Study on the Mass Spectrometry Cleavage Pattern of Quinolone Antibiotics

Quinolone antibiotics are extensively used clinically for human treatment and in agriculture. However, improper and excessive use can lead to the persistence of quinolone residues in animal tissues, potentially accumulating in the human body and posing health risks. Investigating the correlation between mass spectrometry cleavage patterns and molecular structural features enhances the analytical framework for detecting trace or unknown impurities in quinolones.

To collect data, we employed triple quadrupole linear ion trap mass spectrometry in electrospray positive ion mode. Primary mass spectrometry scanning was utilized to confirm parent ions, while secondary mass spectrometry scanning enabled the observation of fragment ions. The cleavage characteristics and pathways of the compounds were inferred from accurate mass-to-charge ratios obtained from both primary and secondary mass spectrometry.

Under soft ionization conditions, the compounds generally exhibited characteristic fragment ions of [M+H-H₂O]⁺, [M+H-CO]⁺, and [M+H-H₂O-CO]⁺. Additionally, subtle variations were observed in each compound due to differences in modifying groups. For instance, upon deacidification, the piperazine ring structure underwent breakage and rearrangement, yielding fragment ion peaks devoid of neutral molecules such as C₂H₅N, C₃H₇N, or C₄H₈N. Notably, compounds featuring a cyclopropyl substituent group at the N-1 position typically exhibited characteristic fragments resulting from the loss of the cyclopropyl radical (⋅C₃H₅). Moreover, substituents at the N-1 and C-8 positions, when linked to form a six-membered carbocyclic ring, were prone to cleavage, releasing the neutral C₃H₆ molecule.

Quinolone antibiotics share structural similarities in their parent nuclei, leading to partially similar cleavage pathways. Nevertheless, distinct cleavage patterns emerge due to variations in functional groups. According to the difference of mass spectrometry cleavage patterns, it can provide an identification basis for the measured detection of antibiotics.