CBS 97, 2-5 (2006). HPTLC of gangliosides on silica gel with chloroform - methanol - water 24:17:4 and addition of 2 mM CaCl2, after chamber saturation with filter paper for 3 h, over 80 mm, followed by drying for 5 min at room temperature. Detection by dipping in orcin solution (0.3 % (w/v) in 3 M H2SO4) followed by heating at 100 °C for 3 min. Alternative detection of GM3-bands by derivatization with primulin (0.02 % (w/v) in aceton - water 4:1). Quantitative determination by direct IR-MALDI-o-TOF-analysis. The limit of detection for GM3 was about 50 ng/zone.

CBS 102, 2-3 (2009). A semi-automatic interface for hyphenation of TLC with mass spectrometry, which was based on the ChromeXtractor by Luftmann, is introduced. The interface is connected to a HPLC pump and the MS. By means of an extraction piston any target zone can be eluted from a TLC/HPTLC plate directly into the MS. Example: for identification of the zone at hRf 15 in a standard mixture of caffeine, paracetamol, and acetylsalicylic acid the mass spectrum of the zone is recorded. After subtraction of a background spectrum a mass spectrum free from system peaks is obtained, which shows mainly substance signals - here the mass signal m/z 195 [M+H]+ for caffeine.

Rapid Commun. Mass Spectrom. 23, 2711-2723 (2009). HPTLC in combination with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was used for the analysis of complex lipid mixtures. For the separation of lipids one-dimensional HPTLC on silica gel aluminum foil was used with a two-phase mobile phase. The combination with MALDI-MS allowed the identification of 70 distinct lipid species and the analysis of even minor lipid classes from only very small volumes of human plasma (50 µL).

Phytochem. Anal. 24, 47-52 (2013) TLC of 22 acylated phenolic compounds on silica gel with acetonitrile - water - chloroform - formic acid 12:3:2:1, followed by dipping into 0.2 % methanolic 2,2-diphenyl-1-picrylhdrazyl solution (DPPH radical reagent) for 5 s and kept in the dark for 30 min. Free radical scavenging activity of the acylated phenolic compounds was assessed by coupling with the image processing software ImageJ .

J. Ethnopharmacol. 158, 487-494 (2014). The review described special techniques such as DNA fingerprinting, nuclear magnetic resonance, near infra red and (bio)sensors that combined with chromatographic techniques provide complementary analytical methods able to give rapid analysis responses, to operate directly on complex matrices, to be portable and to have fast analysis times. TLC is mentioned in the identification section, HPTLC is mentioned in the test for aristolochic acids in herbal drugs.

Trends Anal. Chem. 85, 75-84 (2016). This review describes different approaches for characterization of fossil resins (including amber and all their various types), including chromatographic methods and the application of TLC for separation and purification of compounds and its coupling with mass spectrometry. Fossil resins are often adulterated with modern resins and some rare and precious fossil resin specimens are imitated by more abundant, cheaper fossil specimen (for example succinite – Baltic amber is often imitated by copal).

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.