TLC as valuable instrument for preliminary proceedings suitable for chromatographic systems in HPLC separation problems. Reasons and preconditions for TLC as pilot procedure are given. 62 pesticides of 6 different substance classes, i.e. triazines, phenoxycarboxylic acids, urea herbicides, aniline derivatives, phosphoric acid esters, etc., are used for transmission of retention characteristics to HPLC. TLC of triazines on RP-8 with acetonitrile - water 3:2, of phenoxycarboxylic acids on RP-18 with acetonitrile - water - acetic acid 15:9:1, of urea herbicides on CN with hexane - tetrahydrofuran 3:2, of aniline derivatives on NH2 with hexane - tetrahydrofuran 7:3, of phosphoric acid esters on silica with hexane - tetrahydrofuran 3:2, of further pesticides on diol with hexane - tetrahydrofuran 7:3.

Chromatographia 47, 529-536 (1995). 2D-TLC on silica gel with hexane - ethyl acetate 7:3 for the 1st direction and hexane - acetone for the 2nd. Identification by comparison of the retention values. Also HPLC and mass spectrometry.

J. Chinese Trad. Patent Med. (Zhongchengyao) 25 (7), 538-540 (2004). TLC on silica gel with 1) petroleum ether - ethyl acetate - butanone - methanol - water 15:25:3:7:1; 2) petroleum ether - ethyl acetate - formic acid 15:5:1. Detection 1) under UV light, 2) by spraying with 5 % potassium iodobismuthate solution and heating at 105 ºC for 5 min. Identification by finger print technique. Quantification of betaine by densitometry at 514 nm.

Acta Chrom. 11, 204-214 (2001). Electric fields have been shown to affect peak width, peak area, and other chromatographic properties in reversed-phase TLC on silanized silica gel and RP-18. To eliminate electroosmotic flow, thin layer electro-chromatography was performed on unwetted layers. Horizontal and vertical modes of thin-layer electrochromatography were investigated, but only for chromatographic systems in which van der Waals forces are the sole interactions. Analytes were polycyclic aromatic hydrocarbons and hexane or heptane was used as mobile phase. The electric field affects the chromatographic process not only by replacing capillary flow by electroosmotic flow.

LC-GC Europe 16, 2-5 (2003). Overview of utility of the technique for the identification and quantification of pharmaceutical compounds and related substances such as UK-137,457 (C31H31NO5) and UK-124,912 (C27H25NO3). Several of the issues that have arisen in the development of TLC-MALDI-MS methods for the successful analysis of pharmaceuticals were adressed in this article. Electrospray deposition method, which was found to be superior to other methods studied and was successfully applied to a range of compounds presented, concerns a method for the deposition of the MALDI matrix onto the TLC plate. Post-source decay analysis can be performed directly on the TLC spots, to aid in structural evaluation of the analyzed compounds. The generation of quantitative data using a structural analogue as internal standard and incorporation into the mobile phase has also been demonstrated. Outlook for next step development of TLC-MALDI-MS in pharmaceutical analysis for more widespread use in industry: enhance sensitivity, mass resolution and reproducibility, availability of commercial instruments that allow the scanning of whole TLC plates rapidly with data-imaging software.

Anal. Chem. 81, 9274-9281 (2009). TLC of dye standards (FD&C Green No. 3, FD&C Red No. 3, eriochromcyanin R), drug standards (3,4-methylene-dioxy-N-methamphetamine, lysergic acid diethylamide, flunitrazepam), and rosemary essential oil on 1) RP-18 with 65 % acetone containing 1.5 % formic acid and 2) on silica gel with chloroform - methanol 9:1. Rosemary essential oil was also separated on silica gel with toluene - ethyl acetate 9:1. Detection under UV 254 nm and in daylight. The combination of laser-induced acoustic desorption and electrospray ionization mass spectrometry (LIAD/ESI/MS) can be used to rapidly characterize chemical compounds separated on a TLC plate.

Quim. Nova. 34, 330-334 (2011). TLC of rosmarinic acid in preparations of Rosmarinus officinalis on silica gel with acetone – formic acid – methylene chloride 50:17:170. Detection under UV 366 nm. Quantitative determination by solid state differential pulse voltammetry (DPV). Linearity was between 0.694x10-3 to 0.526x10-3 mol/L. The limits of detection and quantification were 1.2x10-5 and 3.6x10-5 mol/L, respectively. The intermediate/interday/intraday precisions were 3.03 % and 2.2 %, respectively. Recovery (by standard addition) was 96.3 % for rosmarinic acid. The method presented high recovery levels compared to an HPLC method.

J. AOAC Int. 96, 1167-1174 (2013). The review reports various applications of bioautography tests for determination of wide spectrum of antimicrobials. Based on two direct tests using Bacillus subtilis and Escherichia coli, the review discusses different applications for the screening of analytes in various biological samples. For example, the antibacterial activity of essential oils in conifers is estimated on the basis of the measured area of inhibition zones.