# Get Empowered: Review Window and the Processing Method | Tip #49, Deriving Channels

By December 27, 2017

## Tip #49: Deriving Channels in Empower (Part 3)

Welcome back to Get Empowered! In our last tip-of-the-week blog for Empower Software, we reviewed how to derive a channel in Empower CDS.

• Tip 47: Smooth a chromatogram by Deriving a Channel (part 1)
• Tip 48: Correct for the time offset between detectors connected in series by Deriving a Channel (part 2)

This week we will learn how to subtract a baseline from a 2D chromatogram by Deriving a Channel (part 3).

Do you run steep gradients on your HPLC and the resulting baselines drift upward? Do you run steep temperature programs in the column oven of your GC and have a similar phenomenon? Did you ever want to subtract the rising baseline? It is very easy to do by Deriving a Channel and this will give us the opportunity to explore how we can mathematically combine channels.

Let me show you how it’s done.

### Step 1

We begin by bringing a sample set into Review and zooming in on the baseline of one of the injections. We see the rise in the baseline due to the gradient (Figure 1).

Figure 1

### Step 2

The first thing we need to do is give the blank injection a label either in the Sample Set method prior to acquiring the data, or post-run in Alter Sample (Figure 2).

Figure 2

### Step 3

Then we open the Method Set and derive a new channel (Figure 3). (Reviewed in Tip 48)

Figure 3

### Step 4

On the First (Only) Channel tab, select the channel from the Channel drop-down list (Figure 4). (This example uses single-channel UV data, so it is an easy choice.)

Figure 4

### Step 5

On the Second Channel tab, select a mathematical operator, subtraction in this case (Figure 5).

Figure 5

### Step 6

Select the channel from the Channel drop-down list (Figure 6).

Figure 6

### Step 7

Check the box that says From Injection Labeled and then enter the label for the blank in the empty field (Figure 7). Note the equation that Empower creates, which says subtract the blank channel, from the injection labeled Blank, from all other channels.

Figure 7

### Step 8

Save the Derived Channel with a name, select the processing method in the channel table, and save all changes to the Method Set (Figure 8).

Figure 8

### Step 9

Return to the Main Window. Apply the Method Set, and now the baseline is flat (Figure 9).

Figure 9

### Step 10

Finally, apply the Method Set to the blank injection. The result is a straight line because it is subtracted from itself (Figure 10).

Figure 10

It’s that easy!

Final notes:

1. I would only recommend using this procedure if the baseline is very reproducible.
2. This procedure can be followed using the QuickStart or Pro interface.

Please rate this Empower Tip of the Week

Next week in Empower Tip #50: Empower Tips: A Year in Review.

In this blog, I will summarize what we covered in 2017 and also share with you some questions I received throughout the year. In Tip #51 we will continue the discussion on deriving channels: Deriving Channels in Empower (part 4).

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