Metabolite ID also provides the user with the capability to change the reference scan. In the case of verapamil, it makes sense to perform an additional correlation search using the MS2 spectrum of the N-dealkylation metabolite (MH+: 291) described earlier. This makes sense because any metabolite resulting from the same alkyl cleavage would most likely correlate better with this reference than with the parent drug. Using the logic described for the previous correlation search, the m/z values of 277, 307, and 425 can be flagged as likely metabolites.
Table 3 summarizes the results of these two correlation searches. Further correlation searches using additional reference scans could be performed.
The final step in characterizing the metabolites of verapamil is to evaluate all of the possible combinations of the modifications discovered to this point. The complete list of all possible modifications is listed in Table 4.
Once the metabolite analysis has been completed, Metabolite ID provides a number of different ways to display the final results. The Modification Peak Summary Table , displayed in Figure 6 demonstrates the broad dynamic range over which Metabolite ID can identify metabolites. For the verapamil monkey microsome incubation, metabolites ranging in amounts from 0.2% to 40.4% of the total peak area were characterized.
Mass Frontier Analysis Mass Frontier provides a collection of modules that assist the user in managing, interpreting, and classifying mass spectra. In this publication, Mass Frontier will be used to locate the specific sites of metabolic modifications identified previously with Metabolite ID. The general approach will be as follows:
From Metabolite ID, export the MS2 spectra of the metabolite of interest an