Quantitative Determination of Anastrozole by Liquid Chromatography–Tandem Mass Spectrometry

Anastrozole is a potent and selective non-steroidal aromatase inhibitor and is used for therapy of postmenopausal women with hormone-receptor-positive breast cancer. This paper provides a detailed description of the determination of anastrozole in human plasma by liquid chromatography–mass spectrometry (LC–MS–MS). Plasma-sample pretreatment involved solid-phase extraction using Accubond SPE ODS-C18 cartridges. Chromatographic separation was carried out on a Zorbax Bonus-RP column with a mobile phase consisting of aqueous formic acid (0.2%) (eluent A) and MeOH (eluent B) with a ratio A:B = 30:70 (v/v) that was supplied at flow rate 0.2 mL/min. Detection was performed on an Agilent 6410-2K triple quadrupole tandem mass spectrometer by multiple reaction monitoring in the preset mass range 294.2 → 225.1 using atmospheric-pressure chemical ionization in positive-ion mode. A calibration curve for anastrozole was linear (R2 ≥ 0.97) over the concentration range 0.5 – 20.0 ng/mL with a lower detection limit of 0.5 ng/mL. The described procedures can be applied successfully to both therapeutic monitoring of anastrozole and drug bioequivalence studies.