Determination of 2‐methoxyestradiol in human plasma, using liquid chromatography/tandem mass spectrometry

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Abstract
A liquid chromatography/tandem mass spectrometric (LC/MS/MS) assay was developed for the quantitative determination of 2‐methoxyestradiol (2ME2) in human plasma. Sample pretreatment involved liquid‐liquid extraction with ethyl acetate of 0.3‐mL aliquots of plasma spiked with the internal standard, deuterated 2ME2 (2ME2‐d5). Separation was achieved on a Zorbax Eclipse® C18 column (2.1 × 50 mm, i.d., 5 μm) at room temperature using a gradient elution with methanol and water at a flow rate of 0.25 mL/min. Detection was performed using atmospheric pressure chemical ionization MS/MS by monitoring the ion transitions from m/z 303.1 → 136.8 (2ME2) and m/z 308.1 → 138.8 (2ME2‐d5). Calibration curves were linear in the concentration range of 1–100 ng/mL. The accuracy and precision values, obtained from three different sets of quality control samples analyzed in quintuplicate on four separate occasions, ranged from 105–108% and from 3.62–5.68%, respectively. This assay was subsequently used for the determination of 2ME2 concentration in plasma of a patient with cancer after a single oral administration of 2ME2 at a dose of 2200 mg. Copyright © 2005 John Wiley & Sons, Ltd.