar Chromatogr. 36, 89-97 (2023). HPTLC of remogliflozin etabonate (1) and metformin hydrochloride (2) in bulk and tablet formulation on silica gel with ethyl acetate - methanol - toluene - formic acid 5:2:9:4 (NP) and on RP-18 with water - methanol - glacial acetic acid 5:3:2 (RP). Quantitative determination by absorbance measurement at 226 nm for both methods. The hRF values for (1) and (2) were 56 and 10 for NP and 15 and 88 for RP, respectively. Linearity was in the range of 200-1200 ng/zone for (1) and 1000-6000 ng/zone for (2) in both NP and RP. Intermediate precisions were below 2 % (n=3). LOD and LOQ were 18 and 54 ng/zone for (1) and 105 and 318 ng/zone for (2) in NP and 17 and 51 ng/zone for (1) and 115 and 348 ng/zone for (2) in RP. Recovery was in the range of 100.3-100.8 % for (1) and 100.2-100.7 % for (2) in NP and 100.3-100.7 % for (1) and 100.3-100.8 % for (2) in RP.

J. Planar Chromatogr. 35, 617-625 (2022). HPTLC of montelukast (1) and loratadine (2) mixture in spiked human plasma on silica gel with chloroform - ethyl acetate 4:1. Quantitative determination by absorbance measurement at 280 nm. The hRF values for (1) and (2) were 17 and 39, respectively. Linearity was between 48 and 300 ng/zone for (1) and 90 and 600 ng/zone for (2). Intermediate precisions were below 3 % (n=3). LOD and LOQ were 9 and 28 ng/zone for (1) and 22 and 67 ng/zone for (2), respectively. Recovery was between 99.6 and 102.8 % for (1) and (2).

J. Planar Chromatogr. 35, 635-641 (2022). HPTLC of leflunomide on silica gel with toluene - chloroform - ethanol 2:2:1. Quantitative determination by absorbance measurement at 266 nm. The hRF value for leflunomide was 53. Linearity was between 100 and 600 ng/zone. Intermediate precisions were below 2 % (n=6). LOD and LOQ were 4 and 13 ng/zone, respectively. Recovery was between 100.8 and 103.8 %.

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 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).