Empower Tip: Review Window and the Processing Method

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

Once the apex of a peak has been found, Empower 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.

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

Click the Processing Method tool and click the Integration tab. The default value is 0 for both parameters.

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

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

Finally, if we overlay chromatograms at different concentrations, note the consistency in how Empower places baselines under the peaks. 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.

It’s that easy!