GC-MS and GC-IRD studies on the six ring regioisomeric dimethoxybenzoylpiperazines (DMBzPs).

The dimethoxybenzoylpiperazines show mass spectra characteristic for this set of six regioisomeric substances and the position of ring substitution for the dimethoxy groups can be determined by vapor phase infrared methods. The dimethoxybenzoylpiperazines are characterized by several fragment ions unique to the mass spectra for this set of regioisomeric compounds. Ions at m/z 165 and 182 indicate the presence of the dimethoxybenzoyl and dimethoxybenzamide groups while low mass ions at m/z 56, 69 and 85 are characteristic of the piperazine ring in these isomeric compounds. The mass spectra for these regioisomeric dimethoxybenzoylpiperazines are almost identical and this method alone does not provide for the confirmation of identity of any one of the isomers to the exclusion of the other compounds. The perfluoroacyl derivatives of the six regioisomers were resolved by gas chromatography and their mass spectra showed some differences in relative abundance of fragment ions without the appearance of any unique fragments for specific confirmation of structure. Gas chromatography with infrared detection (GC-IRD) provides direct confirmatory data for the differentiation between the regioisomeric underivatized dimethoxybenzoylpiperazines.