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).

J. Planar Chromatogr. 8, 200-204 (1995). Study of the retention behavior of a series of steroids in liquid - solid chromatography as a function of the concentration of the diluent in ternary nonaqueous mobile phases. The relationship between the retention constant RM and the concentration of a diluent in the mobile phase was linear, with the slope values depending on the molecular structures of the compounds.

J. Planar Chromatogr. 31, 72-78 (2018). HPTLC of equol in ethanolic cattle manure extract on RP-18 with n-hexane – ethyl – acetate – acetone 9:3:2. Detection by planar yeast estrogen screening (pYES) by dipping into a yeast suspension, followed by incubation at 30 °C for 4 h. After incubation, the plate was dried in a 37 °C incubator for 15 min and dipped into the combined reaction buffer followed by incubation at 37 °C for 60 min and 90 % relative humidity. The combined reaction buffer was prepared by mixing 20 mL of buffer C (5.3 g of sodium phosphate dibasic and 0.4 g of potassium chloride were dissolved in about 490 mL water, the solution was adjusted with sodium hydroxide to pH 13, 0.5 g of benzalkonium chloride were added and the mixture was filled up to 500 mL) and 0.2 mL of a freshly prepared X-Gal solution (0.05 g/mL X-Gal in DMSO). Fluorescence evaluation under UV 366 nm. The hRF value for equol was 47.

J. Chromatogr. Sci. 34, 330-333 (1996). Two-dimensional TLC on silica with 1) chloroform - acetone 9:1, 2) cyclohexane - ethyl acetate - ethanol 31:8:1 for both directions. Detection by spraying with 95% ethanol concentrated sulfuric acid, heating at 110°C and visualization under UV. Quantification by HPLC.

J. Planar Chromatogr. 30, 423-426 (2017). 2D-HPTLC of phytoestrogenic active compounds in the root of Glycyrrhiza glabra on RP-18 with hexane – ethyl acetate – acetone 9:3:2 in the first direction and acetone – water 3:2 in the second direction. Effect-direct analysis by dipping into a yeast suspension followed by incubation at 30 °C for 4 h, drying at 37 °C for 15 min and spraying with the combined reaction buffer C (20 mL reaction buffer C is mixed with 0.2 mL of a freshly prepared solution of 0.05 g/mL 4-methylumbelliferyl-ß-D-galactopyranoside in DMSO or 0.2 mL of a freshly prepared solution of 0.05 g/mL 5-bromo-4-chloro-3-indoxyl-ß-D-galactopyranoside (X-Gal) in DMSO). Fluorescence detection at UV 366 nm._x000D_

Sz. Nyiredy, A. Kakuk (eds.): Planar Chromatography 2000, Lillafüred, Hungary, 24-26 June 2000, Res. Inst. for Med. Plants, p. 19-25. OPLC of ethinyl estradiole on silica gel with cyclohexane - ethyl acetate - chloroform 3:1:1. Detection by spraying with sulfuric acid and visual evaluation at 366 nm. The method is compared with the Official British and European Pharmacopoeia monographs. Only with the OPLC method it was possible to separate all impurities, i.e. 6-hydroxy derivatives (both isomers), the oxo-derivatives (6-oxo- and 16-oxo-), the 9(11)-dehydro and the 17-epi-derivatives from the estrone and estradiol. The HPLC method of the 3rd European Pharmacopoeia has to be changed slightly in order to analyze all impurities. The British Pharmacopoeia TLC method was not suitable because of its poor selectivity. Both OPLC and HPLC are suitable for purity testing. The OPLC method was preferred for process-validation because it shows a short analysis time and low eluent consumption (tenfold less than HPLC). The HPLC method was used for critical batches due to its better precision (3,5% RSD).

J. Chromatogr. A 1497, 155-163 (2017). Development of a planar yeast estrogen screen for the determination of estrogen active compounds. Introduction of resorufin-β-D-galactopyranoside, providing the orange fluorescing resorufin after enzymatic cleavage, as the planar yeast estrogen screen (pYES) substrate to determine estrogen active compounds (EAC). For samples containing blue fluorescent components, this substance is better suited than the generally employed substrate 4-methylumbelliferyl-β-D-galactopyranoside, which delivered blue fluorescing 4-methylumbelliferone after enzymatic cleavage by the YES reporter β-D-galactosidase. The mean LOD and LOQ was 3.5 and 6.5 pg/zone for 17β-estradiol (1) and 17α-ethinylestradiol (2), respectively; recoveries were close to 100% for (1) and (2) from spiked water samples in a concentration range of 2–20 ng/L.

J. Planar Chromatogr. 13, 106-113 (2000). Study of the chromatographic behavior of a series of (26) estradiol and estrone derivatives on silica gel with binary nonaqueous mobile phases and on C8- and C18-modified silica with binary aqueous mobile phases. HPTLC on silica gel or silica RP-8 resp. RP-18. Spots were observed under UV 254 nm.