J. Planar Chromatogr. 8, 349 - 356 (1995). TLC of estradiol benzoate on silica (prewashed with chloroform - methanol 1:1 with hexane - acetone - 2-propanol 45:1:1. When testing the peak purity by 2D-TLC, the mobile phase used in the second direction was chloroform - acetone 19:1. Evaluation by spectrodensitometry at 229 nm. - Determination of specificity, analyte stability, linear range, accuracy, precision (repeatability, intermediate precision), detection, and quantification limit, as well as the robustness of the method.

J. Planar Chromatogr. 17, 102-108 (2004). For sample preparation a methanolic salicylic acid solution was sprayed onto a 40x40 cm glass plate. Samples from different positions of the test plate were extracted with methanol and analyzed by HPTLC and HPLC. HPTLC of salicylic acid on silica gel with cyclohexane - isopropanol - chloroform - acetic acid 12:1:1:2. Quantitation by densitometry. Measurement uncertainty in HPTLC and HPLC is relatively small and has no effect on recovery. To come close to the true value the analytical procedure must be managed by well-considered selection of number and positions of sampling locations. TLC is an excellent analytical technique which gives reliable results.

J. Planar Chromatogr. 23, 173-179 (2010). Many manuscripts and already published articles on analytical procedures to be used in pharmaceutical quality control are characterized by several typical methodological failures and misconceptions. The autors present a collection of typical failures, misconceptions, and misleading data from articles published over the last two years in seven well-known chromatographic publications and provide at the same time a list of references describing optimum approaches to validation of specific TLC/HPTLC procedures. In particular, method specificity, linearity, accuracy, and precision very often are not determined properly and in accordance with best practise.

Planar Chromatogr. 8, 269 - 278 (1995). HPTLC of theophylline and structural related substances (i.e. theophyllidine, methylxanthine, theobromine, etophylline, caffeine) on silica with toluene - 2-propanol - acetic acid 16:2:1. Quantification by densitometry at 274 nm.

Part 3. Evaluation and calibration errors. J. Planar Chromatogr. 18, 256-263 (2005). Third part of a series discussing fundamentals of systematic quantitative errors; systematic errors caused in separation systems; evaluation and calibration errors; nonlinear separation and quantitation techniques; the ,sf4’ procedure for finding summarized systematic errors; systematic errors caused by regulation; conclusions and proposals for quantitative PLC. A correlation function is needed to obtain correct quantitative results from the raw data of a chromatogram - i. e. maximum peak height, peak area of part or or all of a PLC spot, a line or a circle (for circular chromatography): Yi = Ai + Bi x Xi + Ci x (Xi)² + Di x (Xi)³. After 1) Introduction (and example), 2) Evaluation, 3) Calibration errors (3.1 Calibration function found by polynomial interpolation, 3.2 Calibration data analysis, 3.3 Data details for polynomial interpolation, 3.4 Analysis of the ,overall data quality’, the ,data Goodnes’, 3.5 Effect of mathematical accuracy, 3.6 Positioning of the calibration sample ,i’ and the number of different concentrations/amounts to use) follows 4) A possible future of sampling and flexible precise positioning not only of the calibration substances.