Quan Peaks, Confirming Peaks and the mysterious Mass Filter
In TraceFinder, the lowest form of identification is the peak, but the lowest form of data aggregation is the compound.
Unlike Xcalibur and LCquan, where each individual trace is a component or associated with a single component, TraceFinder allows for the compound to consist of up to 6 quan components. Each of these components CAN, but does not require, be associated withup to 10 confirming peaks.
Each Confirming Peak is assigned a ratio to the associated quan peak. The relation ship of a Quan to a Confirming lies in that they must exist at the same point in time, thereby they must co-elute chromatographically. Also they must exist in a specified or calculated abundance to each other.
Again, unlike Xcalibur and other apps from Thermo, these two peaks do not have to exist in the same Mass Filter. The Mass Filter is a designation in the data file that narrows down where to recover the Time and Intensity pairs of data that represents the abundance of an ion at a particular point in time. This is what is used to construct the 2-D chromatographic plot.
This means that in a SIM experiment a quan peak can be select from one mass filter and the confirming ion can be from another. In an SRM experiment the quan peak could theoretically be from a positive precursor-product filter and the confirming could be from a negative precursor-product filter. In a Full Scan High Resolution Scan experiment,as from an Exactive type instrument, a Quan peak can be selected from a full scan and the confirming peak can be selected from a HCD or AIF scan. By utilizing this technique with no calibrators samples in a batch of samples a chemist can conduct a screening assay for the present/not present answer set.
The next unique quality of this flexible designation is that multiple quan peaks can be selected for a compound and be from separate filters and at different retention times. this would allow for multiple peaks to throughout the chromatographic assay to represent the total response of a compound. This would be best illustrated by compounds that use chiral separations, where one isomer would elute faster than another but the response of both need to be summed as the total response for the calibration curve and amount calculations. By utilizing this feature there is no exporting of results grids to excel or a LIMS system just to calculate the total compound.
Posted on April 5, 2012, in Data Review, General Use, Method Development. Bookmark the permalink. Leave a comment.
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