E-Journal of Chemistry 7(2), 341-348 (2010). HPTLC of nebivolol hydrochloride and hydrochlorothiazide on silica gel with ethyl acetate - methanol - 25 % ammonia 17:2:1 with chamber saturation. The hRf value of hydrochlorothiazide was 21 and of nebivolol 41. Densitometric evaluation at 285 nm. The method was linear in the range of 200-1000 ng/band for nebivolol and 500-2500 ng/band for hydrochlorothiazide. The recovery was 98.9-102.4 %. Comparison of the HPTLC method with a RP-HPLC method and a UV spectroscopic method gave comparable results. The HPTLC method is suitable for routine quality control.

J. Chromatogr. Sci. 49, 129-135 (2011). TLC of hydrochlorothiazide (HCT), spironolactone (SPR) and their impurities and degradation products on silica gel with ethyl acetate - chloroform - formic acid - triethyl amine 70:30:1:1. Quantification by densitometry. The different method parameters were optimized for maximum separation. The method was applied for determination of HCT and SPR in commercial tablets. Statistical comparison with the also performed HPLC method showed that there is no significant difference in the performance of the methods.

J. Planar Chromatogr. 23, 298-303 (2010). TLC of oxaprozin on silica gel with n-hexane - chloroform - glacial acetic acid 4:1:1 with chamber saturation for 15 min at room temperature. The hRf value of oxaprozin was 56. Quantitative determination by absorbance measurement at 286 nm. The limit of detection and quantification was 16 and 40 µg/mL, respectively. Linearity was between 33 and 433 µg/mL. The recovery was between 98.9 and 101.6 % at different spiking levels. Intra-day precision (%RSD) at different concentration levels was 0.86-1.03 % and inter-day precision 0.99-1.15 %. Oxaprozin was subjected to stress tests (acidic and alkaline hydrolysis) and the method was able to separate the degradation products from the main compound.

J. Sep. Sci. 34, 1-9 (2011). Quantitative structure-retention (QSRR) and quantitative structure-activity relationship (QSAR) studies were performed to correlate the molecular characteristics of seven pairs of cis-trans isomeric bis-steroidal tetraoxanes with their reversed-phase thin-layer chromatography retention and their antiproliferative activity. TLC on 1) RP-18 with mobile phases of 0-14 vol% water in methanol (increment 2 %), 10-30 vol% water in acetone (increment 5 %) and 10-35 vol% water in dioxane (increment 5 %) and on 2) cyano phase with mobile phases of 10-30 vol% water in methanol (increment 5 %), 10-40 vol% water in acetone (increment 5 %). Detection by spraying with sulfuric acid 50 %, followed by heating. In all instances, it was found that the retention of the investigated compounds decreased with increasing concentrations of the organic modifier in the mobile phase.

CBS 105, 10-12 (2010). HPTLC of stratum corneum lipids (ceramides, cholesterol, phosphatidylcholine, squalene, sphingomyelin etc.) on silica gel by automated multiple development with a 8-step gradient from methanol to hexane in the AMD2 with pre-conditioning with 4M acetic acid before step 6. Detection by immersion in copper(II)sulfate reagent followed by heating at 170 °C for 8 min. Quantitative determination by absorbance measurement at 600 nm. Phosphatidylcholine and sphingomyelin remain at the start position, all other substances are separated.

62nd Indian Pharmaceutical Congress Abstract No. F-389 (2010). TLC of amlodipine and telmisartan on silica gel with chloroform – methanol – toluene 10:7:3. The hRf values were 23 and 75 for amlodipine besylate and telmisartan respectively. Quantitative determination by absorbance measurement at 238 nm. The sample was also analysed by spectophotometry and the results by both methods were comparable.

62nd Indian Pharmaceutical Congress Abstract No. F-254 (2010). TLC of amlodipine besylate and telmisartan on silica gel with ethyl acetate – methanol – 25 % ammonia – glacial acetic acid 75:15:1:2. The hRf value was 34 and 60 for amlodipine besylate and telmisartan, respectively. Quantitative determination by absorbance measurement at 226 nm. The linearity was in the range of 500-6000 ng/band for amlodipine and 1000-8000 ng/band for telmisartan. The sample was subjected to various stress conditions and all the degradation products were well resolved from the pure drugs. The method can be used for stability studies.

Acta Chromatographica 20(3), 497-511 (2008). HPTLC of 3-acetyl-11-keto-beta-boswellic acid (AKBA) on silica gel with toluene – ethyl acetate 7:3 at room temperature (25 ± 2 °C) in a twin-trough chamber with chamber saturation. Quantification of AKBA (hRf 52) by densitometry in absorbance mode at 250 nm. The linearity was in the range of 200–1200 ng/band (r=0.9989), recovery was 99.4-100.2 %, and the limits of detection and quantification were 3 and 9 ng/band, respectively. AKBA was subjected to various stress conditions: acid and alkali hydrolysis, oxidation, photodegradation, and dry and wet heat treatment. The degradation products were separated from the pure drug with significantly different hRf values.