Anion Mass Spectrometry of Barbiturates

Recent trends towards increasing abuse of the barbiturates has led to a proposal to legally restrict some of them. The implementation of the resulting legislation might require specific identification of the barbiturates. Such identification is not readily available from electron impact mass spectra and, even when these are supplemented with chemical ionization data, barbiturates differing only in isomeric sidechains are not completely characterized. In this study the anion mass spectra of 30 barbiturates, including all of those commonly available, are presented. The spectra are simple; ions arising from hydrogen atom and sidechain elimination from the initially formed [M]- ion are diagnostic of the barbiturate. For all but two of the barbiturates (butalbital and idobutal) relative peak intensities will discriminate between barbiturates differing only in isomeric sidechains.