Electrospray tandem quadrupole fragmentation of quinolone drugs and related ions. On the reversibility of water loss from protonated molecules

Abstract

Selected reaction monitoring (SRM) of quinolone drugs showed different sensitivities in aqueous solution vs. biological extract. The authors suggested formation of two singly protonated molecules with different behavior, one undergoing loss of H(2)O and the other loss of CO(2), so that SRM transitions might depend on the ratios of these forms generated by the electrospray. These surprising results prompted us to re-examine several quinolone drugs and some simpler compounds to further elucidate the mechanisms. We find that the relative contributions of loss of H(2)O vs. loss of CO(2) in tandem mass spectrometric (MS/MS) experiments depend not only on molecular structure and collision energy, but also, in certain cases, on the cone voltage. We further find that many product ions formed by loss of H(2)O can reattach a water molecule in the collision cell, whereas ions formed by loss of CO(2) do not. Since reattachment of H(2)O can occur after water loss in the cone region and prior to selection of the precursor ion, this effect leads to the dependence of MS/MS spectra on the cone voltage used in creating the precursor ion, which explains the formerly observed effect on SRM ratios. Our results support the earlier conclusion that varying amounts of two ions of the same m/z value are responsible for problems in the analysis of these drugs, but the origin is in dehydration/rehydration reactions. Thus, SRM transitions for certain complex compounds may be comparable only when monitored under equivalent ion-forming conditions, including the voltage used in the production of the protonated molecules in the electrospray ionization (ESI) source.

Fragmentation of Moxifloxacin and Its Analogs by Electrospray Ionization Time-of-Flight Mass Spectrometry

“…The peak for the species formed by the loss of CO 2 was large for analog 1, small for moxifloxacin, and absent for analog 2. These results are consistent with those reported by Neta et al (2010). The high-abundance product ion at m=z 261 in the tandem mass spectrum of analog 1 is formed by the four-membered H rearrangement and McLafferty-type rearrangement (Gross and Veith 1994) from m=z 372 (Scheme 2).…”

Cross-Ring Fragmentation Patterns in the Tandem Mass Spectra of Underivatized Sialylated Oligosaccharides and Their Special Suitability for Spectrum Library Searching

“…Several relaxed scans were performed for exploring potential fragmentation pathways. Similar calculations have been effectively used in previous studies of ion fragmentation under CID conditions [27, 28]. Frequency analyses at the same level of theory were performed to identify real minima and transition state structures on the potential energy surface, for the model structures, 3-SLN and 6-SLN.…”

Ispitivanje reakcija hidrolize i kompleksiranja u rastvorima aluminijum(III)-jona i nekih fluorohinolona metodom elektrosprej-tandem masene spektrometije

“…Губитци H 2 О се не региструју, већ напротив имамо везивање молекула H 2 О са датим јонима што је у потпуности у складу са литературним подацима при проучавању сродних система. [88,143,147]. Ово је последица присуства малих количина воде у јон трапу које је тешко уклонити.…”

“…Примењена је тандем масена спектрометрија са циљем дешифровања путева фрагментације и коначно maLDI спектрометрија. [147,158,159], а настаје губитком воде је мање вероватна јер у извору воде има у вишку и најчешће се јавља присаједињавање воде. Овај сигнал се у нашим експериментима не региструје.…”

“…Губитак CО потиче (у складу са литературом од карбонилне групе једног од везаних лиганда у комплекс и указују да се лакше раскида веза са металним јоном, него са друга два лиганда. Губитци H 2 О се не региструју, већ се региструје присаједињавање молекула H 2 О са датим јонима што је у потпуности у складу са литературним подацима [147,153]. То је последица присуства малих количина воде у јон трапу које је тешко уклонити.…”