Enantioselective determination of ibuprofen in saliva by liquid chromatography/tandem mass spectrometry with chiral electrospray ionization-enhancing and stable isotope-coded derivatization.

Abstract A method was developed and validated for the enantioselective determination of trace ibuprofen (IBU) in saliva using liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS) combined with the derivatization using a chiral ESI-enhancing reagent, ( S )-1-(4-dimethylaminophenylcarbonyl)-3-aminopyrrolidine (DAPAP), and its isotope-coded analog, 2 H 4 -DAPAP ( d -DAPAP). The DAPAP-derivatization enabled the highly sensitive detection [detection limit, 0.15 fmol (equivalent to 30 fg of intact IBU) on the column] and complete separation (resolution 3.1) of the IBU enantiomers. The use of d -DAPAP significantly improved the assay precision and accuracy; the intra- ( n  = 5) and inter-assay ( n  = 5) relative standard deviations did not exceed 6.2%, and good accuracy (101.3–106.1%) was obtained. The developed method was successfully applied to the quantitative analysis of IBU in saliva. Using this method, salivary concentration–time profiles of each enantiomer after a single oral administration of the racemic IBU to healthy subjects were obtained. The area under the salivary concentration-time curve of the ( S )-enantiomer was ca. twice that of the ( R )-enantiomer due to the unidirectional chiral inversion of the ( R )- to ( S )-enantiomer in vivo. Thus, saliva-based noninvasive pharmacokinetic analyses of IBU enantiomers were achieved by this method.