# Get Empowered: Review Window and the Processing Method | Tip #43

By November 14, 2017

## Tip #43: Calculating impurities and setting thresholds (Part 4)

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 will look at calculating impurities in samples and setting thresholds (part 4).

In the last example, we expressed the impurity response as % area against the main peak. Here, we use the thresholds to flag impurities that exceed certain levels.

### 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).

On the left, we see the ICH Thresholds. The Reporting Threshold sets the limit above which the impurity needs to be reported. The Identification Threshold sets the limit above which the impurity needs to be identified, that is structurally characterized. The Qualification Threshold sets the limit above which the impurity needs to be qualified. Qualification is the process of acquiring and evaluating data that establishes the biological safety of an individual impurity at the level specified.

Figure 1

### Step 2

Now that we’ve defined what these thresholds mean, let’s plug in some numbers. I am entering 0.025, 0.05, and 0.075, respectively (Figure 2).

Figure 2

### Step 3

Return to the main window and click quantitate. In the table properties, un-hide the following fields: Impurity, Reporting Threshold, Identification Threshold, and Qualification Threshold. (I add the threshold fields so that I do not have to go back and forth between the main window and the processing method to see what values were set for the thresholds.) Additionally, you can add the fields that indicate if the thresholds have been exceeded (Figure 3).

Figure 3

### Step 4

First take note that any peak with a check mark in the Impurity field means that impurity has exceeded the reporting threshold (Figure 4).

Figure 4

### Step 5

Let’s take a look at the impurity peak named RRT0.623. It has an impurity response of 0.051, which exceeds the reporting threshold and yet it does not exceed the identification threshold of 0.05. How is that possible?

Since the threshold is set for 0.05, the impurity response of 0.051 is rounded down to 0.05. If we modify the identification threshold to 0.050 then the impurity response for this peak is flagged as exceeding the identification threshold (Figure 5). Note that any impurity with a response exceeding the identification threshold results in the peak name and impurity response displayed in red, bold, italicized font.

figure 5

It’s that easy!

Final note:

1. This procedure can be followed using the QuickStart or Pro interface.
2. You can add the fields mentioned in Step 4 to the peaks table in the report method as well.

Please rate this Empower Tip of the Week

Next week in Empower Tip #44: Calculating Impurities (Part 5), Specified impurities

#### More resources:

Do you want Empower Tips sent to your inbox every week?

Questions? Tips of your own? Let us know!