MassQC Help > Metrics > Chromatography > Retention Spread          
Retention Spread

Retention Spread is the middle part of the retention time. One quarter of the peptides elute earlier; one quarter of the peptides elute later. One half of the peptides elute during the Retention Spread period.

This is the period where the peptides are eluting the closest together. It is this critical time period that most stresses the LC system's ability to separate peptides.

Greater Retention Spread means that the peptides elute over a longer period of time which in turn indicates better separation of peaks.

Units:

Minutes (min)

Optimal:

Higher: The more spread out the eluting peptides, the more time is available to trigger MS2 spectra and the more likely it is to identify more spectra.

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:

An ideal standard protein sample will have peptides that elute over a range of times that is similar to times when peptides from biologically significant samples elute. Typically with reverse phase chromatography, there are only a relatively few hydrophilic peptides that elute early and relatively few hydrophobic peptides that elute late. The bulk of the peptides elute in the middle during the Retention Spread.

A change in Retention Spread may indicate that the gradient has changed. For example, because the buffers have changed, the time it takes for the middle 50% of peptides to elute increases; blockages in LC system can cause Retention Spread to lengthen; improper solvent mixing can also increase or decrease Retention Spread.

Related Metrics:

Since this is the most critical region of the LC run, the Retention Spread is used as the basis for the calculation of a number of other metrics. The metrics Peptides per Minute, Spray Instability, Peak Intensity, Total Ion Current, Dynamic Range, MS1 Spectra and MS2 Spectra are all measured over the Retention Spread period of the elution curve.

The Peptides per Minute metric is calculated by dividing by the Retention Spread. If Retention Spread is very small, Peptides per Minute will be meaningless. If very few peptides are detected (low Peptide Count), then the Retention Spread metric may be unreliable.

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