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. 2012 Jun 14;7(6):e39017. doi: 10.1371/journal.pone.0039017

Figure 4. Collision induced dissociation mass spectrometry demonstrates alpha branch chain length.

Figure 4

(A) Purified S. rugosus MAMEs found in the high migrating fraction on the TLC plate were dissolved in chloroform and methanol solution, loaded into a nanospray tip and analyzed by positive-ion mode electrospray ionization mass spectrometry with ion trapping. The ion at m/z 1368.5 [M+Na]+ corresponding to C92 mycolic acid methyl ester was subjected to CID-MS, yielding a fragment ion corresponding to a sodium adduct of the meroaldehyde chain (m/z 1013.9) which indicates a neutral loss of the α-chain-derived C22∶0 methyl ester. (B–C) Bacterial pellets of S. rugosus and S. rotundus were extracted with chloroform, diluted with methanol and analyzed by negative-ion mode electrospray ionization mass spectrometry. Both samples contain an ion at m/z 1330.3 ([M-H]−) corresponding to C92 mycolic acid, which was subjected to CID-MS analysis. The product ion 339 from S. rugosus (B) and ions 339 and 367 from S. rotundus (C) indicate the presence of C22∶0 and C24∶0 α-branch-derived fatty acids.