The other algorithm that Metabolite ID provides for searching for unexpected metabolites is the Correlation Search. This search compares all of the MS2 spectra in a selected data file with the MS2 spectrum of the parent drug specified in the Parent Drug List Manager dialog box. The MS2 spectra are compared based on intensities and masses. The correlation score is a measure of the overlap between the MS2 spectra of a potential metabolite and the reference scan.
The results of a correlation search of the verapamil monkey microsome incubation data file are shown in Figure 5. The table at the left gives the results in terms of Parent M/Z, RT (min), and Correlation. The top chromatogram on the right-hand side is the Modification Summary. It sums together the extracted ion chromatograms of all of the modifications specified in the Modification List Manager dialog box. The second chromatographic trace in Figure 5 is the Correlation Summary. It sums together the correlation score of every MS2 scan in the specified data file. The mass spectrum in the middle of the figure is the MS2 spectrum of the reference scan of verapamil. The spectrum at the bottom of the display is the MS2 spectrum of the scan selected by mouse-clicking in the data table.
The lengthy list of masses can be pared down using the following logic. Mass to charge values that appear at numerous retention times are most likely background ions and can be eliminated. The m/z values that appear too early or too late in the chromatogram relative to the parent drug are also candidates for elimination. Finally, those m/z values that do not exhibit at least 2-3 successive MS2 scans with similar spectra are reasonable candidates for elimination. After applying these constraints to the original table of data, only those modifications at m/z of 330.1 and 441.2 are i