Empower Tip: Review Window and the Processing Method

I receive questions about Detector Noise & Drift and the importance of calculating these values. The way Empower calculates Detector Drift is equivalent to the ASTM method of calculating Drift and some laboratories have SOPs requiring this calculation follow the ASTM method.

Let’s first define Detector Noise and Drift:

1. Detector Noise is the total root mean square noise in the detector signal over a specified time region expressed in detector units. Root mean square is the square root of the mean square. (Mean square is the arithmetic mean of the squares of the numbers.) For more detail go to: https://en.wikipedia.org/wiki/Root_mean_square

2. Detector Drift is the total drift in the detector signal over a specified time region in detector units/hour. Drift is the slope of the least squares line fitted to the data in the region. The slope is calculated by subtracting the y-value of the line at the last data point from the y-value of the line at the first data point and dividing this difference by the time interval in hours. This value is equivalent to ASTM detector drift.

Sound complicated? It is very easy to do in Empower.

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 Detector Noise from the Noise Value for s/n drop-down list.

Go to the Noise and Drift tab. Select Calculate Detector Noise and Drift, enter a Start Time and a Stop Time which provides a region of baseline that is free of peaks and contains at least 60 data points. When setting the Start and Stop time consider the sampling rate which is set in the instrument method.

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

Go to the Results window and we can see the Detector Noise, Detector Drift and Scale to microvolts fields in the Chromatogram Result table.

It’s that easy!