J. Planar Chromatogr. 28, 223-228 (2015). HPTLC of beta-amyrin in the leaves of five different Ficus species (F. carica, F. nitida, F. ingens, F. palmata and F. vasta) on silica gel with toluene - methanol 9:1. Detection with p-anisaldehyde reagent followed by heating. Quantitative determination by absorbance measurement at 550 nm. Precisions (intra- and inter-day) were 1.6-1.8 % and 1.7-1.8 % respectively (n=6). The hRF value was 58. Linearity was between 100 and 900 ng/zone. The LOD and LOQ were 32 ng and 96 ng/zone, respectively. Recoveries were 97.6-98.3 %.

InCom-Sonderband 241-244 (1997). Because of the "in-line quality assessment" of the development and the evaluation in TLC at each step of preparation as well as the evaluation of the quality of the separation process after the chromatographic procedure TLC is - according to the author - the most reliable separation technique.

J. Planar Chromatogr. 28, 213-217 (2015). HPTLC of (1) chlorogenic acid, (2) caffeic acid, (3) faradiol and (4) rutin from Calendula officinalis plant extracts on silica gel previously activated at 50 °C in an oven for 30 min. Automated multiple development (gradient elution) with n-hexane, ethyl acetate containing 2 % acetic acid, and water as mobile phase. Detection by spraying with either 10 % sulfuric acid in methanol or 2-aminoethyl diphenylborinate solution followed by placing in oven at 50 °C for 30 min. (1), (2), (3), and (4) were used as markers to investigate and assess the quantitative errors observed. Accuracy of the sample applicator at different sample volumes, the use of a gradient mobile phase, and post-derivatization contribute to uncertainties of the HPTLC method and need to be carefully selected to minimize errors.

Proc. 9th Internat. Symp. Instr. Chromatogr., Interlaken, April 9.-11., 251-259 (1997). General aspects of quality assurance and validation in connection with TLC and the Camag Video Documentation System (including schematic presentation, flow chart of the validation procedure and a chromatogram of a caffeine standard obtained from the CCD image of the HPTLC).

J. Planar Chromatogr. 28, 241-247 (2015). TLC of (1) citicoline sodium in the presence of its (2) alkaline degradation products in pharmaceutical oral solution on silica gel with ammonia - ethyl acetate - triethylamine 12:7:1. Quantitative determination by absorbance measurement at 272 nm. The hRF value was 35 for (1) and 10 for (2). Linearity for (1) was between 0.6 and 2.2 µg/zone. The intraday precision was 0.2 % and interday precision was 1.2 % for (1). The LOD and LOD of (1) were 41 ng/zone and 237 ng/zone, respectively.

J. Planar Chromatogr. 10, 290-297 (1997). TLC of miltefosine on silica with chloroform - ethanol - p-toluenesulfonic acid (0.25 mol/L) in NH3 25% 7:4:1. Detection by immersion into a copper(II) sulfate solution (10 g copper sulfate were filled up to 100 mL with 8% phosphoric acid) for a few seconds and heated at 180°C for 20 min. Quantification by densitometry at 500 nm. For detection of 1-octadecanol development in dichloromethane - methanol - 25% NH3 (100:1:0.2), followed by immersion into copper sulfate solution. Validation, specificity, linearity, accuracy, detection and quantification limit, precision, robustness, log P determination, method development, experimental details, and results are described in detail. Also published in Proc. 9th Internat. Symp. Instr. Chromatogr., Interlaken, April 9.-11., 289-303 (1997).

J. Planar Chromatogr. 28, 426-435 (2015). HPTLC of methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate and butyl 4-hydroxybenzoate on silica gel with petroleum ether - acetic acid 20:3. Quantitative determination by absorbance measurement at 254 nm. The influence of experimental settings on densitometric evaluation using the TLC Scanner 4 was investigated to assess the impact on signal intensities, peak shape/resolution and quantitative results. Peak positions can shift for up to 0.5 mm for fast scan speeds. For improved quantitative results the scan slit length should be set to 75 % of the band length, the scan speed to 5 or 10 mm/s and data resolution to 25 or 50 μm/step. The resolution mode of the optical system provided higher signal intensities compared to the light mode. Peak broadening was observed for higher scan speeds, whereby the signal height decreased significantly, if compared to the peak area evaluations. The effects of the instrumental settings on the signal intensity were less pronounced for the evaluations via peak area. Hence, peak area evaluations were more robust with regard to the changed settings.

Proc. 9th Internat. Symp. Instr. Chromatogr., Interlaken, April 9.-11., 365-372 (1997). Presentation of the validation of a HPTLC procedure for quantification of caffeine with a Video Documentation System. Validation was performed according to the ICH guidelines, considering the special features of the method. The validation parameters were: selectivity, stability of the analyte, linearity, precision (repeatability and intermediate precision) and robustness. The obtained results were compared with those obtained by the slit-scanning densitometer. HPTLC of caffeine on silica with dichloromethane - methanol 9:1. Evaluation by densitometry at 270 nm. Repeatability 1.59% (densitometer) and 1.21% (CCD camera); intermediate precision 1.22% (densitometer) and 1.12% (CCD camera); robustness 1.47% (densitometer) and 1.37% (CCD camera).