Empower Tip: Review Window and the Processing Method

If you are not in a regulated environment you probably want to calculate Signal to Noise without the USP, EP, or JP formula (Tip 28). One of the options for noise is Baseline Noise. This is the original option that was available with Millennium chromatography software in the 1990s.

We begin by bringing a Sample Set into Review, open a Processing Method and Integrate/Calibrate or Integrate/Quantitate a channel.

Go to the Processing Method window, click the Suitability tab and select Baseline Noise from the Noise Value for s/n drop down list.

The Baseline Noise minimum is either a minimum time interval or minimum number of data points used to calculate baseline noise.

So, how does Empower calculate Baseline Noise? The software calculates noise based on the maximum signal change over a 30-second interval. The reported noise value is an average of two 30-second intervals, as determined by the parameter % Run Time Over Which to Average. To determine the 30-second intervals, the software begins counting from the Baseline Start time and the Baseline End time toward the middle of the chromatogram. In Figure 4 we have a 10-minute run time. 0.5% of 10 minutes is 0.5 minutes. Therefore, region 1 is 0 to 0.5 minutes and region 2 is 10 to 9.5 minutes. Be sure to pick areas of the baseline that only contain noise and not peaks, otherwise, you will have a high noise value reported.

In our chromatogram, we have a 15-minute run time, therefore, if we use 3.5 for the % Run Time Over Which to Average, that will give us 30-second intervals. We set the Baseline Start to 0 and the Baseline End to 15.

Return to the Main Window and Integrate/Calibrate or Integrate/Quantitate. The Signal to Noise is calculated using Baseline Noise for each integrated peak.

Go to the Results window and we can see the Baseline Noise, Baseline Drift and Scale to microvolts fields in the Chromatogram Result table. The Baseline Drift is simply the signal at Baseline End minus the signal at Baseline Start.

It’s that easy!