Electron ionisation mass spectral study of 2-(2-carboxy-4, 5-dimethoxyphenyl)-6,7-dimethoxyisoquinolinium inner salt

The electron ionization mass spectrum of 2-(2-carboxy-4,5-dimethoxyphenyl)-6,7-dimethoxyisoquinolinium inner salt 1 is discussed and general fragmentation routes of its molecular ion are proposed. Comparison of the data obtained for 1 with the EI-MS data of metameric protopine alkaloids (allocryptopine, argemexicaine A, argemexicaine B) and the pseudobenzyloisoquinoline alkaloid taxilamine allows a differentiation between these metamers. The data will be useful for the identification of metabolites of alkaloids of these types in biological matrices.