Empower Tip: Empower CDS User Question

In this tip for Empower Chromatography Data System (CDS), we will pause our series on peak identification to answer an Empower user question on calculating USP signal-to-noise.

Question: How do I calculate USP signal-to-noise using a specified time region in the blank for the noise?

This can be done with a peak Custom Field using intersample syntax.

USP signal-to-noise (S/N) is calculated as 2xHeight of peak/noise.

From the Sample Set Method, Blank is the label for the blank injection and there is only one injection. This is single-channel UV data, therefore, there is no need to specify the channel.

Create a peak Custom Field using intersample syntax. We need the Scale to µV field in the equation because peak height is in µV (microvolts) and peak-to-peak noise is in detector units which in this case is AU.

Go to the Suitability tab in the Processing Method and select peak-to-peak noise from the Noise Value for s/n drop-down.

Go to the Noise and Drift tab in the Processing Method and select the time region from the blank injection from which peak-to-peak noise will be calculated.

Once the Sample Set is processed, take the Result Set into Review. Go to the Results window and in the Chromatogram Result table, we can see the peak-to-peak noise calculated from the blank injection.

Click on a result for one of the standards or samples and the Custom Field is calculated based on the noise from the blank injection specified in the Custom Field.

Important Note: peak-to-peak noise will be calculated for every injection. However, it is the peak-to-peak noise from the blank injection which is used to calculate signal-to-noise for all peaks in all injections.

It’s that easy!