Empower Tip: Processing Methods

In this tip for Empower Chromatography Data System (CDS), we will continue our series on Processing Methods. In the last tip, we resumed our series on Processing Methods and discussed which portions of Processing Methods to use, Tip 322.

In this tip, we will explore how to set up the Processing Method to calculate signal-to-noise ratio, a popular topic of late. Whether you are in a regulated laboratory and must follow one of the pharmacopeias or simply want a signal-to-noise, we will explore the options.

Let’s start with a regulated laboratory that must follow one or more of the pharmacopeias.

When creating a new Processing Method, go to the Suitability tab and select Calculate Suitability Results, and enter a Void Volume Time (mn).

The area within the dark yellow box has the selections for signal-to-noise calculation. The rest of the information on this tab can be ignored. USP chapter <621> states that you should use a blank injection for the determination of noise.

USP noise is peak-to-peak noise and is automatically done. There is no need to select peak-to-peak noise from the Noise Value for s/n.

STEP 2:

If you are on Empower version 3.7.0 then you will have an additional choice of Chinese Pharmacopeia. Versions prior to 3.7.0 only display USP, EP and JP.

Be sure to select the blank in your Sample Set Method.

Once the data is processed, we see the USP signal-to-noise and USP noise calculated for each peak.

An older option is to calculate peak-to-peak noise using a section of baseline within the chromatogram with your peaks of interest. If that is the case, deselect Use noise centered on peak region in blank injection. (Please keep in mind that chapter <621> now says to use a blank injection). USP noise is peak-to-peak noise and is automatically done. There is no need to select peak-to-peak noise from the Noise Value for s/n.

Locate a portion of the baseline within the chromatogram which will be used for the peak-to-peak noise determination.

Go to the Noise and Drift tab and enter that time region over which peak-to-peak noise will be calculated. The difference between the start and stop time must contain at least 60 data points. The segment width is used for calculating average noise and drift. The segment width must contain at least 30 data points. Hint: Check the sampling rate in the Instrument Method which is points per second and then multiply that by the segment width in seconds. This will give you the number of data points in the segment.

Once the data is processed, we see the USP signal-to-noise and the peak-to-peak noise (calculated from the region selected in Step 6). In this case, one peak-to-peak noise is used to calculate signal-to-noise for all peaks in the chromatogram.

It’s that easy!