J. AOAC Int. 104, 975-982 (2021). HPTLC of methionine (1) and paracetamol (2) on silica gel with butanol - dioxane - toluene - methanol 80:25:35:3. Quantitative determination by absorbance measurement at 220 nm. The hRF values for (1) and (2) were 26 and 83, respectively. Linearity was between 2 and 12 µg/zone for (1) 5 and 30 µg/zone for (2). Inter-day and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 612 and 1856 ng/zone for (1) and 1525 and 4620 ng/zone for (2), respectively. Mean recovery was 101.3 % for (1) and 100.6 % for (2). 

J. AOAC Int. 104, 1719-1725 (2021). HPTLC of diflunisal (1) and its impurity biphenyl-4-ol (2) on silica gel with toluene - acetone - acetic acid 7:13:2. Quantitative determination by absorbance measurement at 254 nm. The hRF values for (1) and (2) were 59 and 79, respectively. Linearity was between 0.5 and 3 µg/zone for (1) and 0.3 and 1.7 µg/zone for (2). Inter-day and intra-day precisions were below 1 % (n=3). The LOD and LOQ were 131 and 398 ng/zone for (1) and 72 and 219 ng/zone for (2), respectively. Mean recovery was 100.2 % for (1) and 100.5 % for (2). 

J. AOAC Int. 104, 1430-1441 (2021). HPTLC of eight different fixed-dose combination products of aspirin (1) with ramipril (2), caffeine (3), metoprolol (4), paracetamol (5), atorvastatin (6) and simvastatin (7) on silica gel with toluene - ethyl acetate - 1 % formic acid in methanol 35:65:3. Quantitative determination by absorbance measurement at 229 nm. The hRF values for (1) to (7) were 88, 15, 34, 49, 59, 66 and 78, respectively. Linearity was between 2000 and 6000 ng/zone for (1) and (5), 100 and 300 ng/zone for (2), 600 and 1800 ng/zone for (3), 1000 and 3000 ng/zone for (4), 200 and 600 ng/zone for (6) and 800 and 2400 ng/zone for (7). Inter-day and intra-day precisions were below 2 % (n=3). The LOD and LOQ were 107 and 323 ng/zone for (1), 32 and 98 ng/zone for (2), 17 and 51 ng/zone for (3), 3 and 10 ng/zone for (4), 9 and 27 ng/zone for (5), 109 and 331 ng/zone for (7), respectively. Recovery ranged 99.2-100.8 % for (1), 99.2-100.2 % for (2), 98.2-101.3 % for (3), 99.4-100.6 % for (4), 100.2-101.4 % for (5), 98.7-101.3 % for (6) and 99.6-101.3 % for (7).

J. Planar Chromatogr. 35, 509-517 (2022). HPTLC of tamsulosin hydrochloride (1) and tolterodine tartrate (2) binary mixture on silica gel with ethyl acetate - n-hexane - diethylamine 9:3:1. Quantitative determination by absorbance measurement at 225 nm. The hRF values for (1) and (2) were 40 and 85, respectively. Linearity was between 10 and 200 ng/zone for (1) and 100 and 900 ng/zone for (2). The LOD and LOQ were 3 and 8 ng/zone for (1) and 22 and 66 ng/zone for (2), respectively. Average recovery was 100.1 % for (1) and 100.7 5 for (2).

J. Planar Chromatogr. 35, 519-532 (2022). HPTLC of binary mixtures of the novel oral anticoagulants (NOACs) apixaban (1), edoxaban tosylate (2) and rivaroxaban (3) with the lipid-lowering statin, rosuvastatin calcium (4) on silica gel with toluene - ethyl acetate - methanol - 25 % ammonia 35:45:20:2 (method 1) for the three mixtures, and methanol - 25 % ammonia 199:1 (method 2) for (2)/(3) mixture only. Quantitative determination by absorbance measurement at 291 nm. The hRF values for (1) to (4) were 65, 20, 75 and 10 using method 1, and 40 for (2) and 90 for (4) using method 2. Linearity was between 5 and 45 µg/mL for (1) to (4). Interday and intra-day precisions were below 3 % (n=6). The LOD and LOQ were 0.1 and 0.4 µg/mL for (1), 1 and 4 µg/mL for (2) and (3), 0.4 and 1 µg/mL for (4) using method 1, and 1.4 and 4.7 µg/mL for (2) and 0.4 and 1.2 µg/mL for (4) using method 2. Average recovery was between 97.6 and 102.9 % for (1) to (4).

J Chromatogr Sci, 60 (9), 832-839 (2022). Establishment of two TLC methods for the synchronous estimation of cinnarizine (Cinn) and acefyline heptaminol (Acef) in the presence of reported Cinn/Acef degradation products, as well as theophylline (Theo) as potential impurity of Acef. TLC on silica gel (1) for Cinn with dichloromethane - methanol - formic acid 30:2:1 and (2) for Acef with the same solvents in ratio 150:7.5:4. Quantitative determination by densitometry at 254 nm showed that Cinn and Acef are well separated from their degradation products. The concentration range was 0.2 - 1.8 and 2 - 18 μg/zone for Cinn and Acef, respectively, with mean percentage recoveries of 99.2 / 99.8 and 99.2 / 99.7 for method 1 and method 2, respectively. The method is selective, robust and retained its accuracy in up to 50 % of Cinn/Acef reported degradation products and Theo. Application of the two methods to a coformulated drug product comprising Cinn and Acef with satisfactory results showing statistically no significant differences compared with those obtained by reference ones.

J Chromatogr Sci, 60 (10), 946 - 952 (2022). Study of the mechanism of micellar thin layer chromatography (MTLC) and development of a new simple and sensitive method for simultaneous separation of empagliflozin, linagliptin and metformin hydrochloride ternary mixture. TLC using a micellar mobile phase composed of methanol and aqueous solution of each of three different surfactants, sodium dodecyl sulphate (SDS), benzalkonium chloride (BAC) and polysorbate 80 (tween 80), in ratio of 2:3. Micellar TLC determination at 237 nm. Investigation of the quantitative structure - retention relationships by modeling, evaluating and validating with a molecular operating environment software. Discussion of the basis for selecting surfactants, for example the separation using SDS (anionic surfactant) and BAC (cationic surfactant) depended on ionization potential (AMI-IP), partition coefficient (logP (o/w)) and hydrogen bond donor atoms (a-don), whereas the separation using tween 80 depended mainly on the lipophilicity (RM0), solvation energy (E-sol) and Van der Waals energy (E-vdw).

J Chromatogr Sci, 60 (6), 606-612 (2022). Simultaneous determination of sofosbuvir and daclatasvir, co-formulated as directly acting antiviral agents used for treatment of hepatitis C virus, by TLC on silica gel with ethyl acetate - hexane - methanol 18:1:1. Both substances were quantitatively separated in one analytical run. Quantitative determination by densitometry at 280 nm with linearity range of 0.4 - 25.4 μg/band for sofosbuvir and 0.4 - 12.8 μg/band for daclatasvir. The method is time- and cost-saving, which is even more important for some combinations on the market, such as Darvoni® tablets.