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.

Food Addit. Contam. Part A. 36, 1903-1936 (2019). Review of the potential contribution of bioassays for the analysis of non-intentionally added substances in food contact materials. Planar chromatography coupled to bioassays was discussed for the identification of unknown bioactive molecules in complex mixtures such as foods, beverages and plant extracts.

J. Liq. Chromatogr. Relat. Technol. 43, 580-588 (2020). Retardation factor (hRF) of 42 amino acids in two different eluents (acetonitrile - sodium azide and 1,2 dioxane-sodium azide solutions) were predicted by different quantitative structure-retention relationship (QSRR) methods. The method analyzed the effect of sum of geometrical distances between N and O in separation of amino acids in RP-TLC.

J. Planar Chromatogr. 33, 489-499 (2020). HPTLC of fructose (1), glucose (2) and sucrose (3) in honey on silica gel with 1-butanol-2-propanol - boric acid - water 3:5:1. Detection by spraying with 2 mL of aniline diphenylamine phosphoric acid reagent, followed by heating at 110 ºC for 10 min. The hRF values for (1) to (3) were 14, 32 and 27, respectively. Linearity was between 250 and 1250 ng/zone for (1) to (3). Intermediate precision was below 7 % (n=3). The LOD and LOQ were 22 and 67 ng for (1), 33 and 100 ng for (2) and 21 and 64 ng for (3), respectively. Average recovery was 100.7 % for (1), 101.4 % for (2) and 104.0 % for (3).

J. Planar Chromatogr. 33, 413-418 (2020). HPTLC of metanil yellow in colored sweets on silica gel with ethyl acetate - methanol - 25 % ammonia - water 35:11:5:5. Detection at UV 430 nm. The hRF value for metanil yellow was 56.

J. Planar Chromatogr. 33, 209-217 (2020). HPTLC of patulin in fruit-based food on silica gel with toluene - ethyl acetate - formic acid 5:4:1. Quantitative determination by absorbance measurement at 254 nm. The hRF value for patulin was 53. Intermediate precision was below 4 % (n=5). The LOD and LOQ were 0.66 and 1.99 ng/zone, respectively. Recovery was between 106.0 and 108.6 %.

J. Planar Chromatogr. 33, 301-311 (2020). HPTLC of gallic acid in honey on silica gel with toluene - ethyl acetate - formic acid 6:5:1. Detection by derivatization with 2 mL of 0.4 % DPPH reagent. Quantitative determination under white light. The hRF value for gallic acid was 29. Linearity was between 40 and 140 ng/zone. Intermediate precision was below 4 % (n=3). The LOD and LOQ were 14 and 43 ng, respectively. Recovery was between 99.9 and 101.4 %.

J. Liq. Chromatogr. Relat. Technol. 43, 291-299 (2020). Review of available software and methods for HPTLC image analysis, including preprocessing of data and multivariate treatment of obtained fingerprints. HPTLC fingerprint analysis and quantitative evaluation of HPTLC images for the analysis of food and natural products was also described.