Tip #36: Working with Misidentified Peaks Due to Retention Time Shifts (Part 1)

Welcome back to Get Empowered! In the last tip-of-the-week blog for Empower Software, we explored one of the ways to extract chromatograms and spectra from 3D PDA data (Part 2).

This week I’m starting a new series of posts that will explore how to work with peaks that have been misidentified due to retention time shifts (Part 1).

Retention time shifts in chromatography are not unusual. We can live with these shifts until peaks are no longer identified properly. There are a number of techniques in Empower Software that we can use to correct for misidentified peaks. Let’s start by working with the Retention Time Window.

Step 1

Start by bringing channels into review, in this case one standard and one sample. I modified the chromatogram plot so that we see a stack plot of the standard as compared to the sample (Figure 1).

Figure 1

Step 2

Open the processing method and integrate/calibrate the standard (Figure 2).

Figure 2

Step 3

Then integrate/quantitate the sample (Figure 3).

Figure 3

Step 4

We see that the third peak in the sample chromatogram is not identified and the Peak Type in the Peaks table is unknown. Furthermore, the Peak Type for peak 3 is missing (Figure 4).

Figure 4

Step 5

Let’s assume the peak at 8.033 minutes is peak 3. Why is it not identified properly? Let’s check the Retention Time Window around the peak. Click the Show Components tool (Figure 5).

Figure 5

Step 6

The tall marker indicates where the peak is expected to be and the two shorter markers show you the Retention Time Window. By default, if the apex of the peak is within the Retention Time Window, the peak should be identified properly. However, we see that the apex of the peak is just outside of the Retention Time Window (Figure 6).

Figure 6

Step 7

An easy way to solve this problem is by enlarging the Retention Time Window. Using the mouse, drag one of the small markers away from the peak, thus enlarging the Retention Time Window (Figure 7).

Figure 7

Step 8

Now click the Quantitate tool and the peak is identified properly (Figure 8).

Figure 8

Step 9

Click the Processing Method tool and then the Components tab (Figure 9). We see the Retention Time Window field, which is automatically updated by the action we took in Step 7.

Figure 9

It’s that easy!

Final note:

This procedure can be followed using the QuickStart or Pro interface.

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Next week in Empower Tip #37: Working with Misidentified Peaks Due to Retention Time Shifts (Part 2)

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