Percentage recovery of radiolabeled estradiol in the extracted fraction (mean ± standard deviation). Replicate serum samples containing ¹²⁵I labeled estradiol (1 microcurie) and estradiol (5 pg/mL) were subjected to extraction by each of the three solvents under the various pH and sodium chloride conditions as described in methods. The samples were subsequently spun, and the percentage of radioactivity in the supernatants was determined. The percentage of radioactivity recovered is shown here. The data represents the results of six separate experiments.