Simultaneous Quantitation of Estradiol and Estrone in Serum Using Liquid Chromatography Mass Spectrometry

Accurate measurement of the endogenous estrogens, estrone (E1) and estradiol (E2), is important in the clinical diagnosis and monitoring of multiple disorders. Typically, given the efficacy and low cost, radioimmunoassays (RIA) and enzyme-linked immunoassays (EIA) are used to quantify these hormones in biological samples. Unfortunately, at low levels these assays lack the necessary sensitivity and specificity for diagnosis of certain disorders in adult and pediatric endocrinology and oncology. In response to this need, we developed a fast and sensitive high performance liquid chromatography negative electrospray ionization tandem mass spectrometry (LC-MS/MS) method to measure serum estrone (E1) and estradiol (E2) without chemical derivatization. Samples are spiked with a stable isotopic carbon thirteen ((13)C) labeled internal standard and the estrogens are isolated by liquid-liquid extraction (LLE) with hexane:Methyl-tert-butyl ether (MTBE) (9:1). Following centrifugation and dry down samples are reconstituted with deionized water, and separated on a C18 reverse phase column. The analytes are quantified using a six point calibration curve with a linearity of 2.6-625 pg/ml and with a variability of less than 8 % across analytical range.