Determination of serum amantadine by liquid chromatography-tandem mass spectrometry

Background: Amantadine (1-adamantylamine) is used for treatment of influenza, hepatitis C, parkinsonism, and multiple sclerosis. Current amantadine analysis by HPLC or gas chromatography (GC) requires a laborious sample pretreatment with extraction and/or derivatization steps. We established an LC-MS/MS method without protein precipitation, centrifugation, extraction and derivatization steps. Material and methods: 50 mu l sample+50 mu l of 0.4 mg/l 1-(I-adamantyl)pyridinium bromide as internal standard+1000 mu l water (96-well plate). Of this 25 mu l+500 mu l water (96-well plate; final serum dilution 1:462). LC-MS/MS: Surveyor MS pump, Autosampler, triple-quadrupole TSQ Quantum mass spectrometer (Thermo Electron). Autosampling: 2 mu l of each sample. Chromatography: isocratic water/acetonitrile (60/40 v/v) with 5 g/l formic acid, flow rate 0.2 ml/min, run time 3 min, Phenomenex Luna C8(2) (100 X 2.0 min (i.d.); 3-mu m bead size) column. Mass spectrometry: electrospray atmospheric pressure ionization, positive ion and selective reaction monitoring mode, ion transitions m/z 152.0 -> 135.1 (at 22 eV amantadine) and 214.1 -> 135.1 (at 26 eV internal standard). Results: Calibration curves were constructed with spiked serum samples (amantadine 50-1000 mu g/l, r > 0.99). No carry over (5000 mu g/1). No ion suppression with retention times similar to those of amantadine (1.8 min) and the internal standard (2.1 min). Detection limit 20 mg/l, linearity 20-5000 mg/l, intra-assay/inter-assay CV < 6%/< 8%, recovery 99-101%. Method comparison: LC-MS/MS = 1.23 x GC-45 (Passing-Bablok regression). No significant bias between GC and LC-MS/MS (BlandAltman plot). Conclusion: We consider the sample pretreatment without deproteination, derivatization and centrifugation steps and the specificity of the tandem mass spectrometry as the most important points of our amantadine analysis method. (c) 2005 Elsevier B.V. All rights reserved.