Metabolite ID provides two additional tools that assist in the identification of unknown or unusual modifications. The first is Chro Search and the second is Correlation Search . Chro Search employs an algorithm which sorts the intensities of all the ions in all the MS spectra and reconstructs extracted ion chromatograms for the n most intense ions. The user can customize Chro Search by setting intensity, time range, and mass range thresholds for the search. The results of Chro Search applied to the background-subtracted verapamil monkey microsome incubation data file are shown in Figure 4.
The table along the left-hand side of Figure 4 shows the n most intense ions for which extracted ion chromatograms were constructed. The MS2 spectrum of the parent drug is always displayed in the bottom right-hand corner. The results for m/z 330 (from row 11 in the table) are shown at the top. This represents a loss of 125 daltons from the parent drug. This is not a common metabolic mass loss and would have been difficult to predict otherwise. Inspection of the MS spectrum that corresponds to the apex of the largest peak in the extracted ion chromatogram of m/z 330 clearly indicates that m/z 330 represents the protonated molecular weight of an actual compound. Comparison of the MS2 spectrum of this peak (bottom left) with that of the parent drug (bottom right) reveals a large common fragment ion at m/z 303. This supports the conclusion that m/z 330 represents a metabolite.
Table 2 summarizes the modifications that were found by the Chro Search algorithm for the verapamil monkey microsome incubation data file. The user could probe the data further by modifying the Threshold or Most Intense Chro Search par