Tip #52: Deriving Channels in Empower (Part 5)

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).

In this tip, we will begin to discuss the various options for Deriving Channels when working with PDA data.

If you work with 3D PDA data and look at the Derived Channels list, the choices are Single Wavelength, MaxPlot, Total Plot, Ratio Plot, Timed Wavelength, Non-Contiguous MaxPlot, and Calculated.

What do these choices mean and when would they be used? Since I have already covered Single Wavelength in Tip 50 and Tip 51, let’s talk about MaxPlot.

MaxPlot is a 2D chromatogram that plots each time point at the maximum absorbance across the wavelength range. This is an excellent method development tool because we can “see” all the peaks in the sample chromatogram regardless of lambda max. If we decide to enable the peak purity calculation and/or do any spectral library searching, MaxPlot plays an important role because it is used to determine the Noise Interval and verify that the absorbance for our peaks does not exceed 1.0 AU (hint: future tips).

Let’s get started.

Step 1

We begin by bringing a Sample Set into Review and open the Method Set (Figure 1).

Figure 1

Step 2

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

Figure 2

Step 3

Decide on the wavelength range over which you want MaxPlot displayed. For the Start Wavelength, think about the UV cutoff of the mobile phase and avoid the low wavelengths. Likewise for the End Wavelength, if the sample doesn’t absorb in the visible region, then set the end wavelength near the end of the UV range (Figure 3).

Figure 3

Step 4

Save the Derived Channel and select a generic Processing Method (Figure 4).

Figure 4

Step 5

Return to the main window and apply the Method Set (Figure 5). The MaxPlot chromatogram is displayed. Additionally, the apex spectrum and lambda max for each integrated peak are now displayed in the Spectrum Review window. With this information, we can decide which wavelength(s) to extract and process for quantitative purposes.

Figure 5

It’s that easy!

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

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Next week in Empower Tip #53: Deriving Channels in Empower (part 6).

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