A mass spectrometry-based method for differentiation of positional isomers of monosubstituted pyrazine N-oxides using metal ion complexes.

A series of 11 pairs of substituted pyrazine N-oxides, differing in the substituent position, were examined using electrospray ionization mass spectrometry (ESI-MS) in order to use spectra to assess the differentiation of positional isomers. For each compound, mass spectra were recorded with three different metal cations, namely calcium (II), copper (II) and aluminum (III), with characterization of the observed peaks. Differentiation between regioisomeric N-oxides has been achieved by comparison of the identity and relative intensities of the peaks originating from the adduct ions formed with the metal ions. Principal component analysis (PCA) has been employed to assist in the interpretation of the results obtained with each metal ion, exploring possible trends according to the nature and position of the substituent in the pyrazine N-oxide.