Robust and sensitive LC/MS-MS method for simultaneous detection of acetylsalicylic acid and salicylic acid in human plasma

A liquid chromatography-tandem mass spectrometry method was developed for the simultaneous determination of acetylsalicylic acid (ASP) and its major metabolite, salicylic acid (SAL) in human plasma. The method was validated. ASP and SAL were extracted by single-step liquid-liquid extraction using tert-butyl methyl ether. The ions were detected in multiple reaction monitoring mode at m/z 179.0/137.0 transition for ASP and m/z 136.9/93.0 for SAL. The lower limit of quantification for ASP and SAL was 1 and 80 ng/ml, respectively. The method was successfully applied for the characterization of the plasma concentration levels of ASP and SAL after oral administration of Aspirin Protect 100 to healthy volunteers. The present method can contribute to the improvement of ASP and SAL determination in patients under antithrombotic therapy, and to the reduction of the risk for ASP resistance associated with bioavailability/exposure issues (non-compliance, misdosing, poor absorption).