Fig. 7

Some hypothesized neutral structures of the ion m/z 132 normal mass negative (6A), ion m/z 145 normal mass negative (6B), ion m/z 160 normal mass negative (6C), ion m/z 174 normal mass positive (6D), ion m/z 216 normal mass negative (6E), ion 213 normal mass positive (6F). The fragmentation mass spectra for these ions are reported in the Additional file 1