Chromatograms of 20α-OHP and P
standards. Different concentrations of 20α-OHP and P4, 33, 10, 3.33 and 1 ng/10 μl (A-D, respectively); P4, 10 ng/10 μl (E) and 20α-OHP, 10 ng/10 μl (F) were prepared and run on a Zorbax eclipse C18 column. The mobile phase comprised of acidified water: acetonitrile and sample injection volume of 10 μl was used. The retention time for 20α-OHP (19.1 min) and P4 (22.8 min) is indicated on each peak. Chromatograms of standards used for each 20α-OHP and P4 are boxed separately. The area under each peak corresponds to respective standard concentration.