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).

J. of Chromatogr. Sci. 58 (6), 520 – 534 (2020). HPTLC of 10-hydroxy-2-decenoic acid (10-HDA) in royal jelly products marketed in Egypt, on silica gel with chloroform - acetic acid 10:1. Quantitative determination by densitometry at 210 nm. First and second derivative treatment of the data and comparison between three statistical regression methods: parametric, nonparametric and weighted regression (WR). Derivative treatment of the data improved the sensitivity of the chromatographic signals. The WR method was advantageous over the use of the other two models and resulted in an enhancement of the accuracy and precision of the 10-HDA analysis. Recovery was 99.9 % with WR and 99.6 and 98.6 % with the other statistical methods. Further, the royal jelly standard was subjected to forced degradation studies including the effect of hydrolysis, oxidation, photolysis and dry heat.

J. Sep. Sci. 43, 1566-1575 (2020). HPTLC of phenyl myristate in the bark and leaves of Homalium nepalense on silica gel with chloroform - methanol 9:1. Quantitative determination by absorbance measurement at 254 nm. The hR_F value for phenyl myristate was 49. Linearity was in the range of 100-500 ng/5 µL. Intermediate precisions were below 1 % (n=5). The LOD and LOQ were 3 and 10 ng/5 µL, respectively. Average recovery was  between 90.1 and 95.6 %.

J. Food Compos. Anal. 77, 39-43 (2019). TLC of marine oil omega-3 supplements on silica gel with hexane - diethyl ether - glacial acetic acid 50:10:1. Detection by spraying with anisaldehyde solution, following by heating using a heat gun. Analysis of samples allowed the identification of different sources of omega-3 polyunsaturated fatty acids (PUFA) in their natural triacylglycerol (TAG) or concentrated ethyl ester (EE) forms.

J. Liq. Chromatogr. Relat. Technol. 42, 249-257 (2019). HPTLC of methanolic extracts from the leaves of Paulownia tomentosa on silica gel with chloroform - ethyl acetate - methanol 20:3:2. HPTLC-direct bioautography by dipping into B. subtilis cell suspension, followed by incubation at 28 °C for 2 h. Then the bioautograms were dipped into an aqueous solution of the MTT vital dye (1 mg/mL (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide), followed by incubation at 28 °C for 30 min. Further analysis by using a HPLC-DAD-MS system allowed the identification of apigenin and p-coumaric acid as highly abundant antibacterial components.

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.

J. Planar Chromatogr. 32, 243-249 (2019). HPTLC of stigmasterol (1) and cinnamic acid (2) in Pluchea dioscoridis on silica gel with chloroform - methanol - acetic acid 93:5:2. Quantitative determination of (1) by absorbance measurement at 254 nm. Compound (2) was detected by spraying with p-anisaldehyde and quantified under UV light at 513 nm. The hRF values for (1) and (2) were 57 and 19, respectivley. Linearity was between 200 and 1400 ng/zone for (1) and (2). The intermediate precision was below 2 % (n=6). The LOD and LOQ were 39 and 117 ng for (1) and 43 and 129 ng for (2), respectively. Recovery rate was between 98.8 and 99.4 % for (1) and 98.4 and 99.0 % for (2).

J. Planar Chromatogr. 32, 13-24 (2019). HPTLC of three omega-3 fatty acids, namely docosahexaenoic (1), eicosapentaenoic (2) and alpha-linolenic (3) on silica gel (activated by immersion in a 10 % silver nitrate solution in acetonitrile for 30 min, followed by drying at 60 °C for 30 min) with toluene - n-propanol - glacial acetic acid 200:20:1. Detection by exposure to iodine vapor for 60 min. Quantitative determination by absorbance measurement at 520 nm. The hRF values of (1) to (3) were 15, 26 and 57, respectively. The intermediate precision was below 2 % (n=10). The LOD and LOQ were 174 and 539 mg/mL for (1), 197 and 597 mg/mL for (2) and 201 and 609 mg/mL for (3), respectively. Average recovery for (1) to (3) was between 96.6 and 103.2 %.