Get Empowered: Review Window and the Processing Method | Tip #69, System Suitability
Tip #69: Working with the System Suitability Option (Part 2)
In this week’s tip, we are going to learn how Peak-to-Peak Noise is calculated in Empower CDS (part 2).
I’ve had numerous questions about how Empower Software calculates Peak-to-Peak Noise for USP, EP, and JP Signal-to-Noise calculations. It is not difficult to understand once we take a look at how it works.
Let me show you how it is done.
We begin by bringing a Sample Set into Review, open a Processing Method, and Integrate/Calibrate or Integrate/Quantitate a channel (Figure 1).
Go to the Processing Method window, and click the Suitability tab (Figure 2).
As mentioned in earlier tips, if you are calculating USP, EP, and JP Signal-to-Noise ratios, Empower defaults to Peak-to-Peak Noise for the noise calculation. What exactly is Peak-to-Peak Noise? It’s defined to be the algebraic difference of the maximum and minimum residuals between each data point and the least-square 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
Peak-to-Peak Noise is expressed in detector units. For example, the Peak-to-Peak Noise calculation for a UV detector would be expressed in absorbance units (AU). In the example shown in Figure 3, the Peak-to-Peak 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.
If we calculate noise from the blank injection, we can see the USP Signal-to-Noise and USP noise (Peak-to-Peak Noise) calculated for every integrated peak in the peaks table (Figure 4).
If we calculate noise from a region within the same chromatogram, we can see the USP Signal-to-Noise calculated for every peak and the Peak-to-Peak Noise for the region chosen, as well as the scale to microvolts factor in the Results window (Figure 5).
It’s that easy!
- 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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