J. Chromatogr. Sci. 54 (4), 609-617 (2016). HPTLC of sulbutiamine (SUL) in the presence of different degradation products after subjecting the drug to stress conditions (according to ICH: neutral, alkaline and acidic hydrolysis, oxidation, photodegradation and dry heat degradation), on silica gel aluminum foil with acetone – methylene chloride – ammonia buffer (pH 8.5±0.2) 14:6:1. Densitometric evaluation at 254 nm. The calibration curve was between 0.4–5.0 µg/zone with good correlation coefficients. The LOD and LOQ were 110 and 330 ng/zone, respectively. Structure elucidation of the resulting degradation products by ESI-MS/MS. The results showed that the drug was completely degraded with 0.1 N NaOH, 1 N HCl and 30 % hydrogen peroxide, while it was partially degraded by 0.1 N HCl, 3 % hydrogen peroxide and UV light. The hRf of SUL was 46 and the zone was completely separated from all obtained degradation products.

J. Chromatogr. A 1577, 101-108 (2018). In order to overcome the difficulty of the interpretation of the MS signals present at a low intensity for unknown degradation products or impurities, a new strategy and open-source software called eicCluster was developed. It offered unsupervised machine learning algorithms and powerful interactive visualization tools that made data processing fast and intuitive. The low-intensity HPTLC-HRMS signals were highlighted in a stressed formulation by using eicCluster. Thus, even compound ions present at low intensities were separated in subclusters from background signals (in silico highlighting). The respective preprocessing led to intensity-agnostic signals and the t-SNE algorithm clustered mass signals based on their similarity. The resulting 2D maps allowed a new view on the data set to such low-intensity target molecules in complex mixtures. Moreover, the targeted on-surface synthesis of degradation products (in situ highlighting) was shown to support a fast structure elucidation, when standards are not commercially available. It allowed a better understanding of the proposed degradation reactions in the formulation. Comparison with the results of stressed samples as well as the proposed degradation products of on-surface synthesis proved that in silico and in situ signal highlighting substantially eased structure elucidation and data processing.

Quantification after elution with water.

Direct TLC/SIMS and scanning TLC/SIMS. ) A strip of aluminium sheet coated with silica is used for TLC separation. After chromatography, this strip is subjected to the liquid secondary ion mass spectrometer (SIMS) where it serves as the primary ion target (in place of the usual Ag plate). The method is demonstrated with some thermally unstable sample mixtures such as peptides and drug metabolites.

J. Planar Chromatogr. 1, 135-140 (1988). Description of the record of the first spatially resolved mass spectral images of peptides transfered from an electrophoretic gel to a nitrocellulose membrane. Discussion of the potential of widespread use of MS in the direct analysis of planar chromatograms.

J. Chromatogr. 447, 277-283 (1988). TLC on silica with four solvent systems. Detection under UV 254 nm. Quantification by HPLC after elution with methanol. Reversed-phase TLC on octadecyl- bonded silica with methanol - water 4:1. Detection under UV 254nm and by spraying with vanillin - sulfuric acid - ethanol 3:1. 5:1000.

J. Chromatogr. 471, 389-396 (1989). Demonstration of direct analysis of HPTLC plates by laser microprobe MS. Examination of a series of general organics and ionic surfactants as reference materials and after application to normal-phase HPTLC plates. Identification of unknowns by their spectra before and after chromatography.

Talanta 37, 471-480 (1990). TLC of several bile acids and bile salts on silica with isooctane – ethyl acetate – acetic acid 10:10:2 and butanol – acetic acid – water 4:1:1. Identification by liquid-state secondary-ion MS. Quantification by monitoring the ion intensity for the sample spot and the standard spot developed in parallel.