Anal. Chem. 75, 2493-2498 (2003). Development of two interfaces to connect small-size thin-layer chromatography with electrospray ionization mass spectrometry (ESI-MS) for the continuous analysis of organic mixtures. The interfaces were 1) two bound optical fibers inserted into the RP-18 particles at the exit of a small TLC channel; 2) a small commercial TLC strip with a sharpened tip. A reservoir continuously supplied a makeup solution to the tip of the TLC channel. The high voltage required for electrospray ionization was introduced into the makeup solution or mobile phase through a Pt wire, and electrospray was generated at the tip of the bonded optical fibers and at the sharp end of the TLC strip. Since small-size TLC channels were used, the elution time was short and less than 0.2 µL of sample solution and 200 µL of solvent were required.

Rapid Commun. Mass Spectrom. 23, 3655-3660 (2009). TLC of berberine and palmatine in roots of Berberis barandana on silica gel with butanol - acetic acid - water 14:3:4. Detection under UV 366 nm. Bands were cut out for further analysis by laser desorption ionization mass spectrometry. The hRf value of berberine and palmatine was 56 and 46, respectively.

J. Liq. Chromatogr. Relat. Technol. 34, 864-887 (2011). Comparison of a one dimensional TLC-MS separation and fingerprinting method with a two-dimensional TLC-LC-MS method, when applied to the analysis of phenolic acids and flavonoids from Salvia lavandulifolia. TLC directly or indirectly coupled with mass spectrometric detection proved very useful in the analysis of the phenolic acid and flavonoid fraction selectively extracted from botanical material.

J. Planar Chromatogr. 27, 328-332 (2014). HPTLC of crude extracts of micro-algae Dunaliella bioculata, Phaeodactylum tricornutum, and Scenedesmus obliquus on silica gel with dichloromethane - methanol 95:5. Data analysis of pictures digitally acquired at UV 254 nm and UV 366 nm included baseline correction, chromatogram alignment, principal component analysis (PCA) de-noising and diffusion drift correction. The workflow allowed to obtain a peak list containing hRF values, intensities and areas for statistical analysis.

Food Res. Int. 87, 68-75 (2016). HPTLC of saponins in an extract of Quillaja saponaria on silica gel with chloroform – acetic acid – methanol – water 16:8:3:2. Detection by dipping for 1 s into a matrix solution (2,5-dihydrobenzoic acid 200 mg/mL in acetonitrile – water 9:1 with 0.1 % trifluoroacetic acid 3:7 and 10 mM ammonium dihydrogen phosphate), followed by drying for 90 s under an airstream. Dipping was repeated and the plate was dried for another 4 min. The plate was stored in a vacuum oven at 60 °C ensuring complete desiccation of the matrix coating. The measurement was performed by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF/TOF).

J. Chromatogr. A 1465, 197-204 (2016). Demonstration of a strategy for an improved quality control of propolis shown on the example of 30 French propolis samples based on evaluation of their HPTLC fingerprints in combination with selected mass signals obtained by desorption-based scanning mass spectrometry (MS). Separation of the French propolis sample extracts by HPTLC on silica gel with n-hexane – ethyl acetate - acetic acid 5:3:1 and on RP phase with n-hexane – toluene – ethyl acetate – formic acid – acetic acid 16:6:10:3:3, both in twin-trough chambers with 37 % hydrochloric acid applied on a filter paper in the second trough of the chamber. Analysis of the fingerprints, obtained by two different detection modes, i.e. after (1) derivatization with NP and PEG reagents and fluorescence detection at UV 366 nm and (2) scanning direct analysis in real time (DART)-MS, by multivariate data analysis. The best classification was obtained using both methods, RP-HPTLC-FLD and RP-HPTLC-DART-MS, in combination with pattern recognition techniques, such as principal component analysis. Observation of the characteristic patterns from the two types, in which all investigated French propolis samples were divided. Identification of phenolic compounds, such as caffeic acid, p-coumaric acid, chrysin, pinobanksin, pinobanksin-3-acetate, galangin, kaempferol, tectochrysin and pinocembrin, as characteristic marker compounds of French propolis samples. Confirmation of the presence of two botanically different types of propolis, known as the blue and orange types.

J. Chromatogr. A, 1572, 145-151 (2018). Introduction of on-surface reactions as a new strategy for rapid structure elucidation. This was illustrated by a miniaturized on-surface synthesis-guided identification of two new degradation products (impurities) occurring in a pharmaceutical formulation of the anti-cancer drug ifosfamide, especially in the presence of urea. The respective reagents were applied in the nanomole scale accurately and automated on a HPTLC silica gel plate. After a fast reaction in the start zone, the plate was developed, followed by online elution to high-resolution MS, whereby the on-surface reaction highlighted the impurities. As proof of concept and for benchmarking, it was compared to a reaction mixture obtained from conventional preparative synthesis in a round-bottom flask as well as to different formulations. Image evaluation was performed by videodensitometry. Discussion of the advantages such as: 1) the combination of all relevant steps on one HPTLC plate and its resulting efficiency made surface synthesis on chromatographic phases an optimal tool for signal highlighting in MS, and thus for the assignment of impurities in drugs; 2) the miniaturization of the chemistry process scale down to the μg-level per synthesis (in total 30-60 μg chemicals/reaction), setting a new state-of-the-art standard; 3) the contribution to a greener chemistry by reducing the consumption of chemicals and enhancing the analytical efficiency, when adapted for the quality control of any other chemical product.

Anal. Letters 18, (A4) 503-518 (1985). HPTLC of dyes on silica with MEK - acetic acid - isopropanol 4:4:2.