@article{MinarMilzSpangenberg2018,
  author    = {Minar, Yvonne Anna and Milz, Barbara and Spangenberg, Bernd},
  title     = {Is Equol an Ecologically Relevant Endocrine Disruptor? Equol Determination in Cattle Manure by Effect-Directed Analysis Using the pYES Test},
  series = {Journal of Planar Chromatography},
  volume    = {31},
  number    = {1},
  publisher = {Akad{\´e}miai Kiad{\´o}},
  address   = {Budapest},
  issn      = {0933-4173},
  doi       = {10.1556/1006.2018.31.1.9},
  pages     = {72 -- 78},
  year      = {2018},
  abstract  = {We present a planar chromatographic separation method for the phytoestrogenic active compound equol, separated on RP-18 W (Merck, 1.14296) phase. It could be shown that an ethanolic cattle manure extract contains this phytoestrogenic active compound to a larger amount. As solvents for the mobile phase, hexane, ethyl acetate, and acetone (45:15:10, v/v); acetone and water (15:10, v/v); and n-hexane, CH2Cl2, ethyl acetate, methanol, and formic acid (40:40:20:5:1, v/v) have been used. After separation, a modified yeast estrogen screen (YES) test was applied, using the yeast strain Saccharomyces cerevisiae BJ3505 containing an estrogen receptor. Its activation by equol induces the reporter gene lacZ which encodes the enzyme β-galactosidase. The enzyme activity is measured directly on the TLC plate by using the substrate MUG (4-methylumbelliferyl-β-d-galactopyranoside) or the substrate X-β-Gal (5-bromo-4-chloro-3-indoxyl-β-d-galactopyranoside). β-Galactosidase cleaves MUG into a fluorescing compound. X-β- Gal is also hydrolyzed and then oxidized by oxygen forming the deep-blue dye 5,5′-dibromo-4,4′-dichloro-indigo. Both reactions in combination with a thin-layer chromatography (TLC) separation allow very specific detecting of equol in cattle manure, although that is a very challenging matrix. Preliminary results show that the average content of equol in liquid manure is roughly 60 μg g-1. The value for urine is 50 μg mL-1.},
  language  = {en}
}
@article{EichnerSpangenberg2019,
  author    = {Eichner, Fabian and Spangenberg, Bernd},
  title     = {Optimized Determination of Caffeine, Equol, and Artemisinin by High-Performance Thin-Layer Chromatography-Direct Analysis in Real Time-Time of Flight-Mass Spectrometry.},
  series = {JPC - Journal of Planar Chromatography - Modern TLC},
  volume    = {32},
  number    = {3},
  issn      = {1789-0993},
  doi       = {10.1556/1006.2019.32.3.4},
  pages     = {197 -- 203},
  year      = {2019},
  abstract  = {We present a planar chromatographic separation method for the compounds caffeine, artemisinin, and equol, separated on high-performance thin-layer chromatography (HPTLC) silica gel plates. As solvents for separation, methyl t-butyl ether and cyclohexane (1:1, V/V) have been used for equol, cyclohexane and ethyl acetate (7:3, V/V) for artemisinin, and ethyl acetate and acetone (7:3, V/V) for caffeine. After separation, the plate was scanned with a very specific time of flight-direct analysis in real time-mass spectrometry (TOF-DART-MS) system using the (M + 1)+ signals of equol, artemisinin, and caffeine. The (M + 1) peak of artemisinin at 283.13 m/z is clearly detectable, which is the proof that DART-MS is applicable for the quantitative determination of rather instable molecules. The planar set-up of DART source, HPTLC plate and detector inlet in a line showed higher sensitivities compared to desorption at an angle. The optimal detector voltage increases with the molar mass of the analyte, thus an individual determination of optimal detector voltage setting for the different analyte is recommended to achieve the best possible measurement conditions. In conclusion, DART-MS detection in combination with an HPTLC separation allows very specific quantification of all three compounds.},
  language  = {en}
}