Get Empowered: Review Window and the Processing Method  Tip #69, System Suitability
Tip #69: Working with the System Suitability Option (Part 2)
Welcome back to Get Empowered! In our last tipoftheweek blog for Empower Software, we learned about Statistical Moments within the System Suitability option (Tip 68).
In this week’s tip, we are going to learn how PeaktoPeak Noise is calculated in Empower CDS (part 2).
I’ve had numerous questions about how Empower Software calculates PeaktoPeak Noise for USP, EP, and JP SignaltoNoise calculations. It is not difficult to understand once we take a look at how it works.
Let me show you how it is done.
Step 1
We begin by bringing a Sample Set into Review, open a Processing Method, and Integrate/Calibrate or Integrate/Quantitate a channel (Figure 1).
Step 2
Go to the Processing Method window, and click the Suitability tab (Figure 2).
Step 3
As mentioned in earlier tips, if you are calculating USP, EP, and JP SignaltoNoise ratios, Empower defaults to PeaktoPeak Noise for the noise calculation. What exactly is PeaktoPeak Noise? It’s defined to be the algebraic difference of the maximum and minimum residuals between each data point and the leastsquare line. The residual is determined by subtracting the y value of the data point predicted by the line from the y value of the data point.
The formula is:
Peak to Peak Noise = max residual – min residual
where: residual  = (yi – ypi) = Value of the data point =Value of the data point predicted by the line 

yi  
ypi 
PeaktoPeak Noise is expressed in detector units. For example, the PeaktoPeak Noise calculation for a UV detector would be expressed in absorbance units (AU). In the example shown in Figure 3, the PeaktoPeak Noise is the sum of both maximum residual (1.07 x10^{6}) and minimum residual (6.57 x 10^{7}), which is 1.72 x 10^{6}. Since peak height is in microvolts, Empower will convert the noise to microvolts using the Scale to microvolts factor.
Step 4
If we calculate noise from the blank injection, we can see the USP SignaltoNoise and USP noise (PeaktoPeak Noise) calculated for every integrated peak in the peaks table (Figure 4).
Step 5
If we calculate noise from a region within the same chromatogram, we can see the USP SignaltoNoise calculated for every peak and the PeaktoPeak Noise for the region chosen, as well as the scale to microvolts factor in the Results window (Figure 5).
It’s that easy!
Final Notes:
 See Tips 29 and 30 for reference.
 This procedure can be followed using the QuickStart or Pro interface.
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Next week in Empower Tip #70 – Working with the System Suitability Option in Empower (part 3)
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