J. Pharm. Biomed. Anal. 8, 253-257 (1990). A densitometric method for determination of complex mixtures of conjugated oestrogens in raw material and tablets was developed. The proposed procedure comprised hydrolysis of sodium sulfate esters of oestrogens and oestradiol, equilenin, 17a-dihydroequilenin, the chloroform extraction of free oestrogens and methyltestosterone (internal standard). TLC on silica with chloroform - cyclohexane - dioxane - triethylamine 45:40:10:6. Quantification by densitometry at 254 and 280 nm. Detection limit 0.06 µg, recoveries 97,1% (conjugated oestrogens) and 103,2% (tablets). The proposed method is simple, rapid, and reproducible.

J. Liq. Chromatogr. Relat. Technol. 39, 264-270 (2016). HPTLC of estradiol hemihydrate on silica gel (1) or RP-18 (2) with dichloromethane – ethyl acetate 4:1 for (1) and methanol – water 9:1 for (2). Quantitative determination by absorbance measurement at 200 nm. The LOD was 239 ng/zone using (1) and 93 ng/zone using (2).

J. Planar Chromatogr. 5, 16-27 (1992). TLC of estrogens (estrone, equilin, equilenin, 17 a & ß-dihydroequilin, 17 a & ß-dihydroequilenin, estriol) on silica, C-2, C-8, C-18, NH2- and diol-modified, with different eluents in one- and two-dimensional separations. The optimized mobile phase based on cyclohexane and ethyl acetate provided best separation of estrogens containing C-17 hydroxy group epimers, those with a C-17 keto group were only separated in mobile phases containing triethylamine (or on NH2-layers in the absence of triethylamine). 2,4-dinitrophenylhydrazones of C-17-keto group estrogens enable their selective detection at 366/>400 nm.

CBS 115, 2-4 (2015). HPTLC of propolis tinctures and standards estrone, 17-estradiol, 17-ethinylestradiol, estriol, bisphenol A, 4-n-nonylphenol, and caffeic acid methyl ester on RP-18W with n-hexane – toluene – ethyl acetate 8:3:2 to a migration distance of 7 cm. For the HPTLC-pYES bioassay the plate was dipped into a yeast cell suspension and incubated for 3 h. Biodensitometric evaluation by fluorescence measurement at 365 nm with a cut-off filter of 400 nm. Elution of the bioactive zones with methanol – ammonium formate buffer (10 mM, pH 4, 49:1) into a ESI-MS. The LOD for 17-estradiol was 0.2 pg/zone and the LOQ 0.5 pg/zone. With this method estrogen effective substances can be detected with no or minimal sample preparation.

J. Planar Chromatogr. 5, 229-233 (1992). TLC of a bis quaternary ammonium steroid on silica with lithium perchlorate (20%) in water - 2-propanol - glycerol 5:90:5. Separation of the decomposition products with sodium iodide (40%) in water - 2-propanol - acetonitrile 5:90:5. Detection with iodine vapor resp. by immersion into a solution of iodine (0.25%) in chloroform - methanol 1:1 (decomposition products). TLC of an estrogen and a progestogen on silica with toluene - ethyl acetate - acetic acid 80:20:3. Quantification by scanning in fluorescence/reflection mode. Practical hints on application, development, detection, and densitometric evaluation; if performed carefully, TLC results are of the same quality as those from HPLC or GC.

J. Planar Chromatogr. 30, 136-141 (2017). 2D-HPTLC of estrone (1), estradiol (2), 17α-ethinylestradiol (3), estriol (4), bisphenol A (5), trans-resveratrol (6), zearalenone (7), and diethylstilbestrol (8) on RP-18W with hexane – ethyl acetate – acetone 11:3:2 in the first direction and acetone – water 3:2 in the second direction. Detection by heating at 110 °C for 10 min, followed by dipping into a mixture of sulfuric acid - water 1:49 for 1 s and heating again at 110 °C for 10 min. Quantitative determination under UV light at 366 nm. The hRf values in the first/second direction for (1) to (8) were 52/27, 36/27, 45/24, 6/44, 41/31, 51/17, 49/22 and 17/47, respectively. 17α-ethinylestradiol was quantified in an effect-directed analysis using the yeast strain S. cerevisiae BJ3505. The activation of the estrogen receptor by estrogen active compounds was measured by inducing the reporter gene lacZ which encodes the enzyme ß-galactosidase. The enzyme activity was determined directly on TLC plate by using the fluorescent substrate MUG (4-methylumbelliferyl ß-D-galactopyranoside). The LOD and LOQ were 31 and 57 pg/zone, respectively.

Acta Pharmaceutica Hungarica 63, 19-27 (1993). TLC of ethinylestradiol, mestranol, norgestrel, norethisterone on silica with toluene - ethyl acetate 2:1. Visualization by spraying with 1% cerium(IV)sulfate solution in 10 % aqueous sulfuric acid and heating at 110 °C for 5-10 min.

J. Chromatogr. A 1509, 147-152 (2017). Presentation of proper sigmoidal dose-response curves which can be linearized by the logit function resulting in logit-log plots in semi-log plots, from a planar yeast estrogen screen (pYES) as known for the evaluation of enzyme-linked immunosorbent assays and radioimmunoassays in microtiter plates. It was assumed to obtain sigmoidal shaped dose-response curves from the measured sign plots because pYES represents the transfer of the receptor assay YES to HPTLC. As no typical sigmoidal curves were obtained when peak areas were plotted against the applied amount on a logarithmic scale, peak heights were examined in the present study, which revealed proper dose-response curves when plotted against the log amount. The presence of sigmoidal dose-response curves from HPTLC-pYES made it possible to transform the signals into logits and, therefore, to create logit-log plots with linear correlations. The working range was up to 500 pg/zone for both 17β-estradiol (1) and 17α-ethinylestradiol (2). The mean recovery by applying logit-log plots for (1) and (2) from spiked water samples (2-20 ng/L) were 90 % and 108 %, respectively, with %RSD≤24 %. Determination of the half maximal effect dose (ED50) of the estrogen active compounds, which was represented by the intersection of the linear graph with the abscissa and also determination of the estrogenic potential in terms of estradiol equivalent factors by using the ED50 values, resulting in 0.64 for (2).