The analysis of estrone and 17β-estradiol by stir bar sorptive extraction–thermal desorption–gas chromatography/mass spectrometry: Application to urine samples after oral administration of conjugated equine estrogens

The development of a sensitive and solvent-free method for the measurement of estrone (E1) and 17β-estradiol (17β-E2) in human urine samples is described. The deconjugated estrogens were derivatized in situ with acetic acid anhydride and the derivatives were extracted directly from the aqueous samples using stir bar sorptive extraction (SBSE). The compounds containing a secondary alcohol function are further derivatized by headspace acylation prior to thermal desorption and gas chromatography/mass spectrometry (GC/MS). A number of experimental parameters, including salt addition, temperature and time, were optimized to increase the recovery of E1 and 17β-E2 by SBSE. The derivatization reactions were also optimized to obtain the highest yields of the acylated estrogens. Detection limits of 0.02 and 0.03 ng mL−1 were obtained for E1 and 17β-E2, respectively. The method was applied to determine the effect of conjugated equine estrogen intake on the excretion of E1 and 17β-E2 in human urine samples. Increased levels of the endogenous estrogens were detected after administering a standard dose of Premarin to a female volunteer. Routine monitoring of estrogen levels is recommended to avoid a high urinary excretion of E1 and 17β-E2, nowadays enlisted as endocrine disrupting chemicals (EDCs), during hormone replacement therapy.