Daughter ion resolution

In addition to the EIEIO experiments, the dual cell has also been employed for collisional activation (CA) experiments. Selected parent ions may be transferred to the analyzer cell for CA. With pulsed valve introduction of the collision gas (argon) into the analyzer cell, it is possible to obtain very high daughter ion resolution. Figure 13 shows a C6H5C0+/C8H9+ doublet from CA of acetophenone and mesitylene, detected at a resolution of 500,000. 

Another advantage of FTMS for MS/MS experiments is that high resolution daughter ion spectra can be obtained. Using a single cell and narrow band (heterodyne) (7, 17) detection, daughter ion... 

MS/MS. The capability of trapping ions for long periods of time is one of the most interesting features of FTMS, and it is this capability that has made FTMS (and its precursor, ion cyclotron resonance) the method of choice for ion-molecule reaction studies. It is this capability that has also lead to the development of MS/MS techniques for FTMS [11]. FTMS has demonstrated capabilities for high resolution daughter ion detection [42-44], and consecutive MS/MS reactions [45], that have shown it to be an intriguing alternative to the use of the instruments with multiple analysis stages. Initial concerns about limited resolution for parent ion selection have been allayed by the development of a stored waveform, inverse Fourier transform method of excitation by Marshall and coworkers [9,10] which allows the operator to tailor the excitation waveform to the desired experiment. 

Figure 13. Isobaric daughter ions from CAD of acetophenone and mesitylene, detected at a resolution of 500,000.

Improvements in the instrumentation, ionization sources, high-resolution mass analyzers, and detectors [67-69], in recent years have taken mass spectrometry to a different level of HPLC-MS for natural product analysis. Mass spectrometry detection offers excellent sensitivity and selectivity, combined with the ability to elucidate or confirm chemical structures of flavonoids [70-72]. Both atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) are most commonly used as ionization sources for flavonoid detection [73-76]. Both negative and positive ionization sources are applied. These sources do not produce many fragments, and the subsequent collision-induced dissociation energy can be applied to detect more fragments. Tandem mass spectrometry (MS , n> 2) provides information about the relationship of parent and daughter ions, which enables the confirmation of proposed reaction pathways for firagment ions and is key to identify types of flavonoids (e.g., flavones, flavonols, flavanones, or chalcones) [77-80]. 

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