Planta Medica 84(9/10), 584-593 (2018). A review with 120 references on DESI technique coupled with MS for natural products. Paragraph on sample preparation (9 references) compares analyte desorption surfaces: either directly from the biological sample, or indirectly from surfaces on which the sample had been imprinted. Direct desorption can be performed only from samples with hard, smooth and regular surfaces, or from cryosections, which are usual for animal tissues. For plants, indirect analysis is preferable because of their wax-rich, hydrophobic, absorbent and/or irregular surfaces. Imprinting of plant organs and tissues can be performed either on glass (however with a very rapid ablation of the analytes from its surface), or on sorbent material, like TLC silica gel or porous polytetrafluoroethylene (PTFE). While PTFE layers are reported as more expensive and better in terms of reproducibility and quantitative analysis, both TLC and PTFE layers have similar performance for analyte retention until desorption.

Food Control. 103, 111-118 (2019). Thin layer chromatography in tandem with surface-enhanced Raman scattering (TLC-SERS) of histamine in tuna samples on diatomaceous earth plates with ethanol - ammonia 3:1. Detection by spraying with Pauly's reagent (equal mixture of 20 mM sulfanilic acid in a 1 M HCl solution and 200 mM sodium nitrite solution, followed by adding 10 % anhydrous sodium carbonate in a 5 % ethanol solution). Gold nanoparticles were deposited on the plate zone and measurements were performed using a Raman spectrometer with an excitation laser wavelength of 785 nm.

J. of Chromatogr. A 1568, 188-196 (2018). Mass spectra by DART-MS were recorded directly in situ the bioautogram, immediately after direct bioautography (DB). This allowed to detect bioactive analytes within the bioautogram and discriminate microorganism cells and polar bioassay medium ingredients which could otherwise stress the MS system. DB-DART-MS was used for bioactive compounds in cosmetics using the Bacillus subtilis and Aliivibrio fischeri bioassays for detection of Gram-positive and Gram-negative antimicrobials. Planar yeast estrogen screen was used for detection of estrogen-effective compounds. HPTLC-DART-MS of parabens in hand creams either on silica gel with petroleum ether - glacial acetic acid 20:3 or on RP-18W with methanol - water 1:1. Detection under UV 254 and 366 nm. Bioassay by immersing the neutralized chromatograms into the bacterial suspensions.

J. Planar Chromatogr. 32, 447-451 (2019). HPTLC of Fritillaria cirrhosa on silica gel with ethyl acetate - methanol - ammonia solution - water 180:20:10:1. Bioautography by dipping into a 0.15 mg/mL solution of substrate Gly-Pro-p-nitroanilide hydrochloride in 50 % of ethanol, followed by ethanol removal in the hood and dipping into a 10 U/L DPP IV enzyme solution in TrisHCl buffer (pH 8.2, 70 mM), followed by incubation at 37°C for 40 min. Detection by dipping into a solution of 0.5 % sodium nitrite in 1.2 M hydrochloric acid, followed by drying slightly for 5 min and dipping into 0.05 % N-(1-naphthyl)ethylenediamine dihydrochloride solution. Further analysis by mass spectrometry using a TLC interface. The hRF value for the dipeptidyl peptidase IV inhibitor was 58.

J. Chromatogr. A 1568, 188-196 (2018). Application of an advantageous combination, the desorption-based direct analysis in real time mass spectrometry (DART-MS) immediately after direct bioautography (DB), i.e., in the presence of microorganisms, bioassay medium and substrate reagent. The method offers a straightforward and efficient mass spectrometric detection of bioactive analytes within the bioautogram. It discriminated microorganism cells and highly polar bioassay medium ingredients which could otherwise stress the MS system. Investigation of DB-DART-MS for bioactive compounds in cosmetics using the Bacillus subtilis and Aliivibrio fischeri bioassays for detection of Gram-positive and Gram-negative antimicrobials, respectively, and the planar yeast estrogen screen for detection of estrogen-effective compounds. Study of the influences of three different bioassay matrices on the analyte response and DB-DART-MS performance on different layers (NP and RP) on the example of parabens in hand creams. Ion suppression was enhanced with increasing culture medium complexity. The mass spectrometric quantification by DB-DART-MS at the ng-level in situ each different bioautogram was verified by comparison to HPTLC-DART-MS. The total paraben content of hand creams 1 and 2 was 0.17–0.20% and 0.30–0.34%, respectively, depending on the method used. It proved that DB-DART-MS is a reliable qantitative bioanalytical hyphenation.

J. Liq. Chromatogr. Relat. Technol. 42, 266-273 (2019). HPTLC of aqueous, fermented plant preparations from Chamomilla recutita L. (1), Allium cepa L. (2), Equisetum arvense L. (3) and Hamamelis virginiana L. (4) of different harvest years on silica gel with ethyl acetate - toluene - formic acid - water 16:4:3:2. The method was combined with effect-directed analysis (EDA) and high-resolution mass spectrometry (HRMS). For α-/β-glucosidase assays, the plate was sprayed with 2 mL substrate solution (60 mg 2-naphthyl-α-D-glucopyranoside or 2-naphthyl-β-D-glucopyranoside in 50 mL ethanol), then sprayed with 1 mL sodium acetate buffer and 2 mL enzyme solution (500 units α-glucosidase), followed by incubation at 37 ºC for 10 min. Analysis of multi-potent compounds was also performed using the 2,2-diphenyl-1-picrylhydrazyl reagent and Gram-positive Bacillus subtilis assays, followed by recording of elution head-based HPTLC-ESI-HRMS spectra. 

Planta Med. 83(17), 1321-1328 (2017). Benzoyl-aconine esters (lipo-alkaloids) produced by transesterification of aconitine (isolated from Aconitum sp.) with long-chain fatty acids were purified by a multistep chromatographic method, including cyclodextrane gel filtration chromatography, centrifugal planar chromatography on aluminium oxide layer using cyclohexane – chloroform – methanol 70:30:1 followed by 70:30:3 and/or preparative thin-layer chromatography on aluminium oxide layer with toluene – acetone – ethanol – concentrated ammonia 70:40:10:3.

Chromatographia 67 (3-4), 315-319 (2008). Presentation of a hyphenation technique of TLC with surface-based spectral methods which require a homogeneous surface for direct and quantitative analysis on the chromatographic plate after separation. Investigation of the suitability of two different chromatographic substrates and one interface for coupling surface-enhanced Raman spectroscopy (SERS) with TLC, since most chromatographic materials do not produce strong background signals in Raman spectroscopy. Evaluation of a chromatographic thin layer, specially produced for Raman spectroscopy measurements, a monolithic silica thin layer and a typical TLC plate with a modified aluminium backplate foil on one side used as an interface. Test analytes were three biologically active diterpenes (gibberellic acid, abietic acid, and kaurenoic acid) which were applied directly onto the surfaces, followed by the addition of silver colloid and measurements by SERS. The strongest signal (excitation at 514.5 nm) for gibberellic acid was obtained using a Raman treated thin layer where the enhancement factor value was determined to be 102, and several fundamental Raman bands for GA were found at 1622, 1593, 1570, 1542, 1366 and 1236 cm-1. However, no useful SERS signals were observed when the monolithic silica layer was used. Similar SERS spectra on modified aluminium backplate were obtained for abietic acid and gibberellic acid, but no SERS spectrum was obtained for kaurenoic acid.