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.

Rapid Commun. Mass Spectrom. 35, 9013 (2021). Review of the application of direct analysis in real time (DART) combined with mass spectrometry (MS) detection in food science and industry published in the period from 2005 to this date. The applications described the use of HPTLC in preparation methods as well as the combination of HPTLC fingerprints and DART-MS with multivariate data analysis for the differentiation of natural propolis products.

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 Chem. 351, 129211 (2021). High-throughput planar solid-phase extraction of 66 multi-class antibiotic residues in muscle tissue, cow milk and chicken eggs on silica gel with acetonitrile - methanol - ammonia 5:3:2 as first front-elution up to 85 mm followed by a second front-elution in the reverse direction up to 25 mm with acetonitrile -water - ammonia 9:7:4. Evaluation under UV 254 nm and 366 nm. Detection of macrolides by spraying with p-anisaldehyde sulfuric acid reagent (methanol - glacial acetic acid - sulfuric acid - p–anisaldehyde 420:50:26:3), followed by heating at 110°C for 3 min. Detection of penicillins by spraying with ninhydrin reagent (500 mg ninhydrin in ethanol - glacial acetic acid 23:2). Detection of lincosamines by spraying with aniline diphenylamine o-phosphoric acid reagent (2 g diphenylamine in methanol – o-phosphoric acid - aniline 90:10:1). Via simple clicks on the image, the auto TLC-MS interface automatically eluted the target zones at the trace level from the TLC plate into a Q Exactive Plus Hybrid Quadrupole-Orbitrap Mass Spectrometer.

J. Liq. Chromatogr. Relat. Technol. https://doi.org/10.1080/10826076.2021.1932521 (2021). HPTLC of gallic acid in the stem bark of Schinus terebinthifolius on silica gel with toluene - ethyl acetate - formic acid - methanol 15:15:4:1. The plates were scanned at 254 nm and 366 nm. The hRF value for gallic acid was 43. Image features were acquired using a combination of two approaches: Haralick texture features and Zernike moments. The GNU OctaveVR software was used to set the architectures of the Artificial Neural Network. The mathematical data provided by the image analysis was correlated with the gallic acid content determined by HPLC. The method allowed the prediction of phenolic content through TLC plate images.

Anal. Bioanal. Chem. 411, 6213-6225 (2019). HPTLC of selected analgesics (acetaminophen), alkaloids (nicotine and caffeine), and steroids (cortisone) on different
stationary phases (silica gel, RP-, cyano-, DIOL- and amino-) with isopropyl alcohol - n-heptane - water 7:3:1. Direct surface analysis of the TLC plates with a flowing atmospheric pressure afterglow (FAPA) ambient desorption/ionization source (TLC-FAPA-MS). The LOD of caffeine was 0.6 ng/zone. Semi-polar stationary phases (cyano and RP plates) showed significantly higher signal abundances for the analyzed compounds in comparison to the polar NP stationary phase.

Chem. Asian J. 15(19), 3044-3049 (2020). The studied rotaxane combines a dibenzocrown of 8 ethers (DB24C8) with an axle chain (Ax) containing two amines, one of them in an aniline group, allowing stability of the rotaxane even when the other one is unprotonated. TLC on silica gel in 4 steps, with detection under UV light or after derivatization with phosphomolybdic acid in ethanol. (1) Before the synthesis of the rotaxane, unprotonated Ax was isolated by preparative TLC of the protonated Ax obtained by addition of HCl or toluenesulfonic acid (TsOH); the mobile phases were chloroform – methanol 10:1 and toluene – tetrahydrofurane 3:2, respectively. The isolated molecules were confirmed as totally unprotonated Ax by NMR, suggesting a complete loss of HCl and TsOH on the silica gel layer. (2) After synthesis, unprotonated rotaxane, pure vs. monoprotonated by the addition of 10 different acids (and purified by column chromatography CC), was applied on TLC plates and developed with dichloromethane – acetone – water 3:16:1; the hRF values were very different, depending on the counter-anions from the used acids. (3) The same behavior (except with sulfuric acid) was observed under the same conditions when CC was omitted (unprotonated rotaxane samples were mixed with each of the acids, or with two acids at the same time for acid-competitive TLC analysis). (4) When unprotonated rotaxane was applied under the same conditions as in step (3) with the sodium salts instead of the acids, the behavior was similar (except for the shapes of the spots, due to the salts in excess). The rotaxane can thus be used for the TLC separation and detection of sodium salts, by forming salts of protonated rotaxane with the anion afforded by these sodium salts. The rotaxane protonation seems to be promoted by the methanol of the spotting mixture; indeed, when step (3) was performed with the mobile phase chloroform – methanol 10:1, a second zone appeared because methanol formed a salt with the rotaxane (identified by NMR).

J Am Soc Mass Spectrom 31(9), 1981-1993 (2020). Low-temperature plasma-mass spectrometry was studied for comparison between direct desorption (DD) and diode laser assisted desorption (LD) in terms of quantitative and qualitative analysis of compounds from cellulose vs. silica gel TLC layers. Compounds (the 20 common amino acids, propofol, nicotine, cotinine, salicylamide, acetylsalicylic acid, paracetamol, caffeine, valprolactone and its isomer 4-ene-valproic acid) were applied on the TLC plates (without development) at different concentrations; a commercial mixture of acetylsalicylic acid, paracetamol and caffeine was also applied on TLC plates, developed with dichloromethane – ethyl acetate 1:50, detection at UV 254 nm and quantitative MS. In general, DD provided good results on cellulose, where LODs where between 0.01 and 2.55 ng/mm2, whereas several compounds remained undetected on silica gel. LD however provided LODs on silica gel from 0.3 to 84 pg/mm2. Tandem MS with collision-induced dissociation was implemented to improve signals, LODs and to characterize the other analytical figures-of-merits (including detection of the main fragment ions, determination of optimal laser beam width and irradiance depending on the compounds). For the two metabolites of valproic acid, the ions and fragments had identical values; therefore, a mix of the two isomers had to be applied and separated with dichloromethane – methanol 50:1 before MS; one half of the plate was visualized for control by dipping into potassium permanganate reagent (7.5g KMnO4, 50g K2CO3, 0.75g NaOH in 1L water).