J. Planar Chromatogr. 25, 331-337 (2012). HPTLC of danazol on silica gel with hexane - acetone 3:2. Quantitative determination by absorbance measurement at 291 nm. The hRf value of danazol was 55. Linearity was in the range of 200-1200 ng/zone. Limits of detection and quantification were 1 and 4 ng/zone.

of Chromatogr. A 1231, 59-65 (2012) Reversed-phase HPTLC of lutein, lycopene and beta-carotene standards on RP-18 (pre-washed by development with dichloromethane – methanol 1:1) with methanol – acetone 1:1 with 0.1 % of 2-tert-butylhydroquinone. The hRf value was 4 of lutein esters, 24 of beta-carotene, 32 of lycopene, and 68 of lutein. Quantitative determination of lutein by densitometry at 450 nm. The repeatabilities were %RSD = 3.4, 1.3 and 1.6 at levels of 5 ng, 15 ng and 25 ng, respectively (n = 6). The calibration curve was best fit with a polynomial function in the range of 5-30 ng. The LOD was 1.5 ng, the LOQ 5 ng. With these chromatographic conditions also dietary carotenoids lutein esters, lycopene, free lutein and ß-carotene from food supplements were identified. It was shown that the standards remain stable on the plate for 1 h after chromatogram development.

J. Planar Chromatogr. 25, 433-438 (2012). HPTLC of quercetin (1) and kaempferol (2) in the leaves of Centella asiatica on silica gel with toluene - ethyl acetate - chloroform - formic acid 6:4:4:1. Quantitative determination by absorbance measurement at 240 nm. The hRf of compounds (1) and (2) were 35 and 48, respectively. Linearity was in the range of 100-1000 ng/band. Limits of detection and quantification were 54 and 165 ng/band for (1) and 68 and 207 ng/band for (2), respectively. Intra-day relative standard deviation of (1) was between 5.3 and 6.5 % and of (2) between 5.1 and 11.4 %. Inter-day relative standard deviation of (1) was 2.1-6.6 % and of (2) 2.6-5.8 % (n=6). Recovery was found to be 98.1 % for (1) and 90.1 % for (2).

J. Planar Chromatogr. 25, 30-35 (2012). HPTLC of rutin (1), narcissin (2), nicotiflorin (3) and isoquercitrin (4) on silica gel with ethyl acetate - 1,2-dichloroethane - acetic acid - 85 % formic acid - water 100:25:10:10:8. Quantitative determination by absorbance measurement at 360 and 387 nm. Intraday and interday precisions were in the range of 1.5-1.9 % and 1.6-1.9 %, respectively. Recovery was found to be 98.2-101.4 % for (1), 98.0-101.1 % for (2), 98.2-100.5 % for (3) and 98.1-101.9 % for (4).

J. Planar Chromatogr. 25, 368-373 (2012). HPTLC of rebamipide on silica gel with toluene - methanol - triethylamine 16:9:1. Quantitative determination by absorbance measurement at 230 nm. The hRf of rebamipide was 59. Linearity was in the range of 100-600 ng/band. Limits of detection and quantification were 6 and 18 ng/band, respectively. Intermediate intra-day/inter-day precision was below 1.7 % (n=3). Recovery (by standard addition) was between 100.1 and 100.9 %. The proposed HPTLC method is equivalent to a reported HPLC method.

CBS 110, 10-11 (2013). New HPTLC silica gel plates specially suited for coupling with MS and TLC plates for coupling with NMR. These MS-grade HPTLC plates are low in impurities and show less background noise, the layer thickness is 100 µm. HPTLC of human insulin and its secondary components on MS-grade silica gel with 2-butanol - pyridine - ammonia 25 % - water 39:34:10:26, detection under UV 366 nm after treatment with fluorescamine and by elution with the TLC-MS Interface and Q-TOF MS analysis in ESI positive mode, the eluent was acetonitrile - water 19:1. Separation and identification of insulin and desamido insulin was achieved, even though there is only 1 Da mass difference.

CBS 109, 10-12 (2012). HPTLC of steviol glycosides (stevioside, rebaudioside, dulcoside A, steviolbioside) on silica gel (pre-washed with methanol and dried at 100 °C for 15 min) with ethyl acetate - methanol - acetic acid 3:1:1 over 60 mm. Detection under white light after immersion in ß-naphthol reagent (2 g in 180 mL ethanol with 12 mL 50 % sulfuric acid) and heating at 120 °C for 5 min. Quantitative absorption measurement at 500 nm after derivatization. LOD was 10 ng/band and LOQ 30 ng/zone. Using the calibration curve method the LOQ was reduced to 12 ng/band via peak height and 20 ng/band via peak area. The calculated expected tolerance range over the whole procedure inclusive sample preparation considered recovery rates at 3 different concentration levels (0.02, 0.13, and 0.20 %) in milk-based matrix. The accuracy (recovery tolerance limit of 92-120 %), repeatability (3.1-5.4 %) and intermediate precision (4.0-8.4 %) were highly satisfying, exemplarily shown for stevioside in milk-based matrix. ANOVA was successfully passed to prove the working range. With the newly developed and validated HPTLC method, steviol glycosides in Stevia leaves, Stevia formulations, and food products were investigated.

J. Liq. Chromatogr. Relat. Technol. 36, 1528-1539 (2013). HPTLC of mebeverine hydrochloride (1), metronidazole benzoate (2), diloxanide furoate (3) and metronidazole (4) in pharmaceutical suspensions on silica gel with hexane - acetone - triethylamine 35:15:3. Quantitative determination by absorbance measurement at 254 nm. The hRf values of compounds (1) to (4) were 10, 34, 49 and 64, respectively. Linearity was 0.4-2.4 µg/zone for (1), 0.3-2.0 µg/zone for (2) and 0.4-2.4 µg/zone for both (3) and (4). Intermediate precision was below 1.2 %. Recovery (by standard addition) was 99.9-100.1 % for compounds (1) to (4). Comparable results were obtained when compared with reported RP-HPLC methods.