Empower Tip: Review Window and the Processing Method

I’ve had numerous questions about how Empower calculates Peak to Peak Noise for the USP, EP, and JP Signal to Noise calculations. It is not difficult to understand once we take a look at how it works.

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.

As mentioned in earlier tips, if you are calculating USP, EP and JP Signal to Noise Empower defaults to Peak to Peak Noise for the noise calculation. What exactly is Peak to Peak Noise? Peak to Peak Noise is 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

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.

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.

It’s that easy!