Tip #47: Deriving Channels in Empower (Part 1)

Welcome back to Get Empowered! In the last tip-of-the-week blog for Empower Software, we explored how Liftoff% and Touchdown% work in the processing method when using the ApexTrack peak integration algorithm. This week we start a new series on Deriving Channels.

Let’s get started.

The term Deriving a Channel can mean several things. Some examples are:

• Performing a mathematical operation on a channel such as smoothing.
• Mathematically combining two or more channels to obtain a total response for analytes that live in different channels.
• Extracting a 2D channel from a 3D channel, such as extracting a single wavelength from a wavelength range collected with a Photo Diode Array detector.

And there are many more applications. For part 1 of this tip, let’s explore a simple example of smoothing a channel of data collected with a UV detector.

Step 1

We start by bringing an injection into Review in Empower Software. The method set has been opened and applied. Note the signal-to-noise ratio for the relatively small peak at 5.625 minutes is 139/1 and the height is 1767 microvolts (Figure 1).

Figure 1

Step 2

Zooming in on the baseline between 8 and 12 minutes, we see some short-term noise in the baseline (Figure 2). Our goal is to smooth the baseline thus reducing the noise in this region.

Figure 2

Step 3

In the method set window we see Derived Channels under the Method Set tree. Right-click on Derived Channels and select New, Derived Channel (Figure 3).

Figure 3

Step 4

On the First (Only) Channel tab, select the channel of data you want to work with from the drop-down list (Figure 4).

Figure 4

Step 5

On the Filter/Offset tab, select the amount of smoothing from the drop-down list (the higher the number, the more smoothing is applied) along with the type of smoothing (Figure 5).

Figure 5

Step 6

Click OK and, when prompted, enter a name for the Derived Channel (Figure 6).

Figure 6

Step 7

Add the Processing Method in the Processing Method field (Figure 7).

Figure 7

Step 8

Return to Empower’s main window and after applying the method set, note the signal-to-noise ratio for the same peak is now 172/1 due to the reduction in noise and the height is now 1757 microvolts (Figure 8). (Smoothing smoothes all data points across the chromatogram, hence the slight reduction in peak height.)

Figure 8

Step 9

Finally, we see a zoomed view of both chromatograms between 8 and 12 minutes and clearly the smoothed chromatogram has less noise than the original (Figure 9).

Figure 9

It’s that easy!

Final notes:

1. Savitzky-Golay smoothing averages data points. For more detailed information Google a book called Chromatographic Integration Methods by Norman Allen Dyson. There is a good section on filtering and smoothing chromatographic signals.
2. This procedure can be followed using the QuickStart or Pro interface.

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Next week in Empower Tip #48: Deriving Channels in Empower (part 2)

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