# Get Empowered: Review Window and the Processing Method | Tip #42

By November 8, 2017

## Tip #42: Calculating impurities in samples (Part 3)

Welcome back to Get Empowered! In the last tip-of-the-week blog for Empower Software, we discussed how to calculate impurities in samples.

This week we continue the discussion and look at another example (Part 3).

Previously, we wanted to express the impurity response as % adjusted area while excluding certain peaks such as a system peak from the calculation. In this example, we are going to express impurity response as % area against the main peak. We could create a custom field to make the calculation or we could use the features in Empower Software that are designed just for this purpose.

Let me show you how.

### Step 1

Let’s start by bringing a sample set into Review, open the processing method, click the processing method tool, and click the Impurity tab (Figure 1).

Figure 1

### Step 2

For the Impurity Response, select % Area Against Main Component from the drop-down list (Figure 2).
The calculation is (area of peak / area of main peak) x 100.

figure 2

### Step 3

Now let’s select the name of the main peak from the Main Component drop-down list (Figure 3).

Figure 3

### Step 4

Return to the main window and click quantitate. The original %Area is next to the Impurity Response (Figure 4).  (I did adjust the precision for the %Area field from 2 to 3.)

Figure 4

If we look at Impurity E the original %Area is 0.561% and now, compared to the main peak, it is 0.568% – which makes sense, since the area of the peak is now compared to the area of the main peak, which less than the total area for all peaks. (Hint – remember that you can see the total area by going to the Results window within Review and check the middle table called Chromatogram Result.)

It’s that easy!

Final note:

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

Please rate this Empower Tip of the Week

Next week in Empower Tip #43: Calculating Impurities (Part 4), Working with thresholds

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