Identification of Barbiturates Using High Performance Liquid Chromatography-Particle Beam EI/CI Mass Spectroscopy

Abstract

The procedure described uses a high performance liquid chromatograph (HPLC) coupled to a quadrupole mass spectrometer via a particle beam interface for the determination of barbiturate identity. The object was the development of a general LC-MS method capable of performing routine analysis. The use of the particle beam interface as a sample introduction technique was selected because of its relatively simple nature and the ability to adapt existing HPLC methods with only minor modification. Chemical ionization (CI) using methane as a reagent gas generated base peak molecular ions for all of the barbiturates analyzed. Electron ionization (EI) at 70 eV caused sufficient fragmentation to allow the analyst to discriminate barbiturates when identical molecular weights were encountered. In those case where highly similar EI and CI spectra are produced, chromatographic separation provided clear distinction of analyte identity. Conversely, when very different spectra are encountered, base line resolution of the analytes was not necessary for accurate identification. When nearly co-eluting spectrally similar analytes are encountered, careful evaluation of the EI+ mass spectra revealed the presence of specific mass peaks exclusive to a particular barbiturate. These mass peaks are used to confirm identity.