Get Empowered: Review Window and the Processing Method | Tip #46

By December 6, 2017

Tip #46: Setting Liftoff% and Touchdown% in the Processing Method

Welcome back to Get Empowered! In the last tip-of-the-week blog for using Empower Software for chromatography data analysis, we completed our series on Calculating Impurities in samples and discussed creating impurity groups. This week we are going to explore how Liftoff% and Touchdown% work in the Processing Method when using the ApexTrack peak integration algorithm.

In a previous tip, we explored how to set the peak width and detection threshold when using the ApexTrack algorithm (Tip #22). Recently I’ve had several questions about how baselines are determined using ApexTrack. These parameters are easy to use once you understand how they work.

Let me show you.

Step 1

Once the apex of a peak has been found, Empower CDS determines the baseline placement under the peak. It calculates two slope difference thresholds based on the values entered for Liftoff% and Touchdown%. Both the Threshold in the Traditional Algorithm and these parameters are a signal-based mathematical determination of peak starts and ends. This is very different from the force peak event, which is purely time-based.

Step 2

We start by bringing channels of data into review. Open the Processing Method, click integrate, and note the baseline placement for all three peaks (Figure 1).

Empower Tips: Note the baseline placement for all three peaks | figure 1

Figure 1

Step 3

Click the Processing Method tool and select the Integration tab. The default value is 0 for both parameters (Figure 2).

Empower Tips: Integration tab/ default value | figure 2

Figure 2

Step 4

Modify the Touchdown% to a value greater than 0, in this case 1 (Figure 3).

Empower Tips: Modify the Touchdown% | figure 3

Figure 3

Step 5

Return to the main window, click integrate, and observe the change in the baseline for all three peaks (Figure 4).

Empower Tips: Observe the change in the baseline | figure 4

Figure 4

Step 6

Finally, if we overlay chromatograms at different concentrations, note the consistency in how Empower Software places baselines under the peaks (Figure 5). This is because the slope difference threshold is proportional to peak height, which means small peaks have small slope difference thresholds and large peaks have large slope difference thresholds.

Empower Tips: Consistent baselines under the peaks | figure 5

Figure 5

It’s that easy!


I learned how Liftoff% and Touchdown% work in the Processing Method in Empower! #EmpowerTips Click To Tweet


Final notes:

  1. The Liftoff% and Touchdown% can be set globally as illustrated here and/or can be set using timed events depending on your chromatography. Modifying the Touchdown% can help in cases of tailing peaks as we saw in this example.
  2. For more detailed information please see the Empower 3 Data Acquisition and Processing Theory Guide, section 2.3 Baseline Location.
  3. This procedure can be followed using the QuickStart or Pro interface.


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Next week in Empower Tip #47: Deriving Channels in Empower

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