Determination of theophylline in serum by high performance liquid chromatography mass spectrometry with atmospheric pressure chemical-ionization (APCI HPLC/MS)

A method for the determination of theophylline (TH), without derivatization, in serum by isotope dilution mass spectrometry using labelled [1,3-N-15(2)-2-C-13]theophylline (LTH) as internal standard is described. After deproteinization, the analyte is directly injected into a high performance liquid chromatography-mass spectrometer operating with atmospheric-pressure chemical-ionization (APCI HPLC/MS). The concentrations of TH in sera measured by APCI HPLC!MS are compared with results from gas chromatography - isotope dilution mass spectrometry (GC-ID/MS), high performance liquid chromatography (HPLC) and fluorescence polarization immunoassay (FPIA). The accuracy, precision and recovery of the APCI HPLC/MS and GC-ID/MS methods are discussed. The coefficient of variation (CV) determined from duplicate samples was less than 2%. The detection limit was 10 ng/ml at a signal-to-noise ratio of 3:1.