Anal Chim Acta 1129 (2020) 76-84. Demonstration of a new hyphenated HPTLC-S9-AChE assay for detection of neurotoxic chemicals, including metabolic activation, at levels consistent with the threshold of toxicological concern (TTC) for organophosphates (OPs). The high sensitivity allows for the direct application of packaging migrates or extracts on the HPTLC plate without additional requirement steps. HPTLC of the ethanolic standards chlorpyrifos (CP), quinalphos (QP), eserine (ER), parathion (PT), nonylphenol (NP) and tris(nonylphenyl) phosphite (TNPP) at five different levels in the range of 0.5-10 mL/band (overall range for all six chemicals 0.1-1000 ng/band) on silica gel. After application, drying and pre-wetting the application bands by immersion up to 10 mm in water, then spraying the S9 mixture (7 mL each, 0.1 mg/mL) immediately on top of the start zones, followed by incubation at room temperature for 30 min. After drying plates for 20 min and 5 min chamber saturation, development with ethyl acetate - methanol - water 5:5:2 for ER; n-hexane - ethyl acetate - ethanol 16:3:1 for QP and PT; n-hexane - toluene - ethyl acetate 5:4:1 for CP, NP and TNPP. Evaluation in 254 nm, 366 nm and white light. Detection by immersion in AChE solution (6.6 U/mL plus 1 mg/mL bovine serum albumin in Tris-HCl buffer, 0.05 M, pH7.8) for 2 s, and incubating at 37 °C for 25 min, then immersing into the substrate-chromogenic solution (ethanolic solution of 1-naphthyl acetate  - aqueous solution of Fast Blue B salt 1:2 , 3 mg/mL each) for 1 s, drying for 10 min. Evaluation in white light, absorbance measurement at 546 nm (mercury lamp) using an inverse scan. The advantages of this straightforward workflow were demonstrated by comparison with the status quo microtiter plate assay. The method is a pragmatic new tool in risk assessment in general and can be transferred to further toxicities of interest and any other category of complex sample mixtures.

Anal Chim Acta 1154 (2022). Development of a compact and miniaturized integrated nanoGIT+active system developed for food systems. It enables on-surface metabolization, immediate separation, multiple imaging and effect-directed detection on the same adsorbent surface and also shows bioactivity changes. Presentation of a scheme for simulation of on-surface digestion, separation and detection in successive steps: (1) food sample (e.g., starch, caseine protein and rape seed oil) in contact with enzyme system (HSA: human saliva α-amylase, PPep: porcine pepsin and Panc: porcine pancreatin plus bile extract), (2) start of metabolization by moistening of the HPTLC silica gel layer and digest including effect-directed detection ion over the incubation period, (3) HPTLC development of the conversion products with 2-propanol - ethyl acetate - water 3:3:1 for starch, 1-butanol - acetic acid - water 4:1:1 for casein, petroleum ether - diethyl ether - acetic acid 80:20:1 for rapeseed oil, and petroleum ether - ethyl acetate - cyclohexane 25:11:14 for turmeric, each followed by drying for 3 min. Documentation in white light, UV 254 nm, and fluorescence detection at 366 nm. Detection of metabolites from starch, caseine protein and rapeseed oil by immersion with 2g in 180 mL ethanol plus dropwise 8 mL 50 % sulfuric acid (followed by plate heating at 120°C, 5 min for saccharides degraded from starch) and densitometry at 434 nm and 475 nm. Detection of the amino acids and peptides degraded from the caseine protein by spraying with ninhydrin reagent (500 mg in 230 mL ethanol and 20 mL acetic acid) followed by heating at 110°C for 5 min and densitometry at 490 nm and 520 nm. Detection of the fatty acids degraded from rapeseed oil by immersion in primuline reagent (250 mg in 50 mL water plus 200 mL acetone) and densitometry by fluorescence measurement at 366/>400 nm. Effect-directed detection of the turmeric separation with the tyrosinase assay using levodopa as substrate, positive control kojic acid, evaluation by densitometry 546 nm with a specialized software. Verification by comparison with state-of-the-art in vitro assays. The developed method is more comprehensive and cost-/time-efficient, and attractive for nutritional, health and pharmaceutical sciences, drug development, medicinal research and for lean laboratories.

J Chromatogr. A, 1652, 462377 (2021). Samples were vanilla tinctures, water − ethanol − ethyl acetate 1:1:1 extracts of vanilla-flavored food products and of natural Vanilla sp. (Orchidaceae) pods, oleoresin, paste and powders, as well as calibration standards of vanillin (1) and ethylvanillin (2). HPTLC on silica gel with n-hexane – ethyl acetate 1:1 for profiling, 3:2 for quantification. Other mobile phases were also tested and given in the supplement. Compounds (1) and (2) (hRF 68 and 82, respectively) were quantified by absorbance densitometry (at maximal wavelength 310 nm, deuterium lamp, scanning speed 10mm/s). Contents were found to be between 1 μg/g and 36 mg/g for (1) and null for (2) except in one tincture (62 µg/mL). Derivatizations performed for five assays: A) to detect radical scavengers, immersion (speed 3 cm/s, time 5 s) into DPPH• (0.5 mM in methanol), followed by drying for 90 s at room temperature and 30 s at 60 °C; B) to detect activity against Gram-negative bacteria, immersion (speed 2 cm/s, time 3 s) into Aliivibrio fischeri suspension, followed by recording the bioluminescence; C) to detect activity against Gram-positive bacteria, immersion (speed 3.5 cm/s, time 6 s) into Bacillus subtilis, followed by incubation 2 h at 37 °C, immersion in MTT solution, incubation for 30 min at 37 °C and heating for 5 min at 50 °C; D) to detect acetylcholinesterase (AChE) inhibitors, immersion (speed 2.5 cm/s, time 2 s) into AChE solution (666 units in TRIS buffer 0.05M, with bovine serum albumin 0.1 %, pH 7.8), incubation for 25 min at 37 °C and immersion into substrate solution (α-naphthyl acetate 0.1 % and Fast Blue salt B 0.18 % in ethanol – water, 1:2; E) to detect tyrosinase inhibitors, spraying with enzyme solution (400 unit/mL, in phosphate buffer 0.02 M, pH 6.8), followed by 2 min drying, immersion into substrate levodopa (18 mM in phosphate buffer, pH 6.8), 10 min incubation at room temperature and drying. For identification, zones of interest were transferred with methanol from underivatized HPTLC layer through a TLC-MS interface and a filter frit directly to a Quadrupole-Orbitrap MS (heated electrospray ionization, probe heater at 270°C, spray voltage 3.5kV, lock masses acetic acid for negative, dibutyl phthalate for positive ionization, mode full HR-MS scan in m/z range 50–750). Afterwards, the following substances assigned by MS were confirmed by using HPTLC comparison with standards: (1) and (2), vanillyl alcohol, vanillic acid, ethyl vanillyl ether, coumarin, 4-hydroxybenzoic acid, 4-methoxybenzoic acid, 4-hydroxybenzaldehyde, 4-allyl benzoic acid, oleamide, triacetin.

J. Food Sci. 85, 1781-1792 (2020). HPTLC of scented (joha) rice and black rice variety on silica gel with chloroform - methanol 19:1 + 0.1 % formic acid and butanol - acetic acid - water 4:1:5. Detection by spraying with p-anisaldehyde and visualization under UV light at 200, 250 and 350 nm. The husk of the selected rice varieties contained the nonpolar metabolites whereas the seeds contain nonpolar as well as polar metabolites.

Sens. Actuators. B. Chem. 299, 126902 (2019). TLC-surface-enhanced Raman scattering (TLC-SERS) of melamine contaminated milk samples on silica gel with acetone - chloroform - ammonia 14:1:4. Then 2 μL gold nanoparticle were drop onto the analyte spot. Quantification using a Raman microscope equipped with a CCD detector to acquire the surface-enhanced Raman scattering spectra. Excitation wavelength was 785 nm. A parallel representation model of the triple-spectral data was constructed using a pure quaternion matrix. Quaternion principal component analysis (QPCA) was utilized for feature extraction and followed by feature crossing between the quaternion principal components to obtain final fusion of spectral feature vectors.

Sens. Actuators. B. Chem. 325, 128753 (2020). Leucomalachite green (1) and malachite green (2) and certain amount of highly dispersed potassium iodate titanium dioxide composites (0.1 M titanium butoxide was used as a precursor with 5 % potassium iodate solution to prepare KIO3-doped TiO2 nanoparticles). The sample was developed with chloroform - methanol 4:5. Detection by dipping into 5 % potassium iodine, followed by heating and then dipping into a zinc ion solution followed by heating at 80 °C. Linearity was in the range of 0.3–8.0 μg/mL for (1) and 0.1–4.0 μg/mL for (2), respectively. LOD and LOQ were 1.7 and 5.2 μg/kg for (1) and 0.9 and 2.7 μg/kg for (2), respectively.

J. Spectroscopy & Spectral Anal. 41 (2), 388-394 (2021). SERS, as a fast and sensitive analytical technology, is widely employed in the fields of analytical chemistry, environmental detection and food safety. However, the real-life samples are mostly mixtures, and an accurate determination of the analytes in complex samples cannot be performed directly by using SERS. TLC as a separation technique is easy to operate, low cost, fast and high-throughput, and has been widely used in the fields of synthetic chemistry, analytical chemistry, medicinal chemistry, and food science. Further, the zones isolated by TLC are first visualized using iodine vapor coloring or fluorescence, and then combined with SERS for efficient qualification and quantitation of the zones of interest. Therefore, the technology of TLC combined with SERS (TLC/SERS) suits rightly for determination of various kinds of complex samples. Moreover, due to the small sample size and the relatively simplicity of the experimental equipment used, it is also suitable for the rapid field screening and detection of relatively complex samples. Introduction of the enhancement mechanism of SERS and the preparation of the active substrate, and demonstration of the broad prospects of TLC/SERS application in the fields of environmental pollutant analysis, food safety monitoring, traditional Chinese medicine and biomedicine identification etc by providing a set of successful application examples.

Food Addit Contam Part A. 38, 1778-1787 (2021). HPTLC of deoxynivalenol (1), 3-acetyldeoxynivalenol (2), 15-acetyldeoxynivalenol (3), zearalenone (4) and nivalenol (5) in Chilean cereals on silica gel with toluene - ethyl acetate - formic acid 1:8:1. Detection by dipping into a solution of 10 % aluminium trichloride in 50% methanol, followed by heating at 120 °C for 15 min. Quantitative determination by absorbance measurement at 366 nm. The hRF values for (1) to (6) were 39, 50, 45, 60 and 20, respectively. Linearity was between 20 and 160 ng/zone for (1) to (5). The LOD and LOQ were 120 and 160 µg/Kg for (1), 120 and 200 µg/kg for (2) and (3), 80 and 120 µg/kg for (4) and 120 and 160 µg/kg for (5), respectively. Recovery was between 88.6 and 111.5 % for (1), 93.6 and 108.3 % for (2), 91.0 and 111.0 % for (3), 84.3 and 114.2 % for (4) and 86.0 and 112.5 % for (5).