Ions and Linked Scans

The determination of metastable ions has found much interest, because of their structural and theoretical significance. Several techniques have been developed and some of them are discussed here. Some of the techniques can be made more powerful by means of forced fragmentation in a field-free region (collision-induced dissociation). This process is essential for MS/MS experiments (see Chapter 20.7). Metastable ions are gaining new relevance in time-of-flight instruments with reflectrons (.see Section 20.5.3). 

In a magnetic sector instrument the signals of metastable ions appear as broad, mostly gaussian peaks in normal mass spectra. The location m may be calculated from the precursor ion mass nip and the product ion mass nia using the relation  

These signals are normally lost in double focusing instruments, although in Nier-Johnson type mass 

A simple and inexpensive way of obtaining MS/MS information is the use of linked scans in sector field instruments. The advantage over the MIKES technique is that the resolution is generally better and that all double-focusing instruments can be used. The two sectors and the acceleration voltage are linked together by functions that allow 

Neutral Loss Scans. Among several other possibilities for linking the fields and voltages in a double-focusing mass spectrometer, the neutral loss scan is the only one which deserves a brief discussion here. The scan function is 

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