CBS 100, 13-15 (2008). HPTLC of caffeine on silica gel with ethyl acetate - methanol - 25 % ammonia 90:15:1 (for samples of energy drinks) or chloroform - ethanol - 37 % acidic acid - acetone - water 54:27:10:2:2 (for samples of headache tablets). Detection under UV 254 nm. Quantitative determination by absorbance measurement at UV 274 nm. Automated online extraction with an HPTLC/MS interface connected to a ESI mass spectrometer. Without any internal standard the caffeine mass signal was recorded in the selected ion monitoring mode at m/z 195 [M+H]+. The method was validated. Repeatability was 5.6 % (%RSD, n=6) and reproducibility of the plate mean value was 1.5 % (%RSD, n=3).

Anal. Chem. 81, 3056-3062 (2009). TLC of organic dyes and pigments (alizarin, purpurin, carminic acid, lac dye, crocin, Cape jasmin) on silica gel with toluene - acetic acid - methanol 9:2:2. After sample application a centrifuged citrate-reduced silver colloid was spotted on top of the applied zones. SER spectra were recorded soon after application of the colloids.

Rapid Commun. Mass Spectrom. 24, 1721-1729 (2010). Ambient proximal probe thermal desorption (TD) sampling of substances from a HPTLC plate and coupled with secondary ionization by atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI). The method does not require a specialized ionization source. Different anaytical parameters and performance metrics are reported and the method covers a wide range of analyte types including explosives, dyestuffs, herbicides and pharmaceuticals.

J. Planar Chromatogr. 26, 395-401 (2013). HPTLC of 17alpha-ethinylestradiol (1), 17beta-estradiol (2) and estrone (3) on silica gel with chloroform - acetone - petroleum 11:4:5. The method was combined with the Yeast Estrogen Screen for the detection of estrogenic effects in sediment extracts of a river. Quantitative determination by absorbance measurement at 320 nm. The hRf values of compounds (1) to (3) were 74, 61 and 84, respectively.LOD and LOQ were calculated for the estrogenic model compound (1): LOD was 0.46 pg without prior development of the TLC plate and 0.48 pg after development, LOQ was 0.8 pg without development and 1.6 pg after development.

Rapid Commun. Mass Spectrom. 29, 474-484 (2015). The paper describes the modification of the standard Direct Analysis in Real Time mass spectrometry (DART) SVPA-3DS system for a reliable direct scanning of planar objects without the use of any internal standard. Optimization is focused on the substrate movement relative to the ion source outlet and the mass spectrometer inlet as well as substrate carrier and a special transfer tube. For the repeated DART-MS scanning along five identical deposited bands a mean precision of 2.7 % was obtained. A signal decay of 62 % was observed after five scans, which means that repeated analyses are possible at a decreasing signal intensity. After HPTLC of methyl-4-hydroxybenzoate and butyl-4-hydroxybenzoate, mean determination coefficients of 0.9937 and 0.9906 were obtained for five calibrations on five plates, respectively. The mean recovery of two control standards was 94 % with a mean repeatability of 9 % (n=5) obtained on five different plates.

J. Chromatogr. A 1459, 145-151 (2016). Presentation of a novel method for coupling TLC with ion mobility spectrometry (IMS) using laser desorption technique (LD). Sampling of the compounds (explosives like trinitrotoluene, 1,3,5-trinitro-1,3,5-triazacyclohexane, pentaerythritol tetranitrate, 2,4-dinitrotoluene and 3,4-dinitrotoluene; amino acids like alanine, proline and isoleucine, nicotine and diphenylamine mixtures) on the layer surface within less than 80 s after TLC separation by using the LD-IMS technique without the need of any further manipulation or preparation. The TLC plate was moved in desired directions by the motorized micro-positioning stage towards the right position of the fixed laser. TLC-LD-IMS offers an additional separation dimension, allowing separation of overlapping TLC analytes, and reveals possibility for fast and effective analysis of the mixtures due to the scan rate for LD being adjustable.

J. Chromatogr. A 1509, 147-152 (2017). Presentation of proper sigmoidal dose-response curves which can be linearized by the logit function resulting in logit-log plots in semi-log plots, from a planar yeast estrogen screen (pYES) as known for the evaluation of enzyme-linked immunosorbent assays and radioimmunoassays in microtiter plates. It was assumed to obtain sigmoidal shaped dose-response curves from the measured sign plots because pYES represents the transfer of the receptor assay YES to HPTLC. As no typical sigmoidal curves were obtained when peak areas were plotted against the applied amount on a logarithmic scale, peak heights were examined in the present study, which revealed proper dose-response curves when plotted against the log amount. The presence of sigmoidal dose-response curves from HPTLC-pYES made it possible to transform the signals into logits and, therefore, to create logit-log plots with linear correlations. The working range was up to 500 pg/zone for both 17β-estradiol (1) and 17α-ethinylestradiol (2). The mean recovery by applying logit-log plots for (1) and (2) from spiked water samples (2-20 ng/L) were 90 % and 108 %, respectively, with %RSD≤24 %. Determination of the half maximal effect dose (ED50) of the estrogen active compounds, which was represented by the intersection of the linear graph with the abscissa and also determination of the estrogenic potential in terms of estradiol equivalent factors by using the ED50 values, resulting in 0.64 for (2).

Anal. Chim. Acta 159, 359-363 (1984). TLC of pyrene on silica with ether - 3-methylpentane 4:3. Detection by site-selection spectroscopy with excitation at 363.8 nm.