Anal. Bioanal. Chem. 411, 1181-1192 (2019). HPTLC of cholesterol in fresh egg yolk on silica gel with n-hexane - ethyl acetate - acetic acid 15:9:1. Detection by dipping into p-anisaldehyde sulfuric acid reagent solution for 1 s (1 mL p-anisaldehyde with a refrigerated solution of glacial acetic acid/concentrated sulfuric acid in methanol in a ratio of 1:2:100). Quantitative determination by absorbance measurement at 525 nm. Evaluation under daylight and UV light. The method allowed to study cholesterol-lowering properties of 12 lactic acid bacteria (LAB) in the absence or presence of 0.3 % bile salts. The hRF value for cholesterol was 71. Linearity was between 1 and 10 μg. Intermediate precision was below 7 % (n=3). The LOD and LOQ for cholesterol were 0.2 and 0.8 μg, respectively. Recovery was between 96.6 and 100.1 %. 

Anal. Bioanal. Chem. 412, 7441-7451 (2020). HPTLC of mono- (1) and diacylglycerol (2) emulsifiers (E 471) in whipping creams on primuline impregnated silica gel with n-pentane - n-hexane - diethyl ether 9:9:22. Quantitative determination by fluorescence measurement at UV 366/> 400 nm. The hRF values for (1) and (2) were 10 and 52, respectively. Linearity was between 1.5 and 20 ng/zone for (1) and (2). Intermediate precision was below 7 % (n=4). The LOD and LOQ were 1.8 and 5.7 ng for (1) and (2). Recovery was between 95 and 105 % for (1) and 86 and 95 % for (2).

Anal. Bioanal. Chem. 412, 2237-2249 (2020). HPTLC of sphingomyelin (1), phosphatidylcholine (2), and triacylglycerol (3) fractions from preadipocytes and adipocytes on silica gel with chloroform - ethanol - water - triethylamine 30:35:7:35 for (1) and (2) and hexane - diethyl ether - acetic acid 80:20:1 for (3). Detection by dipping into primuline (dissolved in acetone - water 4:1) and under UV light at 366 nm. Lipid fractions were further analyzed by electrospray ionization-ion trap mass spectrometry.

J. Liq. Chromatogr. Relat. Technol. 44, 148-170 (2021). Comprehensive review of the contribution of HPTLC to the analysis of lipids in the last ten years. Advances in detection, identification and determination of main classes of lipids and their subclasses separated by HPTLC in different matrices were discussed. The review described techniques for scanning densitometry of lipids through direct detection and on-plate staining using inorganic and organic agents, immunostaining of glycosphingolipids and labeled lipids. Techniques coupling HPTLC with mass spectrometry were also discussed, including extraction-based interfaces, ionization of lipids, on-plate matrix assisted laser desorption and ionization, and its application in the analysis of sphingolipids, neutral lipids and fatty acids and phospholipids.

Heliyon 6(8), e04654 (2020). HPTLC of ethanolic extracts of three algae (100µg/band) on silica gel, along with carotenoid standards (10µg/band), developed with toluene – acetone 7:3. Detection under white light. Carotenoids appeared orange or yellow, chlorophylls green, pheophytins dark khaki. Carotenoid patterns of the algae were very different depending on the family: red alga Eucheuma denticulatum (Solieriaceae) contained mainly zeaxanthin and lutein (hRF 44) and β-carotene (hRF 88), but also β-cryptoxanthin (hRF 69-71) and fucoxanthin (hRF 39); brown alga Sargassum polycystum (Sargassaceae) contained mainly fucoxanthin, and also cryptoxanthin; green alga Caulerpa lentillifera (Caulerpaceae) contained mainly zeaxanthin, but also astaxanthin (hRF 61) and canthaxanthin (hRF 77) in smaller amounts. Separately, HPLC-MS was used to confirm and quantify these compounds, which was necessary for carotenoids with similar hRF values: zeaxanthin and lutein (hRF 44), and β-carotene and lycopene (hRF 88).

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.

Biochem. Biophys. Res. Commun. 534, 1069-1075 (2021). HPTLC of gangliosides in human and mouse siglecs on silica gel with chloroform - methanol - 0.2 % calcium chloride 60:25:4. Immunostaining by dipping into cyclohexane containing 0.1 % poly (isobutyl methacrylate) for 1 min, blocked by incubation in PBS containing 1 % BSA at room temperature for 1 h, incubated with premixture of Sig7EcFc WT or R124A and anti-hIgG + M + A-HRP in PBS containing 0.1 % BSA or S2-566 (anti-diSia antibody) in PBS containing 1 % BSA at room temperature for 2 h, and washed 5 times with PBS. Horseradish peroxidase activity was detected by chemiluminescence. Sig7EcFc corresponds to extracellular domain of Siglec-7 fused to the human IgG1 Fc region.