J. Planar Chromatogr. 6, 438-445 (1993). Multiple development in TLC provides a straightforward means of improving the separation capacity obtained by normal development. Maximum separation power in isocratic multiple development is obtained when the distance between the solvent entry position and the sample application position is minimized and when the solvent entry position and the solvent front are incremented at each development step. Concerning the resolution the solvent selectivity is the most important parameter. A further advantage of multiple development methods is the ease of automation and the possibility of incorporating solvent gradients into the separation strategy.

(Basics and Applications of HPPLC.) Dünnschicht-Chromatographie InCom Sonderband 1996, 112-123. Description of HPPLC (completely instrumentalized circular thin layer chromatography under (if required, high) pressure), e.g. advantages, basics, practical solution of problems, special aspects of the qualitative evaluation and quantification, and application areas.

CBS 82, 9-11 (1999). HPTLC-AMD of glucose, maltooligosaccharides, anhydrosugars, transglycosidation products, fructose and its derivatives, maltulose, Amadori-compounds and Heyns-compounds on silica gel. Caramelization: isocratic 23-step gradient based on chloroform - methanol - 0.05 % aqueous boric acid 20:11:2 with 3 mm increments of the developing distance. Maillard-reaction: isocratic 3-step gradient chloroform - dichloromethane - methanol - water 35:15:35:6 over 25, 50, 75 mm developing distance. Detection by dipping in aniline-diphenylamine-phosphoric acid reagent, followed by heating at 120 °C for 10 min. Quantification by absorbance measurement at 385 nm.

CBS 95, 14-15 (2005). HPTLC-AMD of lipids from drug formulations with an 11-step gradient based on ethyl acetate. Detection by dipping in an aqueous copper sulfate solution followed by heating at 150 °C for 30 min. Quantitative determination by absorbance measurement at 675 nm, evaluation of peak area with calibration according to Hill kinetics.

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.

J. Planar Chromatogr. 3, 504-510 (1990). Multiple and stepwise development combined with gradient elution as a highly suitable method for the systematic determination of crop protection agents. The migration distance is highly reproducible (on the same HPTLC plate and on different ones). Screening and confirmation gradients coupled with reflectance spectroscopy (multiwavelength scanning) and postchromatographic, microchemical derivatization make it possible to detect crop protection agents in drinking, table, and ground waters. At least 100 substances can be checked for their presence on one HPTLC plate. Example: HPTLC separation of 21 crop protection agents in ground and drinking water with AMD. Two 23-step gradients (33 runs) based on acetonitrile, dichloromethane, hexane, formic acid, NH3 25% and on tert buthyl methyl ether, acetonitrile, hexane, formic acid, NH3. Multiwavelength scanning by adsorbance at 190, 220, 240, 260, 280, and 300 nm

J. Planar Chromatogr. 6, 386-393 (1993). Novel solvent gradient, with a linear eluotropic strength profile, comprising binary solvent mixtures from methanol to hexane. The chromatographic behavior of 55 compounds selected as models from phase I and phase II drug metabolism transformation has been studied using this linear solvent gradient with both manual and automated multiple development. The data obtained demonstrate the potential of HPTLC with linear solvent gradients for the separation and characterization of drugs and metabolites.

(HPTLC separation of low-molecular carbohydrates). Dünnschicht-Chromatographie InCom Sonderband 1996, 139-147. HPTLC of thermolysates of sugars (1,6-anhydroglucose, D-glucose, dextrin and starch) on silica with a two-step resp. a 23-step AMD development based on chloroform-methanol-water. Detection by spraying with aniline-diphenylamine-phosphoric acid and drying for 5 min at 105 °C. Quantification by densitometry at 385 nm.