Waters : Empower Tip #261 | Empower CDS User Question, Calculating Peak Resolution (part 2)

Tip #261: How to calculate resolution between peaks that are in different channels, using custom fields

In this week's tip for Empower Chromatography Data System (CDS), we will provide an alternative approach to the Empower CDS user question we discussed last week in Tip #260.

Q: How can I calculate resolution between two peaks that are in two different channels?

In last week's tip, we answered this question by adding the two channels together and calculating the resolution between the two peaks using System Suitability in the Processing Method.

This week we will answer the same question with an alternative approach by creating a Custom Field to calculate resolution between the two peaks. This would be a Peak Custom Field using Intersample syntax.

Let's get started.

Step 1

We have a stack plot of the two channels of data, each with its own peak eluting at different retention times (figure 1).

figure 1

Step 2:

Be sure to enable System Suitability in the Processing Method as we will need the 'Width at Tangent for USP Resolution' values for our Custom Field (figure 2).

figure 2

Step 3

The calculation for USP Resolution = 2(RT2-RT1)/(W1+W2), where RT is the 'retention time' and W is the 'width at Tangent' for USP Resolution (figure 3).

figure 3

Step 4

Intersample syntax is 'label.injection.channel (field). (Refer to Empower Tip #93 for more details on creating intersample Custom Fields) (figure 4).

figure 4

Step 5

The properties of the Custom Field can be viewed (figure 5).

figure 5

Step 6

The result displaying the resolution between the two peaks in the two different channels is different from the value calculated in Tip #260. The baseline in the combined chromatogram is different from the baselines in the individual chromatograms resulting in different baseline noise, different peak starts/stops and different peak widths. The key is to pick one approach for consistency in the calculations (figure 6).

figure 6

It's that easy!

Final Note: This can be done with either the Pro or QuickStart interface.

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Next time in Empower Tip #262- we celebrate the fifth Anniversary of the Empower Tip of the Week blog!

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