IDENTIFICATION OF BARBITURATES USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY PARTICLE-BEAM EI CI MASS-SPECTROSCOPY/

The procedure described uses a high performance liquid chromatograph ( HPLC) coupled to a quadrupole mass spectrometer via a particle beam in terface for the determination of barbiturate identity. The object was the development of a general LC-MS method capable of performing routin e analysis. The use of the particle beam interface as a sample introdu ction technique was selected because of ifs relatively simple nature a nd the ability to adapt existing HPLC methods with only minor modifica tion. Chemical ionization (CI) using methane as a reagent gas generate d base peak molecular ions for all of the barbiturates analyzed. Elect ron ionization (EI) at 70 eV caused sufficient fragmentation to allow the analyst to discriminate barbiturates when identical molecular weig hts were encountered. In those case where highly similar EI and CI spe ctra are produced, chromatographic separation provided clear distincti on of analyte identity. Conversely, when very different spectra are en countered, base line resolution of the analytes was not necessary for accurate identification. When nearly co-eluting spectrally similar ana lytes are encountered, careful evaluation of the EI(+) mass spectra re vealed the presence of specific mass peaks exclusive to a particular b arbiturate. These mass peaks are used to confirm identity.