The mass spectra of substituted pyridazines, phthalazines, and related compounds are reported and discussed. Molecular ions are a prominent feature of all the spectra, and fragmentation modes may be usefully correlated with both the type of heterocycle and its substitution pattern. Fragmentation patterns have been substantiated by extensive high resolution studies and appropriate metastable ions.

Skeletal-rearrangement fragments are observed in the mass spectra of all anils derived from aromatic aldehydes. The rearrangement processes have been studied by high-resolution mass spectrometry and in certain cases by deuterium labelling. All processes are of the general type [ABC]+ → [AC]+ +B.

The mass spectra of substituted isoxazoles are reported and discussed. The spectra of isoxazoles are strikingly different from those of oxazoles because the initial fragmentations of isoxazoles involve N-O bond fission. Specific skeletal-rearrangement processes are observed in many spectra, and it is proposed that they proceed through azirine and oxazole intermediates. Certain fragmentations have been studied by deuterium labelling. The hydrogens attached to an isoxazole ring do not randomize with the hydrogens of the methyl and phenyl substituents.

The mass spectra of a series of a-diketones are reported and discussed. Fragmentation patterns have been substantiated by exact mass measurements, metastable ions, and in two cases, by deuterium labelling studies. The McLafferty rearrangement is not observed in the spectra of aliphatic α-diketones; fragmentation proceeds by α-cleavage. The fragmentation modes of those cyclic α-diketones studied depend largely on the ring size. Molecular ions are observed in all spectra.

permitted identification of phenytoin and several of its metabolites.Supported by NIH Grant #GM36143. References[11 Markey, S. P., and Abramson, F. P., J. Chromatogr, 235, 523 (1982).[2] Abranson, F. P., and Markey, S. P., Biomed. Env. Mass Spectrom. 13, 411 (1986 Markey and Abramson [1] developed a microwave-powered chemical reaction interface, a device which converts a complex organic molecule in the presence of a reactant gas into small stable molecules which are detected by mass spectrometry. For a given reactant gas the molecules formed are a representation of the elemental composition of the original anlayte. The combination of the reaction interface and a mass spectrometer produces an isotope-or element-selective detector for samples either introduced directly into the reaction interface or flowing from a capillary gas chromatograph column.Microgram and submicrogram samples of a variety of proteins were analyzed for their sulfur content relative to their carbon content by introducing the samples directly into the reaction interface. With CO, as the reactant gas, S02 at m/z 64 is produced. This quantifies the amount of sulfur which was introduced into the reaction interface. In the presence of N 2 , HCN at m/z 27 is produced and is used to quantify the carbon content of the sample.The observed ratio of S/C for various proteins correlated well with the elemental formulas [2].In the presence of S02, 4NO at m Iz 30 and 5 NO at m/z 31 are produced. Following administration of 50 mg of triple-labeled 5,5-diphenylhydantoin (1, 3("N); 2('C)] to a male beagle dog, a urine sample was selectively analyzed for its