Get Empowered: Review Window and the Processing Method | Tip #54, Deriving Channels

By January 31, 2018


Tip #54: Deriving Channels in Empower (Part 7)

Welcome back to Get Empowered! In our last tip-of-the-week blog for Empower Software, we reviewed Deriving Channels in Empower.

  • Tip 47: Smooth a chromatogram by Deriving a Channel (part 1)
  • Tip 48: Correct for the time offset between detectors connected in series by Deriving a Channel (part 2)
  • Tip 49: Subtract a baseline from a 2D chromatogram by Deriving a Channel (part 3).
  • Tip 51: Subtract a 2D baseline from 3D PDA data by Deriving a Channel (part 4).
  • Tip 52: Derive MaxPlot from 3D PDA data (part 5)
  • Tip 53: Derive TotalPlot from 3D PDA data (part 6)

In this tip, we will discuss another option for Deriving Channels in Empower Software when working with photodiode array (PDA) data, called RatioPlot.

RatioPlot plots the ratio of absorbance at one wavelength to absorbance at another wavelength. Prior to the development of the Photodiode Array detector, and chromatography software with peak purity algorithms, RatioPlot was used to determine peak purity (spectral purity).

The theory is if the ratio of absorbance is constant across a peak then it is spectrally pure. The challenge is knowing which wavelengths to select.

Let me show you how it is done.

Step 1

We begin by bringing a channel of PDA data into Review and open the Method Set (Figure 1).

Empower Tips: PDA data into Review/Method Set | Figure 1

Figure 1

Step 2

Go to the Method Set window and Derive a Channel, selecting RatioPlot (Figure 2).

Empower Tips: Selecting RatioPlot | Figure 2

Figure 2

Step 3

Decide on the wavelengths and enter those values followed by the Minimum Value. The Minimum Value is the minimum response allowed for numerator and denominator (Figure 3).

Empower Tips: Decide on the wavelengths/Enter values followed by the Minimum Value | Figure 3

Figure 3

Step 4

Save the Derived Channel and select a generic processing method (Figure 4).

Empower Tips: Derived Channel / Select a generic processing method | Figure 4

Figure 4

Step 5

Return to the main window and apply the Method Set. The RatioPlot is displayed (Figure 5).

Empower Tips: RatioPlot is displayed | Figure 5

Figure 5

Step 6

If we zoom in on the top of the peak between 3 and 4 minutes we see the RatioPlot is flat, i.e., the ratio is constant across the peak, which indicates the peak is spectrally pure (Figure 6).

Empower Tips: Ratio is constant across the peak /indicates the peak is spectrally pure | Figure 6

Figure 6

Step 7

If we zoom in on the top of the peak between 1.3 and 1.5 minutes we see it has a bit of a rounded shape, i.e., the ratio is not constant across the peak which indicates the peak is not spectrally pure (Figure 7).

As it turns out, there is an impurity in the front of the peak, which could easily be determined using the peak purity function in the processing method. Stay tuned for a future tip on that.

Empower Tips: Ratio is not constant across the peak/indicates the peak is not spectrally pure | Figure 7

Figure 7

It’s that easy!

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Final note: This procedure can be followed using the QuickStart or Pro interface.

 

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Next week in Empower Tip #55: Deriving Channels in Empower (part 8).

 

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