MassQC Help > Metrics > Dynamic Sampling > Low Intensity Trigger Point          
Low Intensity Trigger Point

The Low Intensity Trigger Point is. for low abundance peptides, the intensity on the extracted ion chromatogram (XIC) curve where the where the MS2 scan is triggered.

High value of the Low Intensity Trigger Point mean that the mass spectrometer is efficiently sampling the signal for the lower intensity MS2 scans. A low value for Low Intensity Trigger Point means that only a small portion of the available signal is being used for peptide identification.

The Low Intensity Trigger Point metric is the percentage of the maximum MS1 peak which is sampled for MS2. The metric is the median value of this measurement over all the times that MS2 is sampled. For this calculation only the smaller half of the MS1 peaks are considered.

Units:

Percent (%)

Optimal:

Higher: Higher percentage means that more of the available ion current is being sent to MS2.

The most reproducible LC-MS performance is when this metric remains in a narrow range over a series of runs. Wide variability in any metric means your process is not reproducible.

What the Metric Detects:

Under ideal circumstances, chromatographic peaks would be sampled at their maximum intensity. That is, the Low Intensity Trigger Point metric would be 100%. If the Low Intensity Trigger Point is too low, there may be insufficient ion current for the MS2 spectra triggered from low intensity MS1 peaks to have a signal-to-noise ratio that is adequate for successful peptide identification.

Related Metrics:

The Low Intensity Trigger Point is the same as the Trigger Point except it is calculated only for the MS1 peaks with low intensity. Only peaks less than the Peak Intensity metric value are considered to be low intensity peaks.

Since the Low Intensity Trigger Point is a percentage of the peak height, an unusually high Trigger Point may indicate that there are many peaks just above the trigger point. In other words the MS/MS instrument may set to trigger MS2 scans at a very low intensity, that is, it is triggering on noise. An unusually low Peak Intensity or high Signal to Noise metric may be further symptoms of too low a trigger point.

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